Geology and ground-water resources of Hale County, Texas

Abstract

Hale County, in the southern High Plains of Texas, has an area of 1,033 square miles. The land surface is one of low relief, and the regional slope is about 10 feet per mile toward the southeast. Surface runoff drains into numerous playa lakes and two intermittent streams: Running Water Draw and the Double Mountain Fork of the Brazos River. The Ogallala formation of Tertiary age is the principal water-bearing formation in the county. The Ogallala lies on red beds of Triassic age throughout most of the county and on rocks of Cretaceous age in approximately the southern fifth of the county. The Triassic and underlying Permian rocks are not fresh water bearing in the county. The Cretaceous rocks, on the other hand, are in direct hydraulic connection with the Ogallala, and a few wells tapping them yield large quantities of water from cracks and solution channels in the limestones. The Ogallala formation is overlain by thin deposits of sand, gravel, silt, and clay of Pleistocene and Recent age. These younger rocks are, for the most part, above the water table and, consequently, are not water bearing. The water in the Ogallala formation occurs principally as unconfined water in layers and lenses of sand and gravel. The hydraulic properties of the Ogallala were determined by a long-term aquifer test at Plainview, where coefficients of transmissibility ranging from 24,000 to 38,000 gpd per foot were measured. The coefficient of storage was determined to be about 0.14. The aquifer is recharged from precipitation in Hale County and in the southern High Plains northwest of the county. The water moves generally southeastward at about 2 inches a day. Ground water in Hale County is used principally for irrigation. In 1955 more than 3,700 wells were used to irrigate 470,000 acres; about 560,000 acre-feet of water was pumped. About 5,000 acre-feet was pumped for other purposes, including municipal, industrial, stock, and domestic uses. The water in the Ogallala formation in Hale County is suitable chemically for irrigation and most other uses; however, it should be softened for more satisfactory domestic use. The high silica content indicates that the water may be unsuitable for use in boilers. The fluoride content is excessive. It is estimated that in 1955 about 39 million acre-feet of water was in storage in the Ogallala formation in Hale County; however, only about 16 million is theoretically available to wells, and a somewhat smaller amount is practically available. About 3 million acre-feet was removed from storage during 1938-55. Water levels in wells have declined more or less steadily since 1938, and it is apparent that the ground-water resources of the county are insufficient to support large-scale perennial irrigation such as that of 1955.