Conjunctive Use Planning of Surface Water and Groundwater in Southern California

Featuring William W-G. Yeh, Ph.D.
Distinguished Professor, Department of Civil and Environmental Engineering
Henry Samueli School of Engineering and Applied Science
University of California, Los Angeles

Location:  Engineering Hall 2430 Colloquia Room
Free and open to the public

Abstract
Over the years, several groundwater basins in southern California have experienced over-pumping of groundwater.  This has caused the decline of water table, land subsidence, and other negative environmental impacts.  To recover the water table, surplus imported surface water is being used to recharge the groundwater basin by means of surface ponds and injection wells.  By controlling the total water resources of a region, conjunctive use planning of surface water and groundwater increases the efficiency, reliability, and cost-effectiveness of water use.

This presentation presents the results of a conjunctive use study in southern California.  Historically, the town of Yucca Valley located in the southwest part of the Mojave Desert in southern California relies on groundwater pumping from the Warren groundwater basin as its sole source of water supply.  This significant dependency has resulted in a large imbalance between groundwater pumping and natural recharge, causing groundwater levels in the basin to decline substantially from the late 1940s to 1994. Consequently, in 1995 an artificial recharge program was proposed and implemented for the purpose of recovering the groundwater levels.  However, the rise in groundwater levels due to artificial recharge has entrained septage stored in the unsaturated zone and caused nitrate concentration in the groundwater to increase simultaneously.  This paper develops an optimal pump and recharge strategy for a planned conjunctive use project to remove the high nitrate concentration, while maintaining groundwater levels at desired elevations at specified locations as well as meeting water demand.  A simulation model for flow and mass transport is coupled with a management model to determine the optimal pumping and recharge pattern.