Browsing by Author "Deb, Mithun"
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Item A surface porosity approach for eliminating artificial ponding in coastal salt marsh simulations(Coastal Engineering, 2022-11-23) Deb, Mithun; Kirby, James T.; Abdolali, Ali; Shi, FengyanHydrodynamic processes over marsh topography are significantly affected by surface defects such as cuts and rills on channel berms and platforms. These meter-scale features are often missing in the model representation due to the spatial resolution available from data sources, as well as incomplete resolution in the model grid itself. To minimize the artificial hydraulic isolation in the numerical models, we propose implementing an effective porosity algorithm on the marsh surface by considering the fine-scale topography over marsh depressions that control the drainage process. The modification is carried out to eliminate artificial ponding effects observed in model simulations in Bombay Hook National Wildlife Refuge, DE, USA using the original FVCOM code. Results from the revised and original FVCOM models are compared with pressure gauge data collected from an isolated depression in the marsh platform. The new implementations for proper wetting and drying are efficient and accurate for hydrodynamic modeling inside a complex salt-marsh system, which constitutes a major breakthrough in the context of increasing need for better understanding of physical and morphological changes in valuable coastal ecosystems.Item Sensitivity of tidal hydrodynamics to varying bathymetric configurations in a multi-inlet rapidly eroding salt marsh system: A numerical study(Earth Surface Processes and Landforms, 2021-12-22) Deb, Mithun; Abdolali, Ali; Kirby, James T.; Shi, Fengyan; Guiteras, Susan; McDowell, ConorWe describe the development of a high-resolution, two-dimensional hydrodynamic model for a multi-inlet rapidly eroding tidal wetland on the western shore of Delaware Bay, using the finite-volume, primitive equation community ocean model (FVCOM). Topo-bathymetric surveys, together with water surface and current velocity measurements during calm and stormy conditions, have been conducted to support model validation. The tested model is then used to quantify the tide-induced residual transport and asymmetry at major inlet entrances to determine the governing hydrodynamics. We chose a skewness method to calculate the tidal asymmetry and serve as a proxy for sediment transport estimates. The effects of the dredging of an artificial entrance channel and progressive channel deepening in shifting wetland hydrodynamics are shown by developing a scenario analysis. Model results show that the artificially dredged channel has altered the volume exchange at other inlet entrances and increased the net seaward export. The changes in the characteristic frequency of the frictional dissipation in the channel and the system's natural frequency are investigated using a simple ocean–inlet–bay analytical model. Subsequently, we have compared the channel friction scale to the inertia scale and observed that the new connection and gradual channel deepening reduce the overall frictional dominance. Ultimately, the study has shown how the short- and long-term channel bathymetry changes, mainly the artificially dredged channel and progressive channel deepening, can affect the connected system's net circulation and trigger internal marsh erosion.Item Tidal hydrodynamics in a multi-inlet wetland system: toward improved modeling of salt marsh flooding and draining(University of Delaware, 2020) Deb, MithunModeling hydrodynamics and sediment transport inside a multi-inlet wetland system is a challenging task due to constraints on model efficiency, accuracy and representation of physics, the scarcity of field data for model validation, and more importantly, the availability of high-resolution data sets of marsh topography and channel bathymetry. Lack of field data sets, model assumptions, and limitations often lead to wrong interpretation of the system’s nature. To correctly predict the changes in governing hydrodynamics and morphology of shallow wetland environments, it is essential to resolve the complex interaction between the tidal channel and marsh surface with the best possible accuracy. In this thesis, we describe the development of a high-resolution 2D numerical model for a rapidly eroding tidal wetland system using the Finite-Volume, primitive equation Community Ocean Model (FVCOM). Topo-bathymetric survey data and water surface and current velocity measurements during calm and stormy conditions have been collected in support of model development and validation. The model is then used to perform a morphology scenario analysis to evaluate the effect of anthropogenic and natural disturbances in altering overall wetland hydrodynamics. The study has also shown the role of horizontal model resolution around the marsh channel shoreline and surveyed bathymetry data in improving the model calculations for major physical processes such as channel surface phase lag, tidal wave characteristics, and flow asymmetry. Hydrodynamic processes over marsh topography are seen to be significantly affected by surface defects such as cuts and rills on the marsh platform. Inadequate representation of these meter-scale features from spatial resolution available from data sources such as LiDAR, as well as the incomplete resolution in the model grid itself, lead to artificial ponding over the isolated marsh depressions, with resulting effects on estimates of sediment fluxes and hydroperiod. A new set of mass and momentum conservation equations is proposed using a surface porosity technique to improve the dynamic wetting and drying over artificially isolated depressions. This model improvement is essential for accurate predictions of marsh hydroperiod and volume flux that primarily controls the sedimentation rate and overall morphological evolution. Ultimately, by solving these critical processes, the study has provided useful solutions to improve the present-day limitations in numerical modeling of salt marsh flooding and draining.