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w ~ 00 ~ hydrologic cycle can have a significant impact on salinity5. These natural variations in runoff can cause a fluctuation in average annual salinity concentration of over 300 mg/l TDS at Imperial Dam. By contrast, the plan of implementation, as set forth in this Review, will reduce the average salinity concentration by approximately 100 mg/l at Imperial Dam by 2010. The federal regulations provide for temporary increases above the 1972 levels if control measures are included in the plan. Should water development projects be completed before control measures are identified or brought on line, temporary increases above the criteria could result and these increases will be in conformance with the regulation. Wi th completion of control projects, those now in the plan or those to be added subsequently, salinity would return to or below the criteria level. Uses and Associated Impacts of Salinity The Colorado River, from its headwaters in the Rocky Mountains to its mouth in the Gulf of California, is utilized for a wide variety of purposes. A portion of the flow is transported out of the Colorado River basin for use in adjacent river basins. In the Colorado River basin, irrigation, municipal and industrial, powerplant cooling, fish and wildlife, and recreation are the major uses of river water. Colorado River water users in the Lower Basin have suffered signifi':'~'1t economic impacts due to long-term continued use of water with elevated salinity levels. These damages are estimated to have reached over $300 million per year under current salinity concentrations. I f the proposed plan of implementation for salinity control, as set forth in this Review, is not implemented these damages could triple by 2010. Agricultural water users suffer from higher salinity waters throl..lgl: -educed crop yields, added labor costs for irrigation managemerlt, and added drainage requirements. The urban user incurs additional cost due to more frequent replacement of plumbing and water using appliances, use of water softeners and the purchase of bottled water. Industrial users and water treatment and waste water utilities incur reductions in the useful life of system facilities and equipment from increased levels of salinity. A significant impact in the Lower Basin is that imposed by local and regional water quality standards and management programs, to protect local ground water supplies. Reaulatory agencies have placed restrictions on the reuse of, or recharge of, waters that exceed specified salinity levels. If the river's salin'i ty continues to increase, these regulatory actions would result in 5 Progress Report No. 14, Quality of Water, Colorado River Basin, January 1990, USBR 20 "