San Antonio Creek Water Availability

San Antonio Creek Valley

San Antonio Creek Hydrogeology Studies

Located in Santa Barbara County, California, the San Antonio Creek Groundwater Basin is a rural agricultural area that is reliant on local water supplies, predominantly groundwater. Because of the growth of irrigated agriculture in the area, water demands have increased significantly, taxing local groundwater supplies. Groundwater resources are also used to supply local inhabitants, as well as parts of Vandenberg Air Force Base (VAFB).

Santa Barbara County, VAFB, and the U.S. Geological Survey are working together to better understand the water resources and demands in the San Antonio Creek Groundwater Basin. The cooperative study, referred to as the San Antonio Creek Groundwater Availability Project, seeks to help stakeholders plan for future water use by providing data that will help assess the quantity and quality of the area’s water supply, and by establishing tools to allow stakeholders to effectively utilize the available water resources.

map detailing the location of the San Antonio Creek groundwater basin in California

The U.S. Geological Survey is working on this project in cooperation with:

Surface-Water Monitoring

Historical water budgets for the San Antonio Creek Valley have indicated that infiltration from streamflow during ephemeral winter runoff events is a major source of recharge to the groundwater system (Martin, 1984). Similarly, groundwater discharge to Barka Slough is the major natural discharge from the basin and is critical for maintaining riparian wetland habitat supporting endangered species. For these reasons, as part of a comprehensive hydrologic investigation, it is important to make field measurements that can be used to determine independent estimates surface water movement throughout the basin and estimates of groundwater/surface water interactions.

Streambed Electrical Resistance Sensor in a dry San Antonio Creek

image of a USGS well drilling rig

Groundwater Monitoring

Groundwater is the main source of water in the San Antonio Creek Valley. Demand for groundwater in the predominantly rural valley has increased significantly because of the establishment of extensive irrigated agriculture on formerly non-irrigated land. Groundwater withdrawals have resulted in measured water-level declines ranging from 35 to more than 100 feet since the 1950s. There is concern by many stakeholders that continued water-level declines may have negative impacts on groundwater supply. To plan for future use, it will be important to evaluate the quantity and quality of the groundwater in the valley and establish tools to allow stakeholders to make informed management decisions.

Water Chemistry

Historical water-chemistry data will be used in conjunction with data collected as part of this study. Water chemistry samples will be collected from monitoring wells installed as part of this study, including two multiple-well monitoring sites (monitoring different depths in the aquifer) and eight shallow monitoring wells. Samples will also be collected from about 15 existing wells (locations to be determined). These samples will be analyzed for chemical and isotopic constituents to help evaluate the regional source(s), flowpath(s), and age(s) of water from wells. This information will be used to help characterize the groundwater-flow system and document differences in water chemistry, both areally and vertically within the basin.

collecting groundwater sample in glass bottle that will be tested for quality

Screenshot of the Interactive Map of Groundwater and Surface Water Monitoring in San Antonio Creek Valley

Interactive Map

In order to understand the integrated hydrologic system, many different types of data are being gathered from both the surface water and groundwater system. Learn about these data types and explore them with the interactive map.

Geologic & Hydrologic Models

An integrated hydrologic model will be developed as part of this study to more accurately assess and simulate the integrated surface water and groundwater system in San Antonio Creek Valley. The analysis of this integrated system will be done by refining the geohydrologic framework of the valley, as well as developing new recharge and hydrologic models.

stratigraphic section