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<br />approximately 3:00 p,m, on the same day, This flow of31,OOO cfs would be maintained for 48 <br />hours, After the 48 hour period, Reclamation would downramp the release at a rate of 1,500 <br />cfslhour beginning at 3 :00 p,m, until reaching the nonnal point in the release schedule, but not <br />lower than a release rate of 20,000 cfs, The flows would begin as soon as possible (allowing time <br />for mobilization offield crews) after receiving the Final Biological Opinion (BO), provided it <br />biologically supports this sediment conservation management action, Reclamation is currently <br />releasing flows between 17,000 cfs to 23,000 cfs, with upramp and downramp rates within the <br />limits prescribed in the ROD, This generally means that by noon on a given day, releases from <br />Glen Canyon Dam are at 23,000 cfs, <br /> <br />Rational for Conducting the 1997 Fall Test flow in October <br /> <br />Beginning August 10, 1997, ungaged tributaries below Glen Canyon Dam (GCD) have produced <br />significant inputs of fine sediment to the Colorado River ecosystem, These contributions followed <br />a period of very limited sediment influx since the spring 1996 experimental4S,OOO cfs flood, <br />High-constant flows between 21,000 and 27,000 cfs during Water Year 1997 appear to have <br />scoured the remaining volume of channel-stored sand in the system to levels near those that <br />existed after 1986; the end of the last high-flow period. <br /> <br />Preliminary flow/sediment modeling results generated by the U,S, Geological Survey (USGS) for <br />several recent floods on the Paria River indicate that the minimum cumulative volume of sand <br />delivered to Marble Canyon has reached about 1,7 times the mean annual delivery, and that the <br />silt and clay ration has likely exceeded twice the mean annual delivery (based on records between <br />1924-1996), <br /> <br />Results from the 1996 experimental flood indicated that short-duration flood flows from Glen <br />Canyon Dam that coincide with periods of high sediment availability in Marble Canyon may be an <br />effective means of sediment conservation (through rapid deposition of fine sedinient along <br />shorelines and in eddies), Results from the 1996 experiment also suggest that rapid deposition of <br />fine sediment occurred simultaneously with coarsening of sediment on the river bed, Without <br />periodic high flows to drive this transport/deposition sequence it is thought that fine sediment <br />entering the river channel is gradually moved to Lake Mead by typical Record-of-Decislon dam <br />operations (fluctuating, and particularly high-constant flows). <br /> <br />One of the recommended strategies for the removal of jeopardy and recovery of endangered and <br />native fish in Grand Canyon is to mimic, or simulate, a natural hydrograph to the degree possible, <br />The recent heavy rains and high inflow to Lake Powell would have resulted in higher flows <br />through the Grand Canyon, which would have varied in volume and magnitude in accordance <br />with weather events. <br /> <br />The Glen Canyon Dam EIS cited preservation of habitat for endangered fish as one of the reasons <br />it was important to maintain mass balance of sand, which is the intended purpose of this action, <br /> <br />3 <br />