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0()2557 ".lodeled f~equenc:'- Under m aggressive operating strategy, the modeled frequency of unavoidable spills is 4 years out of the 32 years modeled, However. since Lake Powell has not completely t1lled since 1986 and there have been recent concerns about making such very high releases, Reclamation has moderated the aggressiveness of the monthly release pattern. 1: nder the existing, more moderate strategy, the modeled frequency of such spills is 5 years out of the 32 years modeled. By additionally restricting January releases to 1.2 MAF. this modeled frequency increases to 6 spill years out of the 32 years modeled, We expect that with the implementation ;fthe measures described above. an additional 4 years in the model period would be determined to be BHBF years even though an unavoidable spill did not eventually occur. resulting in a combined total of 10 spill and BHBF years out of32 years modeled, Long Term Frequency The result is that when the reservoir is full, there is a relatively high likelihood (1 year in 3) that a spill or BHBF will occur, On a long term basis, this proposed approach will result in a spill and BHBF frequency of about 1 year in 6, Of course. the appropriateness of this frequency would be dependent on a careful evaluation of all affected resources, a long term sediment balance analysis, and concurrence on the release ofa BHBF in months other than March or April. Of this last contingent. months later than April are the more likely scenario due. to late season forecast increases, but also could occur prior to March if the snowpack and resulting runoff forecast are unusually large. If the above or similar recommendations are adopted, the frequency ofspiIls and BHBF's created by deliberate bypasses of the powerpIant will approximately double, and increase the hydrologic dynamics believed to enhance the Grand Canyon ecosystem. TItis may serve in part to offset the impacts thought to be the result of daily fluctuating flows. As a way to compensate for decreased power generation revenues due to the increased frequency ofpowerplant bypasses. and to evaluate the effects of fluctuating flows in combination with the effects of increased frequency of spills and BHBF's. we recommend that Reclamation and the Western Area Power Administration be instructed to operate the powerplant with the full range of fluctuations now provided for in the GCDEIS Record of Decision. Recommendations for Additional Economic and Environmental Resource Studies Since some have suggested a linkage between BHBF's and fluctuating releases, we recommend that the GCMRC be instructed to develop and initiate a program of research to evaluate the scientific and economic impacts of fluctuating flows within powerplant capacity in conjunction with the increased frequency of spills and BHBF's. There is a als?, a strong.lleed for resource evaluations respecting the proposed increase in spillslBHBF frequency, The resource relationship between BHBF's and high powerplant releases should be thoroughly investigated. Additional discussions should determine if this is 8