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~'j. ~"'~ ,'.; J..:.......:). Affected Environrnent & Consequences 3-21 Table 3-14. Anticipated Channel Width Changes, Alternative E-3 't,=0.03 't, = 0.04 Wm=35 Average Adjusted Adjusted Adjusted Reach End current average Increase, average Increase, average Increase, Station width, ft width, ft ft width, ft ft width, ft ft I 143600 72 83 11 72 0 87 15 2 135392 82 101 19 82 0 83 1 3 128615 78 118 40 78 0 84 6 4 120075 54 103 49 57 3 88 34 5 113160 99 120 21 99 0 99 0 6 100360 59 93 34 59 0 88 29 7 89597 55 76 21 55 0 89 34 8 80565 60 67 7 60 0 91 31 9 66242 57 54 0 57 0 94 37 10 53204 58 123 65 66 8 86 28 11 46355 55 99 44 55 0 89 34 12 32835 62 91 29 62 0 88 26 13 22480 62 95 33 62 0 87 25 14 7116 73 87 14 73 0 82 9 Length-weighted average 92 26 67 1 89 23 Note: Reach locations shown in Figures 3-1 and 3-2, The Sponsors used an alternative approach to confirm the results of the analysis. The alternati ve approach assumes that alluvial channels in similar geomorphic settings tend to develop similar ratios of width to depth (WID) at bankfull stages. Using published data for similar rivers as well as information gathered from study of the Uncompahgre River between the South Canal and Montrose, the Sponsor estimated that the Uncompahgre below the Project tailrace would adjust itself to attain a WID ratio of 35. Results of this analysis are shown in Tables 3-12 through 3-14, Generally, channel width estimates using WID of 35 are between the two estimates using the critical particle size methodology. Mussetter Engineering (MEI) believed that an appropriate single-point estirnate for widening would be the lesser of WID = 35 or'tc = 0.03 for each reach. Applying this algorithm to values in the above tables leads to average widening is thus 16 feet for the 750 cfs alternation, 19 feet for the 850 cfs, and 25 feet for the 950 cfs. Applying MEI's estimates to each reach in the affected 27-mile stretch of the Uncompahgre River indicates that (for the 950-cfs alternative), a total of 83 acres of the current floodplain will be slowly converted to channel bottom. This figure reduces to 67 acres for Alternative E-2, and 53 acres for Alternative E-3. A substantial portion of this ground is currently wetlands. Impacts to these areas are discussed in section 3.10. The balance is un vegetated sand and gravel bars, waste ground or non-wetland vegetation. Effects on these latter areas, as well as landowners in general, are discussed in section 3.12. AS Lateral Hydropower Project July 2000 ">'" ,<".-.:. - ".- ~'-'