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1 j CHAPTER III GAINS ALONG THE REACH their system. Consequently, no canal administrative spills are estimated to return to the river from the East GVIC Mainline Canal. 7) All of the lateral administrative spills and irrigation return flows in the East GVIC 1 Mainline Canal service area uniformly return to the Reach. 8) Based upon an estimate provided by the manager of the OMID, 90 percent of the administrative spills and return flows from the upper Orchard Mesa Ditch No. 2, return to the Reach. 9). Return flows and administrative wastes in the western portion of Orchard Mesa Ditch No. 2 drain into the Gunnison River rather than the Colorado. 10) All of the administrative spills and on-farm returns in the Orchard Mesa Ditch No. 1 service area, return to the Colorado River. 11) The water distribution estimates developed for the Grand Valley Salinity Control Project were used to estimate the amount of water delivered to the irrigation systems within the Reach. 12) There is a lag from the time the water begins to seep from the irrigation system and the time the water is actually returned to the Reach. It is assumed that by July, an equilibrium has been achieved and that the amount seeping from the irrigation systems is equal to the amount entering the river. Based upon the above assumptions, estimated gains in the Reach from irrigation practices are presented in tables 1 and 2. This water is assumed to return more or less uniformly along the Reach. The distribution of these return flows is likely to be concentrated at several points along the Reach, either through surface or sub-surface water courses, but for this report, a uniform distribution has been assumed. The benefit of this return water to the endangered fish is limited at the upstream end of the Reach because, in theory, the downstream end of the Reach might have the estimated flow of water, but the upstream end would not have any of the returns. 1 17 1