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2346 Station Below Hoover Dam Below Parker Dam A t Imperial Dam Flow Weighted Average TDS 723 mg/L 747 mg/L 879 mg/L In response to this policy and related Federal and State program enforcement guidelines, the CRWQIP was selected as part of the implementation plan to prevent salinity concentrations in the Colorado River from exceeding the standards. In June 1974, Congress enacted the Colorado River Basin Salinity Control Act, Public Law 93-320, which, among other things, directed the Secretary of the Interior to expedite completion of plan- ning reports on salinity control units in the CRWQIP, including the Colorado River Indian Reservation Unit. Colorado River Salinity The average salinity of the Colorado River at Imperial Dam in 1977 was approximately 820 mg/L, but because of increased use of river water it is expected to increase significantly in the future. There is no universally accepted projection of the future salinity; a number of Federal and State agencies have made projections using various assumptions regarding hydrologic conditions and construction of proposed projects that will cause additional diversions. However, most of the projections indicate that, with the implementation of three salinity control projects Y authorized under Public Law 93-320 but without additional salinity control measures, the salinity will exceed 879 mg/L during the mid-1980's. Summary and Conclusions Approximately 73,000 acres of flood plain land were irrigated on the Arizona portion of the Colorado River Indian Reservation in 1977 and the acreage will increase to 93,046 acres in the future. The water supply available from the Colorado River for irrigable flood plain lands is approximately 620,300 acre-feet (amounting to 6-2/3 acre-feet per acre). Y The Paradox Valley, Grand Valley, and Las Vegas Wash Units. 2