GROUNDWATER MODELING AS A PLANNING TOOL FOR INCREASED UTILIZATION OF A LARGE COMPLEX GROUNDWATER BASIN, LOS ANGELES COUNTY, CALIFORNIA (Invited Presentation)

The Water Replenishment District of Southern California (WRD) manages groundwater for nearly four million residents in 43 cities of southern Los Angeles County. The 420 square mile service area uses about 220,000 acre-feet per year (AFY) of groundwater, which equates to over 40 percent of the total demand for water. WRD ensures that a reliable supply of high quality groundwater is available through its clean water projects, water supply programs, and effective management principles.

For years, WRD has collaborated with the USGS to better understand groundwater within the Los Angeles Coastal Plain in Los Angeles County, California. In 2003, Geohydrology, Geochemistry, and Ground-Water Simulation-Optimization in the Central and West Coast Basins, Los Angeles County, California was prepared by the USGS. The groundwater model included four layers and simulated steady-state groundwater conditions representative of those in 1971 and transient conditions for the period 1971-2000. The groundwater model has been a valuable tool used to evaluate various management scenarios over the past few decades by WRD. In 2021, the groundwater model was updated by the USGS. The updated groundwater model now includes additional layers and an updated geologic interpretation utilizing concepts of sequence stratigraphy to develop a chronostratigraphic (time-based) hydrogeologic-framework model for the water bearing sediments of the Los Angeles Coastal Plain.

This talk will present an overview of each groundwater model and how they’ve been used to evaluate various projects located in southern Los Angeles County. We will discuss the benefits of using state of the art three-dimensional visualization in Leapfrog. We will also discuss various management scenarios developed for one of the most heavily utilized groundwater basins located in southern Los Angeles County. The management scenarios will include two of the largest, most ambitious recycled water projects in the world – Pure Water Southern California project by Metropolitan Water District of Southern California (MWD) and Los Angeles County Sanitation Districts (LACSD) and OperationNEXT by the Los Angeles Department of Water and Power (LADWP).