Property:CSDMS meeting abstract
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At a global scale, deltas significantly concentrate people by providing diverse ecosystem services and benefits for their populations. At the same time, deltas are also recognized as one of the most vulnerable coastal environments, due to a range of adverse drivers operating at multiple scales. These include global climate change and sea-level rise, catchment changes, deltaic-scale subsidence and land cover changes, such as rice to aquaculture. These drivers threaten deltas and their ecosystem services, which often provide livelihoods for the poorest communities in these regions. Responding to these issues presents a development challenge: how to develop deltaic areas in ways that are sustainable, and benefit all residents? In response to this broad question we have developed an integrated framework to analyze ecosystem services in deltas and their linkages to human well-being. The main study area is part of the world’s most populated delta, the Ganges-Brahmaputra-Meghna Delta within Bangladesh. The framework adopts a systemic perspective to represent the principal biophysical and socio-ecological components and their interaction. A range of methods are integrated within a quantitative framework, including biophysical and socio-economic modelling, as well as analysis of governance through scenario development. The approach is iterative, with learning both within the project team and with national policy-making stakeholders. The analysis allows the exploration of biophysical and social outcomes for the delta under different scenarios and policy choices. Some example results will be presented as well as some thoughts on the next steps. +
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At the Visual World Investigation Lab of the Nature Research Center, we are developing a module where museum visitors investigate geomorphic and land-use scenarios through a landscape evolution model. Visitors use touchscreen computers to select simplified inputs for the CHILD model. Model visualizations will be produced for each trial in which they run the scenario. For example, visitors can explore the impact of the percentage of impervious surfaces in a section of urbanized Raleigh that will be adjusted by scaling infiltration parameters, and how the headwaters of the Little Tennessee River would differ if the southern Appalachians were still undergoing tectonic uplift. These scenarios provide relatable experiences to visitors, an opportunity to educate them upon the science behind the scenarios, and the purpose and limitations of models. We will first develop the framework of the module to be able to accept scenarios and its inputs, including digital elevation models, such that others can contribute scenarios. This module is early in its conception, thus we will present our initial framework with the intent to elicit feedback from the community. +
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At the catchment scale, alluvial rivers co-adjust their planform, cross-sectional, and longitudinal geometries in response to changing water and sediment inputs, base level and the transport of this sediment through the fluvial system. In this study, we derive a simple, physics-based model to understand and predict sand-bed river long-profile form and evolution. This model links sediment transport and river morphodynamics, following an analogous approach to that taken by Wickert and Schildgen (2019) for gravel-bed rivers. It allows for planform (width) adjustments as a function of excess shear stress by following Parker (1978); this linearizes the sediment-transport response to changing river discharge, and ultimately suggests a diffusive form for sand-bed river long-profile evolution. Here, we also present model results of gravel- and sand-bed river long profiles under a variety of water- and sediment-supply and base-level conditions to discuss how these may help us to better interpret the geological and geomorphological context of alluvial rivers, and better predict their changes over time. This expression for the long-profile evolution of transport-limited sand-bed rivers provides forward momentum to merge theory and models for gravel-bed and sand-bed river systems, to look at the alluvial river system response as a whole (from bedrock-alluvial transition to the point at which backwater effects become significant) over both human and geological time scales, and to decipher the long-term rate and magnitude of this response to facilitate a better understanding of the evolution of fluvial landscapes. +
At the margins of many glaciers, we observe visually-striking layers of concentrated sediment incorporated into ice near the base of the glacier. Despite the prevalence of these ice-sediment facies, sediment transported in basal ice is rarely quantified in the overall sediment transport budget for glacial systems. Previous facies descriptions have been linked to formation mechanisms that depend on specific configurations of the topography or hydrology beneath a glacier, which remains inconsistent with observations of similar facies across disparate regions, climate zones, and geologic settings. Here, we use detailed descriptions of ice-sediment facies from Mendenhall glacier, Alaska, to inform a numerical model of sediment entrainment in basal ice. We find that the overall volume of entrained sediment is strongly related to the glacier’s thermal regime near the ice-sediment interface. Further, we present a likely mechanism for the formation of dispersed ice facies that explains the natural variability in sediment characteristics observed at Mendenhall glacier and other alpine systems. These results show that ice-sediment facies are a plausible archive for understanding the subglacial environment, even in the absence of additional constraints on temperature or hydrologic connectivity at the bed. +
Barrier island response to sea level rise depends on their ability to transgress and move sediment to the back barrier, either through flood-tidal delta deposition, or via storm overwash. Our understanding of these processes over decadal to centennial time scales, however, is limited and poorly constrained.
We have developed a new barrier inlet environment (BRIE) model to better understand the interplay between tidal dynamics, overwash fluxes, and sea-level rise on barrier evolution. The BRIE model combines existing overwash and shoreface formulations with alongshore sediment transport, inlet stability, inlet migration and flood-tidal delta deposition. Within BRIE, inlets can open, close, migrate, merge with other inlets, and build flood-tidal delta deposits. The model accounts for feedbacks between overwash and inlets through their mutual dependence on barrier geometry.<br><br>Model results suggest that when flood-tidal delta deposition is sufficiently large, barriers require less storm overwash to transgress and aggrade during sea level rise. In particular in micro-tidal environments with asymmetric wave climates and high alongshore sediment transport, tidal inlets are effective in depositing flood-tidal deltas and constitute the majority of the transgressive sediment flux. Additionally, we show that artificial inlet stabilization (via jetty construction or maintenance dredging) can make barrier islands more vulnerable to sea level rise. +
Barrier islands and other coastal landforms are highly dynamic systems, changing in response a spectrum of disturbances from multi-decadal ‘press’ disturbances like sea-level rise (SLR) to often more intense episodic perturbations like storms. As a result, multiple stable ecomorphological states exist on barrier islands. In this study, we use a probabilistic Bayesian network approach to investigate the likelihood of shifts among alternative equilibrium states on Fire Island, New York under three scenarios of shoreline change driven by sea-level rise (SLR). Specifically, we highlight areas that are most likely (i) to become inundated, (ii) to shift from one non-inundated state (or landcover type) to another (e.g., a forest becomes beach), or (iii) to remain in the current landcover state. We explore the effects of these changes on the availability of coastal ecosystem types, piping plover habitat, and anthropogenic development. +
Barrier islands, which comprise ~10% of shorelines worldwide, are ecologically and economically important coastal systems. They also provide numerous ecosystem goods and services, acting as critical buffers that protect the mainland from storms, erosion, and other natural hazards. However, the dynamic nature of barrier island geomorphology and the processes that sustain them create complex coastal management challenges, particularly in response to more intense and frequent storms and rising sea levels. These challenges contribute to infrastructure vulnerability, habitat loss, and increasing maintenance costs for management actions like beach nourishment, negatively impacting coastal communities. Thus, understanding the interplay between natural processes and management decisions is essential for predicting the future of developed coastlines. Here, we apply the CoAStal Community-lAnDscape Evolution (CASCADE) model, a coupled landscape and human dynamics modeling framework, tailoring it to simulate geomorphic change on Hatteras Island, North Carolina — a barrier island in the Outer Banks experiencing severe erosion that threatens both properties and transportation routes along the NC-12 highway. Following a hindcast calibration and test, we assess the likely range of future island behavior under a range of different climate and management scenarios. Our approach integrates geomorphic and human decision-making processes and incorporates diverse datasets, such as LiDAR-derived elevations, historic shoreline change rates, storm records, sea-level rise projections, and management scenarios currently under consideration. This study demonstrates the utility of CASCADE as a tool for understanding coupled human-natural systems and provides a framework for assessing long-term coastal resilience and adaptation strategies under changing environmental conditions in other similar settings. +
Beach ridges are common landforms found along coasts undergoing isostatic rebound or other forms of relative sea-level fall. The development of individual ridges has been attributed to storms, tidal cycles, and even the change in the rate of relative sea-level. However, few studies have investigated the role of autogenic processes in the development of individual ridges. In this study, we modify the existing code for modeling beach/foredune-ridge and swale morphology to examine the development of beach ridges during conditions of falling relative sea-level and constant sediment supply. We show that individual beach ridges can form in the absence of changes in the rate of sea-level change, tidal cycle, sediment supply, and storms. New beach ridges form as the shoreline moves seaward due to relative sea level fall, removing older beach ridges from their source of sediment, thus nucleating new beach ridges. Furthermore, we find that beach ridges grow higher and more frequent with increased rates of sediment supply. This study highlights the importance autogenic processes play in beach ridge development and has significant implications for the ability to decipher between environmental signals using beach ridges as historical archives. +
Bedload flux is notoriously challenging to measure and model with its dynamics, therefore, remains largely unknown in most fluvial systems worldwide. We present a global scale bedload flux model as part of the WBMsed modeling framework. The results show that the model can very well predict the distribution of water discharge and suspended sediment and well predict bedload. Bedload predictions’ sensitivity to river slope, particle size, discharge, river width, and suspended sediment were analyzed, showing that the model is most responsive to spatial dynamics in river discharge and slope. The relationship between bedload and total sediment flux is analyzed globally and in representative longitudinal river profiles (Amazon, Mississippi, and Lena Rivers). The results show that while, as expected, the proportion of bedload is decreasing from headwater to the coasts, there is considerable variability between basins and along river corridors. The topographic and hydrological longitudinal profiles of rivers are shown to be the key driver of bedload longitudinal trends with fluctuations in slope controlling its more local dynamics. Differences in bedload dynamics between major river basins are attributed to the level of anthropogenic modifications, flow regimes, and topographic characteristics. +
Bedrock lithology has been shown to strongly influence how rivers and landscapes respond to tectonic perturbations, yet the specific variables and mechanisms that set how lithology controls river erosion are poorly understood. Recent field and modeling work suggests that one important lithologic control on channel response may be the delivery of large, generally immobile boulders from hillslopes to channels. This raises the possibility that differences in boulder delivery rates between lithologies may cause substantial differences in how landscapes respond to tectonics. An intriguing recent study suggested that in the Mendocino Triple Junction (MTJ) region of northern California, bedrock lithology might control the frequency and size of boulders delivered to channels, and therefore govern channel steepness and river evolution (Bennett et al., 2016). We further test this hypothesis here.
The Central Belt of the Franciscan Complex, a mix of sheared graywacke and mudstone, contains large blocks of more resistant serpentinite, greenstone, and amphibolite that are delivered to channels by earthflows. The adjacent Coastal Belt generally lacks such boulders, and sediment delivery to channels is dominated by shallow landsliding. This geologic setting provides a unique opportunity to test whether boulder abundance exerts a first-order control on landscape form. We use a landscape-scale analysis of channel steepness and active width indices, local topographic relief, lithology, and mapped boulder occurrence to understand the differences between the catchments eroding the Central Belt and those eroding the Coastal Belt. We find that channels are steeper in the Central Belt than in the Coastal Belt, both across the whole MTJ region and when averaged over 10-50 km2 subcatchments. Channels are also generally narrower in the Central Belt. This result could reflect lithologic controls or spatial heterogeneity in erosion rates. To control for the latter, we construct clusters of neighboring subcatchments that are free of knickpoints to explore possible controls of lithologic makeup (percent of a subcatchment underlain by Central Belt rocks) on channel steepness independent of erosion rate variations. We find inconsistent relationships between lithologic makeup and channel steepness within a given cluster of catchments with similar baselevel history. Finally, we compared channel segments adjacent to hillslope failures with segments far from failures. Central Belt channels show greater absolute increases in steepness adjacent to hillslope failures, but relative increases in steepness are consistent between the Central Belt and Coastal Belt.
Our preliminary results suggest that Central Belt channels are steeper and narrower than Coastal Belt channels, but that the lithological influence on steepness is difficult to disentangle from the effects of spatially variable erosion rates. We are continuing to map in-channel boulder size distributions to assess the relative importance of intra- vs. inter-lithologic variability in setting boulder concentrations and landscape form.
Besides long-term monitoring in changes of thermal state of permafrost and active layer thickness, the knowledge of permafrost distribution at very fine scales (tens of meters) in discontinuous permafrost is still largely unknown in Qinghai-Tibet Plateau (QTP). A permafrost island was found by using geophysical investigations in the Heihe River Basin in northeastern QTP. Permafrost island was present at PT10 site beneath alpine steppe and coarse soil with a quality of gravel in surface soil (Fig. 1, Fig. 2). In contrast, permafrost is absent at SFGT site with density land cover area and relatively less gravel. The results showed that the ground surface temperature (5 cm) at PT10 site is lower in winter and higher in summer than the SFG site. The presence of permafrost is caused by soil conditions, especially by high thermal conductivity, based on field investigations. To address the controlling factors of permafrost presentences a 1D heat transfer model is used to compare the ground temperature difference between these two sites by only changing the soil conditions. +
Block-mantled hillslopes responding to river incision deliver large blocks of rock to channels. These blocks inhibit fluvial erosion by shielding the bed and reducing available bed shear stress. Block delivery by hillslopes in response to channel incision therefore feeds back on the boundary conditions felt by the hillslopes: larger numbers of blocks, or larger blocks, reduce the rate at which the hillslope boundary condition is lowering. This coupled set of feedbacks can lead to oscillatory behavior in both channels and hillslopes with periods of rapid channel incision interspersed with intervals of little to no incision. For a hillslope with a line supply of blocks (such as might originate from a resistant caprock overlying a less resistant layer), we expect that these feedbacks are strong only when the source of blocks is relatively close to the channel. Once the block source has retreated sufficiently far from the channel, blocks will weather away before reaching the channel and the oscillatory channel-hillslope feedbacks described above will cease. Our questions are 1) For how long after initial river incision through a caprock do oscillatory channel-hillslope feedbacks persist? and 2) How far must the block source retreat from the channel before such feedbacks become negligible?<br><br>We use the new BlockLab 2-D landscape evolution model to assess the spatial and temporal extent of oscillatory channel-hillslope feedbacks. We model a channel incising a lithological sequence consisting of a weak layer underlying a resistant caprock. Blocks from the caprock are delivered to the channel and inhibit river incision. We find that at early time, temporal variation in the erosion rate boundary condition felt by the hillslope is significant. As the resistant layer retreats further from the channel, variations in both the channel erosion rate and the resistant layer retreat rate decline. The rate of these reductions in variability with time is set by competition between 1) the ability of the hillslope to deliver multiple large blocks to the channel (a function of initial block size, block weathering rate, and the distance the blocks had to travel before arriving at the channel), and 2) the ability of the channel to overcome the erosion-inhibiting effects of blocks (set by fluvial discharge and the block erodibility coefficient). We find that after enough model time has passed, the resistant layer has retreated far enough from the channel that block effects on the channel are negligible and oscillatory channel-hillslope feedbacks no longer exist. This distance is primarily a function of initial block size and block weathering rate. Our results indicate that channel and hillslope evolution rates in block-mantled landscapes may be highly unsteady, depending on the strength of coupling between the channels and hillslopes.
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Breaking waves, especially plunging breakers, generate intense turbulence and is crucial in dissipating incident wave energy, suspending and transporting sediment in the surf zone. Therefore quantifying breaking-induced turbulence kinetic energy (TKE) is essential in understanding surf zone processes. Surf zone hydrodynamic data collected at the Large-scale Sediment Transport Facility (LSTF) at the U.S. Army Engineer Research and Development center were used here. One LSTF case, with irregular waves (3 s peak period), is examined here. This case resulted in dominantly plunging type of breaker. Waves and currents were measured simultaneously at 10 cross-shore locations and throughout the water column, with a sampling rate of 20 Hz. In order to separate orbital wave motion from turbulent motion, an adaptive moving average filter is developed, involving a 5-point moving average, with additional 3-point moving average at sections with more fluctuations. This adaptive moving average filter is able to maintain more wave energy as compared with the results from 7-point moving average, while resolve more turbulence energy as compared with the result from 5-point moving average.
The TKE was calculated based on the resolved turbulence. Large TKE was generated at the water surface associated with wave breaking and dissipated rapidly downward. The TKE decreased nearly one order of magnitude downward within 15 cm. The TKE reached a minimum value at approximately 50%-80% of the water depth, and increased towards the bottom due to the generation of bed-induced turbulence. The TKE flux during wave crest and tough indicate that, at the bottom and middle layers of the water column, the TKE is transported dominantly onshore, while for the top layer, it is transported mostly offshore. +
By using a fixed-mesh approach, morphodynamic models have some difficulty to predict realistic equilibrium hydraulic geometries with vertical banks. In order to properly account for bank erosion without resorting to a complicated moving mesh algorithm, an immersed boundary approach that handles lateral bank retreat through fix computational cells is needed.<br>
One of the main goals of the FESD Delta Dynamics Collaboration is developing a tested, high-resolution quantitative numerical model to predict the coupled morphologic and ecologic evolution of deltas from engineering to geologic time scales. This model should be able to describe the creation and destruction of deltas made of numerous channels, mouth bars, and other channel-edge features, therefore requiring an approach that is able to deal with the disruption, destruction, and creation of sub-aerial land. In principle, these sub-aerial land surfaces can be randomly distributed over the computational domain. <br>
We propose a new approach in Delft3D based on the volume of fluid algorithm, widely used in the literature for tracking moving interfaces between different fluids. We employ this method for implicitly tracking moving bank interfaces. This approach easily handles complicated geometries and can easily tackle the problem of merging or splitting of dry regions characterized by vertical vegetated banks. +
By using spatially-varying estimates of seabed bottom drag (z0) the performance of ocean current and tide numerical models may be improved. To an extent, the seabed database dbSEABED is able to supply these values from data on the seabed materials and features. But then adjustments for varying dynamic (wave, flow) conditions are also required. So the data and model must work closely together. We developed methods for calculating inputs of z0 for circulation models in this way. Preliminary outputs from this new globally capable facility are demonstrated for the NW European Shelf region (NWES). +
Cellular automata models have gained widespread popularity in fluvial geomorphology as a tool for testing hypotheses about the mechanisms that may be essential for the formation of landscape patterning. For instance, studies of braided rivers using cellular automata modeling suggested that erodible banks are an essential characteristic for formation of the braid-plain morphology. In wetlands with emergent vegetation and complicated flow patterns, distilling the relevant, nonlinear interactions to a relatively simple set of rules that can be used in cellular automata modeling poses challenges, but the advantage of doing so lies in the ability to perform sensitivity analyses or examine system evolution over millennia. Here I show how a hierarchical modeling strategy was used to develop a cellular automata simulation of the evolution of a regular, parallel-drainage patterned landscape in the Everglades. The Ridge and Slough Cellular Automata Landscape model (RASCAL) suggested that this landscape structure is stable only over a small range of water-surface slopes (the driving variable for flow)—a result that both explains the limited distribution of low-gradient parallel-drainage systems worldwide and would likely have not been detected had a non-hierarchical CAM been used. Additional sensitivity analyses with RASCAL show how interactions between flow, vegetation, and sediment transport can lead to a wide variety of other regular and amorphous landscape patterns, depending on the relative strength of physical and biological feedbacks. Comparisons between RASCAL and well-known CAM models of braided stream dynamics raise interesting questions about the level of complexity that need to be incorporated into models of transitional (low- to high-energy) environments such as wet meadows and small/intermittent streams. +
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Changes in landscape structure are known to affect species macroevolution largely by altering habitat connectivity. Species can disperse across a greater area when habitats expand. Habitat fragmentation reduces gene flow and increases rates of speciation. Conversely, a shrinking habitat increases the likelihood of species extinction.
We integrated macroevolution processes (dispersal, speciation, and extinction) into the landscape evolution modeling toolkit called Landlab. Here, we present a new Landlab component, BiotaEvolver that tracks and evolves the species introduced to a model grid. In one model, surface process components evolve the landscape and BiotaEvolver evolves the species in response to topographic change or other characteristics of the model set by the user. BiotaEvolver provides a base species and users can subclass this object to define properties and behaviors of species types.
We demonstrate BiotaEvolver using scenarios of drainage rearrangement and stream species. Stream captures and high macroevolution process rates occurred within a limited combination of parameters and conditions in hundreds of model runs. The number of species increased most rapidly after a response period following a perturbation. Species numbers declined then became stable after this period. +
Changes in upstream land-use have significantly transformed downstream coastal ecosystems around the globe. Restoration of coastal ecosystems often focuses on local-scale processes, thereby overlooking landscape-scale interactions that can ultimately determine restoration outcomes. Here we use an idealized bio-morphodynamic model, based on estuaries in New Zealand, to investigate the effects of both increased sediment inputs caused by upstream deforestation following European settlement and mangrove removal on estuarine morphology. Our results show that coastal mangrove removal initiatives, guided by knowledge on local-scale bio-morphodynamic feedbacks, cannot mitigate estuarine mud-infilling and restore antecedent sandy ecosystems. Unexpectedly, removal of mangroves enhances estuary-scale sediment trapping due to altered sedimentation patterns. Only reductions in upstream sediment supply can limit estuarine muddification. Our study demonstrates that bio-morphodynamic feedbacks can have contrasting effects at local and estuary scales. Consequently, human interventions like vegetation removal can lead to counterintuitive responses in estuarine landscape behavior that impede restoration efforts, highlighting that more holistic management approaches are needed. +
Changing sea level and ice volume since the Last Glacial Maximum (LGM, 26-19 ka) has been an intensively studied topic for decades, and yet we have still not been able to adequately close the water volume budget at the LGM. At the LGM, global sea level was depressed by approximately 125-135 m relative to the present level. Past researchers have attempted to account for the storage of this water as an estimated 52*106 km3 of land-based ice. However, relative sea level, ice sheet morphology, and isostacy studies at local and regional scales have been unable to reasonably place high enough ice volumes to meet this global total, accounting for only approximately 120 m of sea-level change. This discrepancy has resulted in the so-called ‘missing ice’ problem.
We propose that some portion of this ‘missing’ water was stored not as ice, but in lakes and groundwater. Thus far, no studies have attempted to determine the volume of water stored in lakes and groundwater at the LGM. Groundwater storage could potentially account for a large volume of water, reducing the missing water volume by a significant margin. Differing topography and recharge rates may have resulted in greater terrestrial water storage, which can help us to close the water budget. Indeed, many large proglacial and pluvial lakes are known to have existed and may indicate higher groundwater levels. Furthermore, assessing groundwater levels at 500 year intervals from the LGM to the present day can provide insights into changes in water storage and inputs to the ocean over time.
It is challenging to assess groundwater levels with precision since various factors, including evapotranspiration, topography, and sea level all play a role in controlling groundwater level at a particular location. However, a recent model (Reinfelder et al., 2013) was able to estimate modern groundwater levels on a global scale. By using this model in combination with modelled topography and climate data for the LGM and each 500 year time step, we are able to compare the volume of water stored in the ground from the LGM to the present day to test whether groundwater would be a viable reservoir for LGM water storage. The model provides depths to water table, thus allowing computation of changing storage volumes.
The model covers the entire globe at a resolution of 30 arc-seconds. The large datasets and iterative nature of the model require MSI’s computational power to perform the calculations. So far, preliminary results have shown that over a metre of additional sea-level equivalent water was stored in the ground at the LGM.
Chemical erosion of regolith is of wide interest due to its role in Earth’s topographic evolution, the supply of nutrients to soils and streams, and the global carbon cycle. Theory and experiments suggest that chemical erosion rates (W) should be strongly controlled by physical erosion rates (E), which affect W by removing weathered regolith and regulating mineral supply rates to the regolith from its underlying parent material. A global compilation of field measurements reveals a wide range of relationships between W and E, with some sites exhibiting positive relationships between W and E, some exhibiting negative relationships, and others exhibiting a flat relationship within uncertainty. Here we apply a numerical model to explore the variety of W-E relationships that can be generated by transient perturbations in E in well-mixed regolith.
Our modeling results show that transient relationships between W and E during erosional perturbations can strongly deviate from steady-state relationships. These deviations ultimately result from the time lag in changes in W following imposed changes in E. As a consequence of the lag, a hysteresis develops in plots of W versus E during transients in E. This yields a positive relationship between W and E at some times during a transient perturbation, a flat relationship at other times, and a negative relationship at other times. The shape and duration of these transient hystereses can be modulated by climate and lithology, as the lag time increases linearly with a characteristic regolith production time and decreases with a characteristic mineral dissolution time, both of which are affected by climatic and lithologic factors. Our results show that even in the absence of variations in climate and lithology, however, a range of W-E relationships can be generated by a single perturbation in E. To the extent that these model results capture the behavior of chemical and physical erosion in natural landscapes, these results may aid interpretation of field measurements of W and E.
