Property:CSDMS meeting abstract
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Minnesota’s drainage-ditch network facilitates agriculture by draining standing water, but disrupts hydrological connectivity and the water extent of wetlands. These wetlands are critical for ecosystem health, water filtration, carbon storage, and flood protection (e.g. Hansen et al. 2018, Office of Water 2002). Cowdery et al. (2019) investigated a case study of wetland restoration in western Minnesota, but the study region experienced variable precipitation and environmental factors across pre- and post-restoration periods. In our project, we systematically model drainage-ditch removal and wetland restoration across all Minnesota watersheds. Using computational GIS, we develop a topobathy digital elevation model, which accounts for depressions that currently store water. We run depression-filling algorithms (Barnes 2016, Barnes et al. 2020, Barnes et al. 2021) to first compute water storage in the current landscape. With information on current water storage in hand, we digitally infill drainage ditches and recalculate water storage and extent. These results will isolate the impacts of certain drainage ditches on surface water.
* Barnes, Richard. 2016. RichDEM: Terrain Analysis Software. http://github.com/r-barnes/richdem
* Barnes, R., Callaghan, K. L., & Wickert, A. D. Computing water flow through complex landscapes – Part 2: Finding hierarchies in depressions and morphological segmentations, Earth Surface Dynamics, 8, 431–445, https://doi.org/10.5194/esurf-8-431-2020, 2020.
* Barnes, R., Callaghan, K. L., & Wickert, A. D. Computing water flow through complex landscapes – Part 3: Fill–Spill–Merge: flow routing in depression hierarchies. Earth Surface Dynamics, 9, 105-121, https://doi.org/10.5194/esurf-9-105-2021, 2021.
* Cowdery, T., Christenson, C. A., Ziegeweid, J. The Hydrologic Benefits of Wetland and Prairie Restoration in Western Minnesota - Lessons Learned at the Glacial Ridge National Wildlife Refuge, 2002-15. U.S. Geological Survey Scientific Investigations Report 2019–5041, https://doi.org/10.3133/sir20195041, 2019.
* Hansen, A. T., Dolph, C. L., Foufoula-Georgiou, E., & Finlay, J. C. Contribution of wetlands to nitrate removal at the watershed scale. Nature Geoscience, 11, 127-132, https://doi.org/10.1038/s41561-017-0056-6, 2018.
* Office of Water & Office of Wetlands, Oceans, and Watersheds. Functions and Values of Wetlands. United States Environmental Protection Agency, EPA 843-F-01-002c March 2002, 2002.
Mixed sediment beaches are common across the globe, yet despite this, they have not been as extensively studied as sandy coasts. In the UK, these gravel-rich ‘shingle’ beaches are used as a first line of defence against flooding, limiting the amount of overtopping on heavily developed coasts such as those found on the South East coast. The shingle beach at Pevensey Bay, in East Sussex is the UK’s largest natural flood defence and is maintained through publicly funded, long-term beach management activities, recharge, recycling and by-passing of material. Monthly beach surveys, carried out to inform these works, revealed that the foreshore was experiencing chronic erosion with the loss of approximately 8,000 m3 of sediment each year. Whilst changes to the upper beach are constantly tracked and managed changes occurring just below the waterline were practically unknown.
Identifying the pathways for sediment movement across the nearshore zone was a key objective for this study to help understand the continued erosion of the foreshore. Analysis of multibeam bathymetry and X-Band radar reflectance data revealed the presence of transverse finger bars in the nearshore zone. The bars extended up to 700m offshore and were approximately 80-120m wide, with a maximum amplitude of 0.5m. Weekly-averaged reflectance imagery showed the position of the bars, which are orientated at 45o to the coastline, as the surface roughness of the sea was moderated by the seabed. These high temporal frequency roughness signatures showed that the bars were permanent features on the seabed and that they were migrating at a rate of approximately one wavelength a year. The movement of the bars was triggered by excess wave energy; peak migration rates were reached in the 2020 November to December period, whilst virtually no movement occurred between April and September 2021. Similar spatio-temporal patterns have been observed in erosive and accretive pulses in the upper beach and the link between bar movement and beach response is examined. Gaining a clearer understanding of the movement of sediment within the nearshore zone on beaches such as Pevensey will improve our understanding of how mixed sediment beaches function and brings into question whether active upper beach management is the most sustainable long-term option
Models of bedrock river incision, whether stream-power or mechanistically based, incorporate approximations of bedrock susceptibility to erosion. One or more parameters for a specific basin, lithology or outcrop may be estimated, and related to erodibility, as well as abrasion and plucking characteristics. However, choosing those parameters requires information of bedrock properties, which are either approximated or measured. Field and flume measurements are currently used to obtain physical bedrock properties that can be used for those models. Most studies focus on either field or flume measurements, but it is unclear whether their results are interchangeable. Therefore, we compare field measurements of compressive strength obtained with the Schmidt hammer and fracture intensity and block size with macro-abrasion and attrition rates obtained by flume measurements. We aim to discuss their possible meaning in terms of physical erosion processes and their use for bedrock river incision modeling. +
Models of coastal barrier ecomorphodynamic change are valuable tools for understanding and predicting when, where, and how barriers evolve, which can inform decision-making and hazard mitigation. Present ecomorphodynamic models of barrier systems, however, tend to operate over spatiotemporal scales incongruous with effective management practices (i.e., too fine-scale/event-based or too coarse/long-term). In contrast, we are developing a new model capable of simulating ecomorphologic change of undeveloped barrier systems over several kilometers and decades with a 1-by-1 m planform grid and weekly time step. The model couples aeolian dune growth and vegetation dynamics (DUBEVEG), storm erosion of the beach and foredunes (CDM/SBEACH), storm overwash (Barrier3D), and shoreline/shoreface adjustment (LTA14). We parameterize the model with elevation and vegetation data from North Core Banks, NC, focusing on changes caused by Hurricane Florence (2018). Calibrating free parameters using a genetic algorithm, we find good to excellent agreement with observed and simulated elevation change for representative, small (<1 km alongshore) barrier segments. Future work will include testing the model with multidecadal hindcasts of ecomorphodynamic barrier change; running suites of simulations will allow us to better capture and quantify the probabilistic nature of the dynamic response of barriers to the forces driving coastal evolution. +
Models of landscape evolution provide insight into the geomorphic history of specific field areas, create testable predictions of landform development, demonstrate the consequences of current geomorphic process theory, and spark imagination through hypothetical scenarios. While the last four decades have brought the proliferation of many alternative formulations for the redistribution of mass by Earth surface processes, relatively few studies have systematically compared and tested these alternative equations. We present a new Python package, terrainbento 1.0, that enables multi-model comparison, sensitivity analysis, and calibration of Earth surface process models. terrainbento provides a set of 28 model programs that implement alternative transport laws related to four process elements: hillslope processes, surface-water hydrology, erosion by flowing water, and material properties. The 28 model programs are a systematic subset of the 2048 possible numerical models associated with 11 binary choices. Each binary choice is related to one of these four elements---for example, the use of linear or non-linear hillslope diffusion. terrainbento is an extensible framework: base classes that treat the elements common to all numerical models (such as input/output and boundary conditions) make it possible to create a new numerical model without re-inventing these common methods. terrainbento is built on top of the Landlab framework, such that new Landlab components directly support the creation of new terrainbento model programs. terrainbento is fully documented, has 100% unit test coverage including numerical comparison with analytical solutions for process models, and continuous integration testing. We support future users and developers with introductory Jupyter notebooks and a template for creating new terrainbento model programs. In this paper, we describe the package structure, process theory, and software implementation of terrainbento. Finally, we illustrate the utility of terrainbento with a benchmark example highlighting the differences in steady-state topography between five different numerical models.
Monitoring of subsurface contaminants by N3B Los Alamos, indicates new locations of contaminant leakage below Material Disposal Area L (MDA L) at Los Alamos National Laboratory (LANL). The spread of legacy waste poses a concern of volatile organic compounds (VOCs) reaching the regional groundwater. The purpose of this work is to locate and quantify leak sources at MDA L and estimate the effect of contaminant removal periods on the plume using the LANL-developed finite volume multiphase simulator (FEHM) for gas transport modeling. The most prevalent contaminant in the plume is 1, 1, 1,- trichloroethane (TCA) and this species is used as a tracer to track plume movement in the model. The grid resolution is 10m horizontally and ranges from 1m to 25m vertically, with the higher resolution close to the surface. The model domain is set to LANL atmospheric pressure, constant temperature of 15C, and constant relative permeability set to 0 and 1 (-) for liquid and vapor, respectively. This work simulates saturation-dependent vapor diffusion of TCA via an isothermal two-phase (air-water) process. Over 140,000 nodes set the initial and boundary conditions related to pressure, saturation, and flow data (source/sink parameters). Readjustment of TCA concentrations will take place from November 30, 2016, to May 25, 2023 within the model. Soil vapor extraction (SVE) measurement periods at MDA L will be reflected in the simulations. Post-simulations, short-term SVE will be simulated to compare against SVE data from May 2024. +
Moraines in marine-terminating outlet glacier settings can provide a feedback mechanism for glacier stability or retreat, however, sedimentation dynamics in Greenland are poorly understood. With limited observations, sedimentation contributes to the large uncertainty of ice dynamics in estimating Greenland’s future sea level potential. Recent attempts to couple ice and sedimentation show the importance to include moraine-building processes. To advance our understanding, it is necessary to quantify the impact of sedimentation in Greenland outlet glacier settings on different timescales. We explore the sensitivity of Greenland outlet glaciers to sedimentation dynamics including sediment diffusion (removing sediment from moraines) and glaciofluvial sedimentation (adding sediment to moraines) in a flowline model adapted from Brinkerhoff et al., 2017. We run an ensemble of simulations to investigate these processes on 20 kyr timescales, using different bed topography slopes, surface mass balance scenarios, and with sedimentation coupling turned on versus off. We compare across simulations with parameters like ice volume, sediment volume, ice velocity, and bed topography profiles. We find that sedimentation has a strong control on ice volume change and creates tide water glacier cycles with changes in amplitude over time. In addition, we determine the sensitivity of the tide water glacier cycle to variations in bed topography and surface mass balance. The coupling between sediment and ice dynamics could explain and contribute to the divergent glacier behavior presently seen in Greenland outlet glaciers. This work is important for ice sheet model development and field work efforts to understand the rates and processes driving sedimentation in Greenland. +
Morphological patterns reflect climatic and geomorphic influences throughout a dunefield’s history and can thus be a valuable source for information about past and present environmental conditions. The quantitative assessment and interpretation of such patterns requires precise information about dune locations and arrangements, i.e., dune maps. Mapping dunes based on satellite data has evolved from a simple tool for dryland research to a notable research area. Globally available datasets and the progression of computational infrastructure have facilitated the operation of increasingly elaborate automated algorithms to map spatially extensive areas where manual approaches would be inefficient.
We present a deep learning framework that employs semantic segmentation techniques on optical satellite imagery and medium resolution digital elevation models to map linear dunefields. The workflow includes the access and pre-processing of training and prediction data, with a Neural Network as the centrepiece that is trained and applied to identify dune crests. We conducted a preliminary case study to develop and evaluate the framework on the dunefields of the Kalahari Desert, producing promising results.
Our next step is to leverage the generated dune maps to classify different dune patterns and investigate their relationship with climate and topography. We hope to provide valuable insights into the complex interplay between dunefield morphology and its environmental and climatic drivers. +
Most of the estuaries and lagoons around the globe are unique and have distinct but irregular shorelines and bathymetries and normally surround by highly developed watersheds with expanding agriculture and urbanization in mid and low latitudes. It is important to understand influence of environmental perturbations on the local coastal ecosystems. This project aims to develop a model for water quality and phytoplankton dynamics in the Maryland Coastal Bays during various physical conditions and to provide a prototype to other global estuaries and lagoons. The preliminary results indicated that model was able to well capture the observed seasonal chlorophyll-a and nutrients distribution patterns; and the weak discrepancy in vertical distributions of phytoplankton was mainly caused by dominated wind and tidal mixing effect in the shallow of water column. The research outputs will link modeling with local policymakers for ecological restoration and harmful algal bloom prevention by optimizing the amount of nutrient reduction in freshwater inflow to restore the ecosystem and making timely predictions of harmful algal blooms under different weather conditions. The estimation and discussion towards the spatial and temporal variabilities of phytoplankton distribution under extreme weathers will provide reference for ecological studies in MCBs and other similar lagoon systems around the world. +
Much of modern tectonic geomorphology focuses on interpreting patterns of bedrock river slope and using this information to make tectonic inferences. At its core, this framework often assumes that rivers are readily able to erode bedrock, and that they respond to tectonic and climatic forcing mostly through vertical incision and slope adjustment. However, bedrock rivers must also transport sediment delivered to them by surrounding hillslopes, which may act to amplify or to inhibit incision into bedrock. Rivers also adjust their width in response to climatic and tectonic controls, often much faster than slope adjustments can occur. While the importance of sediment flux and channel width has been understood for some time, these behaviors are hard to predict mechanistically and thus go unaccounted for in many models of landscape evolution. We present a model of river evolution in which channel slope and width freely evolve to optimize sediment transport and bedrock incision in response to stochastic water and sediment discharge. We investigate the impact of both water and sediment discharge variability under varied tectonic forcing and find that equilibrium channel form is controlled by a combination of water and sediment supply variability. We use the model to document measurement biases in rates of river incision (the Sadler effect) which are observed ubiquitously in real landscapes, and to for the first time examine the drivers of variations in this effect. Our results call into question the assumptions underlying the widely used detachment-limited stream power incision model of river evolution and highlight the importance of considering channel width and sediment flux when modeling river behavior and measuring rates of erosion over landscape evolution timescales. +
Much of the estimated 600 Mt of river sediment annually carried by the Ayeyarewady and Thanlwin River system (Myanmar) is delivered to the northern Andaman Sea. This area is influenced by strong tides, monsoon conditions, and periodic cyclones; however the processes that dominate dispersal of riverine material in the coastal ocean of this system have remained largely unquantified. The shelf exhibits a dramatic asymmetry of the surface morphology and sediment texture in the east – to – west direction, and recent field observations indicate that sediment accumulation rates increase toward the west. To explore the role that wave resuspension may play in these patterns, the SWAN (Simulating WAves Nearshore) model was implemented for the northern Andaman Sea, and run to represent both winter and summer time periods. The wave orbital velocities provided by SWAN were then analyzed to estimate the frequency of resuspension of fine-grained sediments throughout the study area. Results showed that wave-driven resuspension is much more frequent during the summer conditions which are characterized by the southwest monsoon; compared to during the northeast winds typical of the winter season. Additionally, the area fronting the Ayeryarwaddy Delta is subjected to energetic waves throughout both the summer and winter conditions, but wave energy decreases dramatically eastward toward the Thanlwin River mouth. +
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NOAA’s National Geophysical Data Center (NGDC) develops and publicly distributes a wide variety of topographic and integrated bathymetric-topographic digital elevation models (DEMs), ranging from the global ETOPO1 and GLOBE, to high-resolution (~10-m cell size) coastal DEMs to support NOAA’s tsunami forecast and warning efforts. We have developed a prototype online tool, using an underlying THREDDs catalog, to view and extract the square-cell models in their native resolution and datums, subset by user extents, and output in netCDF, geotiff, xyz, or ESRI Arc ASCII formats. We have also implemented a command-line get request that bypasses the browser interface. Current models include the 1-minute ETOPO1, 30-second GLOBE topography, the 3 arc-second U.S. Coastal Relief Model (CRM) and Great Lakes Bathymetry, and the 24 arc-second Southern Alaska CRM. In the future, we will be expanding the catalog to include all of NGDC’s public DEMs, and are investigating ways to in-fill gaps between higher-resolution DEMs with data from coarser models. +
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Natural channels are continuously changing their shape, where meanders and other complex configurations appear (e.g. bars, braided rivers, inner confluences, etc.). Channel evolution is strongly determined by the interactions occurring between its banks and the flow. These interactions also determine when a channel stabilizes, i.e. when its width remains constant. Current literature explains the stabilization of channels by the attainment of the equilibrium between sediment diffusion and gravity forces. However, the role of other potentially relevant processes is uncertain and needs to be addressed. Among them are secondary currents close to the banks and the spatial distribution of turbulence. Furthermore, the transition to steady-state banks is not fully understood. We explored these issues aiming to provide a better understanding of bank erosion and channel stability. To do this, we simulated a flatbed channel under 8 conditions, with Shields parameter spanning from 0.03 to 1.78. These simulations solved a 3D turbulent flow by carrying out Large-Eddy Simulations (LES) and the particles’ motion through a Discrete Element Method (DEM). We observed streamwise-aligned vortices appearing close to the banks, which were associated with high levels of TKE and shear stress, as well as flow spanwise velocity fluctuations. These fluctuations were mainly sweeps and ejections, which helped to dislodge sediments from the banks. Once detached, sediments could travel downstream. The role of the turbulence was also observed by separating the diffusive and advective components of the transport, where the initial bank erosion was dominated mainly by the former. Indeed, turbulence roughly explained 90% of sediment flux under erosion and bedload transport conditions. We conclude turbulent events increase shear stress close to the banks, promoting entrainment. Once the flow has transferred enough momentum to sediments, flow mean-velocity and fluctuations decrease. In this manner, shear stress decreases as the channel width increases. Eventually, shear stress reaches the threshold for transport close to the banks. Here, channel stabilization occurs. Notwithstanding that, stresses in the center of the channel are high enough to continue transporting sediments.
Nearshore hydrodynamic modeling necessitates extraordinary computational power to resolve the scales of motions relevant to coastal processes. Thus, coastal models make tradeoffs in the processes resolved. One common tradeoff is wave-averaging, whereby the evolution of bulk properties and statistics of wave fields are modeled. This contrasts the computationally more intensive wave-resolving models, whereby the time-varying motion of individual waves is directly output. However, complex nearshore dynamics are often driven by phenomena that cannot be directly derived from wave-averaged quantities, which limits the breadth of applications for wave-averaged models. Machine learning techniques provide a potential avenue to leverage the power of wave-resolving models for such applications at a lower computational cost. To this end, the wave-resolving, depth-integrated FUNWAVE-TVD modeling based on solving the Boussinesq equation is used in this study. The model was validated against the Dune3 dataset collected at Oregon State University corresponding to wave evolution and breaking in a cross-shore surf zone. A series of similar wave-resolving simulations using the FUNWAVE-TVD model were generated to create a training dataset corresponding to a one-dimensional planar beach under regular wave conditions. Two properties of interest, wave skewness and asymmetry, were calculated from the resulting wave-field and parameterized via the input wave conditions and bathymetry. Preliminary results show that even relatively simple ML models (neural networks and random forests) can provide drastic improvements to commonly used empirical models commonly employed by wave-averaging models, suggesting that ML-based parameterizations of nearshore wave properties provide a viable avenue for improving wave-averaged models. +
Neural networks (NNs) enable precise modeling of complicated geophysical phenomena but can be sensitive to small input changes. In this work, we present a new method for analyzing this instability in NNs. We focus our analysis on adversarial examples, test-time inputs with carefully crafted human-imperceptible perturbations that expose the worst-case instability in a model's predictions. Our stability analysis is based on a low-rank expansion of NNs on a fixed input, and we apply our analysis to a NN model for tsunami early warning which takes geodetic measurements as the input and forecasts tsunami waveforms. The result is an improved description of local stability that explains adversarial examples generated by a standard gradient-based algorithm, and allows the generation of other comparable examples. Our analysis can predict whether noise in the geodetic input will produce an unstable output, and identifies a potential approach to filtering the input that enable more robust forecasting. +
North Core Banks, a long (36-km), low (2.6-m mean elevation), narrow (~1200-m) barrier island in the Outer Banks of North Carolina, was inundated from the sound side and severely eroded by outwash during Hurricane Dorian (September 2019). As the fast-moving Category-1 hurricane moved offshore after a brief landfall at Cape Hatteras, winds shifted to the northwest, forcing a ~2.5-m surge onto the back side of the island. Deeply incised drainages were cut into the island as water ran from the washover platform to the ocean through gaps in the primary dune line, removing ~16% of the island volume. This style of storm impact is less common than typical ocean-side attack by waves and storm surge, and rarely modeled. Model simulations may provide insight into the fate of sands eroded during these unusual and difficult-to-measure events. We used the COAWST modeling system to simulate conditions during Dorian for a typical segment of the island using topography and landcover derived from pre-storm mapping using aerial imagery. The high-resolution (~2-m horizontal grid spacing) model was forced by output from a coarser-resolution model that provided water levels, incident waves, and alongshore currents. The model reproduced the steep cross-island water-level gradients inferred from high-water marks and wrack deposits, and generated washout channels ~2 m deep, cut through pre-existing low spots in the primary dune line. We evaluated model performance by comparing the simulated topography with post-storm topography derived from aerial imagery. The location, depth, and width of the simulated channels matched observations well, but the inland portion of the modeled channels were more linear than the observed dendritic drainages. Model simulations were sensitive to water-level forcing, sediment size, and vegetation patterns. The simulated channels extended into the surf zone and deposited sediments in relatively deep water. This transfer of sand from the island core to the nearshore has implications for barrier island evolution, and the ability to model it with COAWST demonstrates the generality of its morphology components.
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Notice: Kim Picard is 1st author; Phil Hill 2nd author; Andrew Wickert 3rd author<br><br>This work aims to improve the late Quaternary stratigraphic framework for the outer shelf and slope of the Beaufort Sea and to assist in the assessment of geohazards, particularly those related to slope instability. Slope failures have been identified on the upper slope, but the age and triggers of slope failure are poorly understood. Existing conceptual models of late Quaternary stratigraphy of the Beaufort shelf and slope are quite generalized and based on a poorly constrained relative sea level curve. Sea level and stratigraphic modeling are used to test the relationships between glaciation, sea level and sedimentation. The results of the work suggest that glacio-isostatic effects cause the relative sea level (RSL) curve to vary significantly across the Beaufort Shelf particularly in the cross-shelf direction. Stratigraphic modeling with a variable RSL input successfully reproduces depositional patterns in the Mackenzie Trough including distinctive highstand and lowstand wedges and a retrogradational transgressive systems tract. However on the eastern shelf, more pronounced isostatic depression is required to match the known stratigraphy, suggesting deviation from the assumed ice loads or crustal properties in the model. Two outburst floods documented to have occurred in the region would have had a marked effect on shelf edge and slope sedimentation. Modeling suggests significant progradation of the shelf edge and rapid deposition on the slope and outer shelf at lowstand and in the early stage of transgression. +
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Numerical models are effective and efficient tools for understanding the interactions among earth surface processes, including hydrological, biogeochemical, geomorphological, and ecological processes. These models with various complexities test hypotheses and make predictions within certain pre-defined model boundaries. These boundaries, on the one hand, reduce the complexity and noise of the system by ignoring the processes outside the boundary, which may only play a minor role in affecting the dynamics of the modeling system. On the other hand, some key processes that have a first-order control on the system dynamics may be unreasonably excluded from the modeling system. With the rapid growth of interdisciplinary researches, there is a more urgent need of revisiting the definition of the boundaries in the current numerical models to understand the gaps in bridging the boundaries between disciplines. This study is developed to meet this need. We investigated the models in the CSDMS model repositories by analyzing the process integration, boundary conditions, and spatial and temporal scales and summarized the potential gaps between boundaries that the current models present. This is the first study that conducts a comprehensive review of the models in the earth system modeling community, which provide insights for future model development and implementation across boundaries. +
Numerical models play a vital role in understanding river channel and floodplain evolution, yet their setup often requires extensive measured data. Maintaining continuity in monitoring fluvial geomorphology and sediment transport globally poses a significant challenge. This study introduced a remote sensing-based methodology for constructing and calibrating a reach scale 1D hydrodynamic numerical model, particularly suited for data-scarce regions. The effectiveness of this approach was assessed on the Elwha River in Washington.
The methodology employed a supervised image classification technique to extract a river mask, especially useful in areas with significant shadow pixels. Subsequently, channel attributes such as width, sinuosity, and slope were derived, and river segments with similar cross-sectional properties were identified using a multivariate change point approach, resulting in delineation of four distinct segments for the Elwha River. Next, hydraulic calibration of the numerical model accurately simulated water surface elevation (NSE: 0.93, PBIAS: -7%, RSR: 0.27). The sediment transport sub-model provided precise estimates of Suspended Sediment Concentration for mid-discharge values of 70 – 100 m3/s, associated with exceedance probabilities ranging from 0.4 to 0.04. Furthermore, the numerical model accurately reproduced channel deposition-erosion patterns estimated using publicly available aerial imagery from 2015 to 2017 (56 m vs. 48 m). These findings demonstrate the successful utilization of remote sensing datasets to supplement data requirements for numerical model setup and calibration, as well as to generate validation datasets. The methodology holds promise for accurately simulating hydromorphodynamic processes in both data-rich and data-scarce regions. +
Numerical simulation of fluvial morphodynamic processes can identify important dynamics at time and space scales difficult to observe in the field. However, simulations involving large spatial scales and/or the long timescales characteristic of morphodynamic processes are often untenable due to long simulation times. The morphological acceleration factor (morfac) applies a scalar multiplier to the sediment continuity equation, and is often applied in morphodynamic simulations to reduce computational time. While the use of morfac in coastal simulations is relatively common, its applicability in field-scale fluvial models is generally confined to steady-flow simulations over reach-scale spatial domains. Here we explore the viability of using morfac to simulate large-scale, long-term morphodynamics in a gravel-bed river. Using Delft3D to simulate a 60-day period with a significant discharge event in the Nooksack River, Washington, we systematically adjust morfac values (ranging from 5 to 20) to compare with a baseline condition of no acceleration. Model results suggest that morfac based modification of the inflow hydrograph time-series significantly alters downstream flood wave propagation. Higher morfac values result in greater flood-wave attenuation and lower celerity, reducing the morphological impact at locations further downstream. In general, relative error compared to the baseline increases farther downstream, due to this altered flood-wave propagation. Furthermore, even for the lowest morfac values absolute cumulative volume change errors are on the order of 10%, indicating that the use of morfac in fluvial simulations is best restricted to short-term and/or smaller-scale modeling efforts. Funded by the National Science Foundation. +
