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<br />. <br /> <br />B) for native fish <br />. improve survival and recruitment ofHBC by reducing competition and <br />predation from non-native fish (primarily rainbow trout)! <br />. improve and maintain habitat for young native fish <br /> <br />WY 2002 - 2003 Hvdrolo2V Assumption: These experimental flow recommendations <br />assume that WY 2002 and perhaps WY 2003 will be relatively low runoff years with low <br />antecedent reservoir storage in Lake Powell. Thus these recommendations are based on <br />an 8.23 maf water year scenario. As noted above, GCMRC is also developing, with the <br />experimental flows ad hoc group, a longer term set of flow recommendations in view of <br />the need for repeated and long term experimentation as part of adaptive management and <br />in recognition that basin hydrology over the long term will be variable. . <br /> <br />Workin!! Hvpotheses: <br /> <br />--- <br /> <br />. Sediment- Monitoring data indicate that tributary inputs of sand do not <br />accumulate within the river challllel over multi-year periods as predicted by <br />the final EIS, and that such inputs are transported out of the CRE at a <br />relatively fast rate under most ROD operations. On the h~'l;'l ofreoll1t. ITom. <br />the summllJ' 2000 flow experiment. as well as historical sediment-transport <br />aata, new inputs of sand should be retained more effectively within main <br />channel storage sites during extended penoel. of dam releases at or below <br />about 1 0,000 c~. If such operations promote retention of sand (and finer <br />sediment as well), then implementation of a Beach/Habitat-Building Flow <br />-- n . -fotlowing-suchperiods ~huuld greatlyincrewse [he effec[iveIle~s ofsudl---- <br />controlled floods in restoring and maintaining terrestrial sand bars and related <br />resources. More efficient retention of fine sediment and silt prior to <br />controlled floods shall result in more rapid rates of sand bar deposition, as ~ 7 <br />well as sand bars with finer grain-size distributions. Finer-textured sand bars__ . . <br />ma be1ess ron id erosion followin bar building. Enhanced <br />onservation of tributary sediment inputs in the channel should result in <br />elevated suspended-sediment concentrations during BHBF's, leading to rapid <br />depositional rates during sand-bar building. Elevated rates of sand-bar <br />deposition should reduce the required duration for BHBF's, and hence will <br />limit spill volumes. . <br /> <br />. Native Fish-The LCR population ofHBC has not demonstrated a positive <br />response to the mainstem flow regimes under ROD operations. Sediment loss <br />has continued in the CRE under ROD operations as described above. Within <br />the ROD, there is a need to implement experimental flows, which may <br />conserve sediment and improve survival and recruitment ofHBC. The LCR <br />population of HBC is comprised of fish resident in the LCR and in the <br />mainstem near the LCR confluence. Therefore flows, which affect changes in <br /> <br />. <br /> <br />1 It is anticipated that reducing the population numbers ofRET will increase the average size offish in the <br />Glen Canyon reach and may lead to improvement in the overall quality of the Lees Ferry trout fishery. <br /> <br />Version 1.2 - 2/15/02 <br /> <br />2 <br />