Data Release of hydrogeologic data from the San Antonio Creek Valley watershed, Santa Barbara County, California, 2015-2019

The San Antonio Creek Valley watershed (SACVW) is located in western Santa Barbara County about 15 miles (mi) south of Santa Maria, California and 55 mi north of Santa Barbara, California. The SACVW, is about 140 square miles and encompasses the San Antonio Creek Valley groundwater basin. Since the late 1800s, groundwater has been the primary source of water for agricultural, military, municipal, and domestic uses. Groundwater withdrawal from pumping has exceeded the amount of water replenishing the basin, causing groundwater declines of more than 150 feet in parts of the valley between 1947 and 2018, and reducing base flow in San Antonio Creek at the western end of the SACVW. Agricultural water use (primarily for the present-day irrigation of vineyards, and fruit and berry crops), and the lack of other sources of water, has, and will continue to strain the sustainability of the groundwater system. To address these concerns, the Santa Barbara County Water Agency and Vandenberg Space Force Base invited the U.S. Geological Survey (USGS) to engage in a cooperative study to develop a better understanding of the hydrogeologic system, and to provide tools to help evaluate and manage the effects of future development of the San Antonio Creek Valley groundwater basin, and in the encompassing SACVW. Datasets collected as part of this effort were used to assist in the development a numerical integrated hydrologic model of the SACVW. As part of this study the USGS collected hydrogeologic field data and developed a three-dimensional hydrogeologic framework model (HFM) of the SACVW. Hydrogeologic field data included streambed infiltrometer and aquifer slug tests, and measurements from streambed electrical resistivity instruments and temperature rod sensors. The HFM provided a quantitative framework of the aquifer system, including the thickness and extent of each of six hydrogeologic units that comprise the basin-fill aquifer. Infiltrometer tests provided data that can be used to estimate infiltration rate, streambed hydraulic conductivity and specific yield in the SACVW. Aquifer slug tests provided data that can be used to estimate hydraulic conductivity of aquifer units. Streambed electrical resistivity instruments provided data that can be used to estimate stream intermittency and flow patterns, and temperature rod sensors provided data that can be used to estimate streamflow infiltration.