WSP07728 - Laserfiche WebLink

Home Browse Search

SUMMARY (Continued) . .~ (mg/L). The concentration progressively increases downstream as a result of water diversions and salt contributions from a variety of sources. In 1983, the average total dissolved solids (rDS) concentration was about 710 mg/L at Imperial Dam, the last major diversion point of the Color3do River in the United States. In 20 of the last 23 years, average annual TDS exceeded 800 mg/L, with a maximum of 896 mg/L in 1970. Unless con- trol measures are undertaken, the concentrations are expected to increase as the Colorado River Basin States continue to develop their compact- apport ioned waters .1/ w ~ 0> The high salt concentration in the Lower Colorado River Basin ad- versely affects more than 17 million people and about I million acres of irrigated farmland in the United States. Affected most severely are municipal and industrial water users in the Las Vegas, Los Angeles, and San Diego areas and irrigators in the Imperial Valley of southern Cali- fornia who experience economic losses. . According to a 1980 study by the Water and Power Resources Service (now Bureau of Reclamation), estimated economic losses in the Lower Colo- rado River Basin average $540,000 annually for each increase of 1 mg/L when salinity concentrations at Imperial Dam range from 875 to 1,225 mg/L (based on January 1983 prices). The losses consist of $378,000 in munic- ipal and industrial impacts and $162,000 in agricultural impacts per mg/t. The historical salt load fluctuates annually with the overall basin water supply. Between 1949 and 1970, the general trend of the concen- tration at Imperial Dam was upward. Since 1970, however, the concentra- tion has decreased both as a result of Colorado River Storage Project reservoirs mixing high and low water and as 3 result of a generally more moist weather pattern increasing the amount of water available to dilute the salts. Future salinity concentrations at Imperial Dam throuRh 2010 with water quality improvement projects are e~pected to follow an overall rising trend as depletions continue to increase. In response to the Federal Water Pollution Control Act and its amend- ments (Public Law 92-500, October 1972), the seven Colorado River Basin States adopted and the Environmental Protection Agency approved numeric criteria for three points on the Lower Colorado River. The goal of the salinity control program is to maintain concentra- tions at or below these criteria. Depletions within the Colorado River Basin are projected to increase from 9.6 million acre-feet per year in 1983 to 12.6 million acre-feet in 2010. With full development of the I II The waters of the Colorado River were divided between the Upper and Lower Basins by the Colorado River Compact of 1922. The waters were subsequently apportioned among the Upper Basin States (Colorado, New ~exico, Utah, and Wyoming) by the Upper Colorado River Compact of 1948, and among the tower Basin States (Arizona, California, and Nevada) bv the 1964 Supreme Court Decree, Arizona vs. California. . 5-2