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<br />. <br /> <br />. <br /> <br />The GCDEIS and Record of Decision (ROD) include a provision for BHBFs. In the <br />GCDEIS, such flows were to be considered in low reservoir storage years, thus <br />avoiding the need to bypass the power generators, while rejuvenating sand bars and <br />fisheries habitats; however, the requirement for a low reservoir condition was altered in <br />the ROD so that BHBFs were to occur in high reservoir storage years using releases in <br />excess of powerplant capacity required for dam safety purposes. Even though a BHBF <br />test was done in 1996 and both hydrologic, cultural and natural resource criteria were <br />considered before the test flow, neither the EIS or ROD discussed specific hydrologic or <br />natural and cultural resources criteria that should be considered prior to initiating future <br />BHBFs, Details as to magnitude, duration and timing of BHBFs was left to the Adaptive <br />Management Program. <br /> <br />We do know that the 1996 BHBF, which happened in late March, early April, had little <br />detrimental impact on cultural and natural resources. For 1998, and beyond, improved <br />knowledge of other resources, as well as seasonal changes in the relative importance <br />of the resources, is expected to provide important information about the preferred <br />conduct, timing and duration of BHBFs. A rigorous resource evaluation effort has been <br />undertaken by GCMRC to evaluate impacts of a BHBF at various times of the year on <br />Colorado River ecosystem resources, and the draft resource matrix was presented to <br />the TWG on March 18, 1998. <br /> <br />Although the 1996 BHBF test provided experimental evidence that high flows can be <br />used to achieve some sediment management objectives (Grand Canyon Monitoring c= <br />and Research Center 1997), Water Year 1996 was marked byexce . nail low runoff. <:: <br />The BHBF(s) proposed in 1998 will be used to test assumptions about the use and <br />efficacy of high flows, during conditions of high runoff or inflows, to conserve sediment <br />and reinvigorate ecosystem geomorphology, biological and cultural (archeological and <br />traditional land use) resources, and ecosystem processes, Data collected during the <br />test flow will validate existing hypotheses regarding flow effects on sediment, natural <br />and cultural resource management <br /> <br />DESCRIPTION OF THE BEACH/HABITAT BUILDING FLOW(S) <br /> <br />Hydrograph(s) <br /> <br />The proposed 1998 BHBF hydrograph(s) consist of: <br /> <br />(1) a 3-day constant flow at current release levels prior to the BHBF for photo <br />documentation of pre-existing resource conditions; <br /> <br />(2) discharge increased at an upramping rate of 4,000 cfs/hr until a flow of 45,000 <br />cfs is achieved; <br /> <br />(3) an essentially constant flow of 45,000 cfs for 2-4 days, with flow changes less <br />than +/- 1000 cfs per day, followed by <br /> <br />1998 GCD Beach/Habitat Building Flow 5 <br /> <br />Biological Assessment <br />