Doctor of Philosophy (PhD)
Civil and Environmental Engineering
Wave induced erosion accounts for as much as 26% of landloss in coastal Louisiana. This dissertation work, focuses on answering research questions relevant to the design of two shoreline protection methods (a) vegetated wetlands and (b) nearshore breakwaters. Two types of numerical models are used - the three-dimensional (3D) Navier Stokes Equation for small to medium scale experiments and a depth integrated, fully non-linear Boussinesq model for dispersive waves for larger, field scale studies. The former model provides insights into the 3D hydrodynamics of wave interaction with vegetation canopies and breakwaters, while the latter model focuses on the horizontal two dimensional wave induced hydrodynamics. For 3D modeling, flow around vegetation stems, considered as a rigid array of cylinders are explicitly resolved and was used to investigate the influence of stem sheltering and non-linear free surface interaction with emergent stems under wave flow. The model can also simulate the wave breaking on mudflats and transmission over breakwaters and is used to conduct a parametric study of the functional design of a breakwater, placed close to a marsh edge. It was found that the crest elevation with respect to the marsh platform plays a critical role in regulating the wave damage on the platform. A vertical circulation was also found to be existent, driven by over-topped waves, between the marsh edge and the breakwater, which was otherwise absent without the structure. The depth integrated Boussinesq model was used to develop model driven empirical relations for wave breaking induced rip currents, which can flush out sediments through the breakwater gaps. A similar relation was obtained for the wave height immediately behind the gap, which can also cause edge erosion. The results are combined to lay new design guidelines for the design of marsh edge protection structures. Finally, an improved depth integrated vegetation drag formulation, applicable for the fully non-linear Boussinesq equations, using the higher order expansion of the horizontal velocity, is introduced. The new model is validated against laboratory experiments and is extended to simulate the effects of wave induced currents on a natural wetland during peak storm conditions of Hurricane Isaac (2012).
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Chakrabarti, Agnimitro, "Numerical Modeling of Wetland Hydrodynamics" (2016). LSU Doctoral Dissertations. 2721.