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:.~ ex. w w QUALlTi OF \lATER COLORADO RIVER BASIN rnCNRE:>S REPORT SUMr.lARY This report is a presentation of various Io'ater quality aspects of the Colorado River. Although several Io"ater quality parameters are dis- cussed, the major part of" the report is allotted to salinity (total dissolved solidsj because it is presently the cost serious quality prob- lem on the river system. The historical, present =todified. and future salinity conditions of water of the Colorado River down to Imperial Dam are presented in this report. The historical is represented by a tabula_ tion of the recorded or estimated past condition at 17 quality of water stations for the 1941-70 period. The present modified condition includes adjustments of the historic condition based on the assumption that devel_ o~ents completed during the 1941-70 period were in operation for the full period. The fUture condition i~ an estimated projection after the presently authorized developments and some projects proposed for authori- zation are placed in operation. Under historic conditions the average concentration of dissolved solids of the Colorado River at Lees Ferry was about 0.76 ton per acre- foot, beloW' Hoover Darn about 0.94 ton per a.cre-foot, and at Imperial Darn about 1.03 tons per acre-foot for the 1941-70 period. Under present ~ified conditions (that is assuming the projects that started operating sometime during the 1941-70 period W'ere in opera- tion throughout the entire period) the concentrations would have been about 0.83; 1.01, and 1.16 tons per acre-foot, respectively, at the three stations. It has been 8.'Ssumed for purposes of this study that the average rate of pickup of dissolved solids from new irrigated lends W'Ould be in the range of zero to 2 tons per acre. The effect of salts contributed from new lands is thus evaluated by Computations of salinity concentrations using zero tons per acre pickup and 2 tons per acre pickup. It Io~ also assumed no additional pickup of dissolved solids would occur for lands already under irrigation. Under future conditions, 8.'Ssuming negligible salinity control meas_ ures, with all authorized projects and projects proposed for authorization in operation and using the 8.'Ssumed maximum rate of pickup of 2 tons per acre on the new irrigated lands, the concentrations are estima.ted to be 1.04 tons per acre-foot at Lees Ferry, 1.32 tons per acre-foot below Hoover Dam. and 1.64 tons per acre-foot at Imperial Dam. Future Caridi tior,s -