Ground-water withdrawals and changes in ground-water levels, ground-water quality, and land-surface subsidence in the Houston district, Texas, 1980-84

During 1980-84, ground-water withdrawals from the Chicot and Evangeline aquifers in the Houston district decreased from 511 million gallons per day to 444 million gallons per day. This 13-percent decrease was due to the increased availability of surface water and a decreased demand for water. The largest decreases in ground-water withdrawals occurred in the Houston area. Ground-water pumpage was 219.2 million gallons per day during 1984 compared to 254.8 million gallons per day during 1980. Decreases in ground-water withdrawals from 1980 through 1984 occurred in most of the other areas in the Houston district (Pasadena, Katy, Baytown-LaPorte, and Texas City). Large decreases in ground-water withdrawals for rice irrigation in the Katy area were offset by increases in ground-water withdrawals for public supply. Hence, in the Katy area, the quantity of ground water withdrawn during 1984, 148.9 million gallons per day, was only slightly less than the 157.5 million gallons per day withdrawn during 1980.

Water levels generally rose in the eastern part of the Houston district and declined in the western part from spring 1980 to spring 1985. The rise of water levels in wells in the Chicot and Evangeline aquifers was as much as 80 feet and 60 feet, respectively. The decline of water levels in wells in the Chicot and Evangeline aquifers was as much as 40 feet and 80 feet, respectively.

Slight decreases in chloride concentrations in water from the Chicot aquifer occurred in the Alta Loma area between 1980 and 1984. In 1980, chloride concentrations in water from the Chicot aquifer ranged from 250 to 790 milligrams per liter, whereas in 1984, chloride concentrations ranged from 180 to 710 milligrams per liter. Water from one well in the Texas City area had an increase in chloride concentrations from 265 milligrams per liter in 1980 to 300 milligrams per liter in 1984. In water from another well in the Texas City area, chloride concentrations decreased from 760 milligrams per liter in 1980 to 710 milligrams per liter in 1984. The concentrations of chloride and dissolved solids in water from the Evangeline aquifer remained less than 100 milligrams per liter and 500 milligrams per liter during 1980-84.

Land-surface subsidence is still evident in the Houston district. Subsidence rates between 1980 and early 1985 in the eastern and southeastern parts of the Houston district were less than during 1975-79. At the Seabrook site, where a monitor measures most of the subsidence, the average compaction rate during 1980 to early 1985 was 0.04 foot per year while during 1975-79, the rate was 0.14 foot per year. However, subsidence rates in the western, southwestern, and northern parts of the Houston district during 1980 to early 1985 increased from the 1975-79 rates. At the Addicks site, the land surface has subsided at a rate of about 0.17 foot per year from 1980 to early 1985. The subsidence rate from 1975 through 1979 at the site was 0.11 foot per year.