Land-surface subsidence in the area of Moses Lake near Texas City, Texas.




Gabrysch, R.K.
Bonnet, C.W.

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U.S. Geological Survey, Water Resources Divisions.


The pumping of ground water in Harris and Galveston Counties, Texas, has caused a decline in artesian head at Moses Lake of as much as 145 feet (44m), which in turn has caused subsidence of the land surface. The Moses Lake area is about 4 miles (6.4 km) north of the central part of the industrial area of Texas City, but subsidence at Moses Lake has been much less than in the industrial area. Seven wells were drilled at the test site at Moses Lake to collect data on the properties of the clays and on artesian heads in the sands. Most of the subsidence at Moses Lake is probably due to compaction of material above the Alta Loma Sand; therefore, the extensometer record should be valuable for estimating subsidence on a continuing basis. Six clay cores obtained from one well drilled at Moses Lake were tested to determine compressibility characteristics. These data, together with compressibility data on cores from other sites, were used to compute subsidence by the Terzaghi theory of consolidation. The subsidence computed by this method far exceeded the measured subsidence experienced; therefore, the amount of subsidence was determined on the basis of historic changes in stress (mean change in artesian head) and the specific unit compaction as determined from field data.


90 p.


subsidence, ground water, cores, compressibilty, pumping