Simulation-Optimization Framework to Support Sustainable Watershed Development by Mimicking the Pre-development Flow Regime

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Title: Simulation-Optimization Framework to Support Sustainable Watershed Development by Mimicking the Pre-development Flow Regime
Author: Pierpont, Laurel Hughes
Advisors: Dr. E. Downey Brill, Jr.,, Committee Chair
Dr. Emily Zechman, Committee Member
Dr. Margery Overton, Committee Member
Abstract: The modification of land and water resources for human use alters the natural hydrologic flow regime of a downstream receiving body of water. The natural flow regime is essential for sustaining biotic structure and equilibrium within the ecosystem. A typical approach to achieve a hydrologically friendly development is to locate and design stormwater control structures, or Best Management Practices (BMPs), to match peak and minimum flows for design storms. A more aggressive strategy for environmentally sustainable development would ensure that there is no difference between pre- and post-development flow regimes for all storms and at all times through the design of development strategies that maintain the natural flow regime under post-development conditions at the watershed outlet. Many sub-catchments contribute to the composite flow at the watershed outlet of a large watershed, and at each of these sub-catchments, the flow regime may be altered, though the flow regime is maintained at the larger watershed level. This study uses a simulation-optimization modeling framework to analyze a hydrologic metric that represents the total degree of hydrologic alteration for a given development pattern. The objective is to minimize the hydrologic alteration by iteratively updating and modifying the development pattern in the watershed subject to maintaining some pre-defined minimum level of total development. Thirty-three hydrologic indices are used to characterize variation in the flow regime and are represented as one value indicating the hydrologic alteration for that development scenario. Continuous simulation of urban runoff is executed by the Stormwater Management Model (SWMM). Two optimization techniques, Nelder Meade (NM) and Genetic Algorithm (GA), are applied to the watershed as separate search techniques and then combined into a hybrid approach to investigate the methodology. Comparison of the solutions yields a distinct trade-off between total land developed and degree of hydrologic alteration. Results of this study present numerous solutions that are similar from the standpoint of hydrologic alteration, but dramatically different in terms of development pattern.
Date: 2008-04-25
Degree: MS
Discipline: Civil Engineering

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