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<br />002435 <br /> <br />on beaches away from future releases, but also coarsens the main channel bed which reduces <br />future sediment transport. Some sediment experts believe that there is sufficient regeneration of <br />main channel sediment supplies to allow BHBF's in all years that such events would be allowed by <br />the 1996 agreement, even every year if possible. Longer duration spills may have different effects <br />than the short duration BHBF's, so additional sediment transport modeling would help clarify the <br />allowable frequency of such spills. <br /> <br />The positive value of the spillway gate extensions <br /> <br />Although the extensions are not required to limit spillway use to the I in 100 year return period <br />cited in the GCDEIS, some limited value can be gained from their installation during years in <br />which peak releases would be less than 45,000 cfs. In these cases, if the total bypass volume was <br />expected to be 750,000 acre-feet or less, then the entire expected bypasses could be stored behind <br />the extensions and released later in the summer. This might produce some environmental benefits <br />by not releasing greater than 30,000 cfs if such releases would cause ecological harm. <br /> <br />However, it would also carry the dam safety risks associated with purposefully storing more <br />water in the reservoir than was assumed during the design of the spillways. If an extremely rare <br />high inflow event occurred, it could conceivably overtop the dam, even with full use of the <br />spillways. <br /> <br />It appears from this discussion, that only inflow years with a,return period of about I in 100 years <br />would force the use of the spillways and release more than 45,000 cfs. Reclamation believes that <br />current operating practices under the Annual Operating Plan would initiate high powerplant <br />releases and bypasses early enough as required to safely operate the dam, thus meeting the intent <br />of the GCDEIS provision without requiring either the additional storage buffer or the spillway <br />gate extensions. <br /> <br />Date <br /> <br />Eluid Martinez <br />Commissioner, Bureau of Reclamation <br />