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,::> ;,? '-- "''''4 7 water which dissolves salt from the Mancos Shale are reduced and con- ,-' trolled. Some of the major washes traversing the irrigated area and discharging into the river have flows with salinity levels in excess of 6,000 ppm of total dissolved solids. Estimates of the amount and salt concentration of return flows have been made; however, more reliable data and analysis of the surface and ground water ret'un systems are needed before impacts of alternative control programs can be adequately made. The average annual salt budget for the Grand Valley area for the period 1964 to 1970 is given in the following table: Tnf'l()1J' n"tf'ln1aT Rf':lo~1l1 +.cmt Pi,-.k-llp Colo. R. Colo. R. Irri Upland near Plateau Gunnison at State gated Drain- Cameo Creek River Tot Line Area age Total (million tor_s) Av. 1964-70 1.46 0.07 1.43 2.96 3.56 0.46 0.14 0.6 Range 1964-70 1.2- 1.2- 2.4- 3.2- 0.5- 1.6 1.7 3.3 4.14 0.8 An analysis of USGS water quality records (1964-70) indicate an average of about 600,000 tons of salt is added to the Colorado River in the Grand Valley reach. About 140,000 tons annually of the 600,000 ton pickup come from the upland drainage. The balance of about 460,00) tOlli3 is estimated to be added by the irrigation return flows of the Grand Valley and is rela- tively uniform from year to year. Preliminary analysis shows that significant variation in salt loading from year to year appears to be a function primarily of surface and subsurface runoff from upland drainages. Water quality information on the artesian acquifer collected by the U.S. Department of Agriculture in 1<)J5, 1951, and 1973 indicates no change in water quality of the acquifer. Irrigation Systems and Management Improvement Needs - A detailed analysis (by the Colorado Water Conservation Board) of several canal systems for the 1965-71 irrigation seasons indicates that 13 to 30 percent of the water diverted is consumptively used by irrigated crops. Sirrlilar results are reported from Colorado State University research studies. Therefore, about 70 to 87 percent is spilled into surface ditches or percolates into under- lying saline acquifers. This amounts to 10 to 20 feet diverted for each irrigated acre. The maximum consumptive use by crops is 2.5 feet, leaving the balance to return to the Colorado River each year or to be used by phreatophytes in the Valley. Irrigation water budgets of selected canal systems in the Valley for 1965-71 are shown below: