Laserfiche WebLink
<br />M'i'l ~~5 <br />l..;.'.)... -.jl.. <br />Affected Environment & Consequences <br /> <br />3- 14 <br /> <br />but is not carrying enough material to build a new bank on the opposite side. Nearly <br />37,000 feet of the river's banks between the proposed tailrace and Delta have already <br />been protected with large sandstone boulders as riprap. Riprap levees have been built on <br />the upstream approaches to bridges to direct flood waters and at some bends, gravel and <br />riprap levees have been constructed to protect adjacent property. Anchored trees and old <br />car bodies have also been used as bank protection in some reaches. <br /> <br />An important finding of the Sponsors' studies of the Uncompahgre River is that the <br />planform of the river channel is highly dependent upon large, relatively infrequent floods. <br />In truly meandering streams the constant pressure of normal flows and frequent but small <br />floods that cause meander cutoffs and other channel adjustments. On the Uncompahgre <br />River, the episodic floods do most of this work. <br /> <br />During periods between high magnitude and long duration, morphogenetically <br />significant flows, a measure of sinuosity develops as a result of lateral erosion. <br />However, when the relatively infrequent large floods occur, bends of almost any <br />radius of curvature cutoff and the channel sinuosity is significantly reduced. In <br />contrast to meandering channels, this mode of channel adjustment ensures that <br />there is a relatively frequent rework of floodplain sediments (Mussetter <br />Engineering, Inc, 1995) <br /> <br />3.4.2 Impacts of Alternatives - Gunnison River <br /> <br />3.4.2.1 Alternative A (No Action) <br /> <br />Without development, the Gunnison River between the North Fork confluence and Delta <br />would be expected to become more narrow and stable due to the effects of existing <br />upstream water storage projects. Changes caused by the Aspinall Unit on the Gunnison <br />River upstream from the North Fork would continue. As Aspinall Unit operations change <br />to increase spring flows, slowing of this process would occur. Major high water events <br />would continue to be less frequent than under natural conditions, but would continue to <br />be the major factor in channel maintenance. <br /> <br />3.4.2.2 Development Alternatives <br /> <br />With development, reduced flows would increase exposure of the riverbed between the <br />Tunnel and the Uncompahgre River confluence; however, the growth of riparian <br />vegetation is not expected to be significant. Principal project-related flow reductions <br />would occur in the winter when vegetation is dormant. The infrequent high spring flows <br />would continue to control the long-term conditions of the channel. Vegetation that <br />invades the channel would be scoured away during floods. Floods on the Gunnison River <br />would be largely unaffected by development. More extended periods of low flow with <br />the project (see Table 3-9) would allow more short-term accumulation of sediment in the <br />river channel. After high flow periods, the river would appear the same as without <br />development. Alternatives E-2 and E-3 could have slightly different effect than the <br />previously approved Alternative E-!. Because each of these altematives has a lower <br /> <br />AS Lateral Hydropower Project <br /> <br />July 2000 <br /> <br />~ - 'i':';"; _.,,_-, ., <br /> <br />