Guide to San Francisco Bay Area Creeks

Groundwater System

of the Santa Clara Valley

Santa Clara Valley Water District manages the groundwater basin with local supplies and imported water supply from the State Water Project and Central Valley Project. The floor of the Santa Clara Valley is like a thick layer cake of alternating deposits of sandy gravel and clay. Water easily permeates the sandy gravel, but is less able to penetrate the clay layers. Vast amounts of water can be stored in this gravelly aquifer. However, in the middle of the basin, a continuous layer of clay prevents groundwater recharge. This area under the clay layer is the confined aquifer. Around the edge of the valley, there is no continuous clay layer. This is the recharge zone where water in stream channels and percolation ponds will sink down and replenish the groundwater aquifer.

Top of Page Glossary