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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.
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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.
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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.
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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 Amazon River Basin stands out as the most biodiverse system in the world. However, the period when the river started flowing from the Andes to the Atlantic Ocean is still in large debate. Different studies have dated this period from the Late Miocene to the Pleistocene. The lack of a Miocene sedimentary record in the area, along with the limitations of geochronological tools that reach this timescale for shallow deposits, makes it difficult to date the event using onshore sediments, which suggests a possible Miocene age. In this study, we seek to contribute to this knowledge gap by using the landscape to reconstruct the timing of transcontinentalization. We hypothesize that when the proto-Amazon River (eastern) integrated with the western Amazon River system, it led to an increase in drainage area at the Lower Amazon River. This increase must have caused the incision of its substrate, thus lowering the base level of its tributary basins in eastern Amazonia. The lowering caused the propagation of knickpoints in the tributary basins that have been adjusting to the new base level. Widespread waterfalls at common elevations and area-corrected distances in basins provide geomorphic evidence of such base level fall. We collected 20 samples of Be-10 and 6 of Al-26, which can be used to infer erosion rates in these tributary basins. These data reveal erosion rates from 8 to 12 m/Ma. Combining these rates with the channel steepness, we obtained a value of erosional efficiency (stream power’s K) for the region. This value of 2.28 m0.1 yr-1 was used in a linear inversion of the stream power equation to obtain a base level fall age. Preliminary results showed an age estimated around 5 to 10 Myr for the formation of knickpoint clusters, thus within the time window of the commonly proposed Amazon River’s formation. However, this approach relies on linearity to calculate the stream power erosion, and it is best suited for bedrock rivers. We explore how these assumptions (i.e. n=1 and detachment-limited), influence our results by inverting a landscape model using the SPACE 1.0 component (transport and detachment-limited river-based modeling) applied to the Simulation-based inference toolkit to find best-fit sediment-transport and deposition parameters. We then compare the age solutions with the age of the linear inversion, ultimately to assess the uncertainty around the age of the latest base-level fall in the Amazon River.
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! +
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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. +
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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 Gediz Fault, forming the southern margin of the Gediz (Alaşehir) Graben, has been the focus of a number of studies over the last decade that have highly constrained its structural and geomorphic evolution. Consequently, this region now forms an excellent natural laboratory for the investigation of the interplay of lithology and tectonics on long term landscape evolution. Located in the highly tectonically active and seismogenic region of Western Turkey, extension owing to regional geodynamic controls has resulted in a broadly three-phase evolution of the graben. Initial low-angle normal faulting between 16 - 2.6 Ma was followed by high-angle normal faulting along three fault strands that initiated ~ 2 Ma. Subsequent, fault linkage at ~ 0.8 Ma resulted in the present structural configuration. The long-term throw rate of the graben boundary fault, derived from geological piercing points, lies in the range 0.4 - 1.3 mm/yr, while river profile analysis suggests an increase from 0.6 to 2 mm/yr as a result of the linkage. Recent measurements of catchment averaged erosion rates (CAERs) from 10Be and 26Al cosmogenic nuclide analysis indicate that erosion rates within the transient reach of rivers crossing the fault vary from 16 to 1330 mMyr-1. However, CAERs only show weak relationships with unit stream power, steepness index and slip rate on the bounding fault and no clear relationships between erosion rate and relief or catchment slope. This is potentially the result of the strong lithological contrast in the footwall between strong metamorphic rocks and weak sediments, resulting in the sedimentary reaches behaving as gravel-bed or transport-limited channels. A landscape evolution model (LEM) built using Landlab components is used to further investigate the complex interplay between bedrock lithology, uplift, erosion and channel behaviour. First, a simple dipping fault model is used to validate the proposed evolution of the boundary fault. Second, a strong lithological boundary is introduced with and without sediment transport. While, the LEM does not explicitly address different mathematical models of river profile evolution, it confirms the significance of a strong lithological contrast on the geomorphic development of the Gediz region.
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.
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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.
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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. +
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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. +
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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. +
