University of California Water Resources Center

In Southern California and elsewhere in heavily populated arid areas, existing potable water delivery and supply systems are increasingly being overtaxed in meeting current and projected water demands, both on an annual and peak demand basis. In a number of cases, such as portions of Riverside County, Southern Orange County, and San Diego County, numerous small groundwater basins, often with degraded water quality, could be integrated into the local water delivery systems providing new water supply and storage elements to the systems. Several water agencies in Southern California are already trying to accomplish this, however, the complex dynamic nature of the problem make it difficult to assess costs and benefits and to select the optimal alternative.

The purpose of this research is to analyze management alternatives and to develop methods for evaluating costs and benefits in order to optimize the use of these groundwater basins for conjunctive use. The San Juan Basin, located in Southern Orange County, was used as a basis for this research. A mathematical model of the basin was used to evaluate the basin as a storage element for sustained yield, drought emergency reserves, and summer peaking supply. Simulations were also conducted in order to determine the effect of pumping on groundwater TDS. Based on the simulation results, functions for IDS versus yield were developed. These functions were incorporated into an optimization algorithm developed to minimize the cost of water production for specified yield amounts. The results of this procedure for various yield amounts were compared in order to choose a management scheme which provides as much additional potable water as possible for seasonal use while keeping the cost of production comparable with the prices of imported water. Results indicate that groundwater production is economical when compared to importing water.