Ground-water Resources of the San Antonio Areas Texas a Progress Report on Current Studies
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Abstract
The Edwards and associated limestones constitute the principal ground-water reservoir in the San Antonio area of Texas. The reservoir extends along the Balcones fault zone as a hydrologic unit in parts of Kinney, Uvalde, Medina, Bexar, Comal, and Hays Counties. North of the Balcones fault zone, the rocks of the Edwards Plateau store substantial amounts of water that slowly drain out to form the base flow of the perennial streams that have cut their channels into or through the aquifer. Recharge to the reservoir in the fault zone is partly by direct infiltration of precipitation on the outcrop of the Edwards and associated limestones, but to a greater extent by seepage from the streams that cross the outcrop in the Balcones fault zone. During the period 1934-53, the estimated annual recharge to the reservoir has ranged from 129,300 to 1,168,200 acre-feet and has averaged 426,300 acre-feet. Most of the discharge from the reservoir in the San Antonio area has been by springs; however, the quantity of water discharged by wells increased through out the period 193^-53• The largest increase in discharge by wells has been since 1947.- the start of the prolonged drought of recent years. Crops have been irrigated since the founding of the earliest missions in the area, but the amount of water used for irrigation increased greatly during the drought. The amount of water withdrawn for municipal supply has increased as the population and percapita consumption have increased in San Antonio and other cities in the area. During the period 193^-53 the annual discharge from the reservoir ranged from 395,800 to 615,100 acre-feet and averaged 515,800 acre-feet. Most of the recharge to the reservoir is in the western part of the area, and the water moves eastward. The springs serve as natural spillways for the reservoir. The two largest, Comal and San Marcos Springs, are in the eastern part of the area. The recharge to the aquifer exceeded the discharge in only three years between 1934 and 1953* A comparison of the difference betwee
