Tidal hydrodynamics in a multi-inlet wetland system: toward improved modeling of salt marsh flooding and draining
Date
2020
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Publisher
University of Delaware
Abstract
Modeling 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.
Description
Keywords
Flooding and draining, Hydrodynamics, Numerical modeling, Model efficiency, Marsh topography