Property:CSDMS meeting abstract
From CSDMS
This is a property of type Text.
2
Recent research has highlighted the idea that long distance particle motions can be a significant component of the hillslope sediment flux. In this situation, mathematical descriptions of hillslope sediment transport must be nonlocal. That is, the flux at a position x, is a weighted function of conditions around x. This contrasts with local conditions which state that the flux is only a function of conditions at x. There are several ways to incorporate nonlocality into a mathematical description of sediment transport. Here, we focus on implementing and testing a convolution integral-like formulation. In this case, the flux is a convolution integral of a volumetric entrainment rate and a kernel that is related to the probability distribution of particle travel distance. Computation of convolution integrals is typically done by taking advantage of the convolution theorem for Fourier transforms, where a convolution integral becomes multiplication in wavenumber domain. However, in our case, the kernel is a function of position, and therefore precludes us from taking advantage of this method. Here, we apply a method that can reduce the problem back to a proper convolution integral and therefore allows for rapid computation (Gilad and von Hardenberg, 2006). We use this method to demonstrate nonlocal transport on lateral moraines on the east side of the Sierra Nevada. This method has applications in all convolution integral-like formulations including nonlinear filtering. +
Recent trends in Earth system modeling, climate data collection, and computing architecture have opened new opportunities for machine learning to improve ESMs. First, new and cheaper satellites are generating large volumes of observational data (e.g. Arctic and Antarctic DEMs), and massive climate modeling projects are generating large volumes of simulated climate data (e.g. CMIP5, CMIP6, CESM-LE). Second, machine learning applications are driving the design of next-generation computing architectures that will accelerate applications like neural nets without ameliorating the computational bottlenecks (ref: NOAA HPC position paper) that limit existing climate models. Third, the climate science community is becoming increasingly familiar with machine learning techniques. Here, I summarize opportunities for CSDMS practitioners to use machine learning techniques to improve Earth system and Earth surface models. +
A
Recurved barrier spits occur in a wide variety of environments, from active delta complexes to rocky coasts, where spits extend depositionally from a shore that is otherwise eroding. Although controls on spit orientation are often presented in the literature a posteriori (i.e. after the spit has been observed), there surprisingly remains no general model that predicts spit shape and orientation in terms of external variables, such as wave climate, sediment supply, and embayment depth. We study spit shape controls using the Coastline Evolution Model (CEM), a numerical model that evolves the plan-view coast based upon the processes of alongshore sediment transport and barrier overwash maintaining a minimum critical barrier width. Model results demonstrate that the directional distribution of approaching waves serves as a first-order control on spit shape, with waves from multiple directions playing a vital role in spit extension and reshaping. Surprisingly, we find that boundary effects, namely the rate of change of the updrift coast location, play a similarly important role in spit shape. The depth of the platform upon which a spit grows plays another important role, with deeper platforms tending to accommodate more sharply curved spits. Every day, spits act as a type of messenger in disguise, revealing wave forcing, sediment supply, and local geometry. +
Reduction of nitrogen (N), phosphorus (P), and suspended sediment (SS) load has been a principal focus of Chesapeake Bay Watershed management for decades. To evaluate the progress of management actions in the Bay's largest tributary, the Susquehanna River, we analyzed the long-term seasonal trends of flow-normalized N, P, and SS load over the last two to three decades, both above and below the Lower Susquehanna River Reservoir System. Our results indicate that annual and decadal-scale trends of nutrient and sediment load generally followed similar patterns in all four seasons, implying that changes in watershed function and land use had similar impacts on nutrient and sediment load at all times of the year. Above the reservoir system, the combined loads from the Marietta and Conestoga Stations indicate general trends of N, P, and SS reduction in the Susquehanna River Basin, which can most likely be attributed to a suite of management actions on point, agricultural, and stormwater sources. In contrast, upward trends of SS and particulate-associated P and N were generally observed below the Conowingo Reservoir since the mid-1990s. Our analyses suggest that (1) the reservoirs' capacity to trap these materials has been diminishing over the past two to three decades, and especially so for SS and P since the mid-1990s, and that (2) the Conowingo Reservoir has already neared its sediment storage capacity. These changes in reservoir performance will pose significant new kinds of challenges to attainment of total maximum daily load goals for the Susquehanna River Basin, and particularly if also accompanied by increases in storm frequency and intensity due to climate change. Accordingly, the reservoir issue may need to be factored into the proper establishment of regulatory load requirements and the development of watershed implementation plans. (Published in Science of the Total Environment (2013); available at http://dx.doi.org/10.1016/j.scitotenv.2013.02.012. For a pdf pre-print, please contact Qian Zhang at qzhang19@jhu.edu.)
2
Reef islands are carbonate detrital landforms perched atop shallow reef flats of atolls and barrier reef systems. Often comprising the only subaerial, inhabitable land of many island chains and island nations, these low-lying, geomorphically active landforms face considerable hazards from climate change. Sea-level rise and wave climate change will affect sediment transport and shoreline dynamics, including the possibility for wholesale reorganization of the islands themselves. Here we apply a hierarchical modeling approach to quantify the potential responses of reef island systems to future changes. Using parameterizations of sediment transport pathways and feedbacks from previously presented XBeach modeling results, we investigate how sea-level rise, change in storminess, and different carbonate production rates can affect the profile evolution of reef islands, including feedbacks with the shallow reef flat that bounds the islands offshore (and lagoonward). Model results demonstrate that during rising sea levels, the reef flat can serve as a sediment trap, starving reef islands of detrital sediment that could otherwise fortify the shore against sea-level-rise-driven erosion. On the other hand, if reef flats are currently shallow (likely due to geologic inheritance or biologic cementation processes) such that sea-level rise does not result in sediment accumulation on the flat, reef island shorelines may be more resilient to rising seas. This simplified modeling approach, focusing on boundary dynamics and mass fluxes, including carbonate sediment production, provides a quantitative tool to predict the response of reef island environments to climate change. +
Relating scientific results generated from modeling, remote sensing, or instrumental measurements of Earth’s surface to topics of social relevance often poses challenges for theoretical scientists. Theoretical science is treated as divorced from social matters, as a matter of definition, unless specific problems are solved, then it shifts into an applied realm and is viewed as spatially constrained. A paradox results: if scientific results are “merely” theoretical, yet intended to be universal, then it is undetermined whether results would follow everywhere, but if they are collected from actual measures and observations it is undetermined whether the same conditions are everywhere and apply to all spatial and temporal scales. The problem is particularly acute for Earth’s surface which is both physical and has high value for all human beings and infrastructures and all life. It is also the object of theoretical models. So, it is critical for human life and its connections to all life that models aim to model the spatial and temporal reality of Earth’s surface including regional variabilities with their constraints. Social relevance is a value that can be viewed together with physical characterizations as part of understanding landscapes.
Outlined are considerations to help integrate values that express social relevance into the scope of how theoretical science is conducted and approached to address the scale of connectedness of Earth’s surface while expanding the human reach of Earth surface modeling. Inspiration has been taken from recent NSF sponsored initiatives, such as efforts to expand and unify through diversity and inclusion the critical zone (CZRN) and convergence research in Navigating the New Arctic, as well as the open science philosophy of CSDMS, and a recent Greenland Data workshop seeking to unify data management of Greenland. I contribute my synthesis to engage with others about how the application of computational approaches and landscape data management can be used to provide basic platforms for treating and comparing earth surface data at multiple temporal and spatial scales while having “convergence” of social spheres as an underlying consideration. Therefore, the infinite potential at any point on Earth’s surface is representable, relatable, and connectable numerically, and it recognizes and includes the realm of human beings as investigators and inhabitants of any landscape.
Computational thinking may be a source for thinking about expanding who are considered the inhabitants of landscapes and who studies the landscapes, i.e. including diverse identities in research while also unifying them through shared and recognized goals. Expanding the realm of theory in Earth surface processes to include model data about people, life, geographies, climates, processes and their change through time is a new science frontier. The idea that information has many dynamic layers and dimensions and that there are many ways to connect and relate them through time with computational approaches as a starting point may serve as a guide for integrating social value into theoretical research.
River deltas ringing the Arctic Ocean coastline are unique landforms shaped by both highly seasonal cold region hydrology and permafrost features such as thermokarst lakes. These lakes trap, store, and modulate the timing and magnitudes of riverine freshwater, sediment, and nutrients. Future climate warming is expected to thaw permafrost, modifying lake coverage and therefore riverine flux delivery to the Arctic Ocean. How and where thermokarst lake coverage on deltas will change remains highly uncertain, in part due to the difficulty in separating perennially inundated thermokarst lakes which undergo thermal expansion in response to warming, from ephemeral wetlands resulting from interannual and seasonal hydrologic variability. We present a methodology that allows us to classify waterbodies as perennial lakes or ephemeral wetlands, by examining their presence in a 20 year record of Landsat imagery. By analyzing 12 deltas laying on a gradient of temperature and ice content, we find that perennial lakes and ephemeral wetlands have universal but distinct size distributions which result from different mechanisms forming the two waterbodies. We also find that colder deltas have larger lakes on average, mechanistically attributed to thicker and colder permafrost which supports larger lakes by preventing sub-lake unfrozen zones (i.e. taliks) from connecting to the sub-permafrost groundwater table. Lastly, we explore how differences in the spatial patterns of lakes across the deltas may relate to climate variability. These findings provide the basis for quantitative predictions for the trajectory of lake and wetland coverage on arctic deltas under projected warming. +
River morphodynamics can affect overbank flooding if changes to cross-sectional area or roughness reduce the flow conveyance capacity of the channel. Correspondingly, extreme floods can also cause drastic adjustments to river morphology on relatively short timescales. These co-occurring processes raise the question: how do flood dynamics and river morphology co-evolve? The difficulty of conducting rapid field measurements of river geometry during peak flows has limited existing research on channel adjustment and recovery during a flood hydrograph. Here, we leverage a one-month Delft3D simulation to investigate flood hydraulics and river morphodynamics in a November 2021 flood event in the Nooksack River, western Washington State (WA). This flood devastated river-adjacent WA communities along the Lower Nooksack. Flood waters additionally overtopped the levees near Everson, WA and traveled over 25 km north towards the Fraser River, causing extensive and costly damages across the U.S.-Canada border. To understand the feedbacks between river morphodynamics and floods, we analyze streamwise changes in flood hydraulics (flow velocity & shear stress) and morphodynamics (bed elevation change). Within the Everson overflow region, we find that spatial gradients in flow velocity shift between in-bank- and peak-flow conditions. Bed elevation changes are commonly located where hydrodynamic gradients intensify during peakflows. Importantly, at the Everson overflow location, bed deposition co-occurs with a drastic along-channel velocity decrease and overbank flow, suggesting that the hydraulics of overbank flooding can contribute to local morphodynamic adjustment. We additionally investigate how channel adjustments during the first November 2021 flood peak affect flooding during a secondary flood peak occurring two weeks later. These results are of particular interest to the Nooksack River floodplain managers who are eager for insights on the contribution of channel morphodynamics to flooding and who are actively investigating methods to alleviate overtopping including setback levees and dredging.
River profiles are shaped by a combination of tectonic forcing, climatic history, and internal feedbacks. One example of internal dynamics is the self-formation of waterfalls in steep channels, which can cause erosion rates to both accelerate (‘fast waterfalls’) or decelerate (‘slow waterfalls) relative to waterfall-free reaches. We previously used a 1D stream power model with a waterfall rule to show that the self-formation of waterfalls above a threshold slope can alter river long profiles over km scales. In the 1D model, the formation of fast waterfalls results in a uniform-gradient zone maintained by a dynamic equilibrium, while slow waterfalls can cause autogenic knickpoints. However, it is not clear how these findings alter river profile form in a 2D setting in which hillslopes and channels are linked and adjacent basins can interact. Here, we ask the question: are long profile signatures from waterfall formation enhanced or erased by additional internal feedbacks, such as hillslope diffusion and planform channel adjustment? To address this knowledge gap, we implemented our waterfall model in a 2D setting, using Landlab and specifically the SPACE and hillslope diffusion components. Our results in 2D show agreement with the initial 1D implementation, and additional results show that self-formation of waterfalls can alter landscape-scale metrics, including drainage density and slope-area relationships. Additional exploration of natural variability, including stochastic rock strength show that increasing natural variability can expand the length of the affected profile. +
River-bed grain size distributions in fluvial systems set the initial condition for landscape change on the event to millennia scale. These distributions are used to infer characteristic flow conditions or estimate mass flux through a fluvial system, and this is often under the assumption that sediment grain-size distribution on the bed remains static over time. However, recent work has shown that grain size distributions can fluctuate over individual flow events, can be dependent on the sequence of successive flow events, and can change seasonally. This discrepancy can lead to order of magnitude differences in estimating sediment flux or characteristic hydrologic conditions. To constrain bed grain size evolution, we perform numerical simulations using a probabilistic, discrete model of a river bed in which computational cells represent grains randomly distributed across the surface of the bed. Patterns and timing of grain mobilization are determined according to distributions of entrainment thresholds for individual grains and flow rate dependent distributions of velocity fluctuations that vary over hydrographs. Entrained grains are replaced from a static distribution allowing the bed grain size distribution to evolve throughout the simulation depending on the imposed flow condition. Our preliminary model results from varying initial grain size distribution, individual event shape, and flow sequencing show a significant dependence on the range of grain sizes available for transport as well as the total duration of individual flow events, while seasonal variability has a moderate impact on bed grain size evolution. +
Rivers are key drivers of landscape evolution. Transient signals of base level fall propagate up rivers and cause increased erosion rates, which in turn increases channel steepness. In landscapes with horizontally layered rocks, erosion rates vary in both space and time as different layers are eroded and exposed at the surface, complicating how these landscapes respond to base level fall and influencing the topographic expression of different lithologies. Lithologic variations further influence river response by producing sediment, which can armor the channel bed and reduce bedrock erosion. Motivated by the lithologic variability found in the Guadalupe Mountains of Texas and New Mexico, we use the Stream Power with Alluvium Conservation and Entrainment (SPACE) model to test how sediment cover affects channel steepness and erosion rates in horizontally layered rocks. We simulate 1.2 million years of landscape evolution with an imposed uplift rate of 1.0 mm/yr in alternating layers of hard and soft rock, systematically varying the relative amount of alluvial cover. We compare the normalized channel steepness of the model output against the steepness values predicted by the stream power incision model, which is the most commonly used model for interpreting steepness variations in real landscapes. We find that in model runs with sediment cover, channel steepness is systematically higher than predicted by the stream power model in soft rock layers, and lower than predicted in hard rocks. Sediment cover also exerts a strong control on erosion rates. Sediment cover preferentially accumulates over soft rock layers, decreasing erosion rates in these layers while increasing erosion in the unarmored hard rock layers. As the degree of sediment cover is increased, the maximum erosion rate at any given point along the channel decreases. Increasing the sediment cover effectively decreases the erodibility contrast between hard and soft rocks, illustrating the importance of considering the role of sediment when interpreting channel profiles.
Rivers exhibit high temporal variability in their constituent concentrations, which can result in distinct hysteresis patterns of suspended sediment (SS), particulate organic carbon (POC), and dissolved organic carbon (DOC) during various high-flow events. In mountain rivers, this variability may be controlled by the mobilization of streambed sediment, which is enriched with organic carbon and other nutrients and can be evaluated by the entrainment of the armor layer, a group of coarser particles that act as a protective layer to finer sediment. In this study, we test if resulting hysteresis patterns could be controlled by the extent to which the armor layer was mobilized by analyzing POC, DOC and SS patterns during monsoon-driven flow events in two river reaches at the Valles Caldera National Preserve, New Mexico. We collected continuous water samples over numerous flood hydrographs using automated ISCO samplers while also monitoring flow depth, turbidity, and fluorescent dissolved organic matter (fDOM) using YSI EXO2 sondes. Turbidity and fDOM were included because they can be used as proxies for SS and DOC, respectively. To quantify armor mobilization, we deployed tracer particles of different sizes and mapped their location before and after each event. We found that constituent hysteresis changes between clockwise and counterclockwise for different flow events, each with their own streambed mobilization characteristics. Opposite hysteresis occurred for DOC and fDOM than for POC, SS, and turbidity. Additionally, there were poor correlations between DOC and SS, while POC and SS were found to be well correlated. Our results imply that DOC hysteresis might not be related to the release of fines from the streambed, whereas POC is. These findings suggest that the temporal variability of SS and POC can be partly understood by the mobilization and suspension of fine sediment not only seasonally, but also over individual high-flow events. We show how the mobilization of the armor layer can be an important contributor to this variability.
Rivers flowing across permafrost limit the residence time of floodplain soil organic carbon (SOC) by transferring riverbank material to the fluvial network. In this way, permafrost riverbank erosion limits production of greenhouse gases (GHG) in a deepening permafrost active layer. Concurrently, arctic riverbanks are laden with permafrost ice wedges and channels themselves are seasonally occupied by ice; these factors are known to affect fluvial potential to erode and remove material from floodplains. However, we do not know how ice impacts rates of riverbank migration through permafrost, especially in small arctic watersheds where observations are limited. We hypothesize that bank migration into permafrost is best described by melting of bank ice but is also described by slumping of the active layer, and fluvial carrying capacity. First, we develop a model of thermal riverbank erosion. Next, we detail plans to incorporate slumping and mechanical erosion into a holistic icy riverbank erosion model. We will characterize riverbanks along the Canning this field season and use or measurements to calibrate our model. Then, we will test which mechanisms are most significant in forming permafrost riverbanks, as well as describe their evolution under warming mean annual air temperatures. This work is also useful for predicting the future contribution of the arctic rivers to their basin-wide carbon budget. This work has immediate importance for people who traverse or depend on arctic landscapes, but especially those who live within them. Arctic landscape response to climate change is just as much a story about the loss of place and vanishing resources as it is about a dynamic earth system. +
Rivers in natural settings are frequently characterized by downstream variations in channel width. However, the effect of width variations on bed topography and sorting patterns remains poorly understood, especially under conditions of changing sediment and hydrologic regimes. In this study we use two-dimensional numerical modeling to systematically explore how the amplitude and wavelength of sinusoidal width variations affect the shape and location of bars, sorting patterns of surface sediment, and the movement of a sediment pulse. We perform simulations with sediment regimes consisting of constant sediment supply, no sediment supply, and a sediment pulse with no background sediment supply. We also perform steady and unsteady flow simulations to explore the combined effect of hydrograph shape and width variations. Preliminary results indicate that width variations force riffle-pool topography with riffles coincident with wider channel sections and pools at narrow sections. The amplitude of width variations is the dominate factor controlling riffle-pool relief. The wavelength of the width variations controls whether central or side bars develop in the wider channel sections. These numerical simulations are complimented with ongoing physical experiments in a laboratory flume and can potentially be used to guide stream restoration and river management practices under conditions of varying sediment and hydrologic regimes. +
Robust estimate of the critical shear stresses and flocculation is a prerequisite for analyzing the sediment dynamics of tidal flats. To determine the impact of clams (Meretrix meretrix Linnaeus) on critical shear stress and flocculation, in situ measurements were made on both a bare flat and a flat inhabited by abundant clams. on the Jiangsu Coast, China. Near-bed in situ floc size, grain size distribution of suspended particles in sea water, suspended sediment concentration (SSC), salinity, and currents were measured for three consecutive semidiurnal tidal cycles simultaneously at the two stations. Based on the observational data, mean floc size measured by LISST-100x was found to be more than three times the size of dispersed suspended sediment in water samples, suggesting remarkable flocculation processes were occurring. Correlation analysis indicated that the flocculation and break-up process in the study area appeared to be controlled by the variations in SSC and turbulent shear. Negative relationships were found between SSC, turbulent shear and floc size for both stations, but for a given SSC, floc size was usually larger at the clam aquaculture site. The comparison between the two sites shows that the near-bed in situ floc size in the aquaculture mudflat (mean 88 μm) was 70% larger than that in the bare tidal flat (mean 51 μm), suggesting significant biological modulation on the flocculation processes, as the hydrodynamics were very similar between the two sites. The content of extracellular polymeric substances was obviously higher in the sediment layer below the surface seabed at aquaculture site. Further, we find that the sediments on the flat inhabited by clams were more erodible and had a lower critical shear stress for erosion (0.13 N m-2) due to the physical and biological activities of clams. The results further show that the critical shear stress for deposition on the flat with M. meretrix (0.13 N m-2) was 30% greater than that in the bare flat (0.10 N m-2). Our results suggest that changes to the critical shear stress for erosion and deposition caused by the activity of clams can alter the sediment dynamics and geomorphologic processes of flats, as well as abundant filter feeders alter floc properties and enhance flocculation by excretion of exopolymer particles.
Salmonine fishes (salmon and trout) are resilient and have evolved to survive environmental perturbations, including flood, drought, and wildfire. The effects of these perturbations are translated through the landscape by rivers, where aquatic communities can be severely impacted. For instance, after wildfire, rivers can experience increased frequency and magnitude of flash floods, ash and nutrient loading, increased sediment flux from runoff and debris flows, destabilization and physical alteration of fluvial habitat, stream temperature impairment, and either loss or gain of refuge (e.g. deep pools, woody debris, riparian vegetation). Depending on the severity, any one of these effects could drive the extirpation of fish populations, and the response and survival of fish gets increasingly complex when faced with multiple environmental perturbations. Historically, the extirpation of fish populations would not have been as significant a risk to the extinction of entire species or subspecies of salmonids, as unrestricted migration allowed for recolonization by neighboring populations. However, increasing river disconnectivity, due to the introduction of physical barriers, has put native fish species at greater risk of extinction after natural catastrophes. In order to evaluate the viability and recovery of fish populations after catastrophe, we have developed a multi-site structured population viability analysis (PVA) model that is designed to incorporate factors that are unique to the spatial distribution of catastrophe and migration in fluvial networks. Specifically, our multi-site PVA provides the flexibility to vary both the duration and severity (i.e., multi-year catastrophe and habitat recovery) of vital rate adjustment (survival and growth). Our model also allows for a multi-mechanistic approach to vital rate adjustment after catastrophe – this is a particularly important advancement, as fluvial habitats located within the fire perimeter often experience distinctly different impacts than those outside of but downstream of fire. Both of these improvements are necessary as the negative impacts of wildfire on fish habitat and vital rates can last for years or even decades, and commonly used PVA modeling software only allows for impairment to last for one year. Additionally, previous models allow for a “one, all or radial spreading” approach to the spatial distribution of catastrophe, which works for disease but is inconsistent with the flow routing of catastrophe in stream networks. Finally, we have also developed a new metapopulation migration model that accounts for bidirectional river connectivity, a characteristic of migration unique to fluvial environments. Migration behavior in this model is driven by simple probabilities of life-stage structured dispersal and migration distances, measures of habitat suitability (including post-catastrophe adjustment), and site population densities. To demonstrate the utility of our multi-site PVA, we apply it to a case study of Bonneville Cutthroat Trout after the Twitchell Canyon Fire in the Fish Lake National Forest, Utah. The impact on and recovery of trout populations after wildfire was monitored across 14 sites of variable hydrologic, temperature and physical impairment (both within and outside of the fire perimeter). Using these observations along with maps of stream connectivity barriers, we model trout population viability and recovery after wildfire in this site. We also compare our results to model simulations using single year impairment, more similar to that of previous PVAs. Finally, we demonstrate the potential improvements on population recovery through simulations removing individual fish barriers throughout the network. This model presents a new framework for directly linking parameters of landscape change that may vary in both spatial and temporal distribution to the viability of fish populations after natural catastrophe. Plans for future model development include linking the PVA with models of fish bioenergetrics and landscape evolution, which can provide spatially variable predictions of changes in discharge, stream temperature and sediment fluxes after fire. Ultimately, we hope to develop and provide a new management tool for evaluating the overall vulnerability of aquatic organisms to wildfire in watersheds throughout the Intermountain West.
Salt and shale based minibasins are quasi-circular depression connected by submarine canyons of economic importance because they are prime locations of hydrocarbon reservoirs. The history of sedimentation of the minibasins is modulated by sea level changes, and it is strongly influenced by basin topography and continental shelf dynamics. Sedimentation in intraslope minibasins is generally described in terms of the “fill-and-spill” model in which the turbidity currents enter a minibasin and are reflected on the minibasin flanks. After the reflection, the turbidity currents pond and deposit the suspended sediment. As the minibasin fills, the current spill over the lowermost point of the minibasin flanks and reaches the next minibasin downslope, where the fill and spill process starts again. In this stage, deposition still occurs in the upslope minibasin with the formation of channel-levee complexes. In the last two decades field, laboratory and numerical studies focused on the description of (1) the large-scale stratigraphic architecture and evolution of the minibasins and (2) the behavior of the turbidity currents in the minibasin-canyon system. This notwithstanding, questions regarding the spatial distribution of the grain sizes in minibasin deposits, the role of the system geometry and of the flow characteristics of the turbidity current on the depositional pattern still need to be answered. The objective of the present study is to investigate with three-dimensional model simulations how the deposit characteristics change for increasing in slopes of the minibasin-canyon system. In particular, we are using a three-dimensional numerical model of turbidity currents that solves the Reynolds-averaged Navier–Stokes equations for dilute suspensions. Turbulence is modeled with a buoyancy-modified k–ε closure. The numerical model has a deforming bottom boundary to model the changes in elevation and grain size characteristics of the bed deposit associated with sediment erosion and deposition. Here we present the model validation against 1) 2D laboratory experiments of a horizontal minibasin in a constant width flume, and 2) 3D laboratory experiments on two linked minibasins. The model validation is performed comparing measured and simulated deposit geometries, vertical profiles of suspended sediment concentration and spatial distributions of sediment sizes in the deposit. In the near future, we will perform laboratory scale simulations by changing the slope of the experimental minibasin, i.e. the difference in elevation between the entrance and the exit points to study how the depositional pattern changes when the relative size of the ponded accommodation space, i.e. the space at a lower elevation than the spill point, and the perched accommodation space, i.e. the space under an ideal line connecting the spill point and the minibasin entrance.
Salt marsh provides critical estuarine habitat and shoreline protection, and is highly vulnerable to sea-level rise. Models of marsh accretion and resilience to sea-level rise rely on estimates of sediment supply, yet the factors governing sediment supply to marshes and its temporal variation are poorly understood. This presentation focuses on temporal variability in suspended-sediment concentration (SSC) and spatial gradients in SSC at the marsh edge, with two goals: 1) to identify processes important to sediment supply, and 2) to inform the choice of SSC values to use as input to marsh accretion models. We present data collected as part of an investigation of the influence of tides and wind waves on sediment supply to an estuarine salt marsh in China Camp State Park, adjacent to San Pablo Bay, in northern San Francisco Bay (tide range approximately 2 m). The long-term sediment accretion rate in the lower China Camp marsh is 3 mm/year. The marsh vegetation is predominately Salicornia pacifica, with Spartina foliosa occupying the lower elevations adjacent to the mudflat. The marsh is bordered by wide intertidal mudflats and extensive subtidal shallows. In the winter of 2014/2015 and the summer of 2016 we collected time series of SSC, tidal stage and currents, and wave heights and periods in the bay shallows, in a tidal creek, and (except for currents) on the marsh plain. On the mudflats, SSC depends strongly on wave energy, and also varies inversely with water depth, increasing toward the marsh edge and with decreasing tidal stage. Within the marsh, SSC is lower in the Salicornia-dominated marsh plain than at the marsh edge, as expected, but in the Spartina zone SSC is greater than at the marsh edge. This effect is greater in summer, when Spartina is significantly taller and denser, than in winter. SSC over the marsh was typically greater during flood than ebb tides in both seasons, indicating net deposition over the tidal cycle. However, median flood-tide SSC over the marsh, and the inferred deposition, were greater in summer than winter. We attribute the increased SSC and deposition in summer to greater sediment trapping in Spartina, followed by mobilization and transport of sediment onto the marsh during subsequent high tides.
Sandwich Town Neck Beach, MA, USA is a 1300-m long barrier spit on the north shore of Cape Cod that has experienced chronic dune erosion during nor’easters. Repeated mapping with drones and photogrammetry shows that dune erosion varies spatially along the beach. We used the wave model SWAN to compare simulated waves with the observed morphological response along the barrier spit. Local refraction and dissipation of wave energy by the complex nearshore bathymetry produces alongshore variations in wave energy, with regions of diverging alongshore wave power corresponding to the regions of rapid erosion. These regions are also where lower beach profiles are steepest, waves break closest to shore, and wave runup is highest. These results suggest that, while erosion rates may be affected by the availability of sediment from up-drift sources, wave patterns play an important, and maybe dominant, role in determining alongshore variations in dune erosion at Sandwich. +
A
Satellite and field observations find modern carbonate depositional systems to be self-organized, yet the processes generating such behavior are not fully understood. A 3-D forward model of carbonate reef growth rooted in cellular automata is developed to simulate the evolution of self-organized geometry through time. Carbonate landscapes are generated over spatial extents of several kilometers through time scales of millennia at meter-scale resolution. Classes in the model include carbonate factories (e.g., branching and massive coral communities, algal communities) and sinks (e.g., unconsolidated sand). Environmental factors include relative sea level and light intensity, and ecological controls are based on life history traits for the biological facies. Ecological processes within the model include mortality and colonization rates for biological classes, transition probabilities between facies, and rates of vertical accretion. The algorithm results in a self-organized landscape that emulates those observed in nature, such as rims and reticulate structures. Visualizations can be produced by accessing topographic and facies maps generated at each time step. This project’s goals are 1) to investigate which configurations of environmental parameters result in specific spatial motifs, 2) examine the effects of environmental perturbations on reef construction, and 3) understand the importance of biological and physical regimes on the generation of geomorphological features. +
Satellite remote sensing is a powerful tool for terrestrial hydrological studies. In particular studies of droughts and floods - hydrological extremes can be well accomplished using remote sensing. In particular, we will use data from the visible-infrared and microwave sensors on NASA platforms to studies the onset and propagation of droughts as well as spatial extent of flooding. In this talk we will present numerous examples of hydrological extreme events and the use of satellite remote sensing as a tool for mapping the spatial extent and the temporal persistence. The droughts of 1988 and 2012 in the United States Midwest, flooding in 1993 and 1998 are strong examples in United States. There have been numerous such events in Asia in India, Pakistan and China which have affected billions of people who depend on the land and agricultural productivity to a much greater degree than in United States. +
2
Sea level rise presents an urgent threat to the occupants of river deltas. However, while low lying deltaic landscapes are at risk of significant drowning, the ability to harness a river’s sediment delivery system offers deltaic populations a mechanism to control the location and extent of land loss via land building sediment diversions. Despite their well-recognized importance there are few examples of diversions that have been intensively monitored throughout their development to the extent necessary to support engineering decisions.
In order to guide the operational design of two planned diversions in the Lower Mississippi River, we apply Delft3D to simulate diversion discharge through time as a function of the characteristics of the receiving basin. In both cases the conveyance channel connecting the river to the basin is prevented from eroding.
We find that diversions in basins that offer many outlets for flow are more likely to maintain their discharge over a ten-year time horizon. We also find that diversion performance is not significantly affected by substrate erodibilities in the range of those found in the Mississippi River Delta, but that artificially increased bed strength would lead to decreases in performance. Our work also sheds light on the spatial pattern of erosion near a diversion. We find that very little erosion into the substrate occurs away from the immediate vicinity of the outfall channel, but that the evolution of the proximal scour is a critical control on the sustainability of the diversion. Ecological considerations suggest that operating diversions at low flow might be useful, but this practice increases the risk of back flow from the receiving basin. +
Seagrass provides a wide range of economically and ecologically valuable ecosystem services, with shoreline erosion control often listed as a key service, but can also alter the sediment dynamics and waves within back-barrier bays. Here we incorporate seagrass dynamics into the existing barrier-marsh model GEOMBEST++ to examine the coupled interactions of the back-barrier bay with both adjacent (marsh) and non-adjacent (barrier island) subsystems. In our new integrated model, bay depth and distance from the marsh edge determine the location of suitable seagrass habitat, and the presence or absence, size, and shoot density of seagrass meadows alters the bathymetry of the bay and wave power reaching the marsh edge. While seagrass reduces marsh edge erosion rates and increases progradation rates in many of our model simulations, seagrass surprisingly increases marsh edge erosion rates when sediment export from the back-barrier basin is negligible. Adding seagrass to the bay subsystem leads to increased deposition in the bay, reduced sediment available to the marsh, and enhanced marsh edge erosion until the bay reaches a new, shallower equilibrium depth. In contrast, removing seagrass liberates previously-sequestered sediment that is then delivered to the marsh, leading to enhanced marsh progradation. Lastly, we find that seagrass reduces barrier island migration rates in the absence of back-barrier marsh by filling accommodation space in the bay. These model observations suggest that seagrass meadows operate as dynamic sources and sinks of sediment that can influence the evolution of coupled marsh and barrier island landforms in unanticipated ways. +
Sediment creep is ubiquitous and precedes failure (e.g. landslides) in most landscapes. Accurate modeling of sediment creep is therefore crucial for predicting both the long-term (>10 000 years) evolution of landscapes and the short-term (minute to centuries) evolution of landscapes and infrastructures. Current sediment creep transport laws used in landscape modeling are determined empirically over geological time scales and are diffusion-like (Roering et al,2001); yet the mechanics of sediment creep on all time scales remain poorly understood. As a result, creep models used in civil engineering, materials science, and geomorphology are largely disconnected in time scales, goals, and approaches. In particular, excess porous flow from rain infiltration is currently not a governing parameter of any creep model, while large rain events are known to trigger landscape failures.
Houssais et al. (2021) showed experimentally for the first time, that porous flow can be a leading cause of creep, and ultimately the failure (avalanching) of sediment piles, for flow strength (or pore pressure) far lower than classically admitted. Building on the results from Houssais et al., we propose a new equation for sediment creep consistent with the general formalism of the mechanical creep of disordered materials. In our equation, the creep sediment flux is a function of: topographic slope (similar to the equation from Roering et al.), porous flow intensity, grains and fluid properties, and, importantly, time.
We present here the first results of landscape dynamics from the implementation of our new sediment creep function in landlab, for the case of idealized berms (or coastal natural dams), before they breach. The long-term goal of this effort is to compare the model to our topographic and hydrogeologic observations of berms (pre-)breaching on the coast of Monterey County, CA, that occur each winter, as large rain episodes hit the land. This specific case is a good way to test our model validity over time scales from 1 minute to 1 month. In our presentation, we will show preliminary results of the berms creep (pre-breaching) dynamics, using over-simplified equations for the groundwater flow. In the future, we intend to develop a Landlab component of our new creep function, which could be used with Groundwaterdupuitpercolator, a landlab component recently developed to model groundwater flow while modeling landscape dynamics (Litwin et al., 2020, 2022).
In the end, once this model is validated, it will allow us to model sediment creep at all time and rate scales, and better predict chances of, and monitor, sedimentary failures, such as breaching and landslides. Our new model for sediment creep fundamentally addresses our needs for better understanding and forecasting landscape response to changing climate patterns.
Houssais, M., C. Maldarelli, and J. F. Morris, “Athermal sediment creep triggered by porous flow,” Physical Review Fluids, vol. 6, no. 1, p. L012301, 2021.
Litwin, D. G., G. E. Tucker, K. R. Barnhart, and C. J. Harman, “Groundwaterdupuitpercolator: A landlab component for groundwater flow,” Journal of Open Source Software, vol. 5, no. 46, p. 1935, 2020.
Litwin, D. G., G. E. Tucker, K. R. Barnhart, and C. J. Harman, “Groundwater affects the geomorphic and hydrologic properties of coevolved landscapes,” Journal of Geophysical Research: Earth Surface, vol. 127, no. 1, p. e2021JF006239, 2022.
Roering, J. J., J. W. Kirchner, L. S. Sklar, and W. E. Dietrich, “Hillslope evolution by nonlinear creep and landsliding: An experimental study,” Geology, vol.
A
Sediment delivery to low-lying coastal zones must keep pace with, if not exceed, the rate of sea level rise in order to maintain a positive surface elevation. Deltaic lowlands are vulnerable to both sea-level rise and changes in river discharge, but whether the floodplains and coastal areas will ultimately drown depends on a balance of aggradation, eustatic sea level rise and subsidence. The Ganges-Brahmaputra (G-B) Delta is an example of a densely populated coastal system that could be flooded by rapid sea level rise within the next century. Annual monsoonal river flooding and cyclonic storm surges are the principal mechanisms by which sediment is distributed across the G-B floodplain and coastal plain. Stratigraphic reconstructions show that sedimentation in the upper floodplain was more than doubled under the Early Holocene enhanced monsoonal regime, suggesting that the delta may withstand an increase in monsoonal intensity, flooding, and tropical cyclones that are currently predicted in ensemble Community Climate System Model scenarios.
In an effort to improve predictions of climatic forcing on aggradation rates in the G-B floodplain and lower delta, direct sedimentation measurements are paired with a series of model components coupled within the CSDMS Modeling Tool (CMT). A sediment flux model, a floodplain sedimentation model and a tidal-plain sedimentation model will be linked to explore the response of the G-B river system to a future sea-level rise and changes in river discharge. Model algorithms will be validated by sedimentation data collected in 2008 and 2012 from the tidal delta (The Sundarbans National Reserve mangrove forest) and the highly cultivated fluvial-dominated delta plain. Field data will also be compared to model outputs by constraining the spatial patterns of sedimentation across the delta front. In this talk, we present initial sedimentation results and discuss controls on heterogeneous patterns of deposition in the tidal versus fluvial dominated parts of the delta. Early results from individual model components will also be discussed in an attempt to integrate current understanding of the G-B System into a numerical modeling framework.
2
Sediment dynamics on Arctic shelves can impact coastal geomorphology, habitat suitability, and biogeochemical cycling, and are expected to be sensitive to changes in sea ice extent. Variability in coastal erosion, for example, has been related to variations in waves due to changes in sea ice extent, as well as water temperature. Yet, it remains unclear how changes in sea ice extent will impact hydrodynamic and sediment transport conditions on the continental shelf. To analyze this, we are using a coupled hydrodynamic - sediment transport numerical model, the Regional Ocean Modeling System (ROMS) - Community Sediment Transport Modeling System (CSTMS). The model is implemented for the Alaskan Beaufort Sea shelf and currently accounts for winds, sea ice, offshore currents, rivers, waves, and multiple sediment classes. Ongoing work includes finalizing model inputs. The model is being run for the 2019 open water season when sea ice retreats 100 - 300 km offshore. Analysis will focus on spatial and temporal variations in current velocities, waves, bed shear stresses, and sediment fluxes. Preliminary results show that the time-averaged depth-averaged currents, and likely sediment fluxes, are directed eastward along the shelf. Additionally, the largest bed shear stresses occur near the coast and on the shelf-slope break. Future work includes additional analyses, as well as sensitivity tests to better understand how a lengthening open water season and changing weather conditions may influence shelf sediment dynamics. +
Sediment dynamics on Arctic shelves can impact coastal geomorphology, habitat suitability, and biogeochemical cycling, and are sensitive to changes in sea ice extent. Variability in coastal erosion, for example, has been related to variations in waves due to changes in sea ice extent, as well as water temperature. Yet, it remains unclear how changes in sea ice extent will impact hydrodynamic and sediment transport conditions on the continental shelf, motivating this study. To analyze this, we are using a coupled hydrodynamic-sediment transport numerical model, the Regional Ocean Modeling System (ROMS) - Community Sediment Transport Modeling System (CSTMS). The model is implemented for the Alaskan Beaufort Sea shelf and currently accounts for winds. Ongoing work includes accounting for waves, sea ice, and setting up open boundary conditions. In order to analyze variations in hydrodynamics and sediment transport, the model will be run for two open water seasons representing time periods where sea ice retreats 100-300 km offshore. Analysis will focus on spatial variations in current velocities, waves, and bed shear stresses, as well as how model estimates vary between the two time periods. Future work involves accounting for sediment transport in the model and performing sensitivity analyses to better understand how a lengthening open water season may influence the shelf sediment dynamics. +
Sediment transport is a universal phenomenon responsible for the self-organization of bedforms and dunes seen on the surfaces of many planetary bodies. The smallest of these patterns are wind, or impact ripples. Encoded in the sizes and propagation speeds of impact ripples is direct information about the local transport and environmental conditions: sediment fluxes, wind speeds, grain size, etc. However, to get at this information we must understand the processes that govern ripples dynamics. Because of the complexity of sediment transport, our current understanding of ripples is almost purely empirical, and the parameter space of the system has barely been explored.
To aid at the process of understanding impact ripple dynamics in arbitrary environments we turn to a discrete element model (DEM) of sediment transport. Simulated ripples sizes from the DEM quantitatively agree with wind-tunnel and field data and therefore the DEM can be used as an experimental tool to explore the state space of the system. Preliminary experiments suggest that ripple wavelengths scale with the average hoplength of eroded grains, but only above a threshold. Below this threshold wavelengths stagnate and ripples begin to propagate upwind. These “antiripples” have not previously been predicted or observed. Yet simulations suggest that they are persistent for many planetary conditions such as those on Venus and even Earth (for large enough grain sizes). We present additional findings for a range of environmental conditions found in our solar system and beyond, and thus map out a more complete space of possible states for ripple formation in the Universe. +
A
Sedimentary delta formation varies over a wide range of time and space scales. Reduced-complexity models offer a worthwhile means of retaining key dynamics and phenomena in delta morphodynamics through employing approximate but physically reliable descriptions of governing transport equations. To that end, we developed a cellular rule-based model, using a “directed” random-walk to determine the flow field, coupled with empirically based sediment transport schemes, following an Exner equation combining bedload and suspended load. Preliminary results provide physically reasonable 3-dimensional topographical features, as well as dynamic processes like channel avulsions and bifurcations. Stratigraphy is also recorded. The flexibility of the modeling framework makes each building block to be updated separately, which will allow for the ready extension to include additional phenomena such as waves and tides. +
2
Sequence is a modular 2D (i.e., profile) sequence stratigraphic model that is written in Python and implemented within the Landlab framework. Sequence represents time-averaged fluvial and marine sediment transport via differential equations. The modular code includes components to deal with sea level changes, sediment compaction, local or flexural isostasy, and tectonic subsidence and uplift. Development of the code was spurred by observations of repetitive stratigraphic sequences in western Turkey that are distorted by tectonics. +
Simulation models are explicit descriptions of the components and interactions of a system, made dynamic in software. In Coupled Human-Earth Systems Science, we most often employ simulation to conduct controlled experiments in which key socio-ecological parameters are varied, and changes to system-level dynamics are observed over time. An interesting emergent property of these kinds of experiments is that they produce a range of possible outcomes for any set of initial conditions. Thus, rather than use simulations to explain particular case studies from the past, they are better suited to examine the dynamics of ancient systems in a more general way. Model parameters need to be determined and model output needs to be validated, however. So, our simulations *do* need to be connected to empirical data; a useful model must be capable of producing the same *kinds* of patterns observed in the archaeological record (but not *only* these patterns). It is often difficult, however, to connect model output to real data. In this presentation I draw upon research and modeling techniques being developed by the Mediterranean Landscape Dynamics Project to explore ways of connecting the output of simulation models to the kinds of proxy records that we typically use to learn about the past, such as the stratigraphic record, human artifact densities, and phytolith and charcoal accumulation. +
Slow-moving arctic soils commonly organize into striking large-scale spatial patterns called solifluction terraces and lobes. Though these features impact hillslope stability, carbon storage and release, and landscape response to climate change, no mechanistic explanation exists for their formation. Everyday fluids—such as paint dripping down walls—produce markedly similar fingering patterns resulting from competition between viscous and cohesive forces. Here we use a scaling analysis to show that soil cohesion and hydrostatic effects can lead to similar large-scale patterns in arctic soils. A large new dataset of high-resolution solifluction lobe spacing and morphology across Norway supports theoretical predictions and indicates a newly observed climatic control on solifluction dynamics and patterns. Our findings provide a quantitative explanation of a common pattern on Earth and other planets, illuminating the importance of cohesive forces in landscape dynamics. These patterns operate at length and time scales previously unrecognized, with implications toward understanding fluid-solid dynamics in particulate systems with complex rheology. +
Soil creeps imperceptibly downhill, but also fails catastrophically to create landslides. Despite the importance of these processes as hazards and in sculpting landscapes, there is no agreed upon model that captures the full range of behavior. Here we examine the granular origins of hillslope soil transport by Discrete Element Method simulations, and re-analysis of measurements in natural landscapes. We find creep for slopes below a critical gradient, where average particle velocity (sediment flux) increases exponentially with friction coefficient (gradient). At critical there is a continuous transition to a dense-granular flow rheology. Slow earthflows and landslides thus exhibit glassy dynamics characteristic of a wide range of disordered materials; they are described by a two-phase flux equation that emerges from grain-scale friction alone. This glassy model reproduces topographic profiles of natural hillslopes, showing its promise for predicting hillslope evolution over geologic timescales. +
Soil moisture state has a critical role on subsurface-land surface-atmosphere energy and water balance. Yet, there is still no consensus on how to initialize atmospheric-hydrologic models to improve the representation of soil moisture content. Lack of accurate observational soil moisture data is the root of this issue. Although there has been progress in providing remotely sensed soil moisture data (e.g., Soil Moisture Active Passive (SMAP) data), their resolution is not adequate for high-resolution simulations. As an alternative approach, many atmospheric-hydrological simulations use various spin-up periods prior to the start of their analysis to perturb and improve the low-resolution soil moisture with precipitation. It has been shown that such method can improve soil moisture distribution in some studies in comparison to observational data. However, starting simulations from earlier times can cause divergence from accurate initial atmospheric conditions, which were obtained from observational data when simulation reaches the analysis period of interest. Therefore, there is a tradeoff between starting several days or hours before the analysis period in accurate representation of atmospheric data versus soil moisture input. In this study, we evaluated the sensitivity of a high-resolution (150-m) Weather Research and Forecasting (WRF) model to initialization starting point. We ran five nested domains with 12150-, 4050-, 1350-, 450-, and 150-m resolutions to downscale NCEP North American Regional Reanalysis (NARR) to our domain of interest encompassing Baltimore-Washington metropolitan area. The five domains were run in three scenarios starting 4, 7, and 14 days before the analysis period. Land surface temperature (LST) output was compared to LandSat data to investigate the impact of initialization starting point on model’s LST predictability. Results indicate that while the three scenarios underperformed in prediction of the urban heat island, there was no significant difference among the three scenarios. We determined that one of WRF’s thermal roughness parameterizations, which improves LST simulation over nonurban areas, caused significant errors in LST prediction over urban areas. Further simulations and analysis are underway to improve urban LST prediction. The three case scenarios will be compared against LandSat again when urban LST prediction is improved.
Son alluvial fan system, a megafan situated at the foothills of Vindhyans, is governed by the endogenic and exogenic process operating in the Ganga foreland basin. The megafan is interspersed with a number of structural features in the bedrock overlain by quaternary alluvial cover viz., Munger Saharsa Ridge Fault (MSRF), East Patna fault (EPF), and West Patna fault (WPF), some other reported tectonic features. A number of studies have attempted to decipher the recorded signatures of these underlying bedrock structural features and related tectonoclimatic activities in in the form of geomorphic anomalies and sedimentological evidences. In this study, χ‐transform index and χ‐anomalies, in combination with stream channel sinuosity, channel steepness index (ksn), channel concavity index (θ), geomorphology, and field evidences, have been used to examine if these structural features be highlighted on the low relief megafan surface with bedrock-alluvial mixed to thick alluvial cover (upto 1000 m thick). Drainage basin divide (in)stability measured through across divide χ‐anomaly map which proven to be an important tool for quantification of basin and channel network geometry behaviour, has been found to highlight the areas with active structural activities around the reported bedrock structures in the experimental study. Geomorphology and field evidences corroborate the findings of this study. +
Source-to-sink (S2S) studies seek to explicitly link the denudation of continents with the building of basin stratigraphy in an effort to infer tectonic and climatic drivers of surface change. Quantitative models for S2S systems must incorporate geomorphic processes at both source and sink, yet more effort has been devoted to developing landscape evolution models in source terranes than equivalent models for sedimentation in marine basins. In particular, most marine sedimentation models use local linear diffusion approximations for sediment transport, which have been shown to yield reasonable stratigraphy in shallow marine environments but struggle to reproduce diagnostic features of deep marine deposits. The lack of model predictive power in deep marine environments precludes the full closure of S2S sediment budgets.
We present a model for marine sedimentation with two simple modifications allowing non-local sediment transport: 1) a mechanism for sediment bypass on steep topographic slopes, and 2) a parameter allowing long-distance transport over vanishingly gentle slopes. We use Bayesian inference techniques to constrain four model parameters against the stratigraphy of the Orange Basin in southern Africa. We compare modeled against observed stratigraphy over 130 Ma of margin evolution. Our best-fit simulations capture the broad structure of the observed record, and imply non-negligible roles for both non-local model elements: sediment bypass at steep slopes and long-distance runout over gentle slopes. Residual misfit between our best-fit simulations and the stratigraphic data indicate that additional components of transport dynamics—likely hemipelagic sedimentation, grain size variations, or ocean bottom currents—might be required to achieve the longest transport distances observed in the sedimentary record. Results suggest that full closure of Earth’s sediment mass balance for S2S studies requires moving beyond local diffusion approximations, even at the longest timescales. Relatively simple modifications to modeled transport dynamics can lead to better agreement between modeled and observed stratigraphy, and may enable improved inference of landscape perturbations from the stratigraphic record.
Stream channels that cross strike-slip faults play an essential role in the long-term landscape response. So far, numerical models of strike-slip faults have simulated fluvial erosion assuming purely detachment-limited conditions. The detachment-limited theory assumes that the erosion is controlled by material that is detached from the channel bed and is always transported by the flow. As an alternative, erosion in channels can be represented by the transport-limited theory, which assumes that sediment is always available but may or not be transportable depending on the flow capacity. Extreme environments such as the Atacama Desert in Northern Chile, are evidence of strike-slip faulting with channels covered by alluvial deposits, suggesting that the landscape is best represented by a combination of detachment-limited and transport-limited conditions. Based on the most recent strike-slip fault model we incorporate and couple the effect of the SPACE (stream power with alluvium conservation and entrainment) 1.0 Landlab component in Python. The SPACE component can freely transition between detachment-limited and transport-limited conditions offering a closer representation of what is observed in the natural world. The results of coupling SPACE with strike-slip faults models are contrasted against the models that apply only detachment-limited conditions, to identify the action of a layer of sediment in landscape modification under variable strike-slip fault conditions. The concluding remarks of this work contribute to testing the accuracy of simplifying channel erosion processes to the commonly used stream power equation in strike-slip fault settings. +
Stream discharge is often used to drive sediment transport models across channel networks. Because sediment transport is nonlinear, discharge arising from precipitation resolved at 1-hr resolution may simulate bedload differently than discharge arising from daily total precipitation distributed evenly over 24-hrs. In this study, we quantify the bias introduced into a network-scale bedload transport model due to this simplification in forcing. Specifically, we examine the difference between bedload transport capacity driven by 1- vs 24-hr precipitation derived stream hydrographs at channel network locations varying from lowland pool-riffle channels to upland colluvial channels in a watershed where snow accumulation and melt can affect runoff processes. Bedload transport error is expressed as the ratio of cumulative transport capacity driven by 1-h to the 24-h hyetographs. We find that, depending on channel network location, cumulative error can range from 10-20% to more than two orders of magnitude. Surprisingly, variation in flow rates due to differences in hillslope and channel runoff do not seem to dictate the network locations where the largest errors in predicted bedload transport capacity occur. Rather, spatial variability of the magnitude of the bankfull-excess shear stress and changes in runoff due to snow accumulation and melt exert the greatest influence. As bankfull-excess shear stress decreases in the upstream direction, the largest bedload transport capacity errors occur in upland channels. These findings have implications for flood-hazard and aquatic habitat models that rely on modeled sediment transport driven by coarse-temporal-resolution climate data. +
Subglacial hydraulics significantly affects the ice dynamics in Greenland and Antarctic ice sheets, however, has been poorly understood due to the lack of data. Here we present an OpenFOAM-based one-dimensional subglacial model, conduitFoam, to study the hydraulics and ice dynamics of polar ice sheets. This model solves the coupled mass conservation equations for ice and water, the momentum and energy conservation equations for water, with a lake-conduit or moulin-conduit system as constraint boundaries. The model is validated using the theoretical solution applied in early melting stage and lake melting stage of the Greenland ice sheet and can be used to infer the subglacial conduit properties and the ice sheet dynamics in both seasonal and diurnal melting situations. +
Submarine slope failure is a ubiquitous process and dominant pathway for sediment and organic carbon flux from continental margins to the deep sea. Slope failure occurs over a wide range of temporal and spatial scales, from small (10e4-10e5 m3/event), sub-annual failures on heavily sedimented river deltas to margin-altering and tsunamigenic (10-100 km3/event) open slope failures occurring on glacial-interglacial timescales. Despite their importance to basic (closing the global source-to-sink sediment budget) and applied (submarine geohazards) research, submarine slope failure frequency and magnitude on most continental margins remains poorly constrained. This is primarily due to difficulty in 1) directly observing events, and 2) reconstructing age and size, particularly in the geologic record. The state of knowledge regarding submarine slope failure preconditioning and triggering factors is more qualitative than quantitative; a vague hierarchy of factor importance has been established in most settings but slope failures cannot yet be forecasted or hindcasted from a priori knowledge of these factors.<br><br>A new approach to address the knowledge gaps outlined above is using machine learning to quantitatively identify triggering and preconditioning factors that are most strongly correlated with submarine slope failure occurrence. This occurs in three general steps: 1) compile potential predictors of slope failure occurrence gridded and interpolated at desired resolution, 2) compile predictands (specific values that we wish to predict), and 3) recursively test predictor/predictand correlation with observed data until the strongest correlations are found. Potential predictors can be parsed into categories such as morphology (gradient, curvature, roughness), geology (clay fraction, grain size, sedimentation rate, fault proximity), and triggers (seismicity, significant wave height, river discharge). Predictands (i.e. training data) are various proxies for slope failure occurrence, including depth change between bathymetric surveys and sediment shear strength. The initial test sites are heavily sedimented, societally important river deltas, as they host both frequent slope failures and ample predictor/predictand measurements. Once predictors that strongly correlate with submarine slope failure occurrence are identified, this approach can be applied in more data-poor settings to further our current understanding of global submarine slope failure distribution, frequency, and magnitude.
Subsurface flow dynamics are largely controlled by pressure gradients generated by surface flow and differences in permeability. In most models, surface and subsurface flows are decoupled, with effects on one another only considered over relatively large time scales. However, at smaller time scales, these two flows interact and modify each other's structures and properties. In this study, we developed a fully-coupled free-surface/subsurface Large Eddy Simulation model to investigate the spatiotemporal variations in velocity and pressure, particularly near the bed surface. We validated our model by comparing it to experimental data from a laboratory simulation of open channel flow on a simulated salmon redd bed made of coarse granular sediment, using non-toxic index-matched fluid and stereo Particle Image Velocimetry (PIV). Our model accurately captured subsurface flow lines, velocity magnitude and direction, and superficial velocity profiles throughout the water column. With our validated model, we investigated the effects of subsurface hydraulic conductivity on the whole flow field. +
Surface processes are constantly reworking the landscape of our planet with perhaps the most diverse and beautiful patterns of sediment displacement known to humanity. Capturing this diversity is important for advancing our knowledge of systems, and for sustainable exploitation of natural resources by future generations. From a modeler's perspective, great diversity comes with great uncertainty. Although it is understandably very hard to quantify uncertainty about geological events that happened many years ago, we argue that modeling this uncertainty explicitly is crucial to improve our understanding of subsurface heterogeneity, as stratigraphy is direct function of surface processes. In this modeling work (and code), we aim to build realistic stratigraphic models that are constrained to local data (e.g. from wells, or geophysics) and that are, at the same time, subject to surface processes reflected in flume records. Experiments have improved tremendously in recent years, and the amount of data that they generate is posing new challenges to the surface processes community, who is asking more often the question "How do we make use of all this?" Traditional models based on differential equations and constitutive laws are not flexible enough to digest this information, nor were they created with this purpose. The community faces this limitation where the models cannot be conditioned on experiments, and even after exhaustive manual calibration of unobserved input parameters, these models often show poor predictive power. Our choice of inverse modeling and (geo)statistics (a.k.a. data science) was thus made knowing that these disciplines can provide the community with what we need: the ability to condition models of stratigraphy to measurements taken on a flume tank. +
A
Sustainability of the anthroposphere is a result of a multitude of decisions made concerning social, economic and environmental questions. Decision makers who would like to ensure sustainable development as an emerging characteristic of humanity are challenged by the complexity of a planetary system re-engineered by an increasingly powerful global species. Examples of such problems are sustainable urban growth and the food-water-energy nexus. Tools to reliably assess the consequences of decisions from local to global level are not readily available.
In particular, current capabilities for assessing the various impacts of climate variability and change, as well as other changes are inadequate. The Group on Earth Observation (GEO) recognized this emergency and promoted several initiatives that can help address this shortcoming. One of them is the GEO Model Web initiative. The goal of this initiative is to develop a dynamic modelling consultative infrastructure of intercommunicating models and datasets to serve researchers, managers, policy makers and the general public. It focuses on enhancing interoperability of existing models and making them and their outputs more accessible. The development of the Model Web holds the promise of more decision support tools becoming available. These tools would allow decision makers to ask “What if” questions prior to the implementation of decisions and support adaptive management and responsive design. The Model Web will also benefit researchers by making it easier to run model experiments and model comparisons or ensembles, as well as help highlight areas needing further development. The Model Web would support a synchronization across different spatial and temporal scales and across the languages of different disciplines, thus making the System of System (SoS) more intelligent. The beauty of having a SoS like this is that it amplifies the signal. An immediate application is the emerging geodesign approach to the design of sustainable built environments.
The Model Web is developed in the framework of the Global Earth Observation System of Systems (GEOSS) implemented by GEO. The observing, modelling and other systems that contribute to GEOSS must be interoperable so that the data and information they generate can be used effectively. The Committee on Earth Observation Satellites (CEOS) is promoting interoperability through the Virtual Constellations concept, the Sensor Web approach, and by facilitating model interoperability and access via the Model Web concept.
The Model Web is a concept for a system of interoperable models and data capacities communicating primarily via web services. It would consist of an open-ended, distributed, multidisciplinary network of independent, interoperating models plus related datasets. Models and datasets would be maintained and operated and served by a dynamic network of participants. In keeping with the SoS approach, the Model Web initiative will explore the interoperability arrangements necessary to integrate multi-disciplinary environmental model resources. The approach of loosely coupled models that interact via web services, and are independently developed, managed, and operated has many advantages over tightly coupled, closed, integrated systems, which require strong central control, lack flexibility, and provide limited access to products.
Developing a long-term perspective, a logical next step would be the Internet of Models (IOM). Comparable to the already developing Internet of Things (IOT), which is predicted to connect by 2020 more than 50 billion “things” talking to each other without human interaction (or even knowledge), the IOM would have models talking to each other when needed without human interaction. If we compare the IOT to the nerve system of a human body, then the IOM would be the brain of the human being. Key to the development of IOT and IOM are standards that allow “things” and “models” to communicate when needed and to exchange information as needed (similar to the role of standards in the success of the WWW). Frameworks for model interactions are already developing (e.g. Object Modelling System, ModCom, the Invisible Modelling Environment, the Open Modelling Interface: OpenMI, the Spatial Modelling Environment: SME, Tarsier, Interactive Component Modelling System: ICMS, Earth System Modeling Framework: ESMF, SEAMLESS-IF , CSDMS, etc.), but they are not sufficient to achieve the Model Web (or the IOM). A major effort to develop the standards for the IOT is under way, and a similar effort to needed for the IOM standards. The combination of IOT and IOM would greatly enhance science capabilities, early warning, assessments of impacts, etc.
2
A
TITLE: Growth and Abandonment: Quantifying First-order Controls on Wave Influenced Deltas
AUTHORS: Jaap Nienhuis12, Andrew D Ashton1, Liviu Giosan1
INSTITUTIONS: 1. Geology & Geophysics, Woods Hole Oceanographic Institution, Woods Hole, MA, United States. 2. Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, United States
ABSTRACT BODY:
River delta evolution is characterized by cyclical progradation and transgression: the delta cycle. We investigate the growth and decay of the individual or main lobes of deltas with strong wave influence with the aim to quantitatively compare marine to terrestrial controls.
We apply a model of plan-view shoreline evolution to simulate the evolution of a deltaic environment. The fluvial domain is represented by deposition of sediment along the shoreline, developing along a predefined single or multi-channel fluvial network. We investigate the influence of wave climate, fluvial sediment input and network geometry.
For growing deltas, we present a sediment-flux-based approach to quantify the relative influence of fluvial versus marine (wave) controls on morphology. Wave domination requires that the magnitude of the fluvial bedload flux to the nearshore region be less than the alongshore sediment transport capacity of waves removing sediment from the mouth. Fluvial dominance occurs when fluvial sediment input exceeds the wave-sustained alongshore sediment transport for all potential shoreline orientations, both up- and downdrift of the river mouth. For a single delta (or delta lobe), this transition depends not only on the fluvial river sediment flux and wave energy, but also on the directional wave climate.
Channel bifurcation is critical; it splits the sediment discharge from the river, while the potential alongshore sediment flux per channel remains equal. Fluvial dominance persists until sufficient bifurcations have split the fluvial sediment flux among the channels or until the occurrence of a river avulsion. This simplified model allows us to quantify the transition from fluvial to wave dominance and enables comparisons with natural examples near this transition, such as the Tinajones lobe of the Sinu River Delta, Colombia, and the Po Delta, Italy.
During delta abandonment, model results suggest littoral sediment transport can result in four characteristic modes of wave reworking, ranging from diffusional smoothing of the delta (or delta lobe) to the development of downdrift-extending recurved spits. The directional characteristics of the wave climate, along with the pre-abandonment delta shape, determine the mode of reworking. Simple analysis of pre-abandonment delta shape and wave characteristics provides a framework for predicting the mode of delta reworking; model predictions agree with the observed morphology of historically abandoned delta lobes, including the Nile, Ebro, and Rhone. These results provide insight into the potential evolution of active delta environments facing near elimination of fluvial sediment input.
Tectonic strain localization creates spatially anisotropic mechanical strength patterns that are reflected by landscape. Strain in the frictional-brittle crust produces predictable anisotropic cohesion and grain size distribution fabrics that influence spatial strain induced (SI) erodibility patterns where exposed at the surface. We assume that bedload impact is the primary mechanism for bedrock incision and erodibility is an inverse function of cohesion, which can be reduced by more than 2 orders of magnitude at the meter scale due to fragmentation and grain size reduction. The density, position, and orientation of SI anisotropies depends on the magnitude of strain and the tectonic horizontal/vertical shear stress ratio. The influence of tectonic strain on landscape becomes apparent by incorporating 3D strain induced crustal failure in a landscape evolution model. Natural observations and model results suggest naturally occurring SI anisotropy exerts a first order influence on geomorphic metrics for active orogens, including incision rate, 3D stream network geometry, and topographic evolution. Rates of vertical incision and knickpoint migration are orders of magnitude faster along SI anisotropy exposures. Shallowly dipping faults produced in a dip-slip regime are largely protected from vertical incision by unstrained overburden while a steeply dipping fault produced in a strike-slip regime is largely exposed to vertical incision. The strain field controls hydraulic geometry by influencing 1) the spatial distribution of discharge by establishing anisotropic erodibility patterns and 2) slope changes at erodibility transitions and differential uplift in a watershed. The influence of tectonic strain on landscape increases with the horizontal/vertical shear stress ratio because more steeply dipping and interconnected faults are produced. SI anisotropy controls channel network geometry by amplifying long wavelength tortuosity where fault-bound channels connect and muting short wavelength tortuosity along faults. Both effects increase with increasing tectonic horizontal shear strain. Channel width becomes constricted by the width of SI cohesion reduction, causing channel width to become a function of strain rather than reflecting only the hydraulics of a drainage basin.
2
Terrestrial cosmogenic nuclides (TCN) are commonly used to assess denudation rates in soil-mantled uplands. The estimation of an inferred denudation rate (Dinf) from TCN concentrations typically relies on the assumptions of steady denudation rates during TCN accumulation and negligible impact from soil chemical erosion on soil mineral abundances. However, in many landscapes, denudation rates are not steady, and the composition of soil is markedly affected by chemical erosion, adding complexity to the analysis of TCN concentrations. We introduce a landscape evolution model that computes transient changes in topography, soil thickness, soil mineralogy, and soil TCN concentrations. With this model, we explored TCN responses in transient landscapes by imposing idealized perturbations in tectonically (bedrock uplift rate) and climatically sensitive parameters (soil production efficiency, hillslope transport efficiency, and mineral dissolution rate) on synthetic, steady-state landscapes. The experiments on synthetic landscapes delivered important insights about TCN responses in transient landscapes. Results showed that responses of Dinf to tectonic perturbations differ from those to climatic perturbations, indicating that spatial and temporal trends in Dinf serve as indicators of perturbation type and magnitude. Also, if soil chemical erosion is accounted for, basin-averaged Dinf inferred from TCN in stream sediment closely tracks actual basin-averaged denudation rate, showing that Dinf is a reliable representation of actual denudation rate, even in many transient landscapes. In addition, we demonstrate how this model can be applied to a real landscape in the Oregon Coast Range and how model predictions can be compared to field measurements of cosmogenic nuclides and chemical depletion in sediments. Overall, landscape evolution models infused with cosmogenic nuclides can be used to scrutinize methodological assumptions, reveal potential real-world patterns in transient landscapes, and deepen the comprehension of field data.
A
Texas has historically faced severe hurricanes with Ike being the most recent major storm example. It is believed that coastal wetlands might reduce the impact of the storm surge on coastal areas, acting as a natural protection against hurricane flooding, especially for small hurricanes and tropical storms. Numerical analysis is an important instrument for predicting and simulating the flooding extent and magnitude in coastal areas. In recent years, improvements on the understanding of the physics of storm surges have led to the development of physically based numerical models capable of reasonably representing the storm surges caused from hurricanes. Wetlands are represented in the numerical model through their influence on the frictional resistance proprieties and bathymetric changes. To characterize the wetland types and their spatial distribution along the coast, we used six different land use databases from the National Land Cover Dataset (NLCD) (1992, 2001), the National Wetlands Inventory (NWI) (1993) and the Coastal Change Analysis Program (C-CAP) (1996, 2001, 2006). The analyses was conducted for Corpus Christi Bay using a pre-validated, physically based, hydrodynamic model (ADCIRC) and a wind and pressure field model (PBL) representing the physical properties of historical hurricane Bret. The calculations were performed using an unstructured numerical grid with 3.3 million nodes covering part of the Atlantic Ocean and the entire Gulf of Mexico (resolution from 2000 km to 50 meters at the coast). Considering the expected rise in the mean sea level, wetland composition and spatial distribution are also expected to change as the environmental conditions change along the coast. We analyzed a range of Intergovernmental Panel on Climate Change (IPCC) projections for sea level rise (SLR) to simulate wetland alterations and evaluate their impact on hurricane storm surge. The wetland degradation by SLR was spatially simulated using empirical relations for water levels/tides and ecosystem resilience. The choice of wetland database resulted in surge variations of less than 0.1 m in locations inside Corpus Bay. Preliminary studies considering IPCC scenarios (B1, A1F1, B1FI) for 2030 and 2080 plus predicted local subsidence showed that, although the SLR scenarios for 2030 did not affect surge considerably inside the bay (SLR increase removed after simulation), the greater degradation of the wetlands caused by SLR on the 2080 scenarios (0.80 m SLR + subsidence) resulted in surges on the order of 0.3 m higher for Hurricane Bret in selected locations. Future work includes performing analyses using different storm conditions (forward speed, central pressure and storm radius), additional and less conservative SLR scenarios, damage assessment and also include the effects of waves using the coupled version of ADCIRC with UNSWAN.
2
The ADCIRC finite element coastal ocean model is used in real time decision support services for coastal and riverine hydrodynamics, tropical cyclone winds, and ocean wave modelling for public sector agencies including NOAA, FEMA, Coast Guard, and the US Army Corps of Engineers, among others. Recent developments in ADCIRC's real time automation system, the ADCIRC Surge Guidance System (ASGS), have now enabled real time modelling of active flood control scenarios (manipulation of pumps and flood gates) for decision support during riverine floods and tropical cyclone events. During these events, the results are presented to official decision makers with the Coastal Emergency Risks Assessment (CERA) web application, an intuitive and interactive tool that integrates model data with measured data to provide situational awareness across the area of responsibility. Case study events will be described, including official decisions that have been made with ADCIRC in North Carolina (Irene 2011), Louisiana (Mississippi River flooding in 2016), and during the 2017 and 2018 hurricane seasons for Hurricanes Harvey, Irma, Maria, Florence, and Michael. +
The Amazon River Basin is the largest river system in the world, accounting for one-fifth of global freshwater discharge and supplying 40% of the Atlantic Ocean’s sediment flux. Though the Amazon is most often recognized for its rich biological diversity, it also performs a suite of ecosystem functions such as river flow regulation, local climate modulation, and carbon sequestration. Despite its ecological importance, the Amazon experiences thousands of kilometers of deforestation annually with recent rates increasing to levels unseen since the late 2000s. These increased rates of deforestation within the basin have led to changes in sediment concentration within its river systems, affecting not only the ecological balance within the system but also the availability of water to those dependent on river flows. Furthermore, sediment plays an important role in river channel morphology and landscape development, effectively influencing the future topography of the basin. Therefore, it is important to closely examine the relationship between deforestation and suspended sediment in order to characterize the extent of influence anthropogenic activities, such as deforestation, have on rivers.
In this study, we analyze the impact of deforestation from 2001 to 2020 on suspended sediment throughout the Amazon River Basin. These effects are studied by quantifying the spatiotemporal relationships between observed suspended sediment (at gage sites and using a basin wide remote sensing product) and changes in land cover over time. We hypothesize that deforestation will lead to significant increases in suspended sediment flux in adjacent streams and that the effect of deforestation on suspended sediment flux will decrease significantly downstream. We then apply these relationships to developing a new parameter within an existing global-scale sediment flux model, WBMsed. +
The Atlantic basin has experienced heightened storm activity in recent decades setting the perfect condition for both fluvial flooding and coastal storm surges and consequently disrupting the hydrological system and the environmental balance. The Maryland Coastal Bays (MCBs), a shallow interconnected lagoon system with two inlets, is heavily influenced by tides and currents and also sensitive to climate change and storm surge. Despite several existing studies on the Atlantic winter storms impact on the hydrodynamics within the MCBs, a critical knowledge gap relating the interaction between coastal and inland processes still exists. The purpose of this study is to focus on the application of a coupled hydrologic-hydrodynamic model to a compound flooding study to understand the interrelation between simultaneous occurrence of fluvial flooding and storm surges around the St Martin River and the MCBs areas respectively. In this study, CE-QUAL-W2 is used to simulate the hydrological processes while the hydrodynamic processes in the MCBs and adjacent coastal ocean are simulated using 3-D unstructured-grid based Finite Volume Community Ocean Model (FVCOM). The outputs from CE-QUAL-W2 are introduced into adjacent FVCOM grid where the former’s downstream-most segment meets the latter’s land boundary. Comparison of water level elevations computed with and without inflows from CE-QUAL-W2 reveals the extent to which the MCBs are influenced by river input during extreme events and vice versa. A series of sensitivity tests in different scenarios and subsequent comparison with baseline will provide some insight on how effective model results are at simulating such scenario in hydrological and hydrodynamic regimes around the MCBs. The finding from this study on the MCBs is hoped to provide insights into these shallow bays’ response to different dynamics in a holistic manner and to identify probabilities and consequences of what the future may hold. +
The Atlantic coast of New Jersey experienced impacts from distal passages of two hurricanes in fall 2023, including Hurricane Lee in mid-September followed by Tropical Storm Ophelia in late September. A total of 20 beach profiles spaced by 100 meters along the Ortley Beach and surrounding beaches in Ocean County, New Jersey, were established. Weekly beach surveys using RTK-GPS from the edge of the dune to mean low water was conducted from September 14 to October 12, 2023. The data captures the severe dune/beach erosion induced by the passage of TS Ophelia, with large waves and storm surges. The natural recovery processes of beach post tropical storm were interrupted by the subsequent winter storms starting from mid to late October. The systematic beach survey was continued until January 2024, the peak of winter season. Our results indicate that pre-storm beach width plays an important role in protection of dunes and landward infrastructure, the threshold beach width for dune line protection is about 40 m. Given the context of global climate change, the chance of sequence of storms (tropical and winter storms) have considerably increased. Field observations on beach changes induced by storms will enhance our understanding on beach management. +
The Doodleverse (https://github.com/Doodleverse) is an ecosystem of Python software, data, and Machine Learning (ML) models for the application of image segmentation. Image segmentation is pixelwise classification, and is ubiquitously applied across Earth sciences. Imagery is any type of gridded data, including numerical model inputs and outputs. As such, image segmentation is a potentially useful generic tool in numerical modeling exercises, which will be demonstrated using a case study in this poster and epub.
Doodleverse workflows are fully reproducible, such that it is possible to entirely reconstruct a labeled dataset and model from scratch by anyone on any computing platform. There are 3 main software; 1) “Doodler”, a human-in-the-loop ML tool for interactive image segmentation, 2) “Segmentation Gym”, for training image segmentation models, facilitating model experimentation, and 3) “Segmentation Zoo”, a repository of trained models that each do specific tasks, along with code implementation examples. Deep learning models are based on Keras/Tensorflow. Currently, the UNet, Residual UNet, and Segformer model architectures are available.
The focus now is building downstream and demonstrative applications that use Segmentation Zoo models for specific data retrieval, extraction and mapping tasks. They include 1) “CoastSeg”, for mapping coastal shoreline dynamics using satellite imagery; 2) “Seg2Map”, for generic landuse/cover and landform mapping from publicly available high-resolution imagery; and 3) “PingMapper”, for mapping river and lake substrates from sidescan sonar imagery. Watch out for more Doodleverse applications in the future! +
A
The Flood Early Warning System (FEWS) was designed as a hydrologic forecasting and warning system. A major design philosophy of FEWS is to use an open infrastructure to facilitate data import, manipulation, and export from a wide –and expanding – number of data sources. The same can be said of the models that FEWS communicates with. This open infrastructure allows FEWS to be used with novel data sources and models. Given its proven history in hydrologic forecasting, this makes FEWS well suited to modeling and forecasting fluvial influence on coastal and marine systems.
Here we present an example of how FEWS can be extended to use oceanographic data. Our example forecasts stage in the Potomac River, where storm surges, especially during hurricanes, can cause flooding in a densely populated area. We use gridded data from the Integrated Ocean Observing System (IOOS). Data from the Chesapeake Bay Regional Ocean Modeling System (ChesROMS), posted to an OpenDAP server, were accessed from within FEWS. FEWS was used to manipulate the ChesROMS data. For example, the ChesROMS data are disaggregated to produce a time step consistent with available discharge time series, and point data are extracted from the ChesROMS grid at river monitoring sites. The model HEC-RAS is then used to forecast water heights given inputs of stage and discharge. This example illustrates the flexibility of FEWS, and its ability to be used in new areas. +
2
The Ganges-Brahmaputra-Meghna Delta (GBMD), located in South Asia, is the largest river deltaic system in the world covering 41,000 mi2. Roughly the size of Kentucky, the GBMD is an extremely fertile region of protected mangrove forests and intensely cultivated land connected in a complex network of tidal channels, creeks, swamps, and oxbow lakes. Anthropogenic forces, natural subsidence accumulation, and eustatic sea level rise threaten deltas such as the GBMD and the quality of life of the people residing there. Most of the GBMD is located within Bangladesh and provides essential transportation services through inland waterways that carries 50% of cargo traffic and 25% of all passenger traffic mostly through the active northeastern region labeled with a dashed yellow line as shown in Figure 1. Vanderbilt’s multidisciplinary Integrated, Social, Environmental, and Engineering (ISEE) research team’s previous research efforts in Bangladesh focused on the physical characteristics of the deltaic system as climate change and anthropogenic forces affect it, but little is known about how channel closures affects the transportation network. Recent research has made use of available Landsat data combined with Google earth imagery to identify key metrics and attributes of the GBMD in order to link connectivity of distributary fluvial patterns to ecosystem services (Passalacqua et al., 2013). This work aims to integrate previous research using satellite imaging to model the transportation network that uses metrics such as channel width and nearest edge distance combined with available data on freight movement provided by multiple sources of information, such as the World Bank. In later stages of the project, we will use historical data of satellite imagery to capture channel dynamics that will be used to simulate disruptions to the transportation network and analyze subsequent impacts to Bangladesh’s economy. This allows decision makers to better understand how natural and anthropogenic forces affect the coupled human-environment system and to identify critical links within the transportation network that have the largest impact to Bangladesh’s economy when disrupted.
Reference: Passalacqua, Paola, et al. "Geomorphic signatures of deltaic processes and vegetation: The Ganges‐Brahmaputra‐Jamuna case study." Journal of Geophysical Research: Earth Surface 118.3 (2013): 1838-1849.
The Jamuna Valley of the Bengal basin was in part developed by an early Holocene (~10.5 ka) Tibetan-sourced glacial lake outburst megaflood. This same event scoured a smaller, tangential channel east of the Jamuna valley into Sylhet Basin. This flood-carved channel on the western margin of the basin remained unoccupied until delta aggradation allowed the Brahmaputra River to re-occupy it ~7.5 ka. Strong topographic and tectonic influences suggest that the river was primed to occupy the topographically low basin interior. In spite of these conditions, the Brahmaputra remained largely restricted to this marginal paleo-flood course for the next ~2500 years. We use numerical modeling to investigate two possible scenarios driving the persistence of this channel course: (1) local backwater effects from a semi-permanent 10,000 km2 lake within the basin due to enhanced early Holocene Indian Summer Monsoon conditions, and (2) antecedent morphological control of the paleo-flood channel form. We simulate mid-Holocene conditions in Sylhet Basin by perturbing several physical parameters within a 1-D channel profile model and a 2-D depth-averaged hydrodynamic model to determine preferential flow path selection between two possible pathways. Neither a local backwater effect nor a reduction of the topographic slope to simulate pre-subsidence topography along two pathways appear to be plausible explanations for exclusion of flow to the central basin. Instead, the introduction of a scour along the western margin flow path is the only mechanism tested that induces a strong preference for bypass of the basin. Thus, both field and modeling evidence indicate that Himalayan-sourced megafloods modified the lowstand surface of the Bengal basin, creating antecedence that strongly influenced Holocene delta evolution and river channel behavior. These results suggest that geologically instantaneous, event-scale processes may exert long-term control on sediment dispersal patterns and thus preserved stratigraphy at the basin scale, even in large systems with pronounced tectonic and climatic influences.
A
The Landlab project creates an environment in which scientists can build a numerical landscape model without having to code all of the individual components. Landscape models compute flows of mass, such as water, sediment, glacial ice, volcanic material, or landslide debris, across a gridded terrain surface. Landscape models have a number of commonalities, such as operating on a grid of points and routing material across the grid. Scientists who want to use a landscape model often build their own unique model from the ground up, re-coding the basic building blocks of their landscape model rather than taking advantage of codes that have already been written. Whereas the end result may be novel software programs, many person-hours are lost rewriting existing code, and the resulting software is often idiosyncratic and not able to interact with programs written by other scientists in the community. This individuality in software programs leads to lost opportunity for exploring an even wider array of scientific questions than those which can be addressed using a single model. The Landlab project seeks to eliminate these redundancies and lost opportunities by creating a user- and developer-friendly numerical landscape modelling environment which provides scientists with the fundamental building blocks needed for modeling landscape processes. The Landlab will include a number of independent, interoperable components such as (1) a gridding engine to handle both regular and unstructured meshes, (2) an interface for space-time rainfall input, (3) a surface hydrology component, (4) an erosion-deposition component, (5) a vegetation dynamics component and (6) a simulation driver. The components interface with each other using the basic model interface (BMI) and will be fully compatible with the CSDMS Modeling Toolkit. Users can design unique models simply by linking together already-built components into a “new” landscape model within the landlab environment. Alternatively, users can design new landscape models by creating process components that are specialized for individual studies and linking these new components with preexisting Landlab components.
2
The Luke and Higley basins of Phoenix, AZ (USA) were once endorheic basins that gradually filled up with sediments (i.e., they aggraded). At the start of the Pleistocene ( ~2.5 Ma), the Salt and Gila rivers integrated into these basins, changing them to exoreic rivers. Aggradation remained after integration and persisted to the present day, producing a continuous local base-level rise. In the presence of aggradation, the expectation is to observe channel infilling on pediments and alluvial fans. However, we observed the exact opposite condition in some cases: increased incision. We hypothesize that a massive lateral shift in piedmont base-level produced by Salt and Gila rivers integration explains the increase in the local incision, despite the basin aggradation. We tested our hypothesis through a 1D diffusion model representing an idealized piedmont profile under different toe displacement conditions. The diffusion simulations support the hypothesis that base-level rise and lateral shifting can generate piedmont incisions. Indeed, incisions would only appear if u*tan( β)/v > 1, where u, v, and β are the rate of lateral shift, rate of base-level rise, and initial elevation angle of the piedmont, respectively. Our findings suggest that some past sedimentological records of pediments and alluvial-fan systems could have been misinterpreted (i.e., associated with base-level fall). However, additional research is necessary to confirm our initial findings. +
A
The MUltiDisciplinary Benthic Exchange Dynamics (MUDBED) program explored the impact of physical and biological processes on turbidity and sediment properties in a muddy estuary. Hydrodynamics, settling velocity, and erodibility influence suspended sediment concentrations. In turn, flux convergence and divergence modify suspended sediment and seabed properties, thereby impacting Estuarine Turbidity Maxima (ETM). In partially mixed estuaries like the York River, VA variations in stratification and sediment trapping respond to tides, discharge, and winds, and produce a Secondary Turbidity Maxima (STM) that appears seasonally downstream of the main ETM.
A hydrodynamic and sediment-transport model of the York River was developed to examine feedbacks between sediment flux convergence, erodibility, and settling velocity. The Regional Ocean Modeling System (ROMS) was coupled to the Community Sediment Transport Modeling System (CSTMS). The model included bed consolidation by representing critical shear stress for erosion as increasing with depth in the bed and with time since deposition. Multiple grain types were used having settling velocities from 0.1 – 2.5 mm/s. Calculations of turbidity and erodibility showed similar patterns to observations and exhibited high spatial variability in both the along and across channel directions. Sediment trapping in the model led to the development of an erodible pool of sediment near the observed STM. Enhanced erodibility elevated suspended sediment concentrations in that area for some time after sediment convergence processes diminished. This poster will explore the behavior of the model and evaluate the use of the simplified bed consolidation model within a full three-dimensional numerical model. +
2
The Marlborough Fault System (MFS) consists of four main dextral strike-slip faults which link subduction with oblique continental collision in central New Zealand. It is a zone where crustal transfer from one plate to another is occuring, where a subduction interface is developing within a previously intact plate and which varies along and across strike. We use a variety of tools including topographic fabric, river evolution, thermochronology and geological history to understand the deformation that is occurring across the MFS. We show that the eastern and western ends of these faults have had completely different evolutions through time. These apparently continuous strike-slip faults have coalised into through going structures quite recently. The signature of these processes can be found in the landscape. +
The McKenzie River is a major tributary of the Willamette River, itself a major tributary of the Columbia River, and is the primary source of water and power for Eugene, Oregon, a city of 175,000 people. Young (Holocene) High Cascades volcanism defines the headwaters of the Mckenzie River basin, with a significant source at Clear Lake (13,000,000 cubic meters), fed by springs and yearly snowmelt. Upstream of Clear Lake are 3 seasonal lakes, Lost (256,000 cubic meters), Lava (308,000 cubic meters), and Fish (559,000 cubic meters), that fill up during the yearly snowmelt and slowly drain over a period of 1-2 months through Holocene age lava flows. We have established pressure transducers in Lost and Fish lakes, which will ground-truth lake volume time series using LiDAR and high-resolution satellite imagery timeseries. Downstream of Clear Lake are USGS stream gauges which appear to respond to the seasonal lake drainage via variations in base flow. We look at how seasonal lake drainage varies over time as a function of drainage area and snowmelt, as well as the controls these have on Clear Lake’s discharge. The volcanic terrain of the High Cascades creates an unusual hydrologic system in which seasonal lake drainage acts like a massive slug test, which is repeated year after year. This “slug test” could help elucidate the size and resilience of the High Cascades aquifer and the legacy of volcanic landscape construction on surface/subsurface hydrology. +
The Mississippi River is a major source of water and sediment to the Gulf of Mexico. Several restoration strategies for the eastern Louisiana coast are linked to the Mississippi River. Anthropogenic factors, e.g., locks, dams, levees, cutoffs, bank-protection, resulted in substantial change in the sediment load of the Mississippi River. In this study, we compiled historical water and sediment data from ~ 1851 through 1929 and constructed approximate historical sediment rating curves. These historical rating curves are compared to the current records at Tarbert Landing, Baton Rouge, and Belle Chasse. Further, we utilized a 2D morphodynamic model to simulate and quantify the deposition footprint of the historical Caernarvon crevasse event that occurred during the Great Mississippi Flood of 1927 at Breton Sound Basin, LA, USA. This comparative analysis highlighted the change in sediment supply over the past century. We also investigated the implications of this change on the land-building potential from engineered diversions. This analysis also underlined the importance of measuring in-situ fine sediment flocculation parameters due to its present uncertainty and impact on inducing deposition of clay. +
The Orangeburg Scarp along the U.S. east coast is a paleoshoreline that formed during the mid-Pliocene climate optimum (MPCO; 3.3-2.9 Ma), a warm period considered to be an analog for modern climate. At present, the Orangeburg Scarp varies in elevation from ~33 to ~82 m along its ~1000-km length, implying that it has been heterogeneously warped since its formation. Recent studies suggest that some of the variations in the paleoshoreline elevation might be driven by regional sediment loading and unloading. In this study, we use a gravitationally self-consistent sea-level model to quantify the influence of sediment erosion and deposition on sea-level changes since the MPCO along the U.S. east coast. We drive the sea-level model with existing ice models and a new compilation of sediment redistribution, which is inferred from erosion rates in basins draining the Appalachians and deposition rates in the lower portions of these basins and offshore. Preliminary results suggest that sediment redistribution can significantly perturb paleoshoreline elevations along the Orangeburg Scarp, which suggests that accounting for regional erosion and deposition can advance our ability to estimate ice volume during at the MPCO and improve our understanding of the evolution of continental margins. +
The Pacific Northwest is the only region in the conterminous United States with a sizable number of glaciers (328 glaciers totaling ~380 km ). The glaciers of this region have displayed ubiquitous patterns of retreat since the 1980’s mostly in response to warming air temperature. Glacier melt in partially glacierized river basins in the region provides water for downstream anthropogenic systems (e.g., agricultural water supply and hydroelectric power generation) and sensitive ecological systems (e.g., fisheries, upland riparian habitat). While changes in glacier area have been observed and characterized across the region over an extended period of time, the hydrologic consequences of these changes are not fully understood. We applied a state of the art high resolution glacio-hydrological simulation model along with regional gridded historical and projected future meteorological data, distributed observations of glacier mass and area, and observations of river discharge to predict evolving glacio-hydrological processes for the period 1960-2100. We applied this approach to six river basins across the region to characterize the regional response. Using these results, we generalized past and future glacier change across the entire PNW US using a k-means cluster analysis. Our analysis shows that while the rate of glacier recession across the region will increase, the amount of glacier melt and its relative contribution to streamflow displays both positive and negative trends. Among the characteristics that control the direction and magnitude of future trends, elevation dominates and climatic factors play a secondary role. In high elevation river basins enhanced glacier melt will buffer strong declines in seasonal snowmelt contribution to late summer streamflow for some time, before eventually declining. Conversely, in lower elevation basins, reductions in glacier melt will exacerbate negative trends in summer runoff in the near term. +
The Peace-Athabasca Delta (PAD) in Alberta, Canada, is one of the largest inland deltas in the world. The hundreds of shallow lakes and distributary channel networks contribute to the incredible biodiversity in this region and also form the primary transportation routes for summer boat travel and ice roads in winter. Over the last few decades, however, there has been rising concern over declining lake levels. While the complex and changing hydrology is the focus of many studies, little is known about how changing geomorphology will impact lake water storage.
In this work, I will focus on one shallow PAD lake, Mamawi Lake, which is located near the center of the PAD and forms a key hydrologic connection. A subdelta has been forming in Mamawi Lake since 1982 and, as it continues to grow, may compromise hydrologic connectivity and navigability. To investigate past and future subdelta progradation, I will use Delft3D-FLOW as well as field measurements and satellite remote sensing. To develop a model that acceptably mimics subdelta growth, I will compare observed progradation rates and delta form, as determined from the optical satellite record, with predicted delta growth and planform from Delft3D simulations. By iteratively comparing observed and predicted subdelta characteristics, I can optimize model inputs to create a model that best resembles the historical growth of the Mamawi Lake subdelta. Then, with this optimized model, I will run longer simulations (on the order of 100 years) to estimate potential timelines of lake infilling and loss of navigability. +
The South Fork Eel River (SFER) in the northern California Coast Ranges exhibits characteristics indicative of transient landscape adjustment: stream terraces, knickpoints, and more slowly eroding headwater terrain. A tectonically-induced uplift wave is commonly invoked as the driver of transience in this region. The wave is attributed to the northward migration of the Mendocino Triple Junction (MTJ) where the San Andreas fault, Cascadia subduction zone, and Mendocino fracture zone meet. Nested basin-mean erosion rates calculated from 10Be detrital quartz sand increase downstream along the SFER that roughly coincides with the direction of MTJ migration. This erosion trend is attributed to the proportion of adjusted and unadjusted landscape portions upstream of the locations where the nested 10BE samples were collected. Yet to be determined are the conditions that led to transient erosion. Adjusted and unadjusted landscape portions are separated by a broad knickzone that contains 28% of topographic relief along the mainstem. Knickzone propagation and considerable stream incision is suggested by projection of the upper SFER above the knickzone through the highest flight of strath terraces. These terraces are approximately 80 m above the modern valley floor near the outlet of the SFER. Here we evaluate the pattern of transient landscape characteristics predicted by multiple uplift scenarios using the Landlab modeling framework and constraints provided by previous work in this region. Notably, model outcome when uplift is simulated as a wave is incompatible with the tectonic history of the region and field observations, and the gradient of uplift along modeled streams has an important control on knickpoint generation. +
The Sundarbans National Forest (SNF) is a critical cultural, ecologic, and economic resource to the country of Bangladesh. Despite widespread land use changes in the surrounding region, sedimentation within the SNF has managed to keep pace with local rates of sea level rise (e.g., Rogers et al., 2013). This study explores some of the controls on sedimentation, with the goal of investigating their vulnerability to future change. Specifically, we examine the depth and frequency of platform inundation, suspended sediment concentration (SSC), sediment grain size, and the volume of water exchanged, and how these factors vary across time scales ranging from spring-neap tidal cycles through monsoon-dry season cycles. We observe pronounced seasonality, with the monsoon season experiencing the most frequent platform inundation, highest SSC, and greatest volume of water exchanged. Sediment grain size appears to vary spatially rather than seasonally, with a gradual decrease in grain size away from the primary tidal channel: the nominal sediment source. Of particular interest is how the seasonality of SSC varies between primary tidal channels like the Shibsa River, and the smaller tidal channels delivering sediment to the platform. On the Shibsa, spring tide SSC maxima during the monsoon and dry season are similar (~1.3 g/l), while neap tide SSC maxima are <0.5 g/l in either season. In channels within the SNF, monsoon spring tides exhibit peak SSC >1 g/l, while dry season SSC is always <0.5 g/l. Understanding why the source of local sediment (i.e., the primary tidal channel) behaves differently from the channels delivery that sediment to the platform presents an important knowledge gap that future research will examine in detail. +
The U.S. Geological Survey (USGS) is one of the largest providers of U.S. hydrologic data, which are used in informing policy, managing water resources, and countless scientific studies. Modern science is increasingly conducted by performing analysis on data that are first loaded from an online database into a local computational environment. To facilitate open and reproducible hydrologic science, the USGS has developed dataRetrieval (R), dataretrieval (Python), and DataRetrieval.jl (Julia): three packages providing multi-language access to hydrologic data from the U.S. Geological Survey, as well as the multi-agency Water Quality Portal. The Julia, Python, and R programming languages are open source, high-level (easy to program), have large communities of scientific users and developers. Notably, these three languages are the core languages supported by Project Jupyter, and run in the Jupyter Notebook, a popular web-based interactive computing platform.
These packages, collectively the “data retrievals,” allow scientists to programmatically access USGS hydrologic data in Julia, Python, and R. The “data retrievals” enable more than simply the retrieval of environmental data, they also provide tooling for data discovery, enabling users to find monitoring sites and identify what types of data are available at which locations. These functions represent foundational building blocks allowing for the creation of fully reproducible hydrologic workflows from data acquisition to output plots, tables, and reports. +
The U.S. Geological Survey is tasked with developing sustainable integrated hydrologic models that are interoperable with models from partner agencies and academia.
As a steppingstone towards integrating hydrologic models in a compiled code framework, we have developed a Python package for hydrologic process development and prototyping. This code base, named “pywatershed”, can seamlessly interact with our compiled code framework (MODFLOW 6) via its BMI interface. One can obtain numerically identical results from a model enhancement prototyped in Python or implemented in compiled code.
The advantages of code prototyped in Python are lower cost (person*hours) and greater approachability (less specialized programming knowledge required). The drawback of prototype code is that it may be slower to run for certain applications. A prototyping approach supports proof-of-concept development and model hypothesis testing, particularly for domain experts who may be more comfortable in Python and who bring new approaches or novel data to integrated model applications. The prototyping approach supports a cost-benefit analysis for making decisions to implement certain hydrologic process representations within the compiled code base.
The current state of this evolving Python package will be described, including: 1) the modular, self-describing design based on control volumes and conservation of mass and energy, 2) numerical performance based on the numpy Python package, the numba Python package (just in time compiling), and compiled Fortran modules called from python, 3) goals and challenges of developing flexibility in the space and time representation of hydrologic processes and the management of fluxes and states between process representations, and 4) the current and upcoming set of hydrologic process representations.
Example notebooks will demonstrate many features of pywatershed. Planned developments will be described and community participation is welcomed.
The US east coast is heavily developed, necessitating adaptive approaches to mitigate property and infrastructure risk from storm events and shoreline changes. One soft-structural approach, beach nourishment, comprises artificial shoreline progradation for property protection. Construction of groins, a hard-structural approach, traps alongshore transported sediments, leading to updrift shoreline growth. Groins create a depositional sediment shadow in their lee, shrinking downdrift shorelines, thereby forcing communities to decide whether to protect properties or to retreat. Our research focuses on how these alternative adaptations may affect coastal risk. We present two field scenarios: West Hampton Dunes, NY, which decided to protect downdrift property through beach nourishment, and Oakwood Beach, NY, which decided to accept buyout offers from federal disaster relief funds. We build a coupled geo-economic model to explore management drivers and controls on coastal morphology and real estate and to analyze the emergent indicators within a two-community system. We quantify benefits as a function of beach width, number of housing rows, and federal property buyouts; costs are a function of groin construction, groin maintenance, and beach nourishment. We compare the net benefits of downdrift nourishment, retreat, and groin removal for different groin lengths, background erosion rates, baseline property values, and discount rates. Results elucidate which approach is most beneficial for coastal adaptation, providing a simple framework to compare future strategies for West Hampton Dunes. This geo-economic tool may prove useful as lawmakers continue to scrutinize fiscal implications of alternative adaptations to coastal risks. +
The USGS Model Catalog compiles and connects data, software, and publications about scientific models developed by the U.S. Geological Survey (USGS) or developed by external organizations and used in USGS investigations. The primary audience for the USGS Model Catalog is researchers who want to learn more about USGS modeling, such as researchers who want to explore existing models and documentation on a specific topic; early career researchers who want to see what models exist in their discipline; or members of large, integrative projects who want to discover opportunities for linking different process models. The catalog is composed of modular features that we hope other projects can build upon. The data model and repository component are published at https://doi.org/10.5066/P9WU0F71 and https://doi.org/10.5066/P9IVG9VZ.
The catalog is never complete! Come take a look at what's there now, learn what we're planning, and give input about what content and features would help you and your communities. Visit the catalog at https://data.usgs.gov/modelcatalog. +
A
The Underworld code was designed for solving (very) long timescale geological deformations accurately, tracking deformation and evolving interfaces to very high strains. It uses a particle-in-cell based finite element method to track the material history accurately and highly-tuned multigrid solvers for fast implicit solution of the equations of motion. The implementation has been fully parallel since the inception of the project, and a plugin/component architecture ensures that extensions can be built without significant exposure to the underlying technicalities of the parallel implementation. We also paid considerable attention to model reproducibility and archiving — each run defines its entire input state and the repository state automatically.
A typical geological problems for which the code was designed is the deformation of the crust and lithospheric mantle by regional plate motions — these result in the formation of localised structures (e.g. faults), basins, folds and in the generation of surface topography. The role of surface processes — redistributing surface loads and changing boundary conditions, is known to be significant in modifying the response of the lithosphere to the plate-derived forces. The coupling of surface process codes to Underworld is feasible, but raises some interesting challenges (and opportunities !) such as the need to track horizontal deformations and match changes to the topography at different resolutions in each model. We will share some of our insights into this problem. +
2
The WBMsed model offers a unique framework for studying river flux dynamics, ranging from basin to global scales. When it was first published in 2013, WBMsed included a spatially and temporally explicit suspended sediment flux module, developed within the WBMplus (FrAMES) hydrological framework. Since then the model has been used for a range of studies and been extended to include a bedload, water density, and particulete nutrients modules. The model's hydrological and geomorphic processes were improved to better represent riverine and landscape dynamics. These include the introduction of a flooding mechanism, spatially-explicit river slope, and land use inputs. Here we will outline these model development and its use for river and coastal studies. +
The Weather Research and Forecasting Model Hydrological modeling system (WRF-Hydro) is an open-source community model and has been used for a range of projects, including flash flood prediction, regional hydroclimate impacts assessment, seasonal forecasting of water resources, and land-atmosphere coupling studies. We modified the CASCade 2 Dimensional SEDiment (CASC2D-SED) model and adapted it to the WRF-Hydro platform. The model mainly contains two components: (1) sediment erosion and transport from overland to channel, and (2) sediment transport through the channel to the watershed outlet. Based on USLE formula, sediment is eroded by overland flow with consideration of soil type, vegetation type as well as bed slope. Following through the direction of steepest slope, the eroded sediment is transported grid by grid all the way to the channel, meanwhile deposition process is parameterized by sediment’s settling velocity, time step and water depth. Once sediment gets into channel, it will be carried by the stream flow to the watershed outlet. To test its robustness, we adapted WRF-Hydro sediment model to the watershed of Goodwin Creek, Mississippi, USA. A preliminary model-data comparison indicates our model is capable of reproduce water and sediment discharge during a storm event. +
The Whitewater River in southeastern Minnesota is one of numerous tributaries of the upper Mississippi River. However, unlike many of the tributaries to the Mississippi north of the Whitewater River, which received glacially derived sediment and water directly from the Laurentide Ice Sheet margin, the Whitewater watershed remained ice free. Instead, glacial–interglacial cycling predominately shaped the watershed via changes in base-level and sediment inputs on the mainstem Mississippi. Thus, the aggradation and incision of the mainstem upper Mississippi acted as the primary source of glacial signal in the watershed. In this study, we seek to understand how the complex glacial history of the upper Mississippi River impacted the long-profile evolution of the Whitewater River. To do this, we combine one-meter LiDAR topography with the topographic analysis package, LSDTopoTools to study the modern channel network and adjacent terraces. By extracting modern and historic river terraces, we are able to reconstruct channel long-profile changes over time. We pair this study with bedrock geology composition and depth to bedrock for the watershed to understand transitions within the watershed from transport to detachment limited and linkages between bedrock type and channel morphology. This work allows us to better constrain how glacial–interglacial signals propagate through fluvial systems via tributaries. This information can better inform our understanding of how tributaries respond to mainstem changes and how these changes propagate over time. +
The accumulated history of crater production and destruction is recorded in crater size-frequency distributions (CSFDs), which can be leveraged to understand the evolution of planetary surfaces and atmospheres. For example, researchers used the size-frequency distribution of craters interbedded with fluvial deposits to provide an upper-bound of ~1.9 bar on paleo-atmospheric pressure at the time of river activity on Mars. Interpretations of paleo-atmospheric pressure are most sensitive to preservation and mapping of smaller craters (<50 m), which may be influenced by fluvial reworking. We simulated river-delta development with coeval crater production; river-delta simulation is completed with pyDeltaRCM and craters 10 to 300 m are generated according to an imposed crater production function and placed randomly and with a parameterized geometry. We quantified preservation of craters in the stratigraphy after 1, 10, or 100 Ma of coupled landscape evolution. Our results indicate that crater preservation is highly variable (ranging fully eroded to fully preserved), but preserved fraction generally increases with crater diameter. Despite rivers removing a substantial portion of smaller craters (>40% of craters <50 m are at least partially eroded); exponential increase in crater counts with decreasing size overwhelms any meaningful fluvial preservation bias. Our findings bolster previous studies that assert fluvial reworking is a secondary controls to atmospheric ablation on CSFDs, indicating that paleo-atmospheric pressure upper-bounds may be translated into estimates (with uncertainty). +
The accuracy of sediment transport models depends heavily on the selection of an appropriate sediment settling velocity. Determining this value for mud suspensions can be difficult because the cohesive particles within the mud can aggregate to form flocs whose sizes are a function of hydrodynamic and physiochemical conditions of the suspension. Here we present a new model for predicting floc size in a dynamic way as a function of the hydrodynamic conditions and inherited floc sizes. The new model is a simple modification to the existing Winterwerp (1998) floc size model. The modification is significant in that it yields predictions that are more inline with observations and theory regarding the upper limit on ultimate floc size. The modification we propose is to make the ratio of the applied stress on a floc over the strength of the floc a function of the floc size relative to the Kolmogorov microscale. The outcome of this modification is that flocs are not allowed to surpass the Kolmogorov microscale in size and that calibrated aggregation and breakup coefficients obtained at one suspended sediment concentration can be used to predict floc size under other concentration values without recalibration of the coefficients. In this paper, we present the motivation for the modification, the functionality of the modification, and a comparison of the updated model with laboratory and field data. Overall the model shows promise as a tool that could be incorporated into larger hydrodynamic and sediment transport models for improved prediction of cohesive mud transport. +
The active volcano Ol Doinyo Lengai is located in the magma-rich southern Eastern Branch of the East African Rift and erupts unique low-temperature carbonatites. Between 2007 and 2010, the volcano had several explosions and erupted with ash falls, and lava flows (VEI 3) that caused damage to the nearby communities. Although this volcano has been studied for decades, its plumbing system is still poorly understood, in part, because of the lack of precise observations of surface deformation during periods of quiet and unrest. This study investigates the volcanic plumbing system of Ol Doinyo Lengai and surroundings using data from the permanent Global Navigation Satellite System (GNSS) network monitoring the volcano called TZVOLCANO and Interferometric Synthetic Aperture Radar (InSAR) observations. We calculate velocities for 6 continuously operating GNSS sites distributed around Ol Doinyo Lengai for a timespan between 2016 and 2021 and also process InSAR data for nearly the same time-period to constrain surface motions. We then use the GNSS deformation signals and InSAR observations to solve for magma sources embedded in a homogeneous and elastic half space using the USGS inversion code dMODELS. Both GNSS and InSAR inversion results quantify a deflating spherical geometry source at a depth of ~1.3 km with a volume change ∆V of -0.05 ± 0.01x106m3 located east of Ol Doinyo Lengai and southwest of the dormant volcano Gelai. InSAR inversions alone also suggest a closing dike model at a depth of ~9 km similar to the location resolved for the 2007 Ol Doinyo Lengai dike. This work suggests a shallow magma reservoir exists east of Ol Doinyo Lengai and that the 2007 dike is actively contracting. This magma source influences the onset, size, duration and hazard of eruptions of the volcano, and plays a significant role in triggering slip on border faults during early phases of continental rifting through stress transfer. +
The characteristics of soils control the influence of how land use and land cover (LULC) change the global water, energy, and biogeochemical cycles. Plant health, and the exchange of energy, water and biogeochemical components at the surface interface is partly controlled by soil properties. Different soil types modify vegetation responses to existing climate forcings, and each soil type also responds differently to the same land-use practice. Currently, Earth System Models often use single soil columns with averaged properties and the same properties stay constant over time regardless of LULC changes. This leads to uncertainties in assessing LULC impacts. To improve the estimates of land surface change in Earth System Models, we build a soil degradation model to compute annual soil properties from 850 to 2015.
The model includes three parts: first, to quantify human LULC impacts, we collected 1099 observations from 174 published literature of human impacts of agriculture, pasture, grazing, and vegetation harvest on soil organic carbon (SOC), texture, and bulk density. Under each LULC unit, we defined the combined impact of LULC, management, climate (represented by NPP or moisture index), and soil texture on each soil property based on observations and regression models. In the second part, we link an existing LULC dataset to four hydrologic soil groups from 850 to 2015, based on demonstrated soil preferences for eight LULCs under current conditions. We conclude that humans prefer hydrologic soil groups (HSGs) in order from B, D, C, to A (generally from high to low silt content). This ranking was applied to construct the history of LULC on each soil type at the half-degree grid resolution. Results primarily distribute croplands to HSG B in 850, while HSG A has the most undisturbed area. Over time, preferred soils (HSGs B and D) experience increased use for cropland areas, while poor soils (HSGs C and A) are occupied predominantly by increasing areas in grazing land and secondary non-forests. Finally, based on the established LULC and soil relations from 850 to 2015, we altered soil properties in each soil group according to global variations of environmental factors to model human-induced soil degradation. Vertical and temporal variations are applied based on observations. Results demonstrate how soil degradation occurs under historical LULCs and provide better land surface characteristics to improve Earth systems modeling.
The coastline of SE Alaska was submerged by post-Pleistocene sea level rise from at least 16,000 cal yrs BP until it stabilized about 10,600 cal yrs BP. The submerged continental shelf was modeled using bathymetry and other data to identify areas exhibiting high potential for the occurrence of archaeological sites. Two seasons of underwater archaeological survey have been conducted at this location (NSF OPP -#0703980 and 1108367), using multibeam sonar, side-scan sonar, sub-bottom profiler, real-time video from remotely operated vehicle (ROV), and sea floor sampling using a van veen grab sampler and sediment screening. This data has produced a detailed overview of Shakan Bay, located on the northwest corner of Prince of Wales Island. +
The controls exerted on stream channel form by rock properties contribute to landscape morphology. Here we focus on understanding the effects of bedrock properties on surface processes and landscape evolution in the Guadalupe Mountains of South Eastern New Mexico. We surveyed bedrock reaches in three different watersheds, taking rock samples, Schmidt hammer measurements, and videos of reaches. We used structure for motion to generate orthomosaics of surveyed reaches from the video. We then traced fractures and determined fracture intensity, average length of fractures per square meter, for each reach. XRD data taken from samples collected in the field, along with carbonate dissolution techniques, demonstrates the minerology of reaches. In relatively small watersheds there is little climate variation which is demonstrated using PRISM climate data. Lithologic variance and channel steepness are the main control on differences in rock properties within stream channels. Steeper channels cut across more bedding planes than shallow reaches, influencing both fracture intensity and Schmidt hammer values. At the landscape scale rock strength is reflective of differential weathering due to differences in climate for similar rock types. Results from this study will help to reconcile our understanding of the effect of climate and lithology on surface processes at different scales. It will also create a widely applicable methodology for measuring, interpreting, and comparing various metrics of rock properties. +
The development of bedrock steps and waterfalls in mountain rivers locally changes flow hydraulics and can thereby alter patterns of sediment transport and erosion. While bedrock steps are thought to erode sometimes faster and sometimes slower than river reaches eroding without steps, it is unclear how differences in step frequency and morphology (e.g., the presence of many small bedrock steps and waterfalls versus the presence of a single large waterfall) alter channel dynamics and erosion rates at the reach scale. Furthermore, we do not know whether some or all step-rich channels are part of a transient knickzone or could be formed at steady state. Here, we use cosmogenic beryllium-10 (Be-10) erosion rates to examine whether bedrock steps alter the reach-averaged erosion rate. We find that all step-rich channels erode faster than or equal to catchment-average rates and preliminary analyses show that reach-scale erosion rates increase with increasing sediment flux, increasing grain size, and increasing step frequency. We compare our field results with a reach-scale erosion model we developed that combines both fluvial erosion at bedrock steps and fluvial erosion in reaches lacking steps. Our new reach-scale erosion model allows us to infer changes in erosion rates as a function of step frequency and step and channel morphology (e.g. dimensions of steps, and width and slope of channel between steps). This model will help interpret the impact of bedrock steps on erosion rates and determine their role in either adjusting or maintaining river profiles. +
The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding. Here, I present a cellular automata model of fault scarp and colluvial wedge evolution built using CelllabCTS and the GrainHill sediment physics from Landlab. The model appears to accurately reflect the development of real fault scarps. When one analyzes the model results, one may note interesting groupings of cells with similar sediment transport histories as the fault scarp evolves. These groupings appear to match real world sedimentological facies, such as 'debris' and 'wash' facies, which brings up an interesting question of how best one can compare model results with geological data. I discuss some approaches and quandaries and how one may go about about translating modeling concepts and language into field concepts and language and vice versa. +
The efficiency of fluvial sediment and particulate organic carbon (POC) burial in river deltas strongly depends on their depositional environment, which can range from protected incised valleys to exposed active margins. Here, we hypothesize that the formation and infilling of incised valleys from Holocene sea-level rise led to increases in fluvial sediment burial efficiency, and, consequently, POC burial. To test this, we developed a new incised valley fill model that estimates incised valley volume and fill rates. We apply this model to all river deltas globally (n~11,000), some of which are filled already but many are still infilling since Holocene sea-level rise slowed ~6ka BP. The rate of incised valley infilling is determined based on global model estimates of fluvial sediment and POC supply. We use our model to explore the magnitude of POC burial during the Holocene, including its potential for global climate regulation. +
The escalating rate of forest mortality, fueled by increasing climate variability and the spread of exotic pests and diseases, is a growing global concern. A significant contributor to this issue in North America is the Emerald Ash Borer (EAB), an invasive pest responsible for the widespread destruction of ash trees (Fraxinus spp.), resulting in a sharp increase in the number of snags. Snags, or dead-standing trees, present significant risks to infrastructure, including buildings and electrical distribution systems. Our study focuses on New Jersey, a highly urbanized state with an extensive electric grid that intersects forested areas, many of which are populated with Fraxinus trees. In this research, an annual risk assessment methodology for evaluating the threat that Fraxinus snags pose to the electrical distribution infrastructure is presented, particularly in the context of New Jersey's ongoing efforts to enhance the resiliency and capacity of its electric distribution network through capacity upgrades. Employing an integrated approach composed of GIS, differential equations, and applied regression modeling, our analysis spans three northern New Jersey counties: Warren, Sussex, and Morris. These counties, which are under the utility management of New Jersey Central Power and Light, harbor a significant portion of the state's Fraxinus population, making them crucial areas for assessing the impact of snags on the electrical distribution infrastructure under different network parameterizations. +
A
The evolution of fluvial deltas involves a complex web of processes, many of which are yet poorly understood. In particular, the role of organic matter (peat) accumulation on delta dynamics still remains elusive. Here, we present a simple geometric prism model that couples the evolution of the delta plain with the accumulation of organic-rich sediment. The model is able to explain the observed coupling between the accommodation/peat accumulation ratio and the quality of buried peat/coal deposits in the delta plain. Similarly to multiple modern and ancient organic-rich sedimentary environments, the model preserves the maximum volume fraction of organic sediment in the delta plain when the overall accommodation rate approximately equals the rate of peat accumulation. Further analysis of the model under simple scenarios of base-level rise and pivot subsidence shows that organic matter accumulation can either enhance or alleviate shoreline transgression. +
2
The evolution of human-flood systems is shaped by complex interactions between hazards, policy decisions, individual risk perception, and the exposure of properties. This complexity is further stressed by the changing climate conditions, making it crucial to understand how these systems will evolve and which regions and populations will be most affected. In this regard, we calibrated socio-environmental models across US coastal communities with historical records of flooding hazards, National Flood Insurance Program (NFIP) economic losses, NFIP policy purchases, housing density, and housing values. Next, we forced future projections of sea level rise, storm surge, and rainfall intensity under Shared Socio-economic Pathways (SSP) SSP245 and SSP585 up to 2100 for each coastal communities, and forecasted the future flooding loss, NFIP active policies, housing density, and housing values. We found significant regional and demographic variations in human-flood dynamics. The Pacific coast, due to high rainfall and storm surge threshold has less exposure, but a more sensitive housing market and NFIP participation rate. In contrast, the Atlantic and Gulf coasts are more exposed to hazards but have a less sensitive housing market and NFIP participation. Relative to historical average, we forecast flood loss to increase by 130% (SSP585) and 25% (SSP245) with a modest policy coverage of 16% (SSP585) and 13% (SSP245). Furthermore, we predict socially vulnerable communities to experience disproportionately more economic loss with a slow policy uptake rate, leading to a growing insurance coverage gap under both climate scenarios. Finally, we tested the effect of heightening levees across the US coast on future flood risk, and found that levee investment can stabilize housing markets, but it won’t eliminate flooding risk entirely due to increased rainfall intensity. Understanding how human-flood systems co-evolve under climate risk helps to recognize population and property at risk and make robust mitigation strategies.
The extent to which chemical and mechanical erosion each contribute to the erosion of cave passages in limestone is an open question. In mixed cave riverbeds that are partially alluviated and partially exposed limestone bedrock, we sometimes see clearly scalloped bedrock. The uniquely soluble properties of limestone imply that these scallops that tessellate to comprise the scalloped bedrock are the result of chemical dissolution. However, because we see silt, sand, and gravel, and because when we visit the same reach of the cave river many times, we see those sediment deposits shift in size and location, we infer that there may also be physical abrasion from sediment impacts on the scalloped bedrock surface. In this paper, we compare the equations that describe dissolution of limestone with those that describe abrasion of bedrock to prove that dissolution and abrasion may be co-occurring processes. Using our numerical model, DKARST (Does karst abrasion result in scalloped tunnels?), in conjunction with previous data from dissolution studies, we quantified parameters that delineate four distinct erosional zones according to the likelihood of contribution to overall erosion from dissolution, abrasion, or both processes combined. We then generalized those erosional zones to a range of scalloped bedrock morphology characteristic wavelengths. Our investigation of the role of mechanical erosion to the scalloping of bedrock in caves provides insight into the settling velocities of particles in turbulent flow over rough beds, as well as the relative roles played by mechanical and chemical processes in broader scale landscape evolution, particularly in karst regions dominated by carbonate bedrock. +
The formation and evolution of channel networks is a critical control on coastal landscapes and fluvial stratigraphy. Analysis of drainage networks often divides them into two regions: a dendritic upstream catchment with behavior governed by erosional processes resulting from the interaction of climate and tectonics, and a transition to a distributary reach governed by depositional processes close to the coast. The landscape built by these larger coastal distributaries is typically dominated by low-relief floodplains and numerous smaller stream networks. Despite the importance of these networks in governing the routing of fluids and sediments that build these landscapes, network geometries and characteristics remain poorly studied and understood. The northern Gulf of Mexico coastal plain is a depositional landscape characterized by the channels and deposits of large fluvial systems that have been prograding into the Gulf of Mexico since the Mesozoic, and hosts smaller stream networks locally known as the Coastal River Basins. Using a compilation of lidar bare earth elevation datasets we systematically identify and map these tributary stream networks across the coastal plain. We calculate for each basin a series of stream metrics that include local relief, slope, and length/contributing area. Additionally, our high-resolution (2m) elevation data allows for detailed analysis of the stream heads and drainage divides between each identified basin. We find that the basin divides for these networks are older distributary channel belts built by the larger fluvial systems. This indicates that the organization and geometry of these coastal networks is initially set and controlled by depositional processes, but the resulting basin morphology is nearly identical to those of drainage networks in predominantly erosional settings. We explore how drainage networks can form in depositional settings as the consequence of sedimentary processes such as river avulsion and ridge formation, with important implications for understanding drivers of drainage network formation, the speed and scale of drainage reorganization in coastal settings, flow routing during floods, and fundamental controls on the creation and preservation of fluvial stratigraphy.
The formation of the branching channel network is controlled mainly by water discharge and the boundary shape of receiving basin. The understanding of channel morphology is important because it controls the sediment diversion in a river delta, and determines the sustainability of coastal zones. Numerical models of river deltas have improved remarkably over the past two decades. However, the long-term (millennial scale) simulation of real delta systems remains rare. Here, we attempt to reconstruct the Lafourche Delta channel network, active 1600-600 years before present, with a simple numerical model (Moving Boundary Model for Distributary Channel Networks MB_DCN). Runs with 10 basin boundary shapes and 6 river discharge rate scenarios using the Moving Boundary Model for Distributary Channel Networks (MB_DCN) show that each scenario produced distinguishing channel characteristics including a complex channel network, diverse progradation rates and channel numbers, and number of bifurcations. For the appropriate basin shapes, reasonable water discharges and common sediment transport parameters, MB_DCN produces a channel network that resembles the Lafourche Delta channel network morphology and progradation rates. Our preliminary results suggest that the basin boundary shape and water discharge are the most important control of the distributary channel network in terms of channel geometry and progradation rates. +
The frequency of high temperature events is increasing globally under the current climate change conditions. These extreme events have important consequences for society, affecting public health, the regional habitability and the global economy. We evaluate the changes in frequency and distribution of high temperature events over North America, using three different indices and a set of regional climate simulations from the Coordinated Regional Climate Downscaling Experiment (CORDEX). Our results show an increase in the number of high temperature days per summer, in addition to an increase in the frequency of heat wave events for the 21st century. The results reveal large variability among the regional climate models and boundary conditions from the driving models. The increase in the frequency of high temperature simulations examined over North America advocates for strategies to prevent potential effects on food availability, public health and the environment. +
The geologic history of major river canyons is strongly debated, as is the extent to which river canyons record climatic and tectonic signals. Fluvial and hillslope processes work in concert to control canyon evolution; rivers both set the boundary conditions for adjoining hillslopes and respond to delivery of hillslope-derived sediment. But what happens when canyon walls deliver boulders that are too large for a river to carry? River canyons commonly host large blocks of rock derived from resistant hillslope strata. Blocks have recently been shown to control the shapes of hillslopes and channels by inhibiting sediment transport and bedrock erosion. Here we present Blocklab, a 2-D model within the Landlab modeling toolkit that uses a hybrid discrete-continuum framework to track block transport throughout a river canyon landscape. This is the first process-based model for canyon evolution that incorporates the roles of blocks in both hillslope and channel processes. Our model reveals that two-way negative channel-hillslope feedbacks driven by block delivery to the river result in characteristic planview and cross-sectional river canyon forms. Internal negative feedbacks strongly reduce the rate at which erosional signals pass through landscapes, leading to persistent local unsteadiness even under steady tectonic and climatic forcing. Surprisingly, while the presence of blocks in the channel initially slows incision rates, the subsequent removal of blocks from the oversteepened channel substantially increases incision rates. This interplay between channel and hillslope dynamics results in highly variable long-term erosion rates. These autogenic channel-hillslope dynamics can mask external signals, such as changes in rock uplift rate, complicating the interpretation of landscape morphology and erosion histories. +
The hazards faced by retreating barrier island systems to the increased rates of sea level rise predicted over the coming century and beyond lacks historic precedent. Consequently, exploration of the sedimentological record can provide key insights into how barrier systems might behave in the future. Continental shelves around the world preserve records of former barriers as relict deposits, providing a window into past behaviors. These relict barrier deposits are usually considered to originate from purely allogenic processes, or external environmental forcing, with barrier abandonment typically attributed to episodes of increased rate of sea level rise. However, using a cross-shore morphodynamic model, we show that the internal dynamics of migrating barriers can also result in autogenic deposition of relict sediments even under a constant rate of sea level rise. Subsequently, we propose that allogenic forcing from sea level rise and autogenic forcing from internal dynamics might interact to produce novel barrier retreat behaviors, with the potential to be recorded on the seabed by relict deposits. We model barriers through a range of scenarios with interacting autogenic and allogenic forcing, showing that the morphology of deposits might be used to infer the relative influence of external and internal processes. Intriguingly, our results demonstrate that the internal dynamics of barriers can both amplify and dampen losses of shoreface sediment to the seabed during increased rates of rise, in some cases with internal processes increasing the risk of barrier destruction. Future classification of relict deposits in the field could help explain if and when these allogenic/autogenic interactions have taken place, revealing long term hazards to modern barrier systems that have not previously been described. +
The high speed winds of a hurricane account for 95% of a hurricane’s storm surge. Thus, parametric wind models are vital components of numerical storm surge modeling. These parametric hurricane wind models are used as inputs for a storm surge computation to hindcast and forecast hurricane surge heights. These wind models are dependent on several input parameters including but not limited to the radius at which the maximum wind speed of the hurricane occurs and the speed of the maximum winds. The impact of these input parameters on the final surge computation is not well known. Our study is a sensitivity analysis of the effect of uncertainty in the input parameters on the uncertainty in the final computation of the storm surge model. This study will help us to understand the robustness of a parametric wind model, the parameters that must be precise in order to reduce model error, and can aid in model simplification. +
The impact of climate on tectonics has been the muse of tectonic geomorphologists for more than 30 years. However, few natural examples exist where connections between climate and tectonics are clear. Here, we present a study of the Sangre de Cristo Mountains (SCM), CO, a normal fault system at the northern tip of the Rio Grande Rift. The SCM represents an ideal natural setting to explore the impact of climate on spatial and temporal slip patterns along the range-bounding fault. Preserved glacial moraines and trimlines are used with the Glacier Reconstruction (GlaRe) toolbox to model glacial extents during the last glacial maximum (LGM). A simple line load model is used to explore the impact of glacial melting on clamping stress along the range front fault, and a flexural isostatic model is applied to estimate the footwall response to deglaciation. Results show that glacial melting reduces fault clamping stress, perhaps enabling accelerated fault slip in the post-glacial period. Flexural isostatic results suggest modest footwall uplift of ~4 m due to ice removal. We compare our results to fault displacement, measured from scarps preserved in Pleistocene and Holocene alluvial fans. The spatial pattern and magnitude of Holocene fault displacement are consistent with our flexural isostatic results. Furthermore, Holocene slip rates are at least a factor of three higher than Pleistocene slip rates. We infer that the flexural isostatic response to footwall deglaciation primarily controls the spatial and temporal fault slip patterns during the Holocene. Our results show that climate-modulated glacial ice loading and unloading can pace the spatial and temporal slip on a range-bounding normal fault system. +
The impact of supraglacial meltwater on the motion of the Greenland Ice Sheet is strongly correlated to spatial and temporal variability of meltwater input. Meltwater infiltrates the bed through moulins and can reduce effective pressure and, consequently, accelerate the ice. However, the subglacial conduit system evacuates the water and can adapt to accommodate different water inputs. The timing of water infiltration impacts the ability of the system to reach equilibrium state. With the progression of the equilibrium line higher up on the ice under warming climate, it is essential to predict how increased meltwater is going to affect ice motion. Understanding these processes will reduce uncertainty in global sea level rise predictions.
Temporal variability of meltwater input is difficult to measure on the ice sheet due to the difficulties in instrumenting constantly melting stream beds. Therefore, glacier dynamic models rely on surface mass balance models to simulate the discharge. Those models usually neglect spatial properties of the drainage basin and are not able to reproduce the peak meltwater discharge in supraglacial streams. Lags between peak melt and peak discharge vary from one stream to another, and factors influencing the delay between peak melt and peak discharge have not been thoroughly explored. For this reason, we propose to build a distributed and physically based model using Landlab to reproduce flow routing on the Greenland Ice Sheet. This model will produce discharge values on a grid using three grid layers that calculate: 1) meltwater production, 2) flow direction, and 3) water displacement velocity. Model inputs will be weather, elevation, and snow coverage data. This model will enable us to explore and extract the main parameters influencing lags and predict the spatial pattern of infiltration lags at an ice sheet scale. +
The impacts of climate change on extent of permafrost degradation in the Himalayas are not well understood due to lack of historical ground-based observations. The area of permafrost exceeds that of glaciers in almost all Hindu Kush Himalayan (HKH) countries. However, very little is known about permafrost in the region as only a few local measurements have been conducted which is not sufficient to produce the fundamental level of knowledge of the spatial existence of permafrost. We intend to simulate permafrost conditions in Western Himalayas in India using Hyperspectral and Microwave remote sensing methods and computational models for the quantitative assessment of the current state of permafrost and the predictions of the extent and impacts of future changes. We also aim to identify the strength and limitations of remotely sensed data sets when they are applied together with data from other sources for permafrost modelling. We look forward to modelling ground temperatures using remote sensing data and reanalysis products as input data on a regional scale and support our analysis with measured in situ data of ground temperatures. Overall, we approach to model the current state and predictable future changes in the state of permafrost in Western Himalayas and also couple our results with similar research outcomes in atmospheric sciences, glaciology, and hydrology in the region. +
The increasing demand for sediments as source material for beach nourishment projects highlights the need to understand inner-shelf transport dynamics. At cape-related shoals, from where sedimentary materials are customarily extracted, the variability in particulate transport and related bedform evolution are not well understood.
To analyze bed elevation variability at a shoal adjacent to Cape Canaveral, Florida, an acoustic Doppler current profiler (ADCP) was deployed in spring 2014 at the outer swale of Shoal E, ~20 km south east of the cape tip at a depth of ~13 m. ADCP-derived velocity profiles and suspended particle concentrations were used to quantify instantaneous temporal changes in bed elevation (dζ/dt) using a simplified version of the Exner equation. Using mass conservation, temporal (deposition and entrainment) and spatial gradients in suspended sediment concentrations were calculated, although neither bed-load fluxes nor spatial gradients in velocities were considered.
Calculated values for instantaneous dζ/dt ranged from erosion at ~1e-3 m/s to accretion at 0.5e-3 m/s. Most of the variability was found at subtidal (<1 cycle/day) and tidal (~2 cycles/day) periodicities. Bed changes were small (<0.005 m/s) when tidal motions were important, e.g. from May 6 to 16, whereas subtidal motions at periods of 1 and 8 days dominated erosion/accretion events between May 16 and 31. Values suggest a bed erosion of 3.1e-3 m during ~30 days of the experiment, which was 2 orders of magnitude less, and had a contrary tendency to the average accretion of ~150e-3 m in 37 days measured between July 28 and September 3 at the edge of Southeast Shoal, i.e. ~5 km to the northwest.
In addition to the fact that measurements were not performed simultaneously at the same location, the discrepancy in dζ/dt could be attributed to the underestimation of bed changes due to the exclusion of bed-load fluxes. Despite several uncertainties, these findings provide preliminary evidence regarding the role of seasonal and storm-driven subtidal flows in particulate transport at cape-associated shoals. Our methodology can be used to inform numerical models of sediment transport and morphological evolution along inner continental shelves.
The influence of hydrodynamics on delta morphology is well-understood: fluvial, tidal and wave processes sculpt deltas into characteristic shapes that serve as geomorphic signatures of the underlying dynamics. This work examines how complex interactions between major rivers and tides influence the dendritic, island-dense morphology of the Ganges-Brahmaputra-Meghna Delta (GBMD). In the uppermost delta plain, fluvial processes dominate. Moving downstream, tides begin to interact with fluvial dynamics in a “mixed” process zone. Near the terminus of the GBMD in the Bay of Bengal, tidal processes take over, particularly in the western, abandoned lobes of the delta. This work focuses on how sediment transport and floodplain deposition patterns and rates change along that process transition. Using geomorphic metrics such as island area, aspect and channel sinuosity within new machine learning techniques, we resolved areas of the delta that display similar process signatures. Ideal island cases were selected from several zones across the fluvial-tidal transition. Using Delft3D, we modeled the patterns of geomorphic change that result from multiple flood ranges (low, medium and extreme) and sediment cases (-50%, average +50% suspended sediment concentration of 4 cohesive grain classes). Preliminary results indicate floods can deposit 2 – 3 cm of sediment per year across the delta, albeit in distinct patterns due to local differences in hydrodynamic processes. By using this highly-resolved nested model approach, deposition rates can be upscaled to estimate the amount of sediment being reworked within the individual process zones. The results obtained can then be used to illustrate how the different hydrodynamic zones contribute to the large-scale evolution of the delta, and explore how the system will respond to predicted global sea level rise over the next century. +
A
The interaction of the subsiding, subtropical limb of the Hadley circulation and the easterly North Pacific trade winds establishes a persistent thermal inversion about halfway up the eastern flank of the Big Island of Hawaii. This restricts convective rainfall to the lower elevations, resulting in stream channels that cross an order-of-magnitude rainfall gradient, active ephemerally above the inversion and perennially below it. Above the inversion–capped cloud layer, precipitation is on the order of 400 mm/yr, and the landscape features thin, weakly-developed soils, gentle hillslopes, and ephemeral, shallowly incised bedrock streams and grassland gullies. Below the inversion, where rainfall is >3000 mm/yr, the perennial streams run through 50- to 100-m-deep gulches, with steep forested walls covered by thick tropical soils that are prone to landsliding. Meter- to 50-meter waterfalls are common downstream of the inversion layer, and incision of the deep gulches may proceed by upstream migration of these knickpoints from the coast. The positions of these knickpoints likely reflect the history of lava flows in these catchments, base level changes due to landsliding at the coast, and the statistics of water and sediment discharge above and below the trade inversion and through time.
This landscape has evolved entirely in the last 0.3 Ma, and thus under conditions of glacial-interglacial climate oscillations. During glacial periods, the inversion’s average elevation was likely depressed, although the magnitude of this depression is not well-constrained. An ice cap that was present on Mauna Kea altered the hydrology of the upper slopes of the mountain, providing a continuous source of meltwater to channels that, in the modern setting, are active only during winter storms and rare hurricane strikes. The frequency and intensity of such storms during glaciations are also not well-known.
To quantify these effects, we would like to use climate models to inform landscape evolution models. A key difficulty in coupling these types of models is the separation of time and spatial scales involved. Global climate models typically run on grids of 1 degree or more, at temporal resolution of seconds and run lengths of years to decades. Landscape evolution models (LEMs) reside at the other end of both dimensions, with typical spatial resolutions of meters to km and temporal resolutions of years or decades. The entire duration of a climate model run may be shorter than the timestep of a typical LEM.
We report initial results from our efforts to bridge the relevant scales by downscaling large-scale climate model output for last-glacial and modern times with NCAR’s regional-scale Weather Research and Forecasting (WRF) model. The predicted precipitation fields are input to a hydrologic model to generate realistic discharge statistics useful for landscape modeling. This modeling chain may be validated for the modern climate using atmospheric observations, including the modern distribution of inversion height, and USGS stream gauge data. For glacial periods, the ability of the weather model to correctly predict snowlines on Mauna Kea provides a first-order point of calibration.
2
The interplay between economic development and climate change exerts countervailing effects on human wellbeing, particularly concerning temperature-related mortality. While economic growth may enhance adaptive capacity and healthcare access, climate change intensifies extreme heat events, posing significant health risks. Carleton et al. (2022) and Barrage (2024) have quantified the effects of climate change and income growth on temperature-related mortality, providing insights into future health trajectories. To discern when climate change impacts on mortality become distinguishable from natural variability, this study introduces the concept of Time of Emergence (ToE). By identifying the ToE, this research – one of the first to apply ToE analysis to climate impacts rather than climate hazards – assesses the moment when climate-induced mortality becomes detectable beyond natural fluctuations, offering insights into the timing and magnitude of extreme-temperature impacts. The findings unveil that in warm regions, climate change may impede or nullify the reductions in temperature-related mortality typically driven by development, underscoring the urgency for targeted adaptation measures and policy interventions to mitigate health risks associated with climate change. +
The last 22 ka, since the Last Glacial Maximum (LGM), is known for significant millennial scale changes in global climate (Barker and Knorr, 2021). Sedimentary deposits in lacustrine and marine basins bear archives of corresponding changes in sediment accumulation. Yet given the scale that the global climate exerts on geomorphological processes on Earth’s surface, generalizations of the relationship between the climate and the erosion remain inconclusive. Whether the possible generalizations could even be applied to all regions has also remained unclear.
Erosion rates are a first-order response to climate of a region. The variability of erosion rates through time are needed for dating of buried surfaces, quantifying soil carbon budgets, and assessing landscape stability. Until now, a truly global analysis of comparing interregional erosion rates has not been available. Recent work in Madoff and Putkonen (2022) addresses this by generating global maps of regional erosion rates since the LGM. These results are supported by corresponding published sediment accumulation rates in sink areas corresponding to given watershed. Results show the spatial extent of higher erosion rates and larger ranges of variability through time in the Arctic and subarctic in contrast to the tropics and mid-latitudes. These results also indicate that the regional variability decreases the further from the past ice sheets a given location is. Finally, a clear take home message from these results is that the regional erosion rates vary both through time and space for the past 22 ka.
* Barker, S., Knorr, G., 2021. Millennial scale feedbacks determine the shape and rapidity of glacial termination. Nature Communications. 12.
* Madoff, R.D., Putkonen, J., 2022. Global variations in regional degradation rates since the Last Glacial Maximum mapped through time and space. Quaternary Research. 1–13. https://doi.org/10.1017/qua.2022.4 +
The long-term (3000 years) morphodynamics of backbarrier tidal basins is studied using a shallow-water hydrodynamic and wind-wave model (Deltf3D-FLOW-WAVE), modified to include fully-coupled marsh organogenic accretion, biostabilization, drag increase, and wave-induced marsh edge erosion. The latter process is implemented with a novel probabilistic algorithm. In simulations run with only sand, a flood tidal delta forms adjacent to the inlet, but marshes do not establish. In simulations run with only mud, instead, marshes establish at the basin margins and prograde seaward. If enough mud is supplied to the basin from the shelf, marsh progradation counteracts edge erosion. Marsh progradation does not completely fill the basin, but leaves open a few km-wide channels, large enough for waves to resuspend sediment. Starting from a basin (almost) filled with marshes, a drop in the external mud supply or an increase in the rate of relative sea level rise cause the basin to empty out by marsh edge erosion, while the marsh platform, aided by reworking of the sediment released by marsh retreat and mudflat deepening, keeps pace even with fast rates (10 mm/yr) of relative sea level rise. Even if the marsh does not drown, the marsh retreats faster if the rate of sea level rise increases, because more sediment is sequestered to fill the newly created accommodation space and is thus not available for marsh progradation. This study suggests that prediction of marsh erosion requires a basin-scale sediment budget, and that edge erosion, not platform drowning, is likely to dominate marsh loss. +
The low-lying tidal reaches of the Ganges-Brahmaputra delta relies on a system of polders (embanked landscapes) to prevent against tidal inundation and storm surge. These polders have increased the total habitable and arable land allowing the region to sustain a population of ~20 million people. An unintended consequence of poldering has been the reduction of water and sediment exchange between the polders and the tidal network, which has resulted in significant elevation offsets of 1-1.5 m relative to that of the natural landscape. Tidal River Management (TRM) and other engineering practices have been proposed in order to alleviate the offset. Previous work suggests if implemented properly with sufficient suspended sediment concentrations (SSC), TRM can be effective on timescales of 5-20 years. However, communities must also agree on how and when to implement TRM. Here, we expand previous numerical simulations of sediment accumulation through field-based constraints of grain size, compaction, and sea level rise. We then model human decision-making for implementation of TRM practices.
Our sediment model employs a basic mass balance of sediment accumulation as a function of tidal height, SSC, settling velocity, and dry bulk density. Tidal height is determined from pressure sensors and superimposed sea level rise rate, as defined by the representative concentration pathways of the IPCC. SSC varies within a tidal cycle (0-3 g/L) and seasonally (0.15-0.77 g/L). Multiple grain sizes (14-27 µm) are used as proxies for settling velocity by Stokes’ Law. Dry bulk density (900-1500 kg/m3) is determined from sediment samples at depths of 50-100 cm. The human dimension is introduced through an agent-based model for community decision-making regarding TRM. +
The lower Mississippi River drains a watershed of over 3.2 million square kilometers. The continental flux of water, sediment, and nutrients passes through the state of Louisiana in the last stretch of its journey to the Gulf of Mexico. A portion of the river detours, pronounced during high flow events, to the gulf through a series of natural and manmade diversions. Systemic understanding of the Mississippi River sediment and water resources partitioning among various outlets or diversions is crucial to the sustained function of the Northern Gulf of Mexico’s communities, habitats, and industries. This study discusses the development and application of a Delft3D FM 3-dimensional hydrodynamic, salinity, and temperature model of the Northern Gulf of Mexico. We used this model to analyze and quantify the tradeoffs among various management scenarios for freshwater allocation in the lower Mississippi River through existing and proposed infrastructure and natural openings. We also explored the possibility of varying the operational strategies of existing structures to investigate the changes in service and protection to communities in the receiving basins. To maximize the benefits of the Mississippi River’s water, sediment, and nutrients, this study emphasizes the continued analysis of management scenarios as an important step in the preservation and protection of the coast of the Gulf of Mexico while sustaining the support of relevant industries. We synthesized scoring metrics to facilitate communication of the efficacy of various management scenarios. The scoring metrics provide an evaluation framework covering physical, ecological and indirect socioeconomic criteria. This approach can be used for other complex natural systems to explore viable strategies and tradeoffs balancing ecosystem services with socioeconomic interests. +
The lower shoreface, a transitional subaqueous region extending from the seaward limit of the surf zone to beyond the closure depth, often serves as a sediment sink or source in sandy beach environments over annual to millennial time scales. Despite its important role in shoreline dynamics, however, the morphodynamics of the lower shoreface remain poorly understood. Previous work highlights discrepancies between equation-based theoretical equilibrium contours and bathymetric data, indicating that models may not accurately reproduce real shoreface cross-shore profiles. Here, we combine energetics-based suspended sediment transport formulae (Ortiz & Ashton 2016, JGR-ES) with wave climate and sedimentological data from Rockaway Peninsula, NY, to understand controls on shoreface morphology and differences between modeled and empirical equilibrium profiles. Analyzing a full wave climate time series from Wave Information Studies (WIS) spanning 40 years at one hour intervals reveals how different components of the wave climate affect suspended transport rates, particularly at varying depths. This results in a different steady-state, or equilibrium profile compared to one computed using single wave parameter inputs. The computed profile shape further changes when computations include reduction in sediment settling velocity due to offshore sediment fining, based on field observations. These profile are then compared to USGS bathymetric shoreface profile shapes at Rockaway and other locations. Our preliminary results appear to rectify the gap between modeled and empirical equilibrium profiles, moving towards a more thorough understanding the evolution of the lower shoreface. +
A
The majority of process studies on alluvial fans have focused on gravely fans. Many fan systems, however, are sourced from basins composed of fine-grained sediments. Deposition on such fans involves deposition from hyperconcentrated- or mud-flows. Many of such fans occur where there is sufficient vegetation to affect and, often, obscure depositional processes.
The modeling effort to be presented is motivated by the occurrence of fine-grained alluvial fans on Mars that feature a network of distributaries floored with coarser sediment and what we interpret to be fine-grained overbank deposits that comprise the bulk of the sediment. We have identified active fine grained fans in the arid Atacama desert deriving sediment from the higher Andes and lowland deposition dominated by muddy sheetflow sediment.
We are constructing a simulation model for deposition on such fans based on the fan-delta model of Sun et al. (2002). The model routes water and sediment through multiple distributaries that can branch, recombine, and avulse. Modeling flow and bedload sediment through the distributaries is relatively straightforward, but overbank deposition and avulsion processes are more problematic to characterize realistically (e.g. avoiding development of "holes" in fans or preventing evolution to a fixed distributary pattern). Our observation of overbank processes on the Atacama fans demonstrates the importance of sedimentation by long shallow sheetflow floods in addition to local levee aggradation. These processes are being implemented into our fan model. +
2
The modern Ohio River network is a Rubrik’s Cube for anyone interested in dynamic river reorganization. Throughout the Quaternary, the cyclic growth of North American ice sheets forced the Ohio drainage network to oscillate between a north-flowing (towards the Gulf of St. Laurence or Hudson Bay) and west / south-flowing (towards the Gulf of Mexico, i.e., the modern river) configuration. These cycles produced a network of overprinted paleo valleys that reflect multiple episodes of river reorganization (the so-called “Teays” paleo river network). The overprinted nature of these valleys makes it very difficult to assess the timing of specific stream capture events. In order to unravel this complex history of river reorganization, geomorphologists can begin by constraining the timing of individual stream capture events that do not overprint older episodes of drainage reversal.
One such event is likely present in Hocking Hills State Park in central Ohio, known for its hundreds of 30-50 m-tall waterfalls. These knickpoints were likely created when the upper reaches of the Salt Creek watershed were blocked by one of the ice sheets, forming a glacial lake that spilled over a drainage divide and rerouted the channel network from a west-flowing to a south-flowing configuration. The stream capture event would have also produced a local base level drop that created the knickpoints. This hypothesis implies that the knickpoints were all created at the same time; if true, we can constrain the timing of the capture event using catchment averaged erosion rates and knickpoint celerity models.
However, the hypothesis also implies that the waterfalls should be located at the same approximate χ value. This is not the case; rather, there is prominent, N-S trend in χ values. Without an explanation for this trend, any age constraints on the capture timing will be suspect.
We used Landlab-based landscape evolution models (LEMs) to explore several possible explanations for the trend in χ values. We found that following a single capture event, the trend can be explained by the specific combination of (a) the pre-capture channel topology; (b) the precise capture location; and (c) the spatial extent of different rock layers. We believe that this in an “Occam’s razer” scenario, because it allows the χ trend to be explained by a single, stream capture forcing. However, without the insights provided by our LEMs, we would have considered multiple forcings or stream capture events to be more likely. These simulations are a novel and interesting case study in how LEMs can be applied to understand unique complexities of specific field sites and also have important implications for using knickpoint celerity models to assess landscape evolution.
The morphodynamics of coast and estuarine environments are known to be sensitive to environmental change and sea-level rise. However, whilst these systems have received considerable individual research attention, how they interact and co-evolve is largely unknown. Through a novel coupling of numerical models, this research is designed to explore the complex behaviour of these systems in terms of fluid flows and sediment fluxes. This includes elucidating the relative influence of various controls on system behaviour and exploring the effects that variable sea levels and changing wave climates may have on their evolution over the mid to longer term.
This research is being carried out through the modification and coupling of the one-line Coastline Evolution Model (CEM) with the hydrodynamic LEM CAESAR-Lisflood (C-L). Progress to date includes a new version of the CEM that has been prepared for integration into C-L. This model incorporates a range of more complex sedimentary processes in quasi-2d and boasts a graphical user interface and visualisation.
The model is being applied and tested using the long-term evolution of the Holderness Coast, Humber Estuary and Spurn Point on the east coast of England (UK). Holderness is one of the fastest eroding coastlines in Europe and research suggests that the large volumes of material removed from its cliffs are responsible for the formation of the Spurn Point feature and for the Holocene infilling of the Humber Estuary. Over the next century it is predicted that climate change could lead to increased erosion along the coast and supply of material to the Humber Estuary and Spurn Point. How this manifests will be hugely influential to the future morphology of these systems and the flood and erosion risk posed to coastal communities. +
A
The morphodynamics of large anabranching sand-bed rivers is investigated using a numerical model of hydrodynamics, sediment transport, bank erosion and floodplain development, operating over periods of several hundred years. Model sensitivity to key parameters is examined, and simulated channel and natural river morphology are compared in terms of the statistical characteristics of channel width, depth and bar shape distributions, and mechanisms of unit bar, compound bar and island evolution. Model results provide insight into controls on the frequency of mobile sand bars and the stability of larger vegated islands. +
2
The morphology of the Earth’s surface is continuously evolving under multiple factors (tectonics, climatic, etc). As the interface between the lithosphere and the atmosphere, the critical zone provides the prime record of these changes and can be directly monitored. Understanding the physical processes that control temporal changes is important to quantify and predict them.
In this context, we aim to constrain the effect of physical rock weathering on erosion rates and their variation over seasonal cycles. We focus our studies on marly badland catchments in the southeast of France. The Draix-Bléone Critical Zone Observatory allowed data collection and experiments over the last 35 years and represents an ideal environment for this project (Mathys et al, 2005). The marly badland of Draix are subject strong weathering and erosion processes, caused by a variety of physical processes, resulting in the formation of a spatially and temporally variable regolith layer. Significant production of regolith is observed during the winter and rapid washing of slopes during the spring and early summer (Bechet et al., 2016). Based on regolith characteristics from the field we will build a 1D model of the dynamic of the regolith. Characterizing the seasonal variability and climatic dependence of regolith production is a prerequisite to predict yearly variations in sediment flux and its evolution under changing climate conditions.
We sampled the upper part of the regolith in the Draix catchment, in four targeted places, to obtain grain size distributions and water contents. Characteristics of the detrital cover that affect the rate of weathering. High-resolution photogrammetry records will enable comparing surface changes (roughness, thickness, grain size) over the seasons. Furthermore, we cleaned a 1m² surface on a ridge of regolith to monitor weathering processes and estimate regolith production during each season. We aim to repeat this exercise at the end of each season; the resulting difference in thickness removed should represent the new regolith formed
Two years of field campaigns are scheduled. We will use our field observations on the temporal variation of regolith characteristics to inform a 1D model of regolith dynamics. In parallel, the second goal of the project will be to spatialize and implement the latter description into a landscape evolution model based on Landlab (Hobleyet al., 2017) to simulate the effects of regolith dynamics on catchment-scale erosion. The development of this new module will be helpful to follow critical-zone evolution in different soil cover contexts.
References:
Bechet, J., J. Duc, A. Loye, M. Jaboyedoff, N. Mathys, J.-P. Malet, S. Klotz, C. Le Bouteiller, B. Rudaz, and J. Travelletti (2016), Detection of seasonal cycles of erosion processes in a black marl gully from a time series of high-resolution digital elevation models (DEMs), Earth Surf. Dynam., 4, 781–798, doi: 10.5194/esurf-4-781-2016.
Hobley, D. E. J., J. M. Adams, S. S. Nudurupati, E. W. H. Hutton, N. M. Gasparini, E. Istanbulluoglu, and G. E. Tucker (2017), Creative computing with Landlab: an open-source toolkit for building, coupling, and exploring two-dimensional numerical models of Earth-surface dynamics, Earth Surf. Dynam., 5, 21–46, doi: 10.5194/esurf-5-21-2017.
Mathys, N., S. Klotz, M. Esteves, L. Descroix, and J. M. Lapetite (2005), Runoff and erosion in the Black Marls of the French Alps: Observations and measurements at the plot scale, Catena, 63, 261–281, doi: 10.1016/j.catena.2005.06.010.
A
The motion of sediment in water is caused by fluid pressure gradient forces, primarily drag, on sediment grains. Turbulence-resolving experiments show significant temporal and spatial variability of fluid and sediment motion and particle forces at all stages of sediment transport. The signature of turbulence structures and their modification by sediment is apparent from incipient motion to vigorous suspension.<br>
This presentation introduces a numerical model that combines large eddy simulation (LES) of turbulence and the distinct element method (DEM) of granular motion. The LES and DEM models are fully coupled in momentum. Information from the LES is used to specify forces on the DEM particles, and those particle forces are given in an equal and opposite direction in the filtered and discretized Navier-Stokes equations at each grid cell in the finite volume LES.
Parameterization of turbulent sediment transport processes is the basis of any well founded model of morphodynamics in fluvial and marine environments. Current parameterizations rely on a mixture of theory and empirical evidence. LES-DEM simulations can be performed in conditions that are difficult to reproduce in the laboratory and that stretch the limits of theory. It is hard to build an apparatus that can produce sediment transport under field-scale cnoidal waves, on sloping beds, with currents of arbitrary direction, and a range grain size distributions. Further, even in simple unidirectional flows only rough empirical relations exist for the critically important suspended sediment rate of entrainment.<br>
Validation of the LES-DEM approach is essential before development of transport relations for large-scale morphodynamic models. A series of LES-DEM simulations of unidirectional flow over flat beds of medium sand, ranging from no transport, to bedload, to vigorous suspension are presented. Simulations of flat sand beds under oscillatory waves and unidirectional flow downstream of a backward-facing step are compared to laboratory measurements. Simulations over ripples and through vegetation are also presented.<br>
Examples of some of the simulations can be previewed at the links below.<br>
START_WIDGET29f742305bb07dd0-264END_WIDGET<br>
START_WIDGET29f742305bb07dd0-265END_WIDGET<br>
START_WIDGET29f742305bb07dd0-266END_WIDGET<br>
2
The movement of sea ice is influenced by a number of factors, from winds to ocean currents. As climate change continues to occur rapidly, understanding sea ice drift in the Arctic is a key parameter to understanding the effects of rising temperatures in the region. Recent literature has shown that the Arctic and the Antarctic are most affected by global warming, which raises questions regarding climate justice, as most of the carbon emissions causing anthropogenic climate change are produced in other regions. To analyze this impact, we employ artificial intelligence to predict sea ice drift velocity based on external features. Machine learning is the process of computers gaining insights by seeing and correlating large quantities of data. Using external parameters, including wind speed, and drift velocity ground truth as the inputs of the model, we train multiple different architectures and compare the results. Particularly, we experiment with a convolutional neural network (CNN), a random forest (RF), and a support vector machine (SVM). We also experiment with various model specifications. This research leads to a greater understanding of the Arctic’s response to climate change. +
The natural elevation of the vast, flat landscape of the lower Ganges-Brahmaputra-Meghna (GBM) remains remarkably stable despite persistent relative sea level rise (rSLR). This stability stems from the tight coupling of the land and tides through a robust negative feedback induced by periodic flooding with sediment-rich water. As water levels increase, the inundation depth and duration also increase resulting in more sediment deposition. This has a stabilizing effect and largely negates the initial increase in water level such that the elevation surface appears unchanged. We refer to this stable elevation as the equilibrium elevation.
Here, we investigate the strength of the inundation feedback and the resulting equilibrium elevation. We identify three main controls on this feedback - (1) annual rate of rSLR, (2) mean tidal range (TR), and (3) mean suspended sediment concentration (SSC). We explore the realistic parameter space of each using a simple, zero-dimensional mass balance model. Specifically, we ask (1) what equilibrium elevations are feasible, (2) how these equilibrium elevations compare to tides (e.g., relative to mean sea level (MSL) or mean high water (MHW)), and (3) how equilibrium elevation impacts the duration (hydroperiod) and intensity (depth) of a typical inundation cycle. Results show an incredibly robust feedback for most conditions with the notable exception of low SSCs (< 0.1 g/L). This low, yet realistic value of SSC represents a tipping point at which the equilibrium elevation drops precipitously. At higher rates of rSLR (> 8mm/yr) and lower TR (< 2 m) the equilibrium elevation results in complete drowning of the platform. +
A
The overall size of the Chesapeake Bay “dead zone” is quantified by the Bay’s hypoxic volume (HV), i.e., the volume of water with dissolved oxygen (DO) less than 2 mg/L. In order to improve estimates of HV, DO was subsampled from the output of three dimensional model hindcasts at times/locations matching the set of 2004-2005 stations monitored by the Chesapeake Bay Program. The resulting station profiles were then input into an interpolation program to produce Bay-wide estimates of HV in a manner consistent with non-synoptic, cruise-based estimates. Interpolations of the same stations sampled synoptically as well as multiple other combinations of station profiles were examined in order to quantify uncertainties associated with interpolating HV from observed profiles. The potential uncertainty in summer HV estimates resulting from profiles being collected over two weeks rather than synoptically, averaged ~5 km^3. This is larger than that due to sampling at discrete stations and interpolating/extrapolating to the entire Bay (2.4 km^3 ). As a result, sampling fewer, selected stations over a shorter time period is likely to reduce uncertainties associated with interpolating HV from observed profiles. A function was also derived, that, when applied to a subset of 13 stations, significantly improved estimates of HV. Finally, multiple metrics for quantifying Bay wide hypoxia were examined, and cumulative hypoxic volume was determined to be particularly useful, as a result of its insensitivity to temporal errors and climate change. A final product of this analysis is a nearly three-decade time series of improved estimates of HV for Chesapeake Bay. (Submitted March 2013 to Journal of Geophysical Research. For a pdf pre-print contact Carl Friedrichs at cfried@vims.edu .) +
The present study uses the Sedflux stratigraphic model to simulate the Late Pleistocene evolution of the Eastern Beaufort Continental Shelf, Canadian Arctic. During this period, the proximity and the dynamics of the Laurentide Ice Sheet created a complex glacial environment. Modeling such environments thus presents challenges. Modules and input parameters have to be able to simulate major fluctuations in sea-level and sediment supply, an ever evolving source of sediments, a large outwash plain, sudden outburst floods, permafrost aggradation, glacial isostasy, etc. In addition, detailed understanding of glacially-influenced environments in general and the glacial history of the local region specifically make it difficult to estimate parameters such as sediment supply. This poster thus presents the challenges and the potential solutions in using SEFLUX to simulate the stratigraphy of a glaciated shelf such as the Beaufort Shelf. +
2
The propagation of environmental signals through the sediment routing system and their subsequent preservation or removal from the rock record is a central theme in current stratigraphic research. The identification of cyclicity and order in stratigraphic sequences with regard to vertical facies successions, thicknesses, and grain size trends is often used as indicator of preservation of non-random, extra-basinal signals (i.e. climate, tectonics, and base level). However, it is less clear to what extent the processes that alter these signals post-deposition (re-working, scour, and erosion) enhance or diminish cyclicity and order within preserved sediments. Furthermore, stratigraphic trends are often identified in subjective, qualitative terms and may be based more on a priori perception of order derived from depositional systems models than statistically robust trends inherent in the sediment archive. Here, we use a statistical metric to objectively evaluate order vs. disorder in the stratigraphic record in an attempt to identify the likelihood of a disordered (random) response to orderly (non-random) depositional processes. We utilize a quantitative geochemical and sedimentological dataset from the Ganges-Brahmaputra-Meghna delta (GMBD) to identify distinct fluvial sediment packages (defined as meter to 10s of meters thick sand packages similar in scale and character to modern bar forms) and statistical trends in their vertical successions across the delta. We begin by considering that the boundaries of these fining-upwards packages are defined by >50% increases in grain size from one sample to the next in a vertical succession (although other thresholds are evaluated as well). A runs metric “r” is then calculated by identifying streaks of increasing or decreasing sediment package thicknesses and volume weighted mean grain size. This metric is then compared to the output of a Monte Carlo simulation of 5000 synthetic boreholes created by random shuffles of the observed borehole data to determine the likelihood of a similar succession of sediment body thicknesses and grain size trends being generated by chance. Preliminary results indicate that the vast majority of observed thickness successions in the GBMD are statistically “disordered”, with regional variability correlated to discrete geomorphic provinces within the delta. Of note, sediment thickness trends from the main braidbelt exhibit the lowest probability of being generated by random chance, followed by the lower delta plain, and lastly by Sylhet basin, a semi-enclosed sub-basin in northeast Bangladesh that has experienced episodic occupation by the mainstem Brahmaputra River throughout the Holocene. Similar results (with some notable exceptions) are found within grain size runs analyses, with Sylhet basin exhibiting the least amount of order with regard to vertical changes in grain size. Previous studies have identified Sylhet basin as a site of rapid mass extraction, suggesting a possible inverse relationship between stratigraphic order and rates of sediment extraction in fluvial systems. These results lay the groundwork for future studies in the utility of simple statistical measures in identifying random vs. ordered successions of sediment packages as indicators of process-response relationships preserved in the stratigraphic record.
The recent incursion of Data Analytics and Big Data has inspired many fields to venture in. Although a late comer, as compared to financial and bioinformatic areas, geosciences have fast picked up momentum in past two years. We will summarize here quantitative efforts, which require computational means beyond a laptop, in machine learning, deep learning and visualization. The examples will be drawn from (1) delineation of three-dimensional sub-surface three -dimensional fault structure illuminated by tens of thousands of hypocenter from earthquake aftershocks in central Italy using unsupervised machine learning (2) Recurrent Neural Networks (RNN) for delineating earthquake Patterns Based on Complete Seismic Catalog created by large-scale finite element Modelling (3) A highly efficient computational interactive Virtual Reality (VR) Visualization Framework and workflow for Geophysical exploration (4) forecasting the intensity trend of the Earth's natural electromagnetic pulse field signal prior to large earthquakes using chaos theory and radial basis functions (RBF) as deep neural network. +
A
The response of the wave-dominated coasts to sea-level rise is dominated not by inundation, but rather by the dynamic response of sediment transport processes to perturbations of the sea level. In a regime of sea level change, the predominant response of the wave-dominated shoreface depends upon the time-dependent response of the shoreface itself to changes in sea level as well as the potential changes to the shoreline. Sediment transport processes on the shoreface remain poorly understood, complicating predictions of equilibrium shoreface shapes and even net sediment transport directions. However, presuming an equilibrium geometry, energetics-based, time-averaged relationships for cross-shore sediment transport provide a framework to understand the characteristic rates and types of shoreface response to perturbations to either the sea level or the shoreline boundary. In the case of a sea-level rise, we find that the dominant perturbation for a barrier system is not the sea-level rise itself, but rather the movement of the shoreline by overwash. The characteristic response time of the shoreface itself increases significantly at depth, suggesting that the lower shoreface response to a sea level change can be significantly delayed. To study the interactions between the characteristic timescales of shoreface evolution and barrier overwash, we apply a numerical model of barrier profile evolution that couples shoreface evolution with barrier overwash. This integrated model provides a tool to understand the response of barrier systems to changes in sea level over the late Holocene to the modern. The model also investigates the potential behavior of barrier systems as they (and their human occupants) respond to predicted increased rates of sea-level rise over the coming centuries. +
2
The role of climate change on landscapes is one of the most difficult remaining challenges in geomorphology. It is thought that climate primarily modifies landscapes through sediment production and transport in rivers. However, collecting the data needed to resolve the relationship between climate and sediment transport has remained elusive. This issue stems from a lack of a methodology that can work in a wide variety of river environments. Furthermore, this problem is made pressing by a need to understand the coming effects of human-induced climate change.
To address this problem, I developed a model to capture sediment transport using luminescence, a property of matter normally used to date sediment deposition. Luminescence is generated via exposure to background ionizing radiation and is removed by exposure to sunlight. This behaviour is sensitive to sediment transport and could potentially be used to infer sediment transport parameters. I derive the model by performing a simultaneous conservation of sediment mass and absorbed radiative energy expressed as luminescence. The derivation results in two differential equations that predict the luminescence at any point in a river channel network. The model includes two key sediment transport parameters, the sediment transport velocity and the storage-center exchange rate. From these parameters, other key sediment transport variables such as the characteristic transport length-scale and the sediment virtual velocity can be calculated. These parameters can be constrained by determining the model’s luminescence parameters through field measurement and lab experiments.
I test my model against luminescence measurements made in rivers where these sediment transport parameters are well known. I find that the model can reproduce the observed patterns of luminescence in channel sediment and the parameters from the best-fit model runs reproduce the known sediment transport parameters within uncertainty. The success of the model, and the advent of new technology to measure luminescence using portable devices, suggests that it may now be feasible to collect critical sediment transport data cheaply and rapidly. This method can now be used to test outstanding hypotheses of the influence of climate on sediment transport.
The sediment bed and the water column are tightly coupled in shallow water systems including large portions of the continental shelf. For instance, the continental shelf seafloor receives ~48% of the global flux of organic carbon to the seabed and the shelf benthic flux serves as a key source of nutrients for sustaining marine life. Observational studies of sediment-water exchange require concurrent measurements in both compartments; however, these are difficult to obtain and rarely available. Numerical modelling provides a valuable alternative approach to observational studies, however many previous modeling efforts used simple sediment-water parameterizations that did not capture the nonlinearities of benthic-pelagic coupling. Here, we present a coupled benthic-pelagic model that includes realistic representations of biogeochemical reactions in both compartments, and the fluxes at the interface. The model is built on the modeling algorithms for sediment-water exchange in ROMS and expanded to include carbonate chemistry and anerobic reactions in the seabed. The updated model is tested for three sites where benthic flux and porewater concentration measurements are available in the northern Gulf of Mexico summer hypoxic zone. Model-data comparison demonstrates the robustness of the calibrated model in reproducing the porewater concentration-depth profiles of O2, DIC, TA, NO3 and NH4, as well as the benthic fluxes of the former three. Further sensitivity experiments reveal that labile material input, bio-diffusion intensity and anerobic mineralization pathways are the three major factors regulating the benthic fluxes and porewater concentrations of O2, DIC and TA. To conclude, our model results provide important insights into the variation of sediment-water exchange under different environmental conditions. This model has the potential to be used as a research and management tool to quantify the role of shelf sediment in driving bottom water hypoxia and acidification over continental shelves.
The shoreline is a boundary where survey methods change dramatically, where the time dimension is extremely important, where sediment fluxes are very large, where flotsam is trapped, and where numerical/physical singularities occur as the water depth goes to zero. The shoreline boundary oscillates; and as sea-levels rise what is now shore will become sea. Models of likely response of shorelines require detailed data on the sediment/beach/soil substrates.
We investigated how to obtain the best supporting data using the Louisiana area as example. We investigated to what extent the marine and terrestrial data were already in harmony, and what challenges remain in trying to make one seamless dataset. Of course, technologies like LIDAR carry out highly detailed imaging that achieves this to an extent. But we are focused on direct samplings of the ground-truthing type on which physical properties, fabrics, chemical compositions, grain types, genesis, can be directly determined.
Difficulties: Terrestrial surveys have a different data topology, more focused on soil polygons and boreholes; offshore mappings focus on point-samplings, for instance grabs and cores. Soil descriptions focus on layer-profile identities such as “Mollisol”; offshore datasets focus on bulk textures and compositions. Strong semantic differences exist. Terrestrial areas are greatly modified by agriculture and construction.
Positives: We discovered several information-integration pathways for merging the data from the two realms. Exhaustive searching uncovered data on the onshore soils and riverbed sediments to match the marine data (e.g. dbSEABED). Named geographical locations are linkable with coordinates through gazetteers. Computational methods exist to merge polygon and point data sets. In semantics, glossaries provide some information to link onshore and offshore descriptions. Seamless mappings are demonstrated, useful in support of cross-shore morphodynamic models. +
The shorelines of atoll reef islands (also called motu, sandy cays, or islets) frequently are the only available landforms in an atoll system, e.g. Kwajalein Atoll encompasses over 2174 km² but only 16 km2 of that area is emergent land, and thus understanding the drivers of coastal landscape evolution is vital. In particular, atolls are highly vulnerable to several threats of climate change from accelerated rates of sea level rise (causing flooding or potential drowning) to ocean acidification (decreasing coral reef resiliency) to ocean warming (causing coral bleaching). However, we lack a thorough understanding of the potential drivers of landscape change in these systems. In addition atolls can be exposed to high energy wave climates, however, the carbonate reef platform that encircles the inner lagoon of an atoll, commonly filters much of the incident wave energy. This reef platform or reef flat is typically shallow (1-2 m below MSL) with a near constant depth across the reef-flat width; the reef-flat widths range from a 100s meters to over a kilometer on different atolls. Both numerical modeling and field observations have found that these shallow reef-flats are key for driving wave breaking at the ocean edge of the reef flat offshore of the atoll reef islands and decreasing wave energy at the shoreline. As demand for construction materials increases, these carbonate reef platforms have been excavated, with large pits ranging from 10-80 m in width and average depths of 4 m. This study seeks to understand how the presence of excavation pits on reef flats change the wave energy at the shoreline. Utilizing 1D XBeach model, we investigate the impact of varying excavation pit geometry on the shoreline wave energy. We found that the presence of an excavation pit increases wave energy at the shoreline. +
A
The stratigraphic record is the product of sedimentary processes acting over time. The Regional Ocean Modeling System (ROMS) includes algorithms for the processes of erosion, deposition, and mixing of both non-cohesive (sandy) and cohesive (muddy) sediment, and routines capable of tracking the evolution of event-scale stratigraphy with layers as fine as a few grain diameters thick. Thus ROMS allows users to relate process with product over time scales ranging from a few seconds to years, over vertical space scales of 0.1 mm to meters, and over horizontal space scales of meters to hundreds of kilometers. ROMS requires users to specify the number of bed layers to be tracked at compile time. This improves model efficiency on parallel systems, but complicates the task of tracking stratigraphic evolution. In addition to the number of layers, users can control the minimum and maximum layer thickness and the initial stratigraphy. The effect of these choices and the success of the stratigraphy routines is demonstrated with models of idealized estuaries, deltas, and continental shelves. +
2
The surface geology of Late Cretaceous Western Interior Seaway (WIS) has been extensively studied, and many recent studies suggest the presence of dynamic loading due to flat slab subduction. However, it remains unclear how surface processes respond to tectonic forcing originated from either lithospheric flexural isostasy or sub-lithospheric mantle convection. Landscape evolution models represent an ideal tool to test the surface responses under different tectonic histories, each of which is designed to reflect a certain physical mechanism. In this research, we aim to use forward landscape evolution models to investigate the mechanisms accounting for the characteristics in the observed WIS stratigraphy. In our data-oriented landscape evolution models, where we test different scenarios of lithospheric and mantle forcing, the results suggest that only a geographically migratory subsidence can produce tilted strata and shifting depocenter, both of which are key features in the WIS sedimentary record. This implies that the tectonic subsidence of the WIS likely originated from deep mantle downwelling underneath the westward-moving North American plate. Furthermore, this migratory subsidence of mantle origin can also explain the continental drainage reorganization over middle North America after the WIS and the eastward-shifting sediment flux to the Gulf of Mexico during the Cenozoic. +
The tectonic stress fields induced by lateral and vertical variations in the lithosphere induce crustal deformation and lead to the development of fault and topography. Surface deformation and faulting influence channel processes, which may result in changes in drainage patterns. However, there are few studies that systematically compare and examine the connections among the lithospheric stress field, fault development, and observed drainage patterns on global scales. Here, we compare the directions of the lithospheric stress field, the development of fault and topography, and drainage flow patterns. First, we model the lithospheric stress field by computing the gravitational potential energy based on the crustal structure from Crust 1.0 augmented by a thermodynamically derived mantle thickness and density. We obtain the orientations of most and least compressive horizontal stresses and their inferred regimes and compare those with the World Stress Map (2016). We then extract the directions of active faults from the Global Earthquake Model Global Active Faults Database. Lastly, we extract the river flow paths and drainage network patterns from a digital elevation model from the steepest descent direction in the eight-direction flow. Our results show that there is a general correspondence between the predicted and observed patterns of fault orientation and river flow directions with the horizontal most compressive stress direction. The predicted correspondence among stress field, fault, and drainage patterns vary depending on the stress regime and channel order. We find that some locations show river flow patterns consistent with the predicted directions from fault and topographic development based on Anderson’s fault theory, but there are certain locations that show measurable deviations from the predicted patterns. We investigate those areas to better understand the interaction among shallow subsurface stress fields, surface topography, and drainage patterns.
A
The tidal flats of Roberts Bank in British Columbia, Canada contain large areas of the intertidal zone that are vegetated with eelgrass (Zostera Marina and Zostera Japonica). This vegetation has a variable influence on the flow of tidal waters passing over the tidal flats, which we aim to describe in a large-scale 2D hydrodynamic model.
Vegetation on the surface of the tidal flats causes an increase in the roughness that modifies the flow properties. For submerged vegetation, this roughness is most strongly related to the height of the plants in the water; however, for very flexible plants such as eelgrass, the plant height changes with flow velocity since the plants bend with the currents. The roughness is therefore dependent both on flow depth and flow velocity.
Existing studies concerning the effect of flexible vegetation on flow are mostly focused on the small-scale properties of the velocity and turbulence profiles. Such results cannot be directly incorporated into 2D hydrodynamic models. 3D hydrodynamic modeling is computationally demanding and is therefore less appropriate for large-scale studies and engineering applications over large areas. In order to resolve this computational challenge we developed an integrated formulation of the effects of flexible vegetation on the flow, with the following approach: The roughness is represented through an equivalent Manning’s coefficient, which depends on both the water depth and the flow velocity.
Simulations are performed with the Telemac2d model, which has been modified to incorporate the velocity-dependent friction law. Preliminary results show that the proposed law is able to account for qualitative modifications in the tidal flow. In particular, the simulation provides an asymmetric flow pattern that correctly predicts the slower ebb velocities as compared to flood velocities, as observed in the field. +
The understanding of polar regions has advanced tremendously in the past two decades and much of the improved insight into our knowledge of environmental dynamics is due to multidisciplinary and interdisciplinary studies conducted by coordinated and collaborative research programs supported by national funding agencies. Although much remains to be learned with respect to component processes, many of the most urgent scientific, engineering and social questions can only be addressed through the broader perspective of studies on system scales. Questions such as quantifying feedbacks, understanding the implications of sea ice loss to adjacent land areas or society, resolving future predictions of ecosystem evolution or population dynamics all require consideration of complex interactions and interdependent linkages among system components. Research that has identified physical controls on biological processes, or quantified impact/response relationships in physical and biological systems is critically important, and must be continued; however we are approaching a limitation in our ability to accurately project how the Arctic and the Antarctic will respond to a continued warming climate. Complex issues, such as developing accurate model algorithms of feedback processes require higher level synthesis of multiple component interactions. Several examples of important questions that may only be addressed through systems analyses will be addressed. +
2
The watershed of the Tapartó and Farallones rivers and the La Arboleda stream in the central zone of Colombia’s western mountain range are known to have experienced important debris flow events historically. In the same manner, there is geomorphological evidence that suggests a complex dynamic associated with the conditions of high slope, heavy rainfall and a soil profile with an important development.<br>The geomorphological analysis carried out in these watersheds enabled recognition of different levels of deposits in addition to their stratigraphic characterization. Likewise, radiocarbon dating allowed the establishment of ages between 100 +/- 30 and 2010 +/- 30 years for the different levels of deposits characterized. The integration of geomorphological and stratigraphic information along with radiocarbon dating allowed for the differentiation of the debris flow dynamics of each of the basins and suggests the existence of three phases. The first is an ancient one (with deposits older than 2000 years), followed by a sub-recent dynamic (represented by levels between 1500 and 2000 years old) and a current dynamic, with low incised deposits systems and ages that do not exceed 500 years. Finally, it was established that even though these basins have great potential for the generation of debris flow events of significant magnitude, the deposits show a tendency of decreasing magnitudes in the last 1000 years.<br>These analyses and their results are input to the construction of knowledge in relation to the understanding of this phenomenon in tropical environments and the generation of elements that would allow to address the problem in other zones with similar characteristics in throughout the country. +
A
The west coast of North America is the setting for one of the world’s largest coastal upwelling regions. Large rivers drain from North America into the northern eastern Pacific Ocean, delivering large loads of sediments, as well as nutrients, organic matter and organisms. The Eel River discharges into the North Pacific just north of Cape Mendocino in Northern California. Its annual discharge (~200 m3/s) is about 1% that of the Mississippi, but its sediment yield (15 million tons/yr) is the highest for its drainage area (9500 km2) in the entire continental US. This strongly seasonal signal, generated largely by winter storm events that flush sediment and detritus into the river and down to the sea, generates dramatic nutrient pulses that may play a role in the timing and magnitude of offshore phytoplankton blooms. Understanding how the interannual variability of weather, moderated by slower trends in climate, affects these pulses, which in turn may alter offshore nutrient availability, is something we hope to explore through a detailed modeling framework. In our coupled modeling framework, the watershed is currently represented by the lumped empirical watershed model HydroTrend for its ability to generate high-frequency water and sediment time series in relatively unstudied basins. The atmosphere is represented by the NCEP North American Regional Reanalysis, a model and data assimilation tool. Eventually, we hope to represent the atmosphere with the Community Earth System Model, a powerful tool for studying climate change projections, which will let us talk about possible future impacts of climate change on coastal productivity. The ocean is represented with the Regional Ocean Modeling System, a powerful and very modular, physically distributed model that can efficiently solve fine-scale resolution grids. The coastal biology will be handled by modification of an iron-limited nutrient-phytoplankton-zooplankton-detritus model. +
2
Theories for vertical bedrock river incision are well developed and widely applied; however, understanding how bedrock rivers laterally erode their banks and develop into wide bedrock valleys is a frontier topic in geomorphology. I use a modified version of the Landlab lateral erosion component coupled with the sediment-flux dependent vertical incision component in Landlab to explore the fundamental question of how valley width and widening rates are related to sediment on the channel bed. The lateral erosion component widens valleys through lateral undercutting and eventual collapse of bedrock valley walls. The modified lateral erosion component allows the user to set a characteristic block size of collapsed bedrock material. Collapsed material with smaller blocks sizes is rapidly transported away from the valley wall, allowing continued widening, while collapsed material with larger block sizes protects valley walls from further widening until it has weathered into transportable grain sizes. Model simulations show that valleys are wider in landscapes where collapsed material is closer in size to bedload sediment and narrower in landscapes where collapsed material is much larger than bedload sediment. I also use the newly modified lateral erosion/valley widening component together with additional Landlab components to explore the effects of variable discharge and changes in sediment flux on valley width and valley widening rates. This set of model experiments is a step towards a more nuanced and quantifiable framework for describing and predicting bedrock valley widening through time. Numerical models that include physical processes of valley widening are necessary for further advances of geomorphic applications such as numerical modeling of climate-driven strath terrace formation and hillslope–channel coupling. +
Theories for vertical bedrock river incision are well developed and widely applied; however, understanding how bedrock rivers laterally erode their banks and develop into wide bedrock valleys is a frontier topic in geomorphology. I use a modified version of the Landlab lateral erosion component coupled with the sediment-flux dependent vertical incision component in Landlab to explore the fundamental question of how valley width and widening rates are related to sediment on the channel bed. The lateral erosion component widens valleys through lateral undercutting and eventual collapse of bedrock valley walls. The modified lateral erosion component allows the user to set a characteristic block size of collapsed bedrock material. Collapsed material with smaller blocks sizes is rapidly transported away from the valley wall, allowing continued widening, while collapsed material with larger block sizes protects valley walls from further widening until it has weathered into transportable grain sizes. Model simulations show that valleys are wider in landscapes where collapsed material is closer in size to bedload sediment and narrower in landscapes where collapsed material is much larger than bedload sediment. I also use the newly modified lateral erosion/valley widening component together with additional Landlab components to explore the effects of variable discharge and changes in sediment flux on valley width and valley widening rates. This set of model experiments is a step towards a more nuanced and quantifiable framework for describing and predicting bedrock valley widening through time. Numerical models that include physical processes of valley widening are necessary for further advances of geomorphic applications such as numerical modeling of climate-driven strath terrace formation and hillslope–channel coupling. +
A
Theories have been proposed using idealized tracer age modeling for ocean ventilation, atmospheric circulation, soil, stream and groundwater flow. In this research we developing new models for the dynamic age of water in hydroecological systems. Approaches generally assume a steady flow regime and stationarity in the concentration (tracer) distribution function for age, although recent work shows that this is not a necessary assumption. In this paper a dynamic model for flow, concentration, and age for soil water is presented including the effect of macropore behavior on the relative age of recharge and transpired water. Several theoretical and practical issues are presented. +
2
There exists a rich understanding of channel forms and processes for rivers with unidirectional flows, and for their estuarine components with bidirectional flows. On the other hand, complementary insight on the transitional reach linking these flows has not been well developed. This study highlights the analyses of high resolution, high accuracy bathymetric surveys along a coastal plain river at 30 - 94 km upstream of the estuary mouth. The goal of this work is to identify geomorphic indicators of the fluvial-tidal transition channel. Trends with sharp breaks were detected in along-channel variations of depth, hydraulic radius, channel shape, bed elevation and sinuosity, but cross-section area of flow provided the greatest insight. The transition channel is characterized as a reach with greater than 50% decline in area of flow relative to the background values at the upstream and downstream ends. Further downstream the river is a mixed bedrock-alluvium system, and a 22 km reach of discontinuous bedrock outcrops has a marked influence on local channel metrics, and corresponding backwater effects on upstream metrics. Despite the confounding effects of bedrock on channel form the transition channel linking estuarine and fluvial channel segments is apparent as a 13 km geomorphic discontinuity in flow area along a channel reach of relatively uniform width. Finally, it is proposed that bedrock outcrops enhance tidal energy dissipation and influence the position of the fluvial-tidal transition reach, and associated geomorphic and hydrodynamic features. +
There is growing recognition that outwash events are potent agents of morphological change in some coastal regions. Outwash associated with inundation from the back side (bay, lagoon, sound, or marsh) occurred during Hurricane Harvey in Texas (2017) and Hurricane Dorian in North Carolina (2019). In both cases, floodwaters crossed the barrier islands and drained to the ocean through gaps in the primary dune lines, incising deep (~2-m) channels 30- 100-m wide in the islands and depositing the sand in the ocean. In both cases, partial recovery occurred within days and months as nearshore and beach processes generated spits, bars, berms, and overwash fans that rebuilt the beach and closed the channels, creating a series of ponds. Normally, washover deposits are quickly (1 – 2 years) revegetated with beach grasses that trap wind-driven sand and initiate dune building. However, in Texas, North Carolina, and several other locations where outwash channels were observed, the channels have remained largely unvegetated and no dunes have appeared. We have adapted a simple conceptual model to account for these observations. The model argues that the rate of vegetation growth depends, at least partially, on the amount of vegetation already present. In the case of overwash, material is deposited on older washover fans or platforms that contain live plants, seeds, rhizomes, and other organic material, and (following others) we suggest that the amount of vegetative material is a function of washover-deposit thickness. In contrast, when washout channels are filled, none of that material is present, and our model assigns these deposits very low initial amounts of vegetative material. Thus, vegetation growth on the two landscapes occurs at different rates, and the former outwash channels are unable to build elevation as quickly, leaving them continuously exposed to overwash events. A quantitative implementation of this model provides results that match well with observations at several sites.
This poster shows a top-down modeling work using a simple climate and economy model to examine pathways to achieve the climate stabilization targets stipulated in the Paris Agreement. A motivation for this presentation is to seek a possibility to complement this type of work with a bottom-up approach such as agent-based modeling so that climate mitigation pathways can be investigated from different angles.
In this work, we raise two issues: 1) Negative emission technologies such as Bioenergy with Carbon dioxide Capture and Storage (BioCCS) play an ever more crucial role in meeting the 2°C stabilization target. However, such technologies are currently at their infancy and their future penetrations may fall short of the scale required to stabilize the warming. 2) The overshoot in the mid-century prior to a full realization of negative emissions would give rise to a risk because such a temporal but excessive warming above 2°C might amplify itself by strengthening climate-carbon cycle feedbacks. It has not been extensively assessed yet how carbon cycle feedbacks might play out during the overshoot in the context of negative emissions.
This study explores how 2°C stabilization pathways, in particular those which undergo overshoot, can be influenced by carbon cycle feedbacks and asks their climatic and economic consequences. We compute 2°C stabilization emissions scenarios under a cost-effectiveness principle, in which the total abatement costs are minimized such that the global warming is capped at 2°C. We employ a reduced-complexity model, the Aggregated Carbon Cycle, Atmospheric Chemistry, and Climate model (ACC2), which comprises a box model of the global carbon cycle, simple parameterizations of the atmospheric chemistry, and a land-ocean energy balance model. The total abatement costs are estimated from the marginal abatement cost functions for CO2, CH4, N2O, and BC.
Our results show that, if carbon cycle feedbacks turn out to be stronger than what is known today, it would incur substantial abatement costs to keep up with the 2°C stabilization goal. Our results also suggest that it would be less expensive in the long run to plan for a 2°C stabilization pathway by considering strong carbon cycle feedbacks because it would cost more if we correct the emission pathway in the mid-century to adjust for unexpectedly large carbon cycle feedbacks during overshoot. Furthermore, our tentative results point to a key policy message: do not rely on negative emissions to achieve the 2°C target. It would make more sense to gear climate mitigation actions toward the stabilization target without betting on negative emissions because negative emissions might create large overshoot in case of strong feedbacks.
A
This presentation addresses an important limitation to scientific productivity in fields that rely on computational modeling of landscape processes. Landscape models compute flows of mass, such as water, sediment, glacial ice, volcanic material, or landslide debris, across a gridded terrain surface. Science and engineering applications of these models range from short-term flood forecasting to long-term landform evolution. At present, software development behind these models is highly compartmentalized and idiosyncratic, despite the strong similarity in core algorithms and data structures between otherwise diverse models.
We report progress on a proof-of-concept study in which an existing landscape model code is adapted and enhanced to provide a set of independent, interoperable components (written initially in C++). These include: (1) a gridding engine to handle both regular and unstructured meshes, (2) an interface for space-time rainfall input, (3) a surface hydrology component, (4) an erosion-deposition component, (5) a vegetation component and (6) a simulation driver. The components can communicate with each other in one of two ways: using a simple C++ driver script, or using the Community Surface Dynamics Modeling System (CSDMS) Model Coupling Framework.
A central element is the gridding engine, which provides the ability to rapidly instantiate and configure a 2D simulation grid. Initially, the grid is an unstructured Delaunay/Voronoi mesh. Because the internal representation of geometry and topology is quite generic—consisting of nodes (cells), directed edges, polygon faces, etc.—the software can be enhanced to provide other grid formats, such as a simple raster or a quad-tree representation. The gridding engine also provides basic capabilities for finite-volume numerics, such as calculation of scalar gradients between pairs of neighboring cells, and calculation of flux divergence within cells.
Our hope is that these interoperable and interchangeable components with simple, standardized interfaces, will transform the nature and speed of progress in the landscape sciences by allowing scientist-programmers to focus on the processes of interest rather than on the underlying software infrastructure.
This presentation discusses the implementation of component-based software design in Eco-hydrologic modeling. As a first step, we present development and integration of a radiation component that uses the local topographic variables to compute shortwave and longwave radiation data over a complex terrain for modeling Eco-hydrologic dynamics. This component is integrated to a central element that develops and maintains a grid, which represents the landscape under consideration. This component communicates with various other components such as ‘vegetation component’ and ‘soil moisture component’. This component is adapted from the Channel-Hillslope Integrated Landscape Development (CHILD) Model code and has been enhanced. Preliminary results of this study demonstrate the advantages of adopting component-based software design such as improved flexibility, interchangeability and adaptability. +
This presentation or poster will discuss the latest developments of the CUAHSI Hydrologic Information System including 1) the new open source server components built using PHP and MySQL specifically to support citizen science; and 2) the desktop application HydroDesktop with its extensions for search and discovery of data on the 100 servers of the CUAHSI data network. The presentation or poster will include a discussion of the potential integration of HIS data sources in CSDMS modeling efforts and potential for integration of the CSDMS modeling architecture with the HydroDesktop client application. +
This research aims to understand the evolution of the shoreface of sandy, wave-dominated coasts. Using energetics-based formulations for wave-driven sediment transport, we develop a robust methodology for estimating the morphodynamic evolution of a cross-shore beach profile. We compare how shallow water wave assumptions and linear Airy wave theory affect the estimation of morphodynamic shoreface evolution, in contrast to previous work, which has applied shallow water wave assumptions across the entire shoreface. The derived cross-shore sediment flux formula enables the calculation of a steady state (or dynamic equilibrium) profile based on three components of wave influence on sediment transport: two onshore-directed terms (wave asymmetry and wave drift) and an offshore-directed slope terms. Equilibrium profile geometry depends on wave period and grain size. The profile evolution formulation yields a morphodynamic Péclet number that can be analyzed in terms of perturbations around the steady-state profile. The diffusional, offshore-directed slope term dominates long-term profile evolution. A depth-dependent characteristic timescale of diffusion allows the estimation of an effective morphodynamic depth of closure for a given time envelope. Theoretical modeled computations are compared to four field sites along the Eastern US coastline. For each of these four field sites, we use hindcast wave data to determine a representative wave height and period using a weighted frequency-magnitude approach. Using the characteristic wave quantities for each site, we compute the equilibrium profile and the morphodynamic depth of closure, showing reasonable similarities between the computed equilibrium profiles and the actual profiles. In addition, the estimated morphodynamic depth of closure matches well with the location of the visually estimated depth of closure (based upon slope break) for each site. Overall, the methodology espoused in this paper can be used with relative ease for a variety of sites and with varied sediment transport equations.
2
This study aims to fundamentally assess the impact of sea level rise (SLR) on vegetated, muddy coastlines. This includes an assessment of the resilience of coupled salt marsh-mudflat and mangrove fringe-mudflat coastlines under different sea level rise scenarios.
Traditionally, the design of coastal protection measures revolved around the use of hard structures to ensure a certain level of design safety against flooding of the coastal hinterland. However, with the effects of climate change: sea level rise, increased intensities and frequencies of storms; these solutions appear to be unsustainable. Building-with-Nature strategies have reinforced the value of vegetated foreshores, as being capable of allowing for a flexible and adaptive response to climate change. They attenuate wave energy, stabilize and may heighten the foreshore at a rate that matches that of sea level rise. Important parameters related to the resilience of vegetated foreshores to sea level rise are site specific and include sediment supply, wave climate, tidal range, sea level rise rates, type of vegetation cover, vegetation dynamics and topography.
Process-based numerical modelling tools are critical towards enhancing the understanding of the processes governing the morphological development of vegetated-mudflat systems. Limited studies have quantified the impact of sea level rise on the resilience of these intertidal systems with a key focus on determining the tipping points and the governing processes for bio-geomorphological development. Therefore, we applied an open-source 2D process-based model (Delft3D) that couples intertidal flow, wave-action, sediment transport, morphodynamic development with the vegetation dynamics for temporal and spatial growth and decay of vegetation and bio-accumulation.
The vegetation growth model was developed using MATLAB, which was then coupled with a depth averaged Delft3D model. For the salt marsh species, the growth model was based on that of a population dynamics approach whereas the mangrove growth model was based on a windows of opportunity approach. The model setup was inspired by conditions within the Dutch South Western Scheldt and the Guyana coastline for the salt marshes and mangroves respectively. The numerical model and the coupling approach were validated quantitatively against existing theory, data and laboratory studies; after which the system’s resilience against sea level rise was examined.
Spatial equilibrium of the marsh-mudflat system was attained within 120 years with wave action and sediment dynamics being key triggers. The mangrove fringe-mudflat model however attains equilibrium on longer timescales. The subsequent imposition of a 100 year period of rising sea-level (1.1m) in salt marsh-mudflat systems revealed the biomass accumulation as a critical determinant for the drowning rate. Though, initially highly resilient against the exponential increase of sea level rise, the marsh system starts to drown as channels incise the platform after 50-60 years. This corroborates recent studies which predict a decline in the carbon sequestration potential of salt marshes within the North Sea. Contrastingly, the mangrove fringe-mudflat system proved resilient after a 100 year period of extreme SLR and the increases in drag gained from their extensive mangrove root network and the below ground biomass accumulation proved to be the main drivers. However, after 150 years, there is a shift in the nature of the system as it starts to drown. Results show survival for both systems in sediment rich areas. Overall, the model can be applied to assess the vulnerability and resilience of vegetated coastal areas impacted by sea-level-rise worldwide. Thereby, proving to be a useful tool for developing countries where data is scare. Both the Delft3D software and MATLAB tools used in this study are open source and freely available online: https://oss.deltares.nl/web/delft3d. The running of the model requires the use of MATLAB versions 2013 or higher. This software can be attained through purchase, student version or trial online: https://nl.mathworks.com/products/matlab.html. With regards to the hardware required, a standard PC with minimum 8GB RAM. Additionally, the MATLAB source code will be made available via the Environmental Modelling and Software Journal (ESM) once published.
This study investigates riverine sediment dispersal within a bedrock confined estuary in British Columbia, Canada using the HydroTrend and Sedflux models. The models are evaluated using multibeam and acoustic backscatter surveys, piston cores, and grab samples across the Skeena Estuary and its contiguous marine areas. The data has been compiled to produce an overview of seabed geomorphology, texture, and sedimentation rates in the estuary and marine approaches. The model HydroTrend was used to estimate incoming sediment load from the Skeena River. Model estimates of suspended sediment load are higher than past estimates due to a large contribution of suspended sediment from a portion of the Skeena watershed previously excluded due to a lack of available hydrographic data. Over thirty kilometres from the river mouth, cores recovered mud sequences in the deeper proximal bedrock confined channels that indicated sedimentation rates of up to 2.83 cm yr-1. These deeper estuarine passages are seaward of the sandy deposits that make up the delta platform. In comparison, sedimentation rates in the further offshore marine approaches to the Skeena Estuary are as low as 0.004 cm/yr. Sedimentation rates within the estuary agree with the SedFlux model outputs using the HydroTrend sediment load results. More specifically, a sedimentation rate of 2.9 cm/yr was predicted using the SedFlux model at the same distance from the river mouth as the mud sequence radiocarbon dated cores. A relatively high sedimentation rate and seaward fining trend in grain size are interpreted as indicators of high riverine input to the seabed regionally. This initial evaluation of model performance encourages further examination of sedimentation conditions in the Skeena Estuary, including those of importance to eelgrass beds and major port development areas. +
This work explores how feedbacks between erosion and sediment production in landscapes with layered stratigraphy influence channel evolution. In layered rocks, contrasts in erodibility cause erosion rates to vary through space and time, complicating landscape response to external forcing from climate and tectonics. Recent studies have used the detachment-limited stream power incision model to explore the complex variations in erosion rates that arise from channel incision through layered rocks. However, these studies do not capture the effect of sediment cover on channel evolution. This work uses the recently developed Stream Power with Alluvium Conservation and Entrainment (SPACE) model (Shobe et al. 2017) to explore how sediment cover influences landscape evolution and modulates the topographic expression of erodibility contrasts in mixed bedrock-alluvial rivers incising through horizontally layered rocks.
The SPACE model allows for the simultaneous treatment of bedrock, fully alluvial, and mixed bedrock-alluvial channels and transitions smoothly between detachment- and transport-limited behaviors. Here, we use the SPACE model to explore how sediment load influences effective erodibility in layered strata, motivated by topographic and lithologic variability found in the Guadalupe Mountains of Texas and New Mexico. We use the Landlab Toolkit to simulate fluvial incision through alternating horizontal layers of hard and soft rock using the SPACE model. While the SPACE model does not treat individual grains, the relative influence of grain size is modeled by systematically varying particle settling velocity and the erodibility of the alluvial across model runs. We find that sediment cover strongly modulates landscape response to uplift, and model runs with “finer” sediment (lower particle settling velocity and more erodible alluvium) reach a steady average elevation more quickly than model runs with coarser sediment. As particle settling velocity is increased, normalized channel steepness increases in soft rock layers and decreases in hard rock layers. We also explore how sediment flux at the watershed outlet varies as soft and hard layers are exposed in different proportions. Finally, we compare how erosion rates vary through space and time as relative sediment size increases. This work illustrates the importance of feedbacks between erosion and sediment production for landscape evolution, particularly in layered rocks where erosion rates vary in space and time.
A
Though it enhances the exchange of porewater and solids with the overlying water, the role that sediment resuspension and redeposition play in biogeochemistry of coastal systems is debated. Numerical models of geochemical processes and diagenesis have traditionally parameterized relatively long timescales, and rarely attempted to include resuspension. Meanwhile, numerical models developed to represent sediment transport have largely ignored geochemistry. Here, we couple the Community Sediment Transport Modeling System (CSTMS) to a biogeochemical model within the Regional Ocean Modeling System (ROMS). The multi-layered sediment bed model accounts for erosion, deposition, and biodiffusion. It has recently been modified to include dissolved porewater constituents, particulate organic matter, and geochemical reactions.
For this talk, we explore the role that resuspension and redeposition play in biogeochemical cycles within the seabed and in benthic boundary layer by running idealized, one-dimensional test cases designed to represent a 20-m deep site on the Louisiana Shelf. Results from this are contrasted to calculations from an implementation similar to a standard diagenesis model. Comparing these, the results indicate that resuspension acts to enhance sediment bed oxygen consumption. +
Through funding provided by the US Integrated Ocean Observing System, five open source 3-D hydrodynamic models for Chesapeake Bay have been compared to each other and to EPA monitoring data for hindcasts of the years 2004 and 2005. The aim of this project is to provide NOAA, EPA, other government agencies, and the larger modeling community meaningful guidance on the relative accuracy, efficiency, complexity and likely utility for federal operational and scenario modeling of a suite of community models available for simulating hydrodynamics and oxygen dynamics in Chesapeake Bay. The focus of the present paper is on the hydrodynamic comparison of:
# the ChesROMS model (http://ches.communitymodeling.org/models/ChesROMS/index.php)
# the CBOFS2 model (http://cedb.asce.org/cgi/WWWdisplay.cgi?265616)
# the CH3D model (http://www.chesapeakebay.net/publication.aspx?publicationid=55318)
# the EFDC model
# the UMCES ROMS model
These models represent a range of resolutions (from ~5,000 to ~50,000 wetted cells). The models do similarly well in reproducing 3-D, time-dependent temperature fields. Bottom salinity is significantly improved with increases in horizontal resolution that better capture the structure of narrow, deep channels. Seasonal variation in density stratification is surprisingly difficult for all the models to capture well, and density stratification is not found to be especially sensitive to horizontal or vertical resolution within the range of resolutions considered. The hydrodynamics in general are not particularly sensitive to refinements in offshore climatological forcing, nor to refinements in riverine input, nor to refinements in spatial resolution of wind forcing. Lateral and longitudinal advection is sensitive, however, to seasonal changes in wind velocity and direction, suggesting that typical seasonal changes in wind forcing may be more important than seasonal changes in local stratification in controlling transfer of oxygen to deep channels susceptible to hypoxia.
2
Throughout the world’s oceans, there are hundreds of coral atolls. These structures provide valuable habitats to plants and wildlife, and the islands on them are home to hundreds of thousands globally. Atoll islands, known as motu, are geologically quite young; they form relatively quickly, over hundreds or thousands of years. While there has been significant work in studying the effect of ocean waves on coastal morphologies, there is little such work specifically focusing on coral atolls and the motu upon them. In this study, we examine the morphologies and morphometrics of over 80 atolls in the Indian and Pacific oceans and quantify the morphometrics of the reef flats and motu with direction-based binning. We gathered recent ocean wave data from over 600 locations around these atolls using NOAA’s Wave Watch III simulations and quantified the local wave climate for each of our atolls. After analyzing these two separate datasets, we compared the effect of local wave climate on atoll morphology. In our analysis, we have found regional trends in wave climate, specifically we have observed directional differences in wave size prevalence between the wet and dry seasons. We have also noted possible relationships between reef width and wave height and between motu width and the 50 year wave height. As we continue to investigate these data, these findings will allow us to better understand the processes driving motu evolution and may be used to infer potential morphological changes in the presence of changing wave climates. +
Tidal inlets are crucial land-forms that control the exchange of water and sediment between the open sea and the back-barrier basin. Despite the well accepted relationship between tidal prism and inlet cross section area, some questions about the geometry of tidal inlets remain open. What processes set their width to depth ratio (or aspect ratio)? What control the presence of a single-threaded versus a compound channel within the same inlet? Do these relationships change with human activities? These questions were investigated by creating and analyzing a database of inlet geometry and numerical modeling. We found that inlet’s aspect ratio has a weak dependence on tidal range, wave height. Despite the scatter, we developed relationships between inlet width and aspect ratio for three separate types of inlets, i.e. engineered inlet, natural inlet with single channel and natural inlet with multiple channels. From the observation, we found that multiple channels tend to form when the width of natural inlet exceeds 1 km. To investigate the long-term morphological evolution of inlets, we developed an idealized barrier-inlet system in Delft3D (a 2D hydromorphodynamic model). We found that two parameters affect the aspect ratio the most: the transverse bed gradient factor for sediment transport (αbn) and the global/maximum dry cell erosion factor (θsd), which controls erosion of dry cells adjacent to a wet cell. Including dry cell erosion is necessary to widen an initially narrow inlet; removing the dry cell erosion effectively “armors” the side of the inlets and thus produces inlets with small aspect ratio. From model sensitivity analysis, we found that αbn = 10 and θsd = 0.8 provides inlet configurations that best match with observations. When inlets were able to widen, we found that aspect ratio has a weak dependency on the initial width. Despite the dry cell erosion and the transverse parameters being a simplified representation of bank erosion processes, their calibration allows to reproduce realistic inlet geometries.
Tidal marshes store blue carbon because biomass production by vegetation exceeds organic matter decomposition. When methanogenic microorganisms drive decomposition, organic biomass decomposes into methane, a greenhouse gas with a higher warming potential than carbon dioxide. As sulfate availability increases sulfate-reducers outcompete methanogens, and methane production decreases. Such a shift from methanogenesis to sulfate reduction as the predominant decompositional pathway can occur within tidal marshes experiencing sea level rise (SLR), as marsh inundation by saline water increases. Additionally, SLR can lead to changes in marsh morphology and extent. To address this interplay, we adapt a cross-shore numerical model for the evolution of a marsh-lagoon system to predict methane emissions over decadal time scales and under different SLR scenarios, via the addition of a novel biogeochemical module. We compute total methane emissions by integrating the methane flux at each location over the width of the marsh platform, which is controlled by the rate of SLR, the wave energy in the lagoon, and the rate of marsh upland migration. We calculate the methane flux at a given location as a function of its distance from the edge of the marsh/lagoon boundary and the labile carbon available for decomposition. We test the morphodynamic component of the model on marshes along the Great Bay near the outlet of the Mullica River in southern New Jersey. The model can reproduce the magnitude of morphological change seen in the historical data from 1986-2020. In particular, the model captures that the marsh is eroding faster at the marsh/lagoon boundary than it is being gained by landward migration of the marsh/mainland boundary. Preliminary results of the coupled biogeochemical and morphodynamic model show that generally methane emissions increase with higher rates of SLR, however certain environmental conditions allow for scenarios in which higher rates of SLR lead to lower methane emissions.
A
Tidal systems are biogeomorphic systems of great relevance, providing important ecosystem services and coastline protection against storms. The dynamics of these systems, currently threatened by the acceleration in the rate of global sea level rise (SLR) and the decrease in sediment supply, are governed by complex interactions between hydrological, ecological, and geomorphological processes. How do salt-marsh ecosystems respond to changes in the environmental forcings? What is the role physical and biological processes and of their interactions through eco-geomorphic feedbacks in controlling salt-marsh dynamic response to these changes and the existence of possible equilibrium states? To address these important issues and improve our understanding of the chief eco-geomorphic processes controlling salt-marsh response to current changes, we have developed a suite of eco-morphodynamic models accounting for complex two-way interactions between ecological and geomorphological processes. We find that vegetation crucially affects the equilibrium marsh elevation, marsh resilience to accelerations in SLR rates, and the morphological features of salt marsh channels. As soon as the platform is colonized by vegetation, plants crucially affect the local hydrodynamic circulation, favor channel incision, enhance particle settling by a reduction of turbulence levels within the canopy, promotes trapping sediment, and provides organic material. Model results suggest that highly productive and sediment-rich marshes will approach new equilibrium states in response to changes in the rate of SLR faster than sediment-poor or less productive marshes. Moreover, marshes exposed to large tidal ranges are more stable, and therefore more resilient to changes in the rate of SLR, than their microtidal counterparts. We also find that marshes are more resilient to a decrease rather than to an increase in the rate of SLR, and they are more resilient to a decrease rather than to an increase in sediment availability. Our modeling approaches emphasize that biological and physical interactions are crucial in determining the observed spatial patterns in the biological and in the geomorphic domains. The existence of feedbacks between physical and biological processes affects the evolutionary trajectories of saltmarsh ecosystems, and the reversibility of such trajectories, thus highlighting the importance of accounting for biogeomorphic feedbacks to obtain realistic representations of the system dynamics in response to climatic changes.
2
To answer geomorphological questions at unprecedented spatial and temporal scales, we need to (a) parse terabyte-scale datasets (DEMs), (b) perform millions of model realizations to pinpoint the parameters which govern landscape evolution, and (c) do so with statistical rigor, which may require thousands of additional realizations.
A core set of operations underpin many geomorphic models. These include determination of terrain attributes such as slope and curvature; flow routing; depression flooding and breaching; flat resolution; and flow accumulation.
Here, I present new, best-in-class algorithms which perform the foregoing. I explain how they are implemented in a high-performance, open source C++ library called RichDEM which is accessible to general practitioners via Python. This design is novel among terrain analysis software and I argue that it is necessary for moving the field forward in a way which allows for rapid scientific development and practitioner adoption. +
To better understand large-scale delta-network responses to fluctuating discharge, we focused on the evolution of a single channel-island node within a delta network. Using the Surface Transport and Earth-surface Processes (STEP) basin, we were able to construct and observe the evolution of mouth-bar systems and subsequent flow bifurcation around an individual island in transport-limited, turbulent conditions. Overhead time-lapse images, laser-altimetry scans, and a low-cost particle tracking velocimetry system allow us to characterize the flow and depositional evolution of our experimental islands. Two alternating discharges that model flood and interflood transport (6 l/s, 0.355 l/s) with uniform sediment (170 microns) were used to create two characteristic sediment advective lengths. Floods transport sediment in full suspension (P_flood at inlet = 0.16), while interfloods transport sediment as bedload (P_interflood at inlet = 2.7). The consequent deposits are distal steep deposits from floods raining sediment out of suspension, and proximal low-angle, leveed deposits from interfloods laterally advecting sediment and floods remobilizing sediment down-system. By varying the frequency of floods (one every 20s-20 mins) while keeping sediment and water mass constant across experiments, we are able to control the time and spatial organization of these two deposit types and examine the effect on bifurcation length and bifurcation incidence time. While the deposits are initially spatially segregated, as the interflood deposit and flood deposit accumulate sediment over time, the interflood deposit encroaches onto the flood deposit. Flow routes from the interflood deposit to the flood deposit and bifurcates because of a preferential slope gradient around the distal deposit. Rather than a single hydrodynamic condition dictating the location of bifurcation, the length to a bifurcation can be described by the intersection of multiple distributions of topographies from the variable flow of solids.
Topography, material properties, and gravitationally driven groundwater flow together act to control hillslope stability. Although it is well known that material strength and hydraulic conductivity differences can alter slope stability via feedbacks with groundwater, comparatively little is understood about the role of stratigraphic sequencing in governing how hillslopes fail. In northwest Washington State, the recent occurrence of the large-volume, high-mobility SR-530 landslide brought focus to hazards associated with large terraces of glacial sediment that inundate the valleys of the western Cascades. However, observations from high-resolution LiDAR topographic data show significant differences between terraces in adjacent valleys, and both geologic and subsurface data show that each site has a unique stratigraphic configuration. Here we hypothesize that variations in the bed thickness and sequencing of glacial sediment packages within ice-marginal terraces control landslide volume and failure style. Using a three-dimensional limit-equilibrium model, Scoops3D, we show that the variable distribution of silts, clays, sands, and tills have a first-order control on both the volume and location of failures along a terrace. Predicted landslide volumes vary by over an order of magnitude between different stratigraphic configurations. Variably saturated groundwater flow simulations show that hydraulic conductivity contrasts between glacial units lead to perched water tables with localized zones of high pore fluid pressure, and in most cases (but not all) the failure pattern set by stratigraphy is amplified by the presence of groundwater flow. Model results from a range of synthetic stratigraphic configurations show that a twofold increase in the thickness of glaciolacustrine clays produces a tenfold increase in predicted landslide volume, consistent with topographic observations. Knowledge of subsurface stratigraphy may therefore help toward quantitative assessment of deep-seated landslide potential in sedimentary landforms.
Transport-limited gravel-bed rivers are ubiquitous across Earth's upland environments. Sediment transport processes, while notoriously difficult, are better-understood than bedrock erosion, meaning that solutions to transport-limited river long profiles can help us gain a physics-based toehold into landscape evolution. Here we demonstrate how the coupling of equations for gravel transport, channel morphodynamics, and simple flow hydraulics that produce steady-state river profiles and show how they respond to changes in climate and tectonics. This coupled set of equations is analytically solvable for special cases, and we have also developed efficient semi-implicit numerical solutions that can solve millions of years of landscape evolution in seconds. Gravel-bed rivers become steeper as the sediment-to-water supply ratio increases, and become less concave as uplift rates (relative to input sediment supply and valley dimensions) increase. These distinctive responses allow us to use transport-limited gravel-bed rivers as recorders of climatic versus tectonic influence on river systems. +
Tropical Cyclones (TCs) are an extreme meteorological event that occurs in many locations globally. These events cause high levels of precipitation and flooding as it makes landfall. Extreme flooding events are known to cause increased suspended sediment flux and discharge in nearby rivers, thus altering sediment dynamics in short time periods. This relationship between TC related precipitation and sediment dynamics of impacted rivers has yet to be studied at a continental scale.
This project will be using the WBMsed model to simulate sediment and streamflow dynamics at a continental scale to find the total influence of TC influenced precipitation from 1990-2019. The products will be analyzed in ArcGIS to find spatial and temporal trends and hotspots of influence. The following research questions will also be answered: (1) What is the influence of TC related precipitation on sediment and streamflow dynamics? (2) How does modern anthropogenic conditions affect sediment and streamflow dynamics influenced by TC precipitation? (3) What will be the future impacts of TC related precipitation on sediment and streamflow dynamics in the United States? +
Tropical Montane Cloud Forests (TMCFs) are located at the headwaters of biodiversity-rich ecosystems like the Amazon and regulate the release of water downstream. Epiphytes are vascular and non-vascular plants that grow in the canopies of TMCFs and hold large amounts of water, regulating temperature and humidity. In order to investigate how epiphytes control canopy microclimate, we developed an uncalibrated, numerical water balance model where we considered epiphytes as a water tank. Water enters the epiphyte tank via fog, precipitation, and dew deposition, and exits the tank primarily through evapotranspiration. The model also considers the role of host tree aerial roots uptaking water from the epiphyte tank. We validate the model against field data collected from cloud forests in Monteverde, Costa Rica. Preliminary results demonstrate that epiphyte temperatures have a phase lag with air temperature, and this lag is responsible for regulating diurnal conditions within the canopy. Under clear sky conditions, epiphytes increase humidity in the canopy during the afternoon and reduce evapotranspiration at night. This work improves our understanding of the hydrologic cycle of TMCFs and will help us understand how resilient these ecosystems are to climate change. +
Tsunami currents can be very dangerous even if there is no onshore inundation, and can create whirlpools and other small-scale structures. With inundation, ships can be carried onshore and become part of the debris field. In this work, the open source GeoClaw tsunami modeling code (www.geoclaw.org) is used to model tsunami tsunami generation, propagation and inundation. The depth-averaged shallow water equations are used to compute the water depth and fluid velocities, which are saved on a fine grid near the region of interest every few seconds. Postprocessing scripts are then used to track the motion of particles in this flow field, making it easy to experiment with different initial particle locations, masses, grounding depths, etc. Developing better algorithms for debris tracking and using them in probabilistic models is a very active research topic for the Cascadia CoPes Hub (cascadiacopeshub.org) and others in the tsunami modeling community. +
Tsunami modeling often combines the need for an ocean-wide simulation with the requirement that a small region of the coast (some community of interest) be simulated with a fine level of resolution (often ⅓ arcsecond, less than 10 meters). In the open ocean we might need 1-4 arcminute resolution, but only in regions that the waves have reached. This is addressed in the GeoClaw software package by using adaptive mesh refinement to place higher resolution grids around the waves based on where the water surface height is significant. We present a method of placing higher resolution grids when there is a small region of interest (say, a single coastal community) by using the adjoint equation. Advantages of this new method are presented, including reduced computational times and the capability to refine only the waves that will impact the specific community during a given time range of interest. +
Two numerical forward stratigraphic models are used to explore the origin of carbonate lacustrine strata characteristics at various scales. The large-scale model (Carbo-CAT; Burgess, 2013) focuses on exploring kilometre scale carbonate stratal heterogeneity developing in extensional settings. New developments include spatial distribution of dissolved carbonate in water controlling carbonate production and subsidence produced by various 3D fault configurations. The small-scale model (Mounds3D) investigates the controls on microbial mound development in the metre to decametre scale. Modelled microbial growth includes precipitation and trapping and binding processes. These are affected by energy, slope and spatial distribution of the microbial community. The model incorporates a depth-averaged hydrodynamic model to assess the impact of transported sediment deposition, erosion and trapping and binding in mound development.
Numerical experiments using these models show the complex relationship between initial conditions, processes and resulting stratal geometry. For example, large-scale models of carbonate systems developing over relay ramps show that their size, shape and facies distribution is controlled by the combined effect of varying basement surface, the platform ability to keep up with relative water-level rise and sediment transport processes. The tests performed with the small-scale model show that, although the initial bathymetry exerts a first order control on initial location of microbial mounds, the dynamic behaviour of the systems suggests that mound spacing is also controlled by local variations on the hydrodynamic and depositional conditions. +
A
Understanding gravel bed river morphology over decadal to centennial timescales is vital to making informed stream management and restoration decisions. Factors such as land use change and climate shifts over such timescales may drastically alter river evolution – with major implications for in-channel and riparian habitat. Given these longer timescales of influence, field-based studies may be unable to fully capture such morphologic shifts. Scenario-based morphodynamic modeling is emerging as a means of quantifying gravel bed river evolution, yet current models are unable to predict changes in stream morphology over the timescales in question and with adequate spatial resolution, a problem due largely to the computational overhead they require. Since the computational overhead required to drive sediment transport has hindered previous modeling efforts, field-based research suggests a potential improvement, in that sediment is often mobilized downstream with characteristic step-lengths. Here we introduce a morphodynamic model which drives sediment transport using a step-length based approach. Such a technique negates the need for frequent recalculation of sediment dynamics in the flow, and correspondingly reduces computational overhead. Upon application of this model to the River Feshie (UK), we observe that it accurately reproduces many bed morphologies observed during annual high-resolution topographic surveys. By employing step-length based sediment transport distributions, the formation and preservation of bed morphologies can be accurately predicted with less computational overhead than was available in previous morphodynamic models. Using this new model, a better understanding of gravel-bed river morphodynamics over longer-term timescales (decades to centuries) may aid in the management of gravel bed streams under shifting discharge and sediment regimes. +
2
Understanding how landscapes acquire their form is complicated by evolution across a large range of spatial and temporal scales. Disentangling causes of landscape evolution should carefully consider scale and scalings, but how best to do so? I summarise the work we have been doing to make use of observations, spectral analyses and forward and inverse modelling to address the following questions. Where and at what scales do fluvial landscapes acquire their physical and chemical properties? How can we use the geometries of landscapes and their compositions to recover information about driving and responsive processes? Demonstrations of how observations of landscape form and chemical concentrations can be combined with simple theory to identify where and how landscapes acquire their geometries and material provenance are given. Spectral analyses of landscape geometries are used to identify scales at which they acquire their form and scaling regimes. Consequently, it is possible to assess whether it is reasonable to ‘stitch together’ observations or theory used to understand geomorphic processes operating at small scales to determine how landscapes acquire their form. In short, that proposition is highly unlikely to be successful because of the existence of erosional ‘shockwaves’ and stochasticity. However, despite local (spatio-temporal) complexity, fluvial landscapes appear to possess emergent, deterministic, simplicity at scales > 100 km, such that processes operating at these scales (e.g. dynamic topography) are manifest in drainage networks with simple, self-similar, scalings (e.g. Brownian noise). The use of upscaling of simple physical models to generate appropriate scaling regimes and statistical insights into how fluvial landscapes acquire their form is explored. Finally, a demonstration of how statistical measures based on Optimal Transport theory can be used to identify optimal landscape evolution models is presented. Wasserstein distances are shown to have significant benefits over more widely used Euclidean measures of misfit, especially when local noise is prevalent.
Understanding sediment dynamics during storms and hurricanes is vital for predicting coastal morphodynamics and improving resilience strategies, especially for the Texas–Louisiana coast.
This study presents preliminary results from an integrated hydrodynamic-sediment transport model of Galveston Bay during Hurricane Harvey. To capture the complex interplay of different hydrological forces, the hydrodynamic model incorporates the combined impacts of wind, precipitation, river, wave, tide, and current. A three-dimensional sediment transport model with a 100-m resolution is developed in the Regional Ocean Modeling System (ROMS) for Galveston Bay. The open boundary conditions are generated from ROMS model (100m) and river discharges of Buffalo Bayou and San Jacinto River will be derived from WRF-Hydro model. The bay bottom sediment input parameters are derived from the Texas Sediment Geodatabase (TxSed), which includes a comprehensive inventory of sediment properties, ensuring simulations with an enhanced level of accuracy and regional specificity. For model modification, river discharge data from the United States Geological Survey (USGS) and/or a WRF-Hydro model will be employed to calibrate and adjust the hydrodynamic model. This study will eventually provide open boundaries and initial sediment conditions for a higher resolution (20m) bayou model focusing on Buffalo Bayou and other rivers feeding into Galveston Bay and will contribute to the development of a detailed river-estuary-ocean continuum model. The outcomes of this research are anticipated to inform future coastal management and resilience planning against storm-induced sediment and contaminant fluxes. +
Understanding the factors that control lateral erosion rates in bedrock channels is a frontier in geomorphology. Lateral erosion rates and the evolution of wide bedrock valleys are linked to bedrock lithology, sediment supply in the stream, and shear stress exerted on channel walls. I use a newly-developed lateral erosion component in the Landlab modeling framework to explore how model results compare with recently published field examples of downstream sweep erosion as a mechanism for gorge eradication and bedrock valley widening. The lateral erosion component dictates that lateral erosion rate is proportional to shear stress exerted on the channel walls in a bend in the river; therefore sharp bends with a smaller radius of curvature will produce faster lateral erosion. Cook et al. (2014) identified a similar mechanism they call downstream sweep erosion (DSE). They suggest that bedrock gorges can be rapidly eroded by DSE when a wide flood plain with a laterally mobile stream exists upstream of the gorge, requiring a sharp bend in the channel to enter the gorge. I set up the model domain to recreate conditions of a low relief area with a mobile channel in the upper part of the model domain and a narrow, high relief gorge in the downstream end of the model domain. I ran modeling experiments under a range of water flux and sediment mobility conditions. The model results show gorge widening that propagates downstream as described by Cook et al. (2014) and preferential erosion of blocks that protrude into the channel. The enhanced lateral erosion at channel bends and the resulting downstream sweep erosion emerge naturally from the models, matching observations in many field areas. Together this suggests that channel curvature is of fundamental importance to lateral erosion rates in bedrock channels. +
Understanding the response of coastal barrier systems to sea level rise is a crucial societal need. Despite the problem having been studied extensively, major knowledge gaps remain. For example, neither the sedimentary record nor existing numerical models have been conclusive in explaining the formation of barrier islands. Here I present a comprehensive 2D model that seamlessly couples cross-shore and along-shore transport, tidal transport, storm surges, and wind waves, and use it to simulate an idealized passive margin during the last 7,000 years. In the early Holocene, when sea level was rising ~20 mm/yr, shoals and ephemeral barrier islands formed, periodically drowned, and then formed again at a landward location. Shoal emergence was triggered by the disequilibrium of the recently submerged shelf, especially for large waves and mild shelf slopes. About 5000 years ago, as sea level rise slowed down to ~1 mm/yr, barriers stabilized and even prograded seaward. The combination of excess sediment in the nearshore and storm surges allowed barriers to accrete above mean high water. When barriers eventually equilibrated to the new sea level rise rate and started to retreat, their retreat rate was highly variable in space and time due to autogenic processes such as inlet formation and backbarrier channel interception. This variability also included multi-decadal periods of localized progradation. Both lag dynamics and autogenic processes confound the relationship between barrier retreat and sea level rise rate. +
Understanding the sensitivities of preserved environmental signals to erosional and transport processes within the sediment generation portion of landscapes is vital in constraining uncertainties within provenance analysis. Here our focus is on populations of detrital zircon U-Pb ages as one of the most ubiquitous sediment provenance methods. Many studies often assume uniform parameters upstream of the sampling site, potentially overlooking variations in erosion rates, zircon size and zircon fertility across landscapes. To tease these uncertainties out, we model synthetic landscapes along with their expected provenance evolution.
Employing the Concentration Tracker component, we systematically manipulate erodibility and zircon fertility within synthetic landscapes to simulate sediment provenance evolution and incorporate zircon concentration into a statistical analysis comparing a null hypothesis of an area-dependent contribution to fractions dependent on mass and zircon abundance. While these scenarios do not necessarily reflect “real” landscapes, we use these simple experiments to understand basic controls on the magnitude of potential biases imparted to the simulated detrital zircon U-Pb datasets.
By exploring these potential biases, we provide valuable insights into the uncertainties inherent in provenance analysis and thus their utility and fidelity in reconstructing histories of past landscape evolution. Ultimately, this research contributes to refining the methodologies used in detrital zircon provenance analysis and enriches our understanding of the processes shaping sedimentary records. +
A
Urbanization and global climate change will severely stress our water resources. One potential unforeseen consequence of these stressors, which is neglected in channel evolution models, is accelerated stream channel erosion due to change in stream water temperature, pH and salinity which affect the surface potential and hence stability of soil colloids. Summer thunderstorms in urban watersheds can increase stream temperature >7 °C and the impact of global warming on average stream temperature is already evident in some stream systems. Initial estimates indicate a 2 °C rise in stream temperature could increase erosion by 30%. Urbanization has significant effects on the pH and salinity of stormwater runoff and as a result on the water quality of headwater streams. Channel erosion and the resulting sediment pollution threaten the sustainability of water resources and urban infrastructure. The goal of this research is to assess the impact of changes in stream water temperature, pH and salinity on stream channel erosion rates and to explore changes in the electrical surface potential of clay colloids as a potential soil stability mechanism. This exploratory research utilizes two reference clays with different permanent surface charges: montmorillonite, and vermiculite. Samples will be eroded in a recirculating sediment flume to determine soil critical shear stress and erodibility. Three water temperatures (12 °C, 20 °C, 27 °C), two pH (5 and 7), and two salinity levels (5 and 50 mg/l NaCl) will be analyzed. Three replicates of each treatment will be conducted for each clay. Additionally, the zeta potential of the clays will be determined under each condition. Research has demonstrated that variations in zeta potential affect liquid limit and shear stress of soil colloids. Results of this research could lead to a reassessment of stream channel stability modelling in urban watersheds and a paradigm shift in urban stormwater management. +
2
Variation in bedrock erodibility along a river profile gives rise to differences in vertical incision rate and influences sediment characteristics such as clast lithology, coarse sediment generation rate, and grain size. In rivers whose beds are eroded, in part, through sediment abrasion, these streamwise sediment dynamics are part of a crucial feedback that sets the dominant fluvial erosion process and determines whether a river exhibits transport-limited or detachment-limited behavior. The role that sediment plays in setting the shape of a river profile is of particular interest in the case of a river’s transient response to external forcing.
Here we present a model that explores river profile evolution in a setting with streamwise bedrock variability. Our model combines theory for five interrelated processes: bedload sediment transport in equilibrium gravel-bed channels, channel width adjustment to flow and sediment characteristics, abrasion of bedrock by mobile sediment, plucking of bedrock, and progressive loss of gravel-sized sediment due to grain abrasion. We envision a generic “range-foreland” system that consists of erosion-resistant, crystalline rocks in the upstream reaches, juxtaposed with softer, more erodible rocks downstream. In this setting, coarse sediment generation is confined to the upstream part of the fluvial system. As the sediment is transported downstream, it creates an alluvial blanket across the soft, fine-grained unit. Bedrock erosion is modulated by the thickness of the alluvial layer.
We use the model to explore the range of transient forms that can occur in such a setting in response to changes in tectonic or climatic regime. We pay special attention to the conditions under which the upstream gravel source either increases the downstream fluvial gradient (by partially shielding the underlying material from incision) or decreases the gradient (by providing tools that amplify the efficiency of abrasion). We also examine the conditions under which erosion is concentrated at the downstream-most reaches of the river profile, versus at the lithologic boundary.
While our work takes its motivation from the Southern Rocky Mountains and High Plains of North America, the model is applicable generally to settings in which a bedrock-incising river traverses multiple lithologies. This work aims to improve our interpretations of the history of river profiles in lithologically heterogeneous environments and inform our understanding of landscape evolution in these settings.
A
Very few in-situ measurements of runoff from the Greenland Ice Sheet (GrIS) exist, though melt water runoff from the GrIS is important to global eustatic sea level, ocean salinity, thermohaline circulation and sea ice dynamics and the transport of sediment and nutrients to fjords and the ocean. We continue to develop the use of NASA MODIS imagery to gauge river discharge of sediment and freshwater into fjords hydrologically linked to the GrIS.
Essential to this remote sensing proxy are accurate models of fjord and plume dynamics. We compare Hutton and Syvitski’s PLUME model results to in situ oceanographic and sedimentological measurements of Greenlandic river sediment/freshwater plumes towards the end goal of exploring the suitability of inverting the PLUME model and combining it with remotely sensed MODIS imagery to estimate river discharge.
Within our study fjords a range of estuarine conditions present a robust test for our plume method, and in turn conditions present a range of complexities to test the suitability of inverting the PLUME model. Fjord conditions range from ocean to river dominated. Some plumes mix very quickly from fresh to near full ocean salinities (22 – 28 PSU). Other plumes maintain low salinities (0 – 10 PSU) to depths exceeding six meters and down fjord over 65 km. Fjord geometries, tidal range, and other conditions impact sediment plume dynamics. These dynamics must be accounted for to link plume imagery to discharge into fjords. +
WBMsed is a spatially and temporally explicit global riverine model predicting suspended and bedload sediment fluxes based on the WBMplus water balance and transport model (part of the FrAMES biogeochemical modeling framework). The model incorporates climate input forcings to calculate surface and subsurface runoff for each grid cell. The prediction of fluvial sediment fluxes is highly dependent on how well its transport medium, riverine water, is simulated. Our analyses indicate that average water discharges are well predicted by the WBMplus model. However, daily freshwater predictions are often over or under predicted by up to an order of magnitude, significantly affecting the accuracy of sediment flux simulation capabilities of WBMsed and indicating that certain hydrological processes are less captured within the model. One of these processes could be temporal storage of water discharge on floodplains, dampening the water hydrograph significantly. In WBMsedv2.0 we incorporate a floodplain reservoir component to improve daily water discharge simulations. The Floodplain reservoir component is used in WBMsedv2.0 to store overbank water flow which are refurbished back to the river once its water level has subsided. Here we compare two methods for determining overbank flow: (1) the log-Pearson III (flood frequency analysis) 5-year maximum discharge recurrence and (2) an empirical relationship between mean river discharge and river width and bank height. +
2
Wave Boundary Layer (WBL) plays an important role in sediment offshore transport and material exchange between seafloor and overlying water, especially during strong wave events when fluid mud (concentration > 10g/L) is formed. We incorporated wave-supported fluid mud (WSFM) processes into the Community Sediment Model System (CSTMS) on the platform of the Coupled Ocean-Atmosphere-Wave-and-Sediment Transport Modeling system (COAWST). A new WBL was introduced between the bottom sigma layer (water) and top sediment bed layer, which accounted for the key sediment exchange processes (e.g., resuspension, vertical settling, diffusion, and horizontal advection) at the water-WBL and WBL-sediment bed boundaries. To test its robustness, we adapted the updated model (CSTMS+WBL) to the Atchafalaya Shelf in the northern Gulf of Mexico and successfully reproduced the sediment dynamics in March 2008, during which active WSFM processes were reported. The CSTMS+WBL model simulated a lutocline between the WBL and overlaid water as well as a stronger onshore/offshore erosion/deposition. Sensitivity tests of free settling, flocculation and hindered settling effects suggested sediments were transported further offshore due to reduced settling velocity in the WBL once fluid mud was formed. +
Wave- and current-supported turbidity currents are new class of turbidity flows that has been discovered over the last three decades. Its significance as a carrying agent of fine sediments over low-gradient shelves has been recognized with growing evidence. Due to their vertical length scales, which are on the order of decimeters, understanding the full range of mechanisms that are responsible for and/or affect these currents cannot proceed without turbulence-resolving numerical simulations and/or high-resolution sensor deployment in a laboratory/field experiments. In this talk the culmination of two-phase, turbulence-resolving simulations, i.e. Direct Numerical Simulations (DNS), of wave- and alongshore current-supported fine sediment turbidity currents across mild bathymetric slopes will be presented. Simulation results show that such turbidity currents follow a logarithmic velocity profile across the shelf whose parameters depend on the sediment concentration, across-shore bathymetric slope, and Reynolds number while it is independent of the settling velocity of the sediments. The numerical simulations also provide significant insights on modelling these turbidities in a regional-scale model which can be used to estimate the location of mud depocenters and the dynamics of submarine geomorphology such as in the clinoform development at the continental margin. +
We develop a hydroclimatological approach to modeling regional shallow landslide initiation by integrating spatial and temporal dimensions of parameter uncertainty to estimate an annual probability of landslide initiation based on Monte Carlo simulations. The physically based model couples the infinite-slope stability model with a steady-state subsurface flow representation and operates in a digital elevation model. Spatially distributed gridded data for soil properties and vegetation classification are used for parameter estimation of probability distributions that characterize model input uncertainty. Hydrologic forcing to the model is through annual maximum daily recharge to subsurface flow obtained from a macroscale hydrologic model. We demonstrate the model in a steep mountainous region in northern Washington, USA, over 2700 km2. The influence of soil depth on the probability of landslide initiation is investigated through comparisons among model output produced using three different soil depth scenarios reflecting the uncertainty of soil depth and its potential long-term variability. We found elevation-dependent patterns in probability of landslide initiation that showed the stabilizing effects of forests at low elevations, an increased landslide probability with forest decline at midelevations (1400 to 2400 m), and soil limitation and steep topographic controls at high alpine elevations and in post-glacial landscapes. These dominant controls manifest themselves in a bimodal distribution of spatial annual landslide probability. Model testing with limited observations revealed similarly moderate model confidence for the three hazard maps, suggesting suitable use as relative hazard products. The model is available as a component in Landlab, an open-source, Python-based landscape earth systems modeling environment, and is designed to be easily reproduced utilizing HydroShare cyberinfrastructure. +
We have implemented algorithms for simulating fine and cohesive sediment in the Regional Ocean Modeling System (ROMS). These include: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of cohesive and mixed (cohesive and non-cohesive) sediment; and biodiffusive mixing of bed sediment. These routines supplement existing non-cohesive sediment routines in ROMS, thereby increasing the model ability to represent fine-grained environments where aggregation, disaggregation, and consolidation may be important. Additionally, we describe changes to the sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. This poster provides examples of these modules implemented in idealized test cases and a real-world application. +
A
We present a method that reconstructs daily snow thermal conductivities using air and ground temperature measurements. The method recovers the daily snow thermal conductivities over the entire snow season. By using reconstructed snow conductivities we can improve modeling of ground surface temperatures. Simulation of the ground surface temperatures by using changing in time snow thermal conductivities could potentially reduce ground temperature modeling uncertainty.
The developed method was applied to four permafrost observation stations in Alaska. Reconstructed snow thermal conductivity time series for the interior stations in Alaska revealed low conductivity values that reach their maximum towards the end of the snow season, while the northern stations showed high conductivity values that reach their maximum towards the middle of the snow season. The differences in snow conductivities between interior and northern stations are most likely due to wind compaction which is more pronounced in the Northern Arctic lowlands of Alaska. +
2
We provide a simple introduction to the Scientific Variables Ontology (SVO) and show how it can be used to tag scientific models and data with information about the scientific variables used by or contained in these types of resources. We demonstrate the application of SVO to a variety of domains by providing examples from CSDMS standard names, CF standard names, and NWIS parameter codes. +
What are the topographic, thermal and hydrologic conditions setting slope stability in frozen and thawing landscapes? We address this question with past and present records to inform models to predict future landscape change. Relict periglacial landscapes and slope deposits constrain timing and magnitude of slope instabilities in past glaciations. Using sediment records from these deposits, we show how hillslope denudation varies as a function of climate at both the Last Glacial Maximum and previous Pleistocene glaciations. In central Pennsylvania, organic geochemistry and plant macrofossils provide ecological constraints on depositional environments and climate conditions in an upland bog with periglacial sedimentation. Nearby we use cosmogenic isotopes to constrain erosion rates and depositional ages of periglacial debris in toeslope deposits. Remote sensing and field surveys in western Alaska summer 2019 will document the topographic and hydrologic controls on modern slope stability, as well as accumulation rate of sediment in the past. Coupling landscape evolution models with permafrost models should be capable of both hindcasting climate conditions from past sedimentology and forecasting slope stability in modern permafrost landscapes. Such models will require soil mobility to be linked to frozen and unfrozen water content, to be developed in collaboration with CSDMS researchers. +
What is the impact of boat-wake generated waves on lakebed sediment? Are large wakeboarding waves (up to 0.5 m in height) driving significant sediment resuspension or transport? Using Delft3D, we investigate the role of boat-wake waves in comparison to wind-waves on driving sediment transport and deposition in East Pond, Belgrade, ME. We approximate boat wakes using a spatially varying pressure field to simulate the boat wake over our time period. We validate our numerical model using field measurements of wave heights and near bed velocity under different boat wakes. We then test the relative importance of boat-wakes on driving morphodynamic change of East Pond in comparison to wind-generated waves given the frequency of use of wakeboarding and water skiing boats compared to the yearly wind climate. Even under the largest boat wakes (wake surfing), there are minimal velocities (< 10 cm/s) at the bed in either shallow or deep depths (4 of 7 m) but wave heights do reach up to 30 cm in deeper waters. Our analyses provide a method for estimating natural vs anthropogenic wave impacts on lake sedimentation and long-term water quality. +
A
When a layer of particle-laden fresh water is placed above clear, saline water, both Rayleigh-Taylor and double-diffusive instabilities may arise. In the absence of salinity, the dominant parameter is the ratio of the particle settling velocity to the viscous velocity scale. As long as this ratio is small, particle settling has a negligible influence on the instability growth. However, when the particles settle more rapidly than the instability grows, the growth rate decreases inversely proportional to the settling velocity. In the presence of a stably stratified salinity field, this picture changes dramatically. An important new parameter is the ratio of the height of the nose region that contains both salt and particles to the thickness of the salinity interface. If this ratio is small (large) the dominant instability mechanism will be double-diffusive (Rayleigh-Taylor) dominant. In contrast to situations without salinity, particle settling can have a destabilizing effect and significantly increase the growth rate. Scaling laws obtained from the linear stability results are seen to be consistent with experimental observations and theoretical arguments put forward by other authors. +
2
When a tree falls into a river becomes instream large wood and promotes fundamental changes in river hydraulics and morphology, playing a relevant role in river ecology. By interacting with the flow and sediment, the instream large wood (i.e., downed trees, trunks, root wads and branches) contributes to maintaining the river's physical and ecological integrity. However, large quantities of wood can be transported and deposited during floods, enhancing the adverse effects of flooding at critical sections like bridges. Accurate predictions of large wood dynamics in terms of fluxes, depositional patterns, trajectories, and travel distance, still need to be improved, and observations remain scarce. Only recently, numerical models can help to this end.
In contrast to other fluvial components such as fluid flow and sediment, for which numerical models have been extensively developed and applied over decades, numerical modelling of wood transport is still in its infancy. In this talk, I will describe the most recent advances and challenges related to the numerical modelling of instream large wood transport in rivers, focusing on the numerical model Iber-Wood. Iber-Wood is a two-dimensional computational fluid dynamics model that couples a Eulerian approach for hydrodynamics and sediment transport to a discrete element (i.e., Lagrangian) approach for wood elements. The model has been widely validated using flume and field observations and applied to several case studies and has been proven to accurately reproduce wood trajectories, patterns of wood deposition, and impacts of wood accumulations during floods. +
When oil spills occur in marine environments, the oil droplets, marine snow, and mineral grains can combine to form Oil Mineral Aggregates (OMAs), which have a wide range of settling velocities and densities. As a result, their properties can strongly influence the eventual fate of the oil. As part of the Consortium for Simulation of Oil-Microbial Interactions in the Ocean (CSOMIO), we evaluated the role of turbidity in partitioning oil into OMAs by incorporating flocculation and aggregation processes into the Community Sediment Transport Modeling System (CSTMS) within the Coupled Ocean-Atmosphere-Wave-and-Sediment Transport (COAWST) modeling framework. Specifically, an existing size-class based aggregation and fragmentation model (FLOCMOD) was adopted to examine the impact of oil on the vertical transport of sediment. FLOCMOD acts as a population balance flocculation model and allows particle exchanges through aggregation, shear breakup and collision breakup. Our one-dimensional SED_FLOC_TOY model represented a muddy 50-m deep site on the northern Gulf of Mexico continental shelf. It was driven by horizontally uniform, steady currents, salinity and temperature, extracted from a three-dimensional hydrodynamic model. The initial sediment distribution was split among 11 floc size classes (ranging from 1 to 1024 micron diameter). Sediment was input at the top of the water column to represent fall out from a freshwater plume. Flocculation processes removed mass from the smaller and larger classes through aggregation and breakup, which resulted in a net increase in sediment mass of the middle sizes. FLOCMOD’s collision and breakup efficiencies were parameterized to represent the presence or absence of oil. Sensitivity tests of collision and breakup efficiencies indicated that total suspended sediment mass was decreased by 40% by increasing/decreasing the collision/breakup efficiency. FLOCMOD was computationally expensive, in this test case, computation was slowed down by 1.5 times after incorporating the aggregation and fragmentation processes.
A
When we build models we create worlds that we hope will inform us about the world in which we live. We hope models will help us understand processes, causes and effects; avoid difficulties; benefit human endeavors; and accommodate and nurture the ecology which has its own beauty and importance, and upon which human existence and our economy depend. Here we discuss how models can be used to achieve these goals by considering the importance of transparency (revealed importance) and refutability (tested hypotheses). We consider models with substantial execution times (for our example one model run requires 20 minutes) and transparency and refutability available using computationally frugal methods. Challenges of using these methods include model nonlinearity; non-Gaussian errors and uncertainties in observations, parameters, and predictions; and integrating information from multiple data types and expert judgment. A synthetic test case illustrates the importance of transparency and refutability in model development. The test case represents transport of an environmental tracer (cfc) and contaminant (pce) in a groundwater system with large-scale heterogeneities. Transparency is served by identifying important and unimportant parameters and observations. The frugal methods identified consistently important and unimportant parameters for three sets parameters for which sum of squared weighted residuals (SOSWR; dimensionless; constructed with error-based weighting) varies between 5606 and 92. Observations important to the parameter values are largely consistent, but the order varies for results using different parameter values because of model nonlinearity. For each set of parameters these results required 17 model runs. Refutability is served by estimating parameter values that minimize SOSWR and evaluating resulting model fit and parameter values. The computationally frugal parameter-estimation method reduced SOSWR from 5606 to 92, displayed no evidence of local minima, and required about 100 model runs each of the 10 times it was executed. The similar important parameters and observations for different parameter sets and performance of parameter estimation suggest the utility of the computationally frugal methods even for models as nonlinear as the one considered here. The value of the kinds of insights gained in this work is highlighted by the 10,000s to 1,000,000s of model runs being conducted in many studies to obtain them.
While many researchers have mapped and tracked coastal erosion in the Yellow River Delta, determining its cause has proven nearly impossible, because myriad natural and anthropogenic processes are simultaneously affecting the delta. These processes include reduced sediment supply, reduced river discharge, changing tide and current patterns, new seawalls, groundwater withdrawal, substrate compaction, oil extraction, burgeoning urban centers, and rising sea level. Here, we use Interferometric Synthetic Aperture Radar (InSAR) to map surface deformation in the delta between the years 2007 and 2011. We find that rapid, localized subsidence of up to 22 cm/y is occurring along the coast, apparently related to groundwater extraction at aquaculture facilities. This finding has important consequences for the sustainability of the local aquaculture industry. Similar subsidence may also be occurring in deltas like the Mekong, though these signals may be difficult or impossible to measure. +
2
Will be sent before April 01, 2023 +
Wind-swept snow self-organizes into bedforms. These bedforms affect local and global energy fluxes, but have not been incorporated into Earth system models because the conditions governing their development are not well understood. We created statistical classifiers, drawn from 736 hours of time-lapse footage in the Colorado Front Range, that predict bedform presence as a function of windspeed and time since snowfall. These classifiers provide the first quantitative predictions of bedform and sastrugi presence in varying weather conditions.<br>The flat snow surfaces we saw were all short-lived. The probability that a surface remained flat, rather than bedform-covered, decreased with time and with the average shear stress exerted on the surface by the wind.<br>The most persistent snow features were an erosional bedform known as sastrugi. The likelihood that a surface was covered by sastrugi increased with time and with the highest wind speeds experienced by the surface.<br>These results identify the weather variables which have the strongest effect on snow surfaces. We expect that these variables will inform and feature in future process-based models of bedform growth. Our observations therefore represent a first step towards understanding a self-organized process that ornaments 8% of the surface of the Earth. +
Woody Plant Encroachment (WPE), an increase in density, cover and biomass of trees or shrubs in native grasslands, has been observed to be a major cause for dramatic changes in arid and semiarid grasslands of southwestern US over the last 150 years. Driven by overgrazing, reduced fire frequency, and climate change, WPE is considered as a major form of desertification. In Landlab, ecohydrologic plant dynamics, wildland fires, grazing, and resource distribution (erosion/deposition) are represented in separate components. Landlab has two existing cellular automata Ecohydrology models, built using these components, to study the impacts of WPE on the evolution of vegetation patterns. In the first model, physically based vegetation dynamics model is used to simulate biomass production based on local soil moisture and potential evapotranspiration driven by daily simulated weather, coupled with a cellular automata plant establishment and mortality rules. In this model, spatial dynamics of disturbance propagation (e.g., fire spread and intensity) is not explicitly modeled. In the second model, a simple stochastic cellular automata model with two state variables, vegetation cover and soil resource storage, are used to model resultant vegetation patterns based on probabilistic establishment-mortality interplay, mediated by post-disturbance resource redistribution, while explicit roles of climate are neglected. In this work, we coupled these two models to investigate the role of disturbances (fire and grazing) in a climate driven dynamic ecohydrologic context. In this coupled model, daily- weather driven physically based vegetation dynamics model is coupled with cellular automata plant establishment model that explicitly simulates spatial disturbance dynamics. The effects of encroachment factors and model complexity on resultant vegetation patterns are studied. +
