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climatic range in the Dolores basin, geomorphic processes in the Dolores River have historically <br />reflected a combination of both snowmelt-driven, montane hydrologic processes and arid, <br />Colorado Plateau processes. Further descriptions of different portions of the Dolores River <br />downstream of McPhee Dam are provided below. <br />McPhee Dam to Bradfield Bridge <br />Under pre-settlement conditions, this 11-mile reach was likely characterized by a channel <br />that meandered along the entire valley bottom and bed morphology characterized by <br />gravelcobble substrates and alternating pool and riffle sequences maintained by frequent (near- <br />annual) pool scour and reworlang of bars during spring high-flow periods. The floodplain <br />flanking the channel likely supported significant riparian habitats of mixed deciduous forest <br />comprised primarily of cottonwood, willow, and box elder (CDOW, 2003). The gradient of this <br />reach is approximately 0.3% (~15 ft/mile), which is lower than the downstream canyon reach. <br />Valley floor width in this reach is 0.25-0.5 pules (CO DNR et al., 1976). Following Anglo- <br />European settlement, much of the floodplain forest was harvested for timber and converted to <br />pasture; these pastures were irrigated by water diversions, and cattle were introduced (CDOW, <br />2003). Despite the negative effects of cattle grazing and diversion of the river's entire flow <br />during lowflow periods on instream habitat conditions in this reach prior to constn~ction of <br />McPhee Dam, high flows continued to perform geomorphic work in this reach in the pre-dam <br />era, maintaining chamlel and floodplain processes and riparian woodlands (Krieghauser and <br />Somers, 2004). Since construction of the dam and reductions in high flows, however, <br />geomorphic processes that support instream and riparian habitats, such as pool scour, bar <br />formation, and floodplain rejuvenation have been largely absent from this reach, resulting in <br />severely limited cover and spawiung habitat and in embedded substrate conditions (CDOW, <br />2003), likely due to a combination of flow modification and historical impacts. In addition, a <br />gravel road constn~cted along this reach has constrained the channel on the east side and limited <br />channel migration. In response to the degraded conditions in this reach, the CDOW has <br />implemented a habitat improvement project intended to establish a river morphology appropriate <br />for the reach's modified flow regime. The project is designed to reduce channel width, restore <br />chamlel sinuosity, increase the potential for overbank flooding, enhance riparian habitat, and <br />improve instream trout habitat, including pool habitat and cover (CDOW 2003). The first phase <br />of this project, implemented in 2003, entailed excavation of pools, construction of rock clusters <br />and other strictures designed to increase cover variability and promote pool scour, and <br />importation of nearly 6000 yds3 of cobble to reduce channel width along a 1500-foot reach of <br />channel in the Lone Dome State Wildlife Area (CDOW 2003). <br />20 <br />