Aquifer-stream interaction in the Lower Carmel Valley, Monterey County, California

Abstract

The Carmel River, which drains a 255 sq. mi. watershed near the Central California coast is the principal source of recharge to the alluvial aquifer of the Carmel Valley. In recent years, there has been considerable controversy as to whether groundwater in the western 6 mi. of the aquifer is subsurface flow of the Carmel River. A major water company which operates wells in this area has maintained that an impermeable confining layer in the upper 50 ft. of alluvium effectively separates streamflow from groundwater. Should this be the case, groundwater would not be subject to laws governing subterranean streams. However, recent streamflow and groundwater investigations and well pumping test results seem to indicate quite the opposite. In reality, the aquifer is for the most part unconfined with seepage from the Carmel River's bed and banks the primary means of groundwater recharge.