Property:CSDMS meeting abstract
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Numerous humanitarian and disaster relief missions require updated topography to provide time-critical support following events such as earthquakes, wildfires, tsunamis, or armed conflicts. Radar techniques are particularly advantageous over other methods (e.g., LiDAR) in these scenarios because they are insensitive to weather and lighting conditions, allowing data collection through clouds and smoke, or at night. Despite these advantages, current radar-based methods for generating topography face significant challenges related to data acquisition logistics, processing complexity, and the specialized expertise needed.
Inspired by recent advances in computer vision and monocular depth estimation, we present a novel approach to generate Digital Elevation Models (DEMs) from single Synthetic Aperture Radar (SAR) images using deep learning. Our method leverages a global dataset of open-source SAR-DEM image pairs to train multiple architectures, including Vision Transformers (ViTs) and fully convolutional networks. We evaluate various supervised and adversarial training strategies across a diverse range of Earth's landscapes. Our approach streamlines topographic reconstruction by working directly in ground coordinates and eliminating specialized pre-processing, making DEM generation more accessible. By utilizing open-source satellite radar data with a 6-day revisit time, our method enables topographic reconstruction at a significantly improved temporal resolution. +
Observations in coastal environments show that seabed resuspension can impact water quality and biogeochemical dynamics by vertically mixing sediment and water, and by redistributing material that has been entrained into the water column. Yet, ocean models that incorporate both sediment transport and biogeochemical processes are rare. The scientific community frequently utilizes hydrodynamic-sediment transport numerical models, but hydrodynamic-biogeochemical models ignore or simplify sediment processes, and have not directly accounted for the effect of resuspension on oxygen and nutrient dynamics.
This presentation focuses on development and implementation of HydroBioSed, a coupled hydrodynamic-sediment transport-biogeochemistry model that was developed within the open-source Regional Ocean Modeling System (ROMS) framework. HydroBioSed can account for processes including advection, resuspension, diffusion within the seabed and at the sediment-water interface, organic matter remineralization, and oxidation of reduced chemical species. Implementation of the coupled HydroBioSed model for different locations, including the Rhone River subaqueous delta and the northern Gulf of Mexico, have helped to quantify the effects of both sediment transport and biogeochemical processes. Results indicate that resuspension-induced exposure of anoxic, ammonium-rich portions of the seabed to the more oxic, ammonium-poor water column can significantly affect seabed-water column fluxes of dissolved oxygen and nitrogen. Also, entrainment of seabed organic matter into the water column may significantly draw down oxygen concentrations in some environments. Ongoing work focuses on how resuspension and redistribution of organic matter and sediment may influence oxygen dynamics in the Chesapeake Bay. +
Observations of the spatial and temporal evolution of thaw and soil moisture changes are needed to understand thermo-hydrologic dynamics in periglacial regions and to inform models that forecast changes in the Arctic. However, obtaining spatially and temporally distributed observations in the Arctic is difficult. Here we develop and investigate the use and accuracy of the parameter estimation algorithm in recovering soil physical properties. We tested our parameter estimation (PE) approach with synthetic data from a continuously modeled electric resistivity tomography transect and co-located synthetic temperature and soil moisture data. The results indicate that developed PE approach is able to identify synthetic porosities and thermal conductivities. +
Ocean waves are key drivers of erosion and cliff retreat along rocky coasts, doing so by delivering energy to the shore upon breaking. Wave energy attenuation increases with increasing distance from the location of breaking. As a result, breaking distance from the shore is one of the most important constraints on wave energy delivery to the coast. A primary factor influencing nearshore wave transformation and energy flux at the shore is shore morphology. We seek to evaluate local morphologic controls to better characterize wave energy delivery to the coast. Local wave climates are characterized utilizing NOAA datasets, and we incorporate the Coastal Relief Model to determine nearshore bathymetry and coastal morphology. We then perform shallow water wave transformations using linear wave theory to specify wave breaking locations along the shore. Here we present preliminary results that suggest that shore morphology, and specifically the gradient of the shore platform, is the dominant control on wave filtering and transformation along the West Coast of the United States. Ascertaining the role of shore morphology in controlling energy delivery to the shore is important for specifying the influence of shore steeping processes on wave transformation and energy delivery, as well as constraining and predicting coastal erosion and cliff retreat. +
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Often a rivers discharge is calculated by constructing an empirical relationship between concurrent, direct measurements of river stage and discharge. In many remote parts of the world however technical and logistical challenges make building of such relationships difficult.
We test and present an alternative approach for use in remote Greenlandic Rivers. We used in-situ stage observations, but converted these measurements into estimates of discharge using a fluid mechanically based model (Kean and Smith, 2005; Kean et al., 2009; Kean and Smith, 2010). We first tested this approach against the one river in Greenland with a well-developed empirical stage- discharge relationship. Modeled relationships agreed well with the empirically derived relationship. We then used this same technique to aid in estimating discharge on two additional rivers in Greenland where only stage measurements were available. This technique presents an alternative option when other methods are logistically prohibitive. In the future this approach may also be useful to aid in estimating river discharge from space. +
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On a broad scale climate controls the distribution of biomes and sets an upper limit for woody plant canopy cover. During last glacial cycle that peaked ~18,000 years (B.P.) in the Late Pleistocene, the southwestern United States was much wetter and cooler than in the Holocene (last 11,000 years) and today. Since the Last Glacial Maximum, wetter and cooler climate in most arid semiarid regions has generally transitioned to drier and warmer conditions, establishing their characteristic (i.e., today’s native) ecosystems and fire regimes 3,000 - 5,000 years B.P. We use the Landlab earth surface modeling toolkit to explore the implications of the climate since the late Pleistocene on ecosystem patterns, using a calibrated model for conditions prior to the Euro-America settlers. Climate is constructed based on paleoclimatic proxies and weather station data. The controls of seedling dispersal strategies of plants and water availability as mediated by aspect are discussed. +
On densely populated deltas, the tendency for river channels to catastrophically avulse poses a hazard to human life and property. Previous work has shown that river avulsions preferentially occur around a spatial node with a distance from the shoreline that is controlled by backwater hydrodynamics, the interplay of dynamic river discharge and standing water near the shoreline. Our ability to forecast the location of future avulsion hazards is limited, however, because avulsions are relatively rare and many deltas are experiencing drastic changes in river discharge and sea level due to land-use and climate change. Building upon previous work, we present a predictive model of delta-lobe morphodynamics and repeated avulsion that is applicable to deltas over a range of spatial scales, sediment supplies, flood regimes, and relative-sea-level-rise conditions. In our model, delta lobes build on top of one another, demonstrating a distribution of avulsion lengths that is sensitive to flow regime and relative sea-level change. Variable flood regimes lead to a consistent avulsion length when low flows (less than bankfull) and high flows (greater than bankfull) compete to intermittently fill and scour portions of the backwater reach. The avulsion node is a spatial maximum in channel superelevation set by the downstream extent of low-flow deposition between erosive high-flows, and in general channels avulse farther upstream when high-flow events are more extreme and more frequent. Relative sea-level rise leads to a more variable avulsion node, driven by intermittent retreat and advance of the delta shoreline as the river periodically shifts the distribution of sediment. If rise rates are sufficiently high to sequester all sediment upstream of the river mouth, avulsions occur progressively farther upstream or not at all. These results have implications for the forecasting of avulsion hazards on modern deltas undergoing relative sea-level rise and human management.
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On earth, landscape morphology is mainly controlled by rivers evolutions and their interactions with hillslopes. But hydrographic network may be re-organized by stream capture and modify deeply the relief. This transition may be induced by several mechanisms (diversion, headward erosion, avulsion, or subterranean filling up). It has interested numerous scientists since a long time (Davis 1895, Blache 1943, Lesson-Quinif 2001 & Le Roux-Harmand 1997-2009…). Here we focus on stream piracies by headward erosion, when an actively eroding low level stream (called the captor) encroaches on the drainage of a nearby stream flowing at a higher level (called the diverter) and diverts part of the water of the higher stream.
During the last decades, several landscapes evolution models (LEM) have been developed to quantify the topography evolution with diffusion and advection equations. These models play an important role in sharpening our thinking to better understand the interaction between landscape evolution processes. LEM were developed basically to simulate erosion, tectonic and climate at different scales of time and space. But, these models were not designed to describe specific mechanisms as the stream capture. It’s one of the aims of this work to evaluate LEM for this purpose.
In this paper, we develop a 1D model based on LEM equations to investigate the stream piracy by headward erosion responses to climatic or tectonic changes. This model incorporates the most common equations used in quantitative geomorphology; diffusion in hillslope, advection in river (detachment-limited mode) and an inequality based on slope and drainage area for the limit between these two domains (Montgomery and Dietrich, 1988). First, simulations on analytical cases highlight the stream head progression mechanism, and the results indicate that this progression rate is mainly controlled by the slope at the captor source. Consequently, the aggradation of the diverter or (and) the incision of the captor accelerate the process. Then, a predictive study with an improved version of GOLEM (software developed by Tucker & Slingerland in 1994) on the Meuse basin shows that several piracies may probably occur in the future. A comparison with the 1D model gives similar results.
The simplicity and the flexibility of the 1D model allow complex simulations in the Meuse basin taking into account: lithological differences of outcropping layers, Meuse deposition tendency, etc. Once the 2D simulations or topography analysis locate potential captures, 1D simulation may intensively be used, as it presents many advantages; weak execution time, simple limits conditions setting, less time for data preparation, etc. Consequently, a sensitivity analysis to estimate piracies ages is realized with the developed 1D model.
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On low-lying coastlines, sand (and/or gravel) washed landward of a beach during storms creates barrier landscapes. This ‘overwashed’ sand also tends to maintain barrier elevation in the face of rising sea level, and barrier width in the face of an eroding shoreline. However, from the point of view of coastal communities, the storm processes that deposit the sand, as well as the sand itself, presents hazards that need to be mitigated, or even disasters that need to be recovered from. The strategies typically chosen to mitigate storm hazards and recover from storm impacts typically involve attempts to prevent overwash processes (e.g. by building and maintaining large dunes) or to undo the effects of overwash processes (e.g. bulldozing overwashed sand off roads and using it to rebuild dunes). Although these mitigation and recovery strategies seem necessary in the short term, they can reduce coastal resiliency in the long term, by tending to make a barrier lower (relative to rising sea level) and narrower (in the case of an eroding shoreline). A lower and narrower barrier is more vulnerable to sunny day flooding and severe storm impacts.
The newly developed CoAStal Community-lAnDscape Evolution (CASCADE) model couples physical processes (storm erosion and sediment redistribution, dune growth, sea-level rise, shoreface and shoreline change, and gradients in alongshore sediment flux) and the effects of management strategies (e.g. overwash removal and dune maintenance, highway relocation, and beach nourishment). Using this model, we examine the outcomes, over decades, of the coupling between natural dynamics and commonly employed management strategies. Modeled outcomes depend on sea-level-rise rate, storm sequences, and initial barrier topography, and they range from developed barrier systems that can be sustained for over a century before becoming uninhabitable (effectively drowned), to scenarios in which highways and/or communities need to be abandoned within decades. Subsequent barrier recovery depends on the final state of the developed system before abandonment, as well as stochasticity in the timing of storms. When different management strategies are employed at different locations alongshore, their effects are coupled via the redistribution of sediment along a curved coastline.
We are also using CASCADE in a participatory modeling collaboration involving managers and planners with the Cape Hatteras National Seashore and the North Carolina Department of Transportation, as well as community representatives. Together, we will examine the range of outcomes, under different climate scenarios, of the strategies being considered for managing a critically threatened transportation corridor along a barrier within the National Seashore.
One possible human response to climate change and other environmental stresses is migration. However, migration is complex, multi-causal phenomenon, and the complexity of human migration poses a challenge for researchers who aim to study the effects of environmental changes on population mobility. This project aims to understand how changing environmental conditions and livelihood opportunities impact migration decisions in coastal Bangladesh. An original agent-based model (ABM) that combines stylized environmental change dynamics with livelihood is developed to understand how these dynamics impact migration decisions as well as what feedbacks may exist between them. The ABM is constructed such that agents represent households, consisting of individuals, within a single origin community. At each step of the model, an agent will first assess the expected utility of its different options within the community, including doing nothing, seeking employment internal to the community, and investing in non-agricultural livelihood options. After assessing livelihood options internal to the community, households with sufficient wealth and a sufficient number of family members will decide whether or not to send a household member as a migrant, also based on expected utility of a migration trip. The model’s representation of natural processes will be simulated in the form of drought, modeled stochastically, that impacts crop yields and crop-associated income. In this initial version of the ABM, agent decision-making is based on simple utility maximization. Future work will incorporate more complex decision-making theories into the model, as well as different destination locations and the possibility of return migration. +
Our understanding of temporal changes in long term regional erosion rates in hundreds of years resolution is currently limited. The existing published research is either restricted in spatial coverage, the time frame is in millions of years, or the erosion rate through time is considered constant. We strive to fill this gap by mapping the regional erosion at a resolution of 3.70° latitude by 3.75° longitude (approximately 412 km x 416 km at the equator) at 500-year resolution for the past 21 ka for all land areas. We employ a transfer function that relates mean annual air temperature (MAAT) with erosion that is derived from published field observations recorded during recent times and transferred through the past 21 ka by using space-for-time substitution with paleo-temperature data from TraCE-21ka, a global climate model. Averaging erosion rates and MAAT by latitudes of the Kӧppen climate zones, a non-linear relationship was established. Among the many findings, the largest variation in erosion rates through time is found in cold regions, such as higher elevations and the Arctic. Furthermore, tropical or sub-tropical regions show minimal variation in erosion through time. +
Outburst floods and debris flows often incorporate large volumes of erodible bed sediment along their runout path. Although this phenomenon is widely recognized and often implicated for volumetric growth of debris flows, the effect of this process on the dynamics and runout extent of large flows has not been directly modeled extensively or systematically. Rather, models that account for this process traditionally utilize simple static volumetric and/or rheological adjustments. However, this process dynamically influences flood and debris-flow evolution in a complex spatiotemporal fashion.
We used D-Claw, a depth-averaged granular-fluid model that accommodates the incorporation of bed material into overlying flow and resultant changes in flow rheology across a wide range of solid concentrations, from dilute suspensions to dense-granular debris flows. We modeled hypothetical lake outburst floods from Spirit Lake, WA into the erodible sediment rich Toutle River Valley. Downstream flood dynamics of clear-water flows were compared to floods that entrain material and transform into down-valley debris flows. We found that while the entrainment of bed material may significantly increase total flow volume (>150%), downstream discharge and runout extent are more similar to clear-water floods than might be expected by volumetric considerations alone. We postulate that the relationship between entrained volume and flow extent depends on complicated site-specific factors such as location of erodible sediment and evolving rheological factors. +
Outlet glaciers convey large quantities of ice, sediment, and water from the interior of ice sheets to the coastal ocean. Beneath ice sheets, sediment is transported by melt water, entrainment in basal ice layers, and deformation of the till layer. Till deformation occurs when the ice sliding velocity exceeds a certain threshold, causing buried clasts to plough the sediment layer (Zoet and Iverson, 2020). Because ice velocity tends to decrease below the ice equilibrium line, but the threshold velocity to induce ploughing stays constant, the glacier will deposit till around the “till equilibrium line,” where the ice sliding velocity drops below the threshold velocity (Alley et al., 1989). Investigating the controls on till equilibrium lines will improve our understanding of erosion and sediment transport beneath glaciers and ice sheets. Here, we implement a numerical model of steady-state till equilibrium line position under a synthetic outlet glacier. We explore the influence of ice sliding velocity, clast sizes and distribution, and effective pressure at the bed. Additionally, we consider the case where the threshold velocity to induce ploughing is not constant, but instead depends on ice and sediment properties.
Zoet, L. K., & Iverson, N. R. (2020). A slip law for glaciers on deformable beds. Science, 368(6486), 76-78.
Alley, R. B., Blankenship, D. D., Rooney, S. T., & Bentley, C. R. (1989). Sedimentation beneath ice shelves—the view from ice stream B. Marine Geology, 85(2-4), 101-120. +
Over 10 percent of the worlds’ population lives less than 10 meters above sea level(McGranahan et al,. 2007), putting them at risk for rising seas and sinking coasts. Additionally, coastal inhabitants preferentially live in locations that are subsiding (Nicholls et al,. 2012), representing a flooding threat to people and infrastructure in coastal cities. Findings from the Intergovernmental Panel on Climate Change (IPCC 2018) outline the risks and impacts of sea level rise on flooding, and go on to identify a knowledge gap regarding the combined effects with coastal subsidence. When drivers of subsidence combine, they can generate sinking rates of 6-100mm/yr, significantly more than the 3-10mm/yr for sea level rise alone (Erkens et al,. 2015), making subsidence an order of magnitude more threatening to coastal cities.
The recent growth in access to C-band Synthetic Aperture Radar (SAR) data through the European Space Agency (ESA) Sentinel-1A/B satellites and the upcoming NASA-ISRO Synthetic Aperture Radar (NISAR) mission provide increased opportunities for differential interferometric synthetic aperture radar (DInSAR) monitoring. Here we developed a dockerized supercomputer workflow that allows us to rapidly generate InSAR pairs from Sentinel 1 imagery using ISCE processing software(Rosen et al., 2012) at ~10 meter resolution.
Results from this workflow are used to create a timeseries of subsidence for Lagos, Nigeria, where rapid urban growth has led to accelerated subsidence throughout the city. This growth has resulted in various flash floods due to infiltration and drainage issues in the last fifteen years(Atufu 2018), and the city is also vulnerable to coastal flooding. Next steps will include inputting our time series to determine how future flood events may impact specific areas of Lagos. Understanding where floods are a higher risk can allow for better distribution of rescue resources, and allow for targeted remediation and recovery efforts.
Over the recent geological past, alternations in the sediment budgets of low-order dryland catchments have left behind pronounced topographic imprints and are observed worldwide. The modern consequences of similar shifts extend from damage to ecosystems and crop yields to worldwide geopolitics. Quantifying erosion trends and understanding potential drivers for changes in the sediment budget is, however, a long-lasting challenge; ephemeral catchments are commonly situated in hydrological and vegetation boundary zones, greatly impacted by fine-scale and episodic erosion-triggered climatic events that are hard to observe and computationally complex over landscape evolution time scales.
This poster presents a set of catchment-scale landscape evolution numerical experiments designed according to field observations and projected climate records for the end of the 21st century derived from a convection-permitting climate model. The results demonstrate how changes in minute-scale rainfall bursts, as measured under modern global warming, could significantly enhance erosion rates and impact multi-century landscape evolution, even without a change in the general wetness level. Further, the presented modeling approach translates the future climate projection over the High Plains of Colorado into changes in vegetation cover along with an increase in sediment yield, which is contrary to the predicted general reduction in precipitation over the region. Modeling results, in conjunction with hints from a study area, reveal key relations between catchment morphology, soil/lithological properties, and vegetation cover that contribute to the understanding of landscape evolution under climatic changes. +
Particle settling velocity and bed erodibility impact the transport of suspended sediment to the first order, but are especially difficult to parameterize for the muds that often dominate estuarine sediments. For example, fine grained silts and clays typically form loosely bound aggregates (flocs) whose settling velocity can vary widely. Properties of flocculated sediment such as settling velocity and particle density are difficult to prescribe because they change in response to several factors, including salinity, suspended sediment concentration, turbulent mixing, organic content, and mineral composition. Additionally, mud consolidates after deposition, so that its erodibility changes over timescales of days to weeks in response to erosion, deposition, dewatering, and bioturbation. As understanding of flocculation and consolidation grows in response to recent technical advances in field sampling, numerical models describing cohesive behavior have been developed.
For this study, we implement an idealized two-dimensional model that represents a longitudinal section of a partially mixed estuary that mimics the primary features of the York River estuary, VA; and accounts for freshwater input, tides, and estuarine circulation. Suspended transport, erosion, and deposition are calculated using routines from the COAWST (Coupled Ocean-Atmosphere-Wave-and-Sediment Transport) modeling system. Here we evaluate the impact that bed consolidation and flocculation have on suspended sediment dispersal in the idealized model using a series of model runs. The simplest, standard model run neglects flocculation dynamics and consolidation. Next, a size-class-based flocculation model (FLOCMOD) is implemented. The third model run includes bed consolidation processes, but neglects flocculation; while the last model run includes both processes. Differences in tidal and daily averages of suspended load, bulk settling velocity and bed deposition are compared between the four model runs, to evaluate the relative roles of the different cohesive processes in limiting suspension in this partially mixed estuary. With an eye toward implementing these formulations in a realistic-grid model, we also consider the computational cost of including flocculation and consolidation.
Particle-based methods in computational fluid dynamics are capable of characterizing the propagation of the inertial terms and complex behavior of a fluid in low-viscosity systems onto an interface with highly viscous or solid materials, providing a high resolution window into fluid dynamics within environments that are fundamentally defined by fluid-solid interaction. The rate limiting feedbacks of wave action, erosion and sediment transport are a multiscale problem, involving kilometer-scale climate forcing and local, submeter Earth responses. We use real-world inputs of dynamic water levels at the mesoscale to drive local particle-based wave solutions towards natural coastal landforms effectively coupling the multiscale transfer of forces produced by topographic relief, wave action and ice collisions. 3D temporal solutions of nearshore currents at multiple scales make it possible to handle the specifics of fluid-solid interactions as the basis for training algorithms and subsequent expansion to larger regions. +
Passive margin stratigraphy contains time-integrated records of landscapes that have long since vanished. Quantitatively reading the stratigraphic record using coupled landscape evolution and stratigraphic forward models (SFMs) is a promising approach to extracting information about landscape history. However, the most commonly used SFM, which is based on an approximation of local, linear slope-dependent sediment transport, fails to produce diagnostic features of passive margin stratigraphy such as long-distance transport from the continental shelf and slope onto the abyssal plain. There is no consensus about the optimal form of simple SFMs because there has been a lack of direct tests against observed stratigraphy in well constrained test cases. Here we develop a nonlocal, nonlinear one-dimensional SFM that incorporates slope bypass and long-distance sediment transport, both of which have been previously identified as important model components but not thoroughly tested. Our model collapses to the local, linear model under certain parameterizations such that best-fit parameter values can be indicative of optimal model structure. Using seven detailed seismic sections from the South African Margin, we invert the stratigraphic data for best-fit model parameter values and demonstrate that best-fit parameterizations are not compatible with the local, linear diffusion model. Fitting the observed stratigraphy requires parameter values consistent with important contributions from slope bypass and long-distance transport processes. The nonlocal, nonlinear model yields improved fits to the data regardless of whether the model is compared against only the modern bathymetric surface or the full set of seismic reflectors identified in the data. Results suggest that processes of sediment bypass and long-distance transport are required to model realistic passive margin stratigraphy, and are therefore important to consider when inverting the stratigraphic record to infer past perturbations to source regions.
Past decades have seen rapid advancements in the field of soil erosion modelling, with a shift away from lumped empirical models and towards fully-distributed physically-based erosion models. The benefits of this shift is that distributed erosion models facilitate the spatial predictions of erosion and deposition across the landscapes by computing runoff and modelling the subsequent detachment, transport, and deposition of sediments. Despite the ability to represent the physical process of erosion spatially, distributed erosion models are validated to discharge and sediment yield at catchment outlets. Spatial information on erosion and deposition rates are seldom used to validate distributed models; this is because both plot and field-scale data on erosion rates are rare. Structure-from-motion (SfM) and multi-view stereo (MVS) algorithms coupled with the use of unmanned aerial vehicles (UAVs) have become a popular tool in geomorphology for modelling topographic change-detection on complex landscapes. We demonstrate the viability of using these techniques to generate spatial validation data; repeat UAV surveys of an agricultural field are used to identify dominant sediment flow paths, depositional zones, and rill/gully erosion processes. This unique spatial dataset allows us to tackle issues of spatial equifinality, model parameterization, and the accurate discretization of the landscape. +
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Patterns of sediment transport and particle residence times influence the morphology and ecology of shallow coastal bays in important ways. The Virginia Coast Reserve (VCR), a barrier island-lagoon-marsh system on the Eastern Shore of Virginia, is typical of many shallow coastal bay complexes that lack a significant fluvial source of freshwater and sediment. Sediment redistribution within the bays in response to storms and sea-level rise, together with the dynamics of marsh and lagoon-bottom plants, largely governs the morphological evolution of this system. There are also important feedbacks between sediment and ecosystem dynamics. This is particularly true in the VCR, which is relatively unaffected by human activities. As a step towards evaluating the impact of hydrodynamics on sediment and ecological processes in the VCR, we employ a single unified model that accounts for circulation, surface waves, wave-current interaction, and sediment processes. This three-dimensional unstructured grid finite-volume coastal ocean model (FVCOM) is validated with field observations of wind- and tide-induced water flow (water level and current velocities) in Hog Island Bay, centrally located within the VCR. We present here the resulting patterns of sediment transport and particle residence times over event and seasonal time scales. Water and particle exchange within the VCR and between the VCR and the ocean is examined with the Lagrangian particle-tracking module in FVCOM. We focus on 3 bays with strongly varying bathymetry and coastline geometry, which are also located along a gradient of nitrogen input to the system. The results indicate that residence time of particles within the system vary greatly depending on the location of particle release, bay morphology, and wind conditions. The implications for morphologic evolution and ecosystem response to climate and land-use changes are evaluated. +
