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ill '-::> -:; N 0) QO W ABSTRACT Rivers draining arid basins increase in salinity content in the downstream area to the point where water users are often significantly damaged, The problem in some cases can be ameliorated by altering upstream water and land use practices. An economic trade off exists between the eost of such upstream efforts and the downstream benefits achieved, This report examines options for salinity management in the Colorado River Basin, The study sought to provide additional information to estimate 1) economie damages caused by various salt concentrations to agrieultural and municipal water users and 2) economie eosts of salinity control measures by upstream water users. Damages were estimated for high salinity levels to provide guidelines to project future eonditions. Controt costs were estimated with a physical model developed to prediet the response of soil, water, and erop factors, Input-output models were used to estimate indireet economic impacts. Agricultural damages for each milligram per liter of salt eoneentration at Imperial Dam in the 900 to 1400 range were estimated to be $33,100 annually, Of the total, $28,200 are in the Imperial Valley and decreasing amounts occur respectively in the Palo Verde. Yuma, Colorado River Indian Reservation, San Diego, Coachella, and Central Arizona areas. Salinity caused damages to plumbing and appliances in the Los Angeles area were estimated to be about $112,000 per mg/1. Comparable estimates were $11,200 for Central Arizona and $11,400 for the Las Vegas area. As for controlled eosts, 80 percent of the initial salt load eould theoretieaIly be at an incremental cost of less than $2,20 per ton, The comparison of the reduction measures showed on-farm practices to be the least expensive alternative for reducing salinity. Based on an approximation that 1 mg/l at Imperial Dam is equivalent to 10,000 tons of salt, the above estimated benefits of salinity reduction would be about $17 per ton, Sa1inity control projeets at Paradox Valley and aereage retirements in the Grand and Uncompaghre Valleys were found to be economically justified but lining the Grand Valley Canal was not, The above estimates are approximations obtained from available data and can be improved by further studies to cover additional cost and benefit effects or by more comprehensive data on the effeets covered, ~_C.