PUMPING STRATEGIES FOR MANAGEMENT OF A SHALLOW-WATER TABLE - THE VALUE OF THE SIMULATION-OPTIMIZATION APPROACH

The simulation-optimization approach is used to identify ground-water pumping strategies for control of the shallow water table in the weste rn San Joaquin Valley, California, where shallow ground water threaten s continued agricultural productivity. The approach combines the use o f ground-water flow simulation with optimization techniques to build o n and refine pumping strategies identified in previous research that u sed flow simulation alone. Use of the combined simulation-optimization model resulted in a 20 percent reduction in the area subject to a sha llow water table over that identified by use of the simulation model a lone. The simulation-optimization model identifies increasingly more e ffective pumping strategies for control of the water table as the comp lexity of the problem increases; that is, as the number of subareas in which pumping is to be managed increases, the simulation-optimization model is better able to discriminate areally among subareas to determ ine optimal pumping locations. The simulation-optimization approach pr ovides an improved understanding of controls on the ground-water flow system and management alternatives that can be implemented in the vall ey. In particular, results of the simulation-optimization model indica te that optimal pumping strategies are constrained by the existing dis tribution of wells between the semiconfined and confined zones of the aquifer, by the distribution of sediment types (and associated hydraul ic conductivities) in the western valley, and by the historical distri bution of pumping throughout the western valley.