Reconnaissance of the chemical quality of surface waters of the San Jacinto River Basin, Texas.




Hughes, L.S.; Rawson, J.

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Surface water in the San Jacinto River Basin is of excellent chemical quality, and is suitable for most municipal, industrial, and agricultural purposes. The kinds and quantities of minerals dissolved in surface water of the basin are related principally to the geology of the runoff area and to rainfall and streamflow characteristics, but the quality of the water is also affected by industrial activities. The rocks exposed in the San Jacinto River Basin are sedimentary deposits that range in age from Miocene(?) to Recent. The formations crop out in belts parallel to the Gulf Coast; the older rocks are exposed in the northern part of the basin, and successively younger rocks crop out toward the coast. Throughout much of the basin, the readily soluble materials have been leached from the surface rocks and soils by the abundant rainfall. Consequently, the water in streams is usually low in concentration of dissolved minerals. Water from the outcrop areas of the Catahoula Sandstone, Lagarto Clay, and Oakville Sandstone in the upper part of the San Jacinto River Basin has dissolved-solids concentrations ranging from 100 to 200 ppm (parts per million); water from the outcrop areas of formations younger than the Lagarto crop out, is usually soft. The chloride concentration in the surface water is generally less than 50 ppm, and streams draining formations younger than the Lagarto Clay generally observed in Cypress Creek and Buffalo Bayou are probably the result of oil-field brine having reached the streams. Lake Houston, the only large water-supply reservoir in the basin, contains water of excellent quality. Water available for storage at potential reservoir sites is also of excellent quality. In the northern part of the basin the activities of man have caused little change in the chemical quality of surface water. In the area downstream from Lake Houston the flow in most of the streams is partly maintained by sewage and industrial effluents from the Houston metropolitan area, and by return flow of irrigation water. The chemical quality of the streams draining the Houston metropolitan area was not studied but is probably poor.


45 p.


surface water; chemical quality; reservoirs