Laserfiche WebLink
• 55 <br />Also considered in this chapter is design of channels requiring restoration for <br />the post-mining condition and restoration of the Newlin Creek channel through <br />the "Prospecting Pit" area. <br />Several factors must be considered in channel design. The first require- <br />, went is the channel must have adequate capacity to pass the design discharge <br />and provide adequate freeboard. In this case, 0.3 feet of freeboard is required <br />by State regulations. Since the channels are located in movable material, there <br />are several components of the depth in addition to the depth calculated by zigid- <br />bed hydraulics. The two major concerns are additional depth due to aggradation <br />and sand wave passage. A third component of depth is superelevation in bends. <br />This occurs on the outside of bends due to forces created by the change in flow <br />[, direction. <br />The final factor to consider is whether the channels will be stable in <br />f terms of the erosion and sedimentation process. This requires sediment trans- <br />port to be nearly equivalent in all reaches so that neither aggradation nor <br />• degradation are excessive. In addition, flow velocities must be low enough to <br />orevent damage to the side slopes of the channels. <br />6.4.1 Minor Diversion Channels <br />Several minor diversions, both existing and proposed, are used to convey <br />runoff from disturbed and/or revegetated areas into sediment ponds (Hydrology <br />Map 2, Appendix A). These diversions are temporary strvMures draining areas <br />less than one square mile. The required design discharge is based on the tw- <br />year, 24-hour precipitation event. There are four existing and six proposed <br />minor diversions. Of the four existing minor diversions, tvo intercept runoff <br />from the Tipple Area and divert it to Sediment Pond "T"; the other two intercept <br />runoff from the reclaimed area and divert it to Sediment Pond "B". Of the six <br />proposed minor diversions, two are proposed for drainage along the haul road, <br />two are proposed for diverting runoff to Sediment Pond "D" (alternative 2), and <br />one diversion is proposed for each proposed Sediment Pond "E" and "F". <br />The hydraulic conditions for each of the existing and proposed minor di- <br />ve_sio^s were calculated by normal depth using the Manning's equation. The <br />slopes for all the diversions were large enough to allow normal depth to be a <br />. ;c^= 3-^roximation. Generally, the proposed and existing minor diversions only <br />...:in a small portion of the watershed unit within which they are contained. <br />9ecause the areas contributing runoff to the minor diversions are very small <br />