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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,
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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