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<br />000340 <br /> <br />Draft - Do Not Cite <br /> <br />16 <br /> <br />August 2003 <br /> <br />Table 2. FWS Flow Recommendations for the Gunnison River near <br />Grand Junction, Colorado. <br /> <br /> Flow Target and Dmation a <br /> DayslY ear ~ Half- DayslY ear ~ <br /> Hydrologic Expected Bankfull Bankfull Instantaneous Peak <br /> Category Occmrence (8,070 cfs) (14,350 cfs) Flow (cfs) <br />Wet 10% 60 - 100 15 - 25 l5,000-23,000c <br />Moderately Wet 20% 40 - 60 10 - 20 l4,350-l6,OOOc <br />Average Wet 20% 20-25 2-3 ~14,350d <br />Average Dry 20% 10-15 0 ~ 8,070d <br />Moderately Dry 20% 0-10 0 ~2,600e <br />Dry 10% 0 0 90D-4,OOOf <br />Long Term Weighted Mean b 20 - 32 4-7 <br /> <br />a This table represents one possible way of..achiev!!tg the long-term weighted mean. Lower value in each range is <br />for mamtenance, higher value in each range is for improvement. <br /> <br />b Weighted values equal days/year x expected occurrence (the sum of all weighted mean values equals the long- <br />term weighted mean in dayslyear). <br /> <br />c Instantaneous eak flows within this range have occurred in these h drolo . cal cate ones since Blue Mesa Dam <br />. These observed instantaneous peaks are desired in the future in coniunction with meetirul the flow <br />~. No.soecific peak flow is recommended to ensure continued variability among y~ <br /> <br />d mected minimum peak flow when recommenda1i~l}~ lire T.lIw.t; actual peak may exceed this value, ensuring <br />continued vanabiilty among years. <br /> <br />e Instantaneous eak flow that has occurred since Blue Mesa Dam has closed. Peak flows e t e or <br />e~ed this level in years when ow JS not reac <br />f Range of peak flows within this categOIY that hll)'e OC'.cUTTM sinC',P. Rlne ~,,,. n..... -V"'" c.1ml~. Lowest number <br />reflects base flow. Peak flows are expected to continue to occur within this range; no snecificilow within fh\s <br />r~~~ recomlU,ended, ensuring -yariabilitv amon~ y~_ <br />Source: McAda (2003) <br /> <br />recommendations of Pitlick et al. (1999) who identified half-bankfull flows as approximately <br />equivalent to the flow required to produce initial motion of sediment particles on the river bed, <br />and bankfull flows as those flows required to produce significant motion of sediment particles on <br />the river bed. Flows above the significant motion threshold resulted in motion of most larger <br />gravels and cobbles of the river bed and were considered important for periodically rejuvenating <br />habitats. In. addition, to the half-bankfull and bankfull recommendations, the FWS identified <br />instantaneous peak flows that should be achieved in each of the hydrologic categories. <br />