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3338 Wood River, However, most of this water is available as excess run-off only during June and July, We have assumed that, on average, an additional 225 cfs could be diverted from the Upper Greybull River to provide water to an enlarged Upper Sunshine Reservoir, Rawhide Creek Reservoir, or Spring Creek Reservoir, If a closer evaluation of diurnal river fluctuations in this area indicates that this is not possible, these three projects would not meet the yield criteria associated with our coarse screening described in Section 4, These projects do not provide the river re-regulating benefits of our coarse screening criteria, The most significant cost item associated with the Blackstone Dam Project is the diversion tunnel in the left abutment. A more detailed assessment of technical feasibility for this concept could significantly increase or decrease the costs associated with this primary alternative. A conservative cost estimate has been provided to date, If lower unit costs for tunneling can be provided by more detailed investigations, significant cost savings could be realized over the Lower Roach Gulch Project. 5.3.2 Secondary Alternatives Enlargement of Upper Sunshine Dam would require that outlet tuonels be constructed in the foundation or abutments of both Upper and Lower Sunshine Dams, A geotechnical assessment of the overall feasibility of this concept would be critical to any further serious considerations, In addition, this alternative would require that each reservoir be drained for at least one irrigation season to construct these features, The environmental and economic impacts associated with draining these reservoirs are expected to be significant and were not included in our initial screening, An important item that was not included in our cost estimate must be considered when evaluating the Shoshone River Transbasin diversion, There is a provision in the WWDC contract with the USBR that allows the WWDC to defer payment for the next 10 years on the soon-to-be- completed Buffalo Bill Reservoir enlargement, Deferred payment may only take place if the State does not use the yield from the project during that IO-year period, The penalty for use of the yield before that time would be approximately $2 million which would add significant cost to the already expensive Shoshone River Transbasin alternative, The key element that most conservation projects cannot provide is timely irrigation deliveries, High value crops such as sugar beets and dry beans must have a constant, reliable supply of water to survive, This can best be provided by storing excess river flows for supplemental use when the flow is not available in the river, The impact of timely water deliveries was not included as part of our initial screening criteria and could be significant for any future conservation project. In addition, lower basin storage should be considered as a very important aspect of water conservation because it provides the ability to capture and reuse existing river flows which are currently wasted during spring run-off and during the winter return flow months, Two key challenges are associated with the groundwater development alternative, These include reduced return flows associated with the interconnection of groundwater in the 940'7''.REPORT\TEX1".vt 5-4