In addition to flood control, The LACFCD is the primary agency responsible for capturing and storing stormwater and replenishing the groundwater in Los Angeles County. The LACFCD's mission is to conserve as much of the stormwater as practicable, especially since approximately 30 to 40 percent of the water used in the County is pumped from groundwater supplies which provides a local water supply alternative to imported water. Without the LACFCD facilities and conservation efforts the groundwater supplies would be depleted in many areas.
In Southern California, storm conditions vary each year because of cycles of changing ocean temperatures and currents. In order to manage highly variable storm conditions and storm runoff, the LACFCD has built dams and spreading ground facilities to store and conserve the stormwater. In typical years, the LACFCD infiltrates more than 270,000 acre-feet (AF) of captured stormwater, imported water, and recycled water into the various groundwater basins in Los Angeles County. In wetter years that number can exceed 700,000 AF and in drier years may be little more than 150,000 AF. The use of water conservation facilities or spreading grounds adjacent to river channels and in soft-bottom channels permits water to percolate into groundwater basins for later pumping. These groundwater recharge facilities are located in areas where the underlying soils are composed of permeable formations and in hydraulic connection with the underlying aquifer.