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<br />001739 <br /> <br />16 <br /> <br />since 1990, despite bar restoration gains achieved by the Beach/Habitat-Building Flow test of <br />1996, and peak power-plant test flows released in November 1997, and May and September <br />2000. Although high-elevation sand bars (above 25,000 cfs) below river mile 61 (Grand <br />Canyon) appear to be in somewhat better condition in 2000 versus 1990, than bars in Marble <br />Canyon, deposits within the actively fluctuating zone continue to show decline throughout the <br />ecosystem. The sand-bar time series (1990 through 2002) suggests that the long-term fate of <br />beaches in the upper, critical reaches of the ecosystem will likely be in continued decline under <br />current ROD operations. Beach data collected in fall 2003, show decline in bar conditions at <br />many sites within the first 100 miles below the dam. The most probable reason for the <br />continuing decline of sand bars appears to be related to depletion of the ecosystem's sediment <br />supply. This trend might be reversed if new fine-sediment inputs from tributaries can be <br />managed more strategically using combinations of power-plant operations and BHBF's <br />following tributary floods. Declining beach trends correlate with the findings of the sediment <br />mass-balance project that indicate that new sand inputs from tributaries are transported <br />downstream relatively quickly rather than being retained throughout the river channel and <br />periodically re-deposited on diminishing bars. <br /> <br />Experimental Flows Update - Fine Sediment Testing in 2004 <br /> <br />Experimental fluctuating flows from 5,000 to 20,000 cfs were conducted in January- <br />March 2003 and 2004. These flows are designed to disadvantage non-native fish in the Glen <br />Canyon reach, but also have an effect on fine sediment transport. Because of the non-linear <br />nature of the relation between sediment-transport and water discharge, higher peak fluctuations <br />tend to transport much more sediment. Analysis of sediment export using rating curves indicates <br />that the 5,000 to 20,000 kcfs fluctuations export 147 - 241 % more fine sediment than Modified <br />Low Fluctuations Flows (MLFF) for a 700,000 acre-feet release month. The high export rate of <br />sediment during these experimental fluctuations is also apparent in the mass-balance plot <br />presented in the previous section (Figure 1.2). <br />Further experimental flows were conducted in November 2004, in response to medium <br />Paria River inputs during September, October, and November. Between July 1 and November <br />11,2004, fine sediment monitoring indicated that between 760,000 and 1,260,000 metric tons of <br />sand had accumulated in Marble Canyon, leading managers to initiate a high-flow test in an <br /> <br />GCMRC FY2006 Annual Work Plan (Draft February 15,2005) <br />