Abstract

Annual recharge data obtained from historical records and mean-annual precipitation data computed from rainfall records were used to develop simple linear-regression equations for use in estimating annual recharge for seven subbasins in the San Antonio area. Adjustments were made to the precipitation parameter to account for the effects of year-end storms. The standard errors of estimate of the regression equations ranged from 26 percent for the Blanco River basin to 45 percent for the area between the Sabinal and Medina River basins.

Annual-recharge estimates computed by use of the regression equations compared favorably with estimates made on the basis of observed streamflow and precipitation data.

The report includes a brief review of the geology and hydrology of the Edwards aquifer, a discussion of the preparation and evaluation of the precipitation data used in the regression analyses, and a brief summary of the method previously used to estimate recharge.

Posted August 2009