Basin Information

Over the past several decades, the Sonoma Valley has experienced significant population growth and land use changes, including increases in irrigated agriculture, primarily vineyards. These increases in population and irrigated agriculture have increased demands on water and groundwater resources, and groundwater levels are declining in portions of the valley.

Groundwater levels

Groundwater levels within Sonoma Valley’s shallow aquifers are generally steady, although localized declining trends have been observed in the El Verano/Fowler Creek area. However, in deep zone aquifers, monitoring of wells and stream levels has indicated that groundwater levels have declined over the past decade or more, and do not recover during relatively wet years. These chronic declines indicate that groundwater withdrawals are occurring at a higher rate than recharge or replenishment.

Groundwater quality

Groundwater quality is generally good within Sonoma Valley. However, wells in southern Sonoma Valley (generally south of Highway 116) have been affected by brackish or salty groundwater. The continued declining trends of groundwater levels to the north could draw the brackish water further north, potentially affecting more northern wells and rendering groundwater unusable.

Groundwater sources and usage

Covering 166 square miles, the Sonoma Valley groundwater basin contains approximately 2,000 domestic, agricultural, and public supply wells. It was estimated that 5.83 billion gallons of water was used in the Sonoma Valley in 2012.  Nearly 60% of the valley’s water supply comes from groundwater. The remainder comes from the Russian River, other local surface water, and recycled water.