Hydrodynamics and Sediment Transport Studies in Tidal Marshes of the Delaware Bay using High Resolution Numerical Models

This thesis presents the development work of high resolution 2-dimensional hydro- and morphodynamic numerical models of the Blackbird Creek and Bombay Hook marshes in the Delaware Bay. The goal was to assess the models ability of representing the complex marsh hydrodynamics, to study sediment transport in marshes and exchange processes between marshes and the adjacent bay and to better understand the sensitivity of these complex ecosystems to changes in the bay environment.;A high resolution numerical mesh was required to resolve the complex marsh geometry in sufficient detail for the studies. An approach was chosen that mostly employed existing data and only a minimum of additional field surveys. Methods were developed to improve the accuracy of bare ground elevations on vegetated tidal flats and to prepare bathymetry data for tidal channels based on a small number of cross sectional measurements.;The model system MARINA2D was tested and validated with the Delaware Bay Model Evaluation Environment from NOAA. Model results of water levels in marshes also showed good agreement with observed data for the Bombay Hook model, yet low water was under predicted in the Blackbird Creek model, likely as a result of higher vertical errors in its initial bathymetry and topography.;The Blackbird Creek model was used to assess the models' performance with respect to water levels and velocities. Analysis of the influence of vegetation on erosion and depositions patterns on tidal flats showed that in order to reproduce realistic conditions vegetation needed to be considered in the model forcing. Furthermore, for development of numerical models for marshes, additional modifications were required to correctly represent shallow flow conditions on tidal flats. Scenarios with high, medium, and low suspended sediment concentrations in the Delaware River identified the sensitivity of sediment budgets in the marsh to sources in the river.;Tracer studies based on hydrodynamic simulations of the Bombay Hook marsh were performed to identify the system's sensitivity to changes in tidal channel geometry and to find the best location for a channel blockage to prevent sediment transport out of the marsh interior that increasingly suffers from losses. The results showed that the system reacts significantly to small changes in channel geometry. Analysis of three blockage scenarios provided enough information to reveal a possible solution for the marsh loss problem, highlighting the benefit of numerical studies as a tool for decision making in marsh management.