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<br />Fisheries
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<br />A cold-water fishery extends from South Fork to Monte Vista, below which a transition OCcurs to a warm-
<br />water fishery. The reach from South Fork to the Farmer's Union Canal is a Gold Medal trout fishery (rainbow
<br />and brown trout), as designated by the Colorado Division of Wildlife. Although habitat is good in Ihis reach, it
<br />could be improved by protection the riparian zone, creating more riffle-pool complexes, and preventing bank
<br />erosion and flooding. The highest potential for habitat improvement exists between South Fork and Del Norte,
<br />although SOme improvements could also be made between Del Norte and Monte Vista.
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<br />Riparian Vegetation
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<br />Key vegetation communities in the study area consist of narrowleaf cottonwood and willow. Cottonwood is
<br />the dominant vegetation upstream of Monte Vista, and willow is the dominant vegetation downstream of
<br />Alamosa. Between Monte Vista and Alamosa both species are prevalent
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<br />Health of the cottonwood community varies along the corridor from excellent to fair. Most of the cottonwood
<br />forest is comprised of a mature age class; regeneration rates are not keeping up with aging of older trees.
<br />Factors adversely affecting cottonwood communities are lack of periodic flooding to promote natural
<br />regeneration, encroachment by agricultural and urban land uses, and, more recently, beaver. Willow
<br />communities appear to be generally healthy, with most adverse impacts being associated with land clearing
<br />and channel maintenance.
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<br />The warm-water fishery below Monte Vista supports a variety of non-native fish, including northern pike,
<br />largemouth bass, yellow perch, black bUllhead, channel catfish, green sunfish, mosquitofish, carp and trench.
<br />The native Rio Grande sucker is no longer found in the channel (only in major tributaries), but the river does
<br />support native populations of brook stickleback, longoose dace, Rio Grande chub, fathead minnow, red shiner,
<br />and white sucker. Lack of /low due to Upstream diversions is the primary habitat threat for these species.
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<br />Review of historical aerial photographs documented a considerable loss of riparian vegetation extent and
<br />density between 1941 and present. This was due to agricultural clearing, urban developmenl, and channel
<br />migration. Photographs also showed that in areas of channel or floodplain Scour, natural regeneration
<br />processes were sUccessful.
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<br />Riparian Habitat Restoration ISsues
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<br />Fallen cottonwood trees, either due to decadence, stream bank erosion or beaver activity, create serious debris
<br />obstructions at bridges and irrigation diversion dams that result in increased /looding problems in the Rio
<br />Grande corridor.
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<br />The following issues were considered important to the riparian habitat component of the RGHRP projecl
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<br />and urban
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<br />Protection of the riparian corridor against further encroachment by agricultural
<br />land Uses
<br />Grazing management to protect the health of the existing riparian vegetation
<br />Allowable periodic flooding of cottonwood and willow communities to promote natural
<br />regeneration
<br />Management of the irrigation diversion system to prevent excessive dewatering of the
<br />stream and remove as many barriers to fish passage as possible
<br />Management of beaver populations
<br />Measures to reduce debris problems associated with fallen cottonwoods during high flows
<br />Enhancement of trout habitat, particularly in the reach from South Fork to Del Norte
<br />POssible protection of southwest willow flycatcher habitat
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<br />Riparian Wildlife
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<br />Wildlife habitat assessments were based on field reconnaissance and analysis of published and anectodal
<br />informalion. Key indicator species were selected to be representative of response of wildlife to habitat
<br />changes. These included: bald eagle, southwestern willow flycatcher, whooping crane, mule deer, beaver,
<br />waterfowl, sandhill crane, heron, shorebirds, raptors, upland gamebirds, songbirds, tiger salamander,
<br />Woodhouse's toad, and northern leopard frog. These indicator species have a broad variety of habitat
<br />preferences, all of which can be found in the study area in varying degrees. In general it was found that areas
<br />with high quality riparian vegetation communities provided high quality habitat for most of the key indicator
<br />species. Adverse impacts on riparian vegetation have similar impacts on wildlife communities.
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<br />It is important that the Rio Grande corridor provide a diversity of habitats _ e.g., mudflats, ponds, riffles.
<br />cottonWood galleries, willow thickets - to support a diversity of native wildlife. Two of Ihe key indicator
<br />species may receive special consideration in the RGHRP.
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<br />within the study reach was completed. An
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<br />Diversion Structures Analysis
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<br />Several factors Control the effectiveness and stability of each point of diversion and conveyance structure.
<br />These include wasteways, debris problems, sedimentation, river migration and river access. Most of the
<br />d""'~ w;<h;. <h, '''dy ".'" ~." """,,", w;<h _". W"'''w"" =;" ,. '''''''H.g <h, b,'""
<br />of sediment within the canal and allow betler regulation of the diversion by allowing sediment continuity and
<br />by returning a Portion of water and sediment to Ihe river downstream of the diversion structure. Debris
<br />problems, sedimentation, river migration, and river access are factors that address the ability of the structure
<br />to function as designed. SpeCifically, debris problems include downed timber and associated trash;
<br />sedimentation manifests itself as the buildup of sediment within the diversion; river migration addresses river
<br />movement away from and toward the diversion as well as the potential for the river to cut around and bypass
<br />the diversion entirely; and river access is defined as the diversion's ability to divert Water. Each diversion and
<br />the factors which control its effectiveness are discussed in the text. Table ES-3 lists the qualitative rating of
<br />each diversion structure (i.e. good, fair, poor).
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<br />ES-
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<br />ES.3.5
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<br />A qualitative and quantitatIve analysis of the numerous diversions
<br />inventory of diversion structures is provided in Table ES-3.
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<br />Wildlife
<br />POrtions
<br />with an
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<br />The Southwest willow flycatcher is listed as endangered by the U.S. Fish and
<br />Service, and a Recovery Plan is currently being prepared that will probably affect
<br />of the study area. Preferred habitat consists of thickets of willow or other shrubs
<br />overs tory of scattered larger trees adjacent to surface waler or saturated soil.
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<br />and have caused problems by damming
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<br />Beaver returned to the study area in the mid 1980s,
<br />sloughs and oxbows and felling cottonWood trees.
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<br />ES-
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