Land-surface subsidence in the Houston-Galveston region, Texas

Abstract

The pumping of large amounts of ground water in the Houston-Galveston region, Texas, has resulted in water-level declines of as much as 200 feet (61 metres) in wells completed in the Chicot aquifer and as much as 325 feet (99 metres) in wells completed in the Evangeline aquifer during 1943-73. The maximum annual rates of decline for 1943-73 were 6.7 feet (2.0 metres) in the Chicot aquifer and 10.8 feet (3.3 metres) in the Evangeline aquifer. During 1964-73, the maximum rates were 10 feet (3.0 metres) in the Chicot and 17.8 feet (5.4 metres) in the Evangeline. The declines in artesian pressures have resulted in pronounced regional subsidence of the land surface. The center of subsidence is at Pasadena, where as much as 7.5 feet (2.3 metres) of subsidence occurred between 1943 and 1973. More than 1.0 foot (0.3 metre) of subsidence occurred at Pasadena between 1906 and 1943. The maximum amount of subsidence during 1964-73 was about 3.5 feet (1.1 metres). In the southern part of Harris County, about 55 percent of the subsidence is a result of compaction in the Chicot aquifer. The area in which subsidence is 1 foot (0.3 metre) or more has increased from about 350 square miles (906 square kilometres) in 1954 to about 2,500 square miles (6,475 square kilometres) in 1973. Estimates of subsidence are based on the amount of water-level decline, the thickness of the clay, and the compressibility of the clay. At Seabrook, it is estimated that for each 1 foot (0.3 metre) of average water-level decline, 1 foot (0.3 metre) of clay would compact 0.000031 foot (0.00094 centimetre). At Seabrook, for 1 foot (0.3 metre) of water-level decline, 0.0248 foot (0.756 centimetre) of subsidence would occur. Planned use of surface water instead of ground water will probably result in some recovery of artesian pressures. If pressure recovery occurs the rate of subsidence should decrease substantially in the more critical areas.