The pumping of large amounts of groundwater in the Houston-Galveston region, Texas, has resulted in water-level declines between 1943 and 1973 of as much as 61 m in wells completed in the Chicot aquifer and as much as 99 m in wells completed in the Evangeline aquifer. The maximum average annual rates of decline for those years were 2.0 m in the Chicot aquifer and 3.3 m in the Evangeline aquifer. From 1964 to 1973, the maximum average annual rates of decline were 3.0 m in the Chicot and 5.4 m in the Evangeline. The declines in artesian pressures have resulted in pronounced regional subsidence of the land surface.

The center of subsidence in the Houston-Galveston region is at Pasadena, Texas, where as much as 2.3 m of subsidence occurred between 1943 and 1973. More than 0.3 m of subsidence occurred at Pasadena between 1906 and 1943. The maximum amount of subsidence during 1964-73 was about 1.1 m.

In the southern part of Harris County, about 55% of the subsidence is a result of compaction in the Chicot aquifer. The area in which subsidence is 0.3 m or more has increased from about 906 sq km in 1954 to about 6,475 sq km in 1973. The annual cost of damage attributed to subsidence for 1969-74 was estimated, in a study by Texas A&M University, to be about $32,000,000 in 2,448 sq km of the area most affected by subsidence.

The pumping rate has been almost stable since 1967,

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and the rate of decline in water levels has decreased significantly. The rate of subsidence has decreased since September 1976. As a result of increased use of surface water, groundwater production decreased about 303 million L/day and groundwater levels rose as much as 18 m in the central part of the region in 1977. Because of the pressure recovery, the rate of subsidence should decrease substantially in some critical areas.

The Harris-Galveston Coastal Subsidence District was created by the Texas Legislature in 1975 to cope with the problem of land-surface subsidence. The District plans to control subsidence by controlling and regulating groundwater pumping.

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