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003129 Page 28 Flow losses from infiltration and evaporation of course occur in all reaches in the Colorado River System. In most reaches, most of the time, the net of flow gains and losses is positive. However, in some of the lower reaches during periods of low flow, the net is negative. The virgin flow data set used in this study represents net losses as a negative flow gain. MODS 1M is not capable of using negative inflows. Thus, it was necessary to modify the program to convert each negative inflow to a demand at the node. This approach has one serious shortcoming--if there is already a demand at the node, the system loss will have the same priority as the demand at the node when in fact the system loss should have the highest priority so that it is satisfied without fail. The nodes where instances of net negative flows occur have been identified (nodes 2, 6, and 28, Table 111-3) and system demands have not been placed on them. At these nodes, demand priority is set to one so that channel losses are satisfied when they occur. Note that Table 111-3 does not include the demands that represent losses. The Gila River enters the Colorado River below Imperial Dam. Although the water resources of the Gila River Basin are fully exploited, there are, from time to time, flows in this tributary which would be credited to deliveries under the Mexican Treaty. These flows are rare and will generally occur during periods of abundant flow when excess flows on the mainstem are sufficient to meet treaty requirements. For these reasons, Gila River flows were not included in this analysis. Return flows from the Well ton-Mohawk Irrigation District flow through Mexico to the Santa Clara Slough. Currently, these flows are not credited to the treaty delivery obligation due to their low quality. Upon completion of desalination plants to upgrade the quality of these waters, they would become