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. . (4) a decrease in discharge to the same constant flow level as that used prior to the BHBF, with the following downramping criteria: (a) a down-ramping rate of 1,500 cfs/hr between flows of 45,000 cfs and 35,000 cfs, (b) a down-ramping rate of 1,000 cfs/hr between flows of 35,000 cfs and 20,000 cfs, and @ a down-ramping rate of 500 cfs/hr between 20,000 cfs and the constant flow level used for the pre-BHBF assessment (if the constant pre-BHBF flow was less than 20,000 cfs); and (5) a 3-day constant flow following the BHBF at the same flow used in (1) above, for photo documentation of post-BHBF resource conditions. The duration of the BHBF will be determined in real time by sediment and drift researchers in Marble Canyon, at the mainstream gage near the mouth of the Little Colorado River (Mile 61), and near Phantom Ranch. These teams will employ Secchi depth and/or drift measurements to detect when sediment and organic transport decreases, indicating when sand and food base depletion occurs. The staggered down- ramp more closely mimics the reduction of flows after a natural flood, ROD flows will resume on the fourth day following the BHBF. The Timing of BHBFs The following BHBF triggering criteria were recently developed and recommended by the AMWG (Report of the Spike Flow Subgroup, October 27, 1997). Considered with effects on cultural and natural resources, an assessment will be made of the appropriateness of a BHBFs to occur sometime between 1 May and 31 July 1998, Hydrologic Criteria . (1) maintain the current January 1 target storage content of 21.5 million acre- feet (MAF) (2) maintain the current July 31 target storage content of 23.8 MAF (3)(1) if January-July monthly releases cannot be maintained at relatively uniform levels (3)(2) if January monthly releases cannot be constrained to 1.2 MAF (4)(a) if January-July inflow to Lake Powell exceeds 13 MAF (about 140% of normal) (4)(b) any time an increasing forecast requires a powerplant monthly release greater than 1,5 MAF, or requires use of the 0,5 MAF storage buffer. 1-- . . . . . For the 1996 BHBF test, considerations which led to selection of the March/April time frame included having flows that took place: 1998 GCD Beach/Habitat Building Flow 6 Biological Assessment