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• For a ground composed of clay or loose sand, velocities of <br />6-fps and up can cause cutting and erosion. Rocky slopes or <br />slopes with trees or dense vegetation will withstand greater <br />velocities with less erosion. <br />The area in the vicinity of Section 16, the upstream end of <br />the fill area, has the greatest velocities in the constriction. <br />Therefore, it will require the protection against erosion. The <br />material in the fill is a mixture of rocky and sandy material. <br />It may need to be reworked so that heavier rocks are protecting <br />the stream banks or riprap may be required, The rocks should <br />have a median size of 12-18 inches. For astable slope, a maximum <br />slope of 2:1 along the bank should be used, See Figure II-A on <br />Page 9 for examples of present stream bank composition. <br />• The east bank of the channel, opposite the fill area, will <br />be experiencing velocities not much greater than tIi.ose naturally <br />occurring within a few hundred feet upstream. Minor. erosion :that <br />may result from this increased velocity will quickly stabilize itself, <br />A natural migration of a stream will change its course and <br />shape over time through a process of erosion and deposition. Even <br />in a stable stream course, isolated spots of erosion will occur. <br />The streambed near Apex Mine #2 is composed mainly of rocks <br />and will not experience any downcutting or erosion due to the <br />increased velocities, other than natural changes. There may be <br />isolated channel erosion near the constriction. Aowever, it is <br />not expected to be widespread due to the type of ground cover <br />. present around the mine site. There are several small trees and <br />medium to dense brush cover that help to stabilize the ground. <br />Examples of the overbank ground cover can be seen in Figure IZ-S <br />on pagn 10.. <br />~~ <br />