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I I I I I I I 1 I I ,. I, ,I I I I t I I C. WATER AVAILABILITY IN LOW FLOW YEARS As indicated in Table IV-C, flows in the Colorado River must drop below 1,810 cfs before OMID water rights will be curtailed. There have been a number of months over the past 61 years of flow records when river flows have been less than this amount (see Appendix F); however, the District manager reports that it has always been possible to maintain canals #1 and #2 at full flow capacity, even during these low flow periods. There are several factors that can be used to mitigate the natural low flows of the Colorado River and which allow OMID to keep its canals at full capacity. These are: 1. When the check dam is closed, OMID can return 272 cfs through the side canal directly to the river above Grand Valley Irrigation Company's diversion. As discussed, this effectively adds 272 cfs to the natural flow. 2. Water from Green Mountain Reservoir can be released into the Colorado River upon request of the irrigators in the Grand Valley. The Bureau of Reclamation has developed scenarios for the low flow years which show how Green Mountain water can add to low flows in the Colorado River. These tables are shown in Appendix F. 3. The lowest monthly flows occur in September and October. During these periods, irrigation demand is lower, and some of the irrigation companies may not be using their full amount of water. The other irrigation companies recognize that OMID needs its full allotment in order to properly operate its pumps and turbines. As long as they have enough water to answer the call from their shareholders, the other irrigation companies are willing to allow OMID to divert their full allotment. Agencies which administer the flow of the Colorado River have traditionally used the year 1977 as the indicator year for minimum flows. The Bureau of Reclamation analysis indicates that if Green Mountain water had been leased in 1977, according to present formulas and administrative rules, minimum river flows in July would be 1700 cfs. Under this flow scenario, there would be adequate water in the river to supply OMID with sufficient water to operate its turbine pumps and provide water to canals #1 and #2 (with full diversions to all other users except the power plant). Although the water right to the power plant has a slightly better water right than the Grand Valley Irrigation Company, this water right is traditionally curtailed first since it is a non-irrigation use. D. WATER QUALITY 1. Salinity Total dissolved solids (TDS) is the water quality parameter of most concern to irrigators in the Grand Valley. Salinity is a water quality parameter closely lV-9