Artesian water in Somervell County, Texas

Abstract

Somervell County is part of the Grand Prairie region of north-central Texas. An excellent supply of artesian water is available from the Trinity reservoir at no great depth. The first flowing well in Somervell County was drilled in 1880, and the first flowing well in Glen Rose, the county seat, was drilled in 1881. Since 1880 more than 500 wells have been constructed, probably more than half of them prior to 1900. Many of these early wells have been abandoned, either because the well hole caved in as a result of the absence or deterioration of casing or because the wells ceased to yield water by natural flow. The artesian water has always been used chiefly for domestic supply and for watering stock. Only a comparatively small area of farm land is now irrigated. The quantity used to supply the needs of tourist camps and outdoor swimming pools forms a relatively large percentage of the total amount withdrawn from the artesian reservoir in Somervell County. The artesian water is contained chiefly in the permeable sandstone beds--the basal sands for the Trinity group. Some shallow wells of small capacity are supplied by water in the crevices and solution channels in limestone that apparently is near the base of the Glen Rose formation and probably derives its water by leakage from the underlying Trinity reservoir. The wells encounter from one to three aquifers, the number depending upon their depth and location. At and around Glen Rose, the area in which most of the flowing wells are concentrated, the first aquifer is the creviced portion of the limestone, which is encountered at about 50 feet but does not everywhere yield water. The second and third aquifers, both of which are part of the 'basal sands' of the Trinity group, are much more uniform and persistent; the second is encountered at Glen Rose at depths of 100 to 135 feet, and the third at depths of about 275 to 330 feet. The artesian reservoir is supplied by water that falls as rain or snow upon the outcrop of the 'basal sands' on the higher lands west and north of Somervell County. These permeable beds dip eastward and southeastward beneath the county and are covered by the less permeable beds of the overlying Glen Rose formation. As the water that reaches the zone of saturation percolates down the dip of the beds it is confined under artesian pressure, and wells that penetrate these beds at lower altitudes yield water by natural flow. Originally the artesian pressure was sufficient to raise the water in tightly cased wells in the northwestern part of Somervell County to a maximum altitude of about 750 feet above sea level, but at Glen Rose the original artesian head was probably not more than 710 feet. From the information avail- able it would appear that the original head of the water in the upper aquifers was not nearly as great as that of the lower aquifer. The head has declined generally throughout the county. At Glen Rose in June 1930 the artesian head of the water from the deepest aquifer of the Trinity reservoir was about 639 feet above sea level, and the head of the water from the upper aquifers was about 15 feet less. The decline in head still continues, but at a very much slower rate than formerly. With the decline in head the size of the area of artesian flow has decreased, though in recent years the shrinkage has been comparatively little. The draft from the artesian reservoir in Somervell County during the summer is estimated at about 1,000,000 gallons a day, distributed as follows: Domestic use, 150,000 gallons; stock use, 60,000 gallons; recreation pools, 250,000 gallons; irrigation, 180,000 gallons; and waste, not including underground leakage, 360,000 gallons. In winter the daily draft is probably about 370,000 gallons less than in summer. The 360,000 gallons a day permitted to flow from wells without being used for any beneficial purposes is an unnecessary drain upon the artesian reservoir. The head of many of the flowing wells in Glen R