Project ID: 2004CA93B

Title: Modeling and Optimization of Seawater Intrusion Barriers in Southern California Coastal Plain

Project Type: Research

Focus Categories: Groundwater, Management and Planning

Keywords: None

Start Date: 03/01/2004

End Date: 02/28/2005

Federal Funds: $18,090

Non-Federal Matching Funds: $24,360

Congressional District: 44

Principal Investigator:
William Yeh

Abstract

Executive Summary

STATEMENT OF THE CRITICAL STATE WATER RESEARCH PROBLEM
Excessive groundwater pumping in the coastal plain in Southern California has resulted in seawater (saltwater) intrusion and land subsidence. In 1940, freshwater pumping wells along the coast of Los Angeles County began to be abandoned due to seawater intrusion. In a pilot study in the 1950s, Los Angeles County started injecting freshwater into a series of injection wells along certain portions of the coast to create hydraulic barriers. These barriers, called seawater intrusion barriers, are designed to raise the water level and to create desired hydraulic gradient at certain strategic locations to stop seawater intrusion and to protect freshwater pumping wells in the coastal groundwater basins. The water used for injection is a blend of imported State Water Project (SWP) water and imported Colorado River Aqueduct (CRA) water.

Today, there are three major seawater barriers in operation which protect a 20,300,000 acre-foot groundwater reservoir from seawater contamination. Approximately 3.2 million residents of the Southern California Coastal Plain depend on groundwater that is protected by the barrier facilities for approximately 35 percent of their potable water supply. Besides being the lowest cost water available, this groundwater reservoir serves as a strategic reserve when imported water supplies are interrupted due to drought or disaster.
Recently, various deficiencies have been noticed in the performance of the barriers. It has been found that various parts of the aquifers have suffered leakage. This leakage of seawater through the barrier has degraded the groundwater basin water quality, reduced the net groundwater basin storage, caused shutdowns of pumping wells, and caused significant losses in basin management activities. Furthermore, a significant loss of injected water (20 percent) has been identified due to seaward migration of the injected water. These deficiencies can be mitigated by optimizing the operation of the barrier facilities or, if necessary, constructing additional injection wells, or both.

Although the seawater barriers have been in operation for some time, there exist no systematic procedures to guide the operation. There is an urgent need to develop a regional groundwater model for the seawater barriers which will predict the flow and transport affected by the barriers. The developed model can be coupled with an optimization model to determine both the optimal operation policy for the injection wells as well as the optimum locations for new injection wells.

Effective operation of the seawater barrier facilities is critical for basin management practices. This will ensure that the groundwater basin is protected from seawater intrusion and continues to provide a reliable source of water supply to the residents in Southern California.

Progress/Completion Report PDF