Introduction__________________________________ _ _ Purpose and scope _________________________________ Previous studies ___________________________________ Description of drainage area ______________________________ Topography, drainage, and diversion _______________________ General geology and quality of ground water __________________ Location of oil fields ________________________________ Methods of investigation ________________________________ Low-flow studies ___________________________________ Salt-load trend studies _____________________________ Analysis of data _____________________________________ 11 Synopsis of quantity and quality of low flows __________________ 11 General ______________________________________ 11 Reach from mile 831.8 to mile 826.3 _____________________ Reach from mile 826.3 to mile 810.6 _____________________ Reach from mile 810.6 to mile 796.3 _____________________ Delineation of source areas of saline inflow ____________________ Synopsis of salt-load trend studies _______________________ Reduction of salinity by diversions of saline low flows _____________ Summary of conclusions ________________________________ 34 References cited _____________________________________ 35

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Periodically since October 1961, the U.S. Geological Survey, in cooperation with State, Federal, and local agencies, has made comprehensive water-quality surveys of selected reservoirs in Texas. During the 1970 water year, the program was expanded to include periodic sampling of many other reservoirs in the State where water-quality surveys were not being made. Water-quality data collected before October 1971 have been published previously. This report contains the results of water-quality surveys of nine reservoirs and chemical analyses of samples collected periodically from 54 reservoirs.