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<br /> <br />. <br /> <br />flood~frequency study is about 90 percent complete. Eventually we hope <br />to cover the entire country with basin.wide or regional flood-frequency <br />reports. <br /> <br />. <br /> <br />Plans are underway for a special report on the drought in south- <br />western United States, to contain basic hydrologic data and discuss the <br />effects of the drought on streamflow, ground water, storage, soil <br />moisture, evaporation, and use of water for irrigation, industry, power, <br />and municipalities. Such a report for southern California is essentially <br />complete. <br /> <br />Water quality problems in the Colorado River basin are of particular <br />concern. The Survey does not have all the answers with respect to the <br />chemical characteristics of ground and surface water and the sediment <br />loads of the streams. Our program includes continued operation of 42 <br />daily chemical quality, 21 sediment load and 33 water temperature stations. <br />As some stations have been operated more than 25 years, a considerable <br />volume of data is available and will be evaluated thoroughly. As a rule, <br />Colorado River Basin water is best in quality in the headwater areas and <br />tends to deteriorate downstream, especially with use, even to the extent <br />of being unfavorable for certain uses. Some tributaries contribute volumes <br />of sediment and dissolved minerals disproportionately large in relation to <br />their volumes of water. While the current program gives a general picture <br />as to principal source areas, additional information is needed to pinpoint <br />the origin of dissolved minerals and sediments before ameliorative <br />measures can be planned intelligenUy, particularly allowance for sediment <br />accumulation in upstream reservoirs. This is especially pertinent to <br />determining effects of transbasin diver sions on the quality of water down. <br />stream. There is no doubt that major diversion.s of good water will impair <br />the quality of waters in lower parts of the basin but to determine the extent <br />will relJ.uire more detailed records than are now available. <br /> <br />. <br /> <br />" <br /> <br />Much information is needed on ground water in the basin. Intensive <br />studies. have been made only in the Grand Junction area in Colorado, Las <br />Vegas Valley in Nevada, and the Gila, Salt, and LitUe Colorado River <br />basins in Arizona, all places where progressive lowering of water levels <br />has indicated overdevelopment. Elsewhere in the basin litUe is known <br />about possibilities of development of wells, 01' their effects upon stream- <br />flow. We are studying consumptive use of water by phreatophytes, mostly <br />useless plants such as salt cedar, which take water through their roots <br />from the groundwater reservoir. These studies will be useful in deter- <br />mining areas where groundwater supplies now wasted may be converted <br />to beneficial use. <br /> <br />II <br /> <br />Last September the Survey, in cooperation with the Bureau of <br />Reclamation, completed determination of evaporation from Lake Mead, <br />using two methods tested at Lake Hefner. Results of the two methods <br />were within 2 percent of each other. A report will be published soon. <br />This work should bring confidence .in a quantity hitherto open to contention. <br />It is hoped the studies can be extended to other reservoirs and sites in <br />the Colorado River Basin. <br /> <br />. <br /> <br />In. recent years a special activity of the Survey has included explora- <br />tion for surface- and ground-water supplies on western ,range lands, <br /> <br />.7- <br />