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I I I I I I I I I I I I I I I I I I I SECTION 1 INTRODUCTION The purpose of this report is to determine the feasibility of diverting water under existing water rights to storage in Chatfield Reservoir which has been made available from the reallocation of storage from flood control to conservation purposes. This work is a supplement to the U.S. Army Corps of Engineers' (Corps) Contract for the Chatfield Storage Reallocation Study ("Study"), Littleton, Colorado. The primary purpose of this work is to perform the tasks described in the Storage Use Pattern tasks of the Work Plan, which states: For each target pool elevation to be evaluated. water use patterns will be developed, including realistic patterns of storage and release. These patterns will be used in various hydrologic modeling scenarios. The storage patterns will reflect storage opportunities under both junior and senior water rights. The release patterns will reflect the potential use of storage considering water supplies for municipal water supply and other decreed purposes. Potential use patterns will consider the conjunctive use of surface and ground water, augmentation supplies, and present carryover storage capacity. Opportunity for maintaining or enhancing recreation and environment values within urban reaches of the South Platte River and at Chatfield and Cheny Creek Reservoirs will also be considered. (Colorado Department of Natural Resources, Colorado Water Conservation Board, December 2001, see Appendix A herein). The tasks described above were accomplished by first developing the target amounts ofreservoir capacity to be analyzed for reallocation from flood control space to additional conservation storage space. Next, an inventory was taken of all of the decrees and applications for decrees currently associated with storage in Chatfield Reservoir to identify the water rights available for storage in the reallocated space. Based on these available water rights, potential diversion to storage in Chatfield Reservoir was estimated. Potential users and uses ofthe reallocated space were then identified and target release schedules were developed for modeling purposes. Storage modeling for various use scenarios was performed to develop representative storage use patterns for the target amounts ofreallocated space. Finally, results were compiled and are presented in this report. It is important to note that the scope of this investigation did not include determining the actual allocation of increased storage in Chatfield Reservoir. An allocation procedure will be developed by the CWCB after further investigations are completed. P:\Data\GEN\CWCB\ChatfieJd\Report 12 .02\RevisedChatReportl 03\Report2~03 .doc 6