Use of Optimization Techniques to Evaluate Ground-Water Management Strategies in the Central and West Coast Basins, Los Angeles County, Californiaby Eric Reichard,
Abstract: The U.S. Geological Survey and the Water Replenishment District of Southern California are engaged in a cooperative study of the geohydrology, geochemistry, and ground-water management strategies in the Central and West Coast Basins in Los Angeles County, California. The study tasks include developing a geographic information system (GIS), collecting water-quality and geohydrologic data from new and existing wells, developing a multi-aquifer simulation model of ground-water flow using MODFLOW, and coupling the simulation model with an optimization algorithm. The ground-water flow model was used to simulate specific water-management scenarios for the next 24 years (1998-2021). The scenarios include base-case (continuation of current trends) expected pumpage and recharge, decreased pumpage in coastal regions, increased pumpage in upgradient forebay areas, and changes in rates of spreading in percolation ponds and of injection at seawater- barrier wells. The simulated scenarios were analyzed for changes in water levels, storage, and fluxes between ground-water basins, subbasins, and aquifers. In order to systematically address these management options, the simulation model was coupled with linear and quadratic optimization programming. Questions addressed with the simulation-optimization model include: What is the optimum balance between saline plume extraction and barrier-well injection in the West Coast Basin? What is the maximum amount of increased pumpage that can occur in the Montebello Forebay without causing unacceptable water-level declines in key areas? What changes in rates and locations (areal and vertical) of injection at the seawater barriers would improve the efficiency of actions to control seawater intrusion into the coastal aquifers? The results of the simulation-optimization model provide local water agencies with powerful tools to weigh various ground-water management strategies against the expected future conditions in the basins.
Subject Headings: Groundwater management | Basins | Optimization models | Hydrologic models | Simulation models | Coastal management | Flow simulation | Pumps | Groundwater flow | North America | California | United States | Los Angeles
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