Colorado - Upper CO River Endangered Fish Recovery Program_Statement of Work

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largest investment of time of senior staff on the study team. As the primary objective of the study concerns water supply availability, it is anticipated that significant time is needed in the evaluation of water supply for each of the alternatives developed. The availability of water must be understood during a wide variety of hydrologic conditions and under multiple operating scenarios. This work will be performed by Grand River Consultants and, augmented where appropriate and most efficient, by the staff of Denver Water and Northern Conservancy District. 4.6.1 Structural Alternatives Water availability investigations for structural alternatives will utilize existing information to the extent possible. However, it is anticipated that a stand-alone spreadsheet model will be developed or updated for each structural component in the Phase 2 study. These models will evaluate long-term water availability and reservoir operation on a daily basis, over an extended period of time that includes significant drought years. The models will consider water physically and legally available to each element. Daily legal water availability on the Colorado mainstem (Shoshone and Cameo calls) will be estimated from Division Engineer records and from simulation results of existing river basin models such as Denver Water's PACSIM model. This information will be input into the stand alone models for each structural element. Water availability on side tributaries (such as Roan Creek or Yank Creek) will be determined from applicable diversion records and stream gages, and from Water Commissioner input. For Wolcott Reservoir and Wolford Mountain Reservoir, existing simulation models previously developed by Grand River will be updated and utilized. For Sulphur Gulch Reservoir, the two Roan Creek Reservoirs, Buzzard Creek Reservoir, and Yank Creek, the development of new simulation tools may be required. Again, existing information will be utilized to the extent possible in this effort. Water availability associated with the 15 Mile Reach Pumpback is not a critical issue. We estimate that water is always available for this alternative and that no significant modeling efforts will be required. Water yield estimates associated with the Orchard Mesa Irrigation District (OMID) improvements will be based upon water savings documented in a recent CalPoly study. This study is currently being updated. The updated study results are anticipated to be available this summer, and will be used in the Phase 2 study. The OMID alternative alone cannot supply the entire 10825 Recovery Program obligation, particularly in dry years. The OMID alternative will only provide 10825 Water to the extent that Green Mountain Reservoir releases to the OMID system are reduced, and that a concurrent surplus in the Green Mountain HUP occurs. Since the OMID water supply alternative is supplemental in nature, it may not be necessary to fully model the daily operation of this scenario. However, the evaluation of the OMID alternative will require an integrated evaluation of the operation of Green Mountain Reservoir at some level of detail. Information regarding the frequency (types of years) and amount of potential surplus water in the Green Mountain HUP Pool will be required. We are hopeful that the integrated Green 10825 Phase 2 Scope of Work Revised May 25, 2007 per CWCB request Page � 2