San Antonio Reservoir Bathymetric Survey and Sedimentation Study

Science Center Objects

Over time, the flow of water into the San Antonio Reservoir has caused the build-up of sediment, decreasing storage capacity. Since water storage is a crucial issue in California, up-to-date information on the reservoir is needed.  To accomplish this, the San Francisco Public Utilities Commission approached the USGS California Water Science Center to conduct a bathymetric (depth) survey and other tests to measure the accumulation of sediment and the present storage capacity of the reservoir.

The San Antonio Reservoir is located in Alameda County, about 5 miles east of the town of Sunol. The reservoir, created in the early 1960s by the damming of San Antonio Creek, has a capacity of 50,000 acre-feet. It is owned and operated by the San Francisco Public Utilities Commission (SFPUC). The reservoir is fed by local watersheds and water from the Hetch Hetchy aqueduct.

Objective

The team from the USGS California Water Science Center will assess the rate of sedimentation and the resultant loss of reservoir capacity and provide updated storage volume data.

San Antonio Reservoir - Aerial View of Study Area

Aerial View of the San Antonio Reservoir Study Area

Science Plan

Scientists will survey the bottom of the reservoir with sonar technology. They will also measure the surface area. Surface measurements ensure more accurate readings, especially when water levels are low. Using this data, scientists will create a digital elevation model (DEM) to determine surface area and storage volume.  Scientists will also collect samples of bed sediment and analyze them for particle size distribution. This data will help to determine the average rate of capacity loss.

The team will then compute the rate of sedimentation by comparing the collected data with prior surveys and pre-dam topography. They will do this by constructing DEMs from the previous data. (Data from this survey will in turn serve as a baseline for comparison with future surveys.)