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<br />n 0 15 3 9 Alternatives. Including Proposed Action <br /> <br />2-19 <br /> <br />. river channelization <br />. anchored trees and brush <br />. channel drop structures <br />. rock gabions along banks <br />. fences <br />. streambank vegetation <br />. hard points <br />. revetment <br /> <br />The two methods selected for use in the updated stabilization program were hard points <br />and riprap revetment. Steambank vegetation, which was proposed in the PElS, was <br />heavily criticized in the Department of the Army Section permit process. Based on more <br />detailed analysis, the Sponsors have opted against its use. Hard points can much better <br />accomplish the stabilization purpose, and do so at minimal environmental cost. <br /> <br />Rock hard points, constructed of Dakota Sandstone, are the preferred method for areas <br />where there is ample room on the opposite bank for channel adjustment and overall flood <br />passage. The hard points would keep flows away from eroding banks. Figure 2-7 shows <br />plan and section views of representative hard points. <br /> <br />Where channel width or risk to nearby infrastructure does not allow for hard points, full <br />riprap revetment would be utilized. Vegetation would be encouraged to grow through the <br />rock. This would be done by incorporating a mixture of topsoil and seeds with the rock <br />during riprap placement. Also, in locations where mature cottonwoods are within the <br />bank area to be protected, stones would be worked between those trees to the extent <br />possible. Locally available Dakota Sandstone would be used for the revetments, as for <br />the hard points. Figure 2-8 is a section view of the bank riprap. <br /> <br />The overall effect of the stabilization program would be to stop erosion of the protected <br />banks, yet generally allow the river to widen as necessary in the other direction. In <br />between stabilization areas, the ri ver would remain similar to its current state, and would <br />be free to widen and meander as necessary to achieve its own stability. Chapter 3 of the <br />SEIR provides a detailed discussion of this process. Stabilization design would ensure <br />that flood passage is not limited. Since proposed protection measures typically would be <br />limited to the geomorphic terraces, the river would largely be free to adjust and evolve on <br />its own, within the broader meander zone defined by the terrace margins. (This <br />movement would also occur under the No Action alternative.) Occasionally, however, <br />protection would have to be placed in the flood plain rather than on the terraces. This <br />would be the case where infrastructure (such as diversion dams and bridge approaches) is <br />located away from the high terraces and the river must be kept in place. <br /> <br />AS Lateral Hydropower Project <br /> <br />July 2000 <br /> <br />. <br /> <br />,J <br /> <br />~". >".,4... :->.'- <br />