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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 1963 are summarized in this report, one of three basic-data reports published yearly by the Edwards Underground Water District. The gathering of these records and data is part of the continuing hydrologic investigation by the U.S. Geological Survey in cooperation with the Edwards Underground Water District, the Texas Water Commission, and the city of San Antonio.

Table 1 shows the annual precipitation at selected stations throughout the San Antonio area for 1963 and the annual average for each of the stations. Rainfall generally was below average during 1963, the second consecutive year of rainfall deficiency in the San Antonio area since the major drought which ended in 1957.

The annual recorded high and low water levels during 1963 in the five key wells in the area are shown in table 2. The water levels generally fluctuated above the midpoint between the record high and low levels, shown also for each key well in table 2. Thus, the aquifer head during 1963 remained well above the record low even after two consecutive years of below-average rainfall.

Recharge to the Edwards and associated limestones is chiefly from streams that lose most of their base flow and a part of their flood flow as they cross the Balcones fault zone on the outcrop of the aquifer. The recharge is estimated from records of continuous discharge at gaging stations on the streams and from seepage studies made prior to 1963, which determined streamflow losses across the Balcones fault zone under different rates of base flow. The monthly mean discharges at the gaging stations during October-December 1963 are shown in table 3. Streamflow records for January-September 1963 have been published by the U.S. Geological Survey (U.S. Department of the Interior, Geological Survey-Water Resources Division, 1963).

Table 4 shows the recharge in each basin of the San Antonio area for 1963 and the average annual recharge for the period 1934-62. The latter was computed from previous recharge estimates (Garza, 1962, p. 12; Garza, 1963, p. 7). Basically, the methods employed by Petitt and George (1956) and Garza (1962) were used for estimating the 1963 recharge, which was considerably below average and the lowest annual total since 1956.