WSP11142 - Laserfiche WebLink

Home Browse Search

Based upon limited available data, the weighted annual average concentration of total dissolved solids at Colona has been about 370 mg/l. Under project operation it is anticipated that the con- centration will be reduced about 5%. At Delta, total dissolved solids have averaged about l,600 mg/l and are expected to increase to about 2,050 mg/l with the project. On a monthly basis, concen- tration of total dissolved solids at Colona will be reduced during the period October through April; increased during the months of May, June, and July; relatively unchanged during August and September with the project. At Delta, concentrations of total dissolved solids will be increased all months with the exception of August, September, and October, which will be reduced slightly under project operation. With Ridgway Reservoir in operation, it is possible that the water in the bottom part.of the reservoir may be anaerobic. If so, metals such as iron and manganese which had previously precipitated would tend to go back into solution since the reduced state of metal would be more soluble. To minimize the possibility of excessive concentrations of metals getting through the proposed municipal water intake, and to provide a gr~er flexibility of operation, a two-level water intake is recommended. An analysis of water quality data indicates that the water stored in project reservoirs would be suitable for irrigation pur- poses. However, the storage would have the effect of providing poorer water quality than at present during the high run-off periods of May and June and improving downstream water quality during the other months because of the mixing of better quality water of May and June with that of the remainder of the year. The U. S. Depart- ment of Agriculture (15) indicates that improved water quality will decrease the volume of irrigation water necessary to maintain a favorable salt balance in the soil. An improvement in water quality could result in.a large savings in water and substantial benefits to a project. Calculations show that the quality of water available for irrigation during late summer and early fall will be improved under project operation. However, during the early part of the irrigation season, the reverse is true and thus will necessitate using more water to maintain a favorable salt balance in the soil. In this instance the benefits which could be applicable to improvement in water quality are offset by the greater quantity of poorer water required. 25