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<br />The Dolores River had the smallest channel. Mean wetted width at the Big Gypsum <br />site was 12 m at 100 cfs and 25 m at 500 cfs. The Big Gypsum slope was 0,15%, <br /> <br />The 2-D modeling analysis simulated very similar habitat conditions for sites with <br />similar channel geomorphology (Anderson and Stewart 2003). Meso habitat compositions <br />based on depth and velocity criteria were very similar at all modeled flows for Lily Park, <br />Clifton and Com Lake, <br /> <br />Site Hydrology <br /> <br />The four rivers for which recent fish population data was available have a wide <br />variety in hydrologic patterns, The current hydrographs for the Yampa River, Colorado <br />River (IS-Mile Reach), Gunnison River and Dolores River ranged from strongly to heavily <br />modified from the native flow conditions, The Yampa experienced the least amount offlow <br />modification for the spring runoff with natural flow reduced by an average of only 6% during <br />the months of April, May and June (Modde et al 1999). In most years, however, Yampa <br />River flows during the irrigation season were typically less than 200 cfs for much of the <br />summer. The Gunnison River was nearly the reverse to the Yampa, Peak flows reduced by <br />least 38% after completion of Blue Mesa Dam (Pitlick et al 1999), but base flows were <br />typically above 600 cfs throughout the year. <br /> <br />The spring runoff flows in Colorado River (Cameo gage) have been reduced by at <br />least 29% (Pitlick et al. 1999). Base flows have increased slightly in the Colorado River, but <br />flows downstream of irrigation canal diversions can be reduced dramatically in some <br />instances (McAda 2003). The Dolores River had both a heavily modified spring hydro graph <br />and historically very low base flows, <br /> <br />Yampa River (Maybell Gage) <br /> <br />Andrews (1980) calculated bankfull flow for the Yampa from the Maybell Gage to be <br />about 9,000 cfs. Peak flows recorded at the Maybell Gage were fairly similar for the years <br />1998, 1999 and 2000, at 10,040 cfs, 9,980 cfs and 9,830 cfs respectively. Peak flows in these <br />three years were near the magnitude of the median peak flow 01'9,980 cfs for the 87-year <br />period of record (Figure 5). Peak flow in 2001 was 7,650 cfs, which was exceeded in 77% <br />of the years during the period of record. The peak flow in 2002 was only 3,420 cfs. and in <br />2003, 12,900 cfs (Figure 5), <br /> <br />In most years flows during August and September were less than 200 cfs, The 87- <br />year median (50% exceedence flow) minimum flow was 117 cfs (Figure 6), Annual <br />minimum flows recorded at the Maybell Gage for 1997, 1998, 1999 were 320 cfs, 115 cfs, <br />166 cfs respectively. In 2000, 2001, 2002 and 2003 the annual minimum flow at the Maybell <br />Gage decreased to 30 cfs, 50 cfs, 1.8 cfs and 43 cfs respectively. The 40-day low-tlow <br />represented a flow typical for a base flow period, The 40-day low-flow from the Maybell <br />Gage for 1997, 1998, 1999,2000,2001,2002 and 2003 were 718 cfs, 290 cfs, 268 cfs, 113 <br />cfs, 110 cfs, 12 cfs and 141 cfs respectively, Peak flow, annual minimum flow and the 40th <br />day low-flow all demonstrated the severity of the 2002 drought event, <br /> <br />8 <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />