Laserfiche WebLink
<br />The major portion of the salt contribution to the Colorado River <br />from the District comes from the Palo Verde Subarea, which was esti- <br />mated to contribute 144,000 tons per year. The Rannells and South End <br />Subareas also contribute large amounts of salt to the river. These <br />subareas are generally in the southwestern portion of the District. <br />The Lower Borrow Pit Subarea and West Side Subarea with minor <br />discharges, and the Central Subarea with a minor salt retention, were <br />considered to be essentially in salt balance. The East Side Subarea <br />appeared to have a considerable salt retention. The reason for this <br />was not apparent in the salt budget ana lys is, and there was concern <br />that an accumulation of small errors influenced the results. Salt <br />precipitation was ruled out because of the large volumes of agricul- <br />tural return flow at relatively low concentrations. <br />The Palo Verde Mesa was served with 17,000 acre-feet of river <br />water containing 18,000 tons of salt. In addition, 5,000 acre-feet of <br />subsurface drai nage from the West Si de Subarea entered the all uvi urn <br />under the Mesa, carrying 8,000 tons of salt. None of the salt enter- <br />ing the Mesa returns to the drainage system on the flood plain. <br />The vari at i on among subareas appears to be caused by vari at ions <br />in ground-water quality. This was initially suggested by inspection <br />of the locations of subareas and the areal distributions of ground- <br />water qual i ty, and a cursory estimate was made to exami ne the pos- <br />sibility. The average quality of the ground water in each subarea was <br />determined by inspection of a copy of Figure 2 on which subarea <br />boundaries had been sketched. The quality of the leaching fraction in <br />each subarea was estimated using information in the Bookman-Edmonston <br />report, and the salt input to the subarea was calculated. It was <br />assumed that the drainage was half ground water and half deep percola- <br />tion from irrigation and seepage. The resulting salt discharge was <br />calculated and compared with the salt imput to determine the net <br />subarea discharge or retention. <br /> <br />002855 <br /> <br />13 <br />