Technical Reports Document Library

The Edwards and associated limestones, the principal aquifer in the San Antonio area, has been the subject of numerous geologic and hydrologic reports. Records of precipitation, water levels, and estimates of recharge to the aquifer during 1967 are summarized in this report, which is part of the basic-data collection published by the Edwards Underground Water District. The compilation of these basic records (and data} is part of the continuing hydrologic investigation by the Uo S. Geological Survey in cooperation with the Edwards Underground Water District and the Texas Water Development Board.

The annual precipitation at selected stations throughout the San Antonio area for 1967 and the annual average for each of these stations are shown in table 1. Rainfall was generally deficient for the first eight months of 1967 and excessive during the remainder of the year.

The recorded high and low water levels in five selected key wells during 1967 are shown in table 2. During the year, the water levels fluctuated near the midpoint between the record high and low levels which are also shown in table 2. Ground water storage and water levels in the Edwards limestone reached a lower point during August than had been experienced for several years.

Recharge to the Edwards and associated limestones is chiefly from streams which lose most of their base flow and a part of their floodflow as they cross the Balcones fault zone on the outcrop of the aquifer. The recharge is estimated from discharge records at gaging stations located above and below the infiltration areas on most of the streams. The monthly mean discharge at the gaging stations for October-December 1967 are shown in table 3. Streamflow records for January-September 1967 are being published by the U. S. Geological Survey (U. s. Department of the Interior, 1967).

The recharge in each basin of the San Antonio area for 1967 and the average annual recharge for the period 1934-66 are shown in table 4. The basic methods employed by Petitt and George (1956) and by Garza (1962) were used for estimating the 1967 recharge, which was below the average annual. In September 1967, the deficient rainfall pattern was broken by the rains that accompanied Hurricane Beulah. Seventy-five percent of the total recharge for 1967 occurred during the last four months of the year.