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<br />"1";~~.,f! <br />Pi"l~,~",'.i...."J <br />\(t.t,~_>-f <br />Affected Environrnent & Consequences <br /> <br />3- t3 <br /> <br />3.4.1 <br /> <br />Existing Conditions <br /> <br />3.4.1.1 <br /> <br />Gunnison River <br /> <br />The Gunnison River is deeply incised between Crystal Dam and the confluence of the <br />North Fork. In less erosive sections, the Gunnison River Canyon is extremely narrow at <br />river level, with a width as much as 200 feet where not restricted by the canyon walls. <br />Cobbles ranging from 2.5 inches to 10 inches in diameter constitute the riverbed. Little <br />sediment is transported through the river between Crystal Reservoir and the Smith Fork <br />due to upstream reservoirs. In the canyon reaches below the North Fork, the river ranges <br />from 120 to more than 400 feet wide. In the broad valley downstream from the canyon, <br />the average width is about 350 feet but varies between 200 and 1,000 feet. <br /> <br />Since the PElS and Record of Decision (ROD) were published, additional studies have <br />been published that discuss the geomorphic processes in the Gunnison Gorge (Elliot and <br />Parker. 1997), These studies concluded that the regulating effects of Aspinall to <br />downstream hydrographs are changing the Gorge. Flood peaks no longer clear the Gorge <br />as much as in the past, and the increased low to moderate flows between flood events are <br />depositing more fine-grained sediments. <br /> <br />3.4.1.2 Uncompahgre River <br /> <br />The Uncompahgre River can be classified as a wandering gravel bed river. Within the <br />27-mile reach affected by the proposed Project, the channel slope ranges from about 17 to <br />over 38 feet per mile. The planform2 varies from braided to meandering to straight and <br />channelized. Human influence is extensive and includes major amounts of streambank <br />protection, instream gravel pits and mines, bridges, diversion dams, and channelized <br />reaches. <br /> <br />There are three primary geomorphic surfaces that affect the river. The valley walls, <br />which include outcroppings of Mancos shale, are the highest and typically bracket an area <br />one-half to one mile wide through which the river winds its course. This valley is most <br />evident when viewing the river from the air. The next level down is the terrace. This <br />feature is generally 7 to 10 feet above the river bottom. Virtually all land on the terrace is <br />irrigated. Below the terrace is the floodplain, which is characterized by banks 3 to 4 feet <br />high. This ground can be severely dissected and eroded and as a result is generally not <br />cropped. Owners and tenants use the land within the floodplain for calving or occasional <br />pasture. The floodplain also contains wetlands and waste ground. Sand bars occasionally <br />form in the river; these features are less than 3 feet in height (Sigma, 1995b). <br /> <br />The river channel varies in width from 60 feet to as much as 450 feet. Below the Selig <br />Canal, the Uncompahgre River bed is well-armored with cobbles. In some sections of the <br />river, both banks are over 6 feet high, while in others the river is eroding the high bank <br /> <br />2 <br /> <br />Planfarm is the shape of an object, in this case the Uncompahgre River, as seen from above. <br /> <br />AS Lateral Hydropower Project <br /> <br />July 2000 <br /> <br />'c," <br /> <br />.li.... ,:;;:_,,~,;- i. <br /> <br />k,~, <br />...~lii <br />