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The monthly consumptive use credits from the changed water rights in the Upper South Platte <br />River basin above Spinney Mtn Reservoir and in the Tarryall River Basin are typically diverted <br />at either the Aurora Intake for direct delivery to meet demands or to storage in Spinney Mtn <br />Reservoir (for later release and use). Aurora's changed water rights in the Upper South Platte <br />and Tarryall River Basins should be represented at the administration gages shown in Table 4. <br />The flow rates for each changed water right are provided in Appendix A-1 for the Upper South <br />Platte water rights and Appendix A-2 for the Tarryall Basin water rights. The flow rates maybe <br />divided into a consumptive use (CU) component that is available for consumptive use by Aurora, <br />a delayed return flow component (DRF) that should be diverted and held for possible subsequent <br />release to the river (usually during the winter), and an instantaneous return flow (IRF) <br />component that is to be bypassed through the gage. The total demand of a water right imposed at <br />the gage would be the sum of the flow rate components and if available flows are less than the <br />sum of components, the water right is reduced. <br />In general, the decreed monthly delayed return flows are stored in a delayed return flow account <br />in Spinney Mountain Reservoir and released during the winter during times with a downstream <br />call on the river. The pattern of release of delayed return flows is typically established as a <br />pattern of monthly percents in each change decree. Rather than attempt to model delayed return <br />flow releases for separate changed water rights, we recommend for SPDSS that a general release <br />pattern (developed from Aurora modeling) such as in Table 11 be applied to the sum of <br />calculated delayed return flows for a season. Any water remaining in the delayed return flow <br />account at the end of the winter is typically made available to meet potable demands. <br />Table 11 <br />Delayed Return Flow Generalized Release Pattern <br />Au Se Oct Nov Dec Jan Feb Mar A r <br />21% 16% 12% 13% 11% 9% 9% 8% 1% <br />Monthly instantaneous return flows were decreed for some changed water rights in the Tarryall <br />Basin to reflect that a portion of the agricultural return flows came back during the irrigation <br />season and was available to downstream water rights. <br />Instantaneous return flows for many of the changed water rights above Spinney Mtn Reservoir <br />were not specifically decreed for each water right but instead considered through agreements to <br />maintain baseflows below Spinney Mtn Reservoir. However, due to the complexity of these <br />agreements we recommend that these baseflow agreements not be modeled. <br />To consider the various stipulated transfers of yield of South Park water rights to other cities or <br />entities (i.e., Englewood and FRICO), we suggest that Aurora's South Park consumptive yield be <br />reduced by about 400 ac-ft in average or wet years and 70 ac-ft in a dry year. Such water <br />removed from Aurora's consumptive use yield should be a release to the river for the benefit of <br />Englewood and FRICO. <br />It is recommended that effluent exchanges listed in Table 7 be included in the SPDSS model for <br />replacement of out of priority diversions at Aurora Intake or the Cherry Creek Wellfield or <br />exchanged to Spinney Mtn Reservoir. <br />City of Aurora Operating Memorandum 21 of 29 <br />