Manipulations of Natural System Functions Within the Mississippi Delta: a Simulation-Modeling Study.

This dissertation uses two estuarine spatial models and energy analysis of two river diversions within the Mississippi Delta to test the hypothesis that natural river inputs maximize marsh coverage and have net societal benefits. Substantial advancements including a higher resolution, variable time-step hydrodynamic module, a mass-balance sediment component, and a marsh colonization routine, distinguished the Mississippi Deltas Model (MDM) from the Barataria-Terrebonne Landscape Simulation Model (BTELSS). These advancements made the MDM capable of simulating the progradation of river deltas with varying river regimes. No Action Plans (NAP), simulated by both models, were used as a baseline of comparison for simulations and predicted continued land loss in the Barataria and Terrebonne basins, and land gain in and around the Atchafalaya and Wax Lake Deltas. The river diversion simulation with the BTELSS resulted in the preservation of 113 km2 of marsh and identified river diversions as alternatives that can slow the rate of land loss in abandoned delta lobes. In the LDM simulations with magnified river flow and sediment discharge increased the growth of the deltas above the NAP rate of 2.5 km2/yr, and reversed the trend in surrounding marshes from land loss to land gain. Areas with diminished river inputs due to jetty construction experienced declines in marsh coverage. The results from the model simulations supported the hypothesis that natural river inputs maximize marsh coverage. The river diversion study demonstrated the ability of energy analysis to compare natural energies and economic resources on a common basis and identified a unique concentration of natural energies that characterize delta settings. By relying primarily upon renewable energies inherent in delta environments to produce both economic and ecological benefits, the diversions represent an important component of sustainable management plans for deltaic systems. The amount of additional energy exported due to the diversions outweighed the economic costs and supported the hypothesis that restoring riverine inputs to deltaic marshes has net societal benefits. By maximizing marsh coverage and producing societal benefits, the optimization of natural riverine inputs is a sustainable approach to protect and restore deltaic ecosystems