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<br />~, <br />J <br />The No Name diversions have been designed at an average gradient of 1%. <br />The drainage area to No Name Diversion No. 1 is about 250 acres, while the drain- <br />age area to No. 2 is approximately 360 acres. These two temporary diversion <br />ditches are designed Eor [he 2-yr/24-hr peak discharge. The SCS (1977) manual, <br />Peak Flows in Colorado, was used to estimate the discharges. A runoff of 0.02 <br />inches was computed for the 2-yr/24-hr rainfall of 1.2 inches. These values were <br />used to compute 2-yr/24-hr peak discharges of 2.0 and 2.5 cfs for Diversions No. <br />1 and 2, respectively. Figure 4.8-2 shows a typical design of a cross-section <br />for the No name diversions with conveyance characteristics for the larger design <br />Elow for Diversion No. 2. A v-notch channel is proposed for the No Name diver- <br />sions. Other diversions not specifically addressed in this section are designed <br />according to the criteria discussed in Appendix T. Map M51 shows the approximate <br />locations of diversion ditches. The design criteria described in Appendix T will <br />be applied to all diversion ditches on areas where topsoil has not been salvaged <br />or has been replaced. For other temporary diversion ditches, such as in No Name <br />and Johnson Gulch, ditches will be adequate to carry the flow from a 2-yr/24-hr <br />event without overtopping. In such instances, erosion within the diversion ditch <br />is irrelevant because the site will be recontoured and topsoil replaced after the <br />life of the diversion. Further, the Elow is directed to sediment control dame. <br />Table 4.8-2a shows diversion ditches located on areas where topsoil has not been <br />salvaged and where the ditch gradient exceeds 1X. The Table shows that all such <br />ditches should be stable given the area draining to them. Diversion ditches will <br />be inspected annually following spring runoff and upgraded or maintained as <br />needed. The location of future temporary diversion ditches may vary but they <br />will be constructed per this section and Appendix T. <br />Control of surface runoff along roads is presented in Appendix P. The measures <br />discussed in this section and the culverts which were previously presented are <br />used to manage runoff from the mine area. <br />4.8.1.3 Poat-Mine Surface Drainage <br />The poet-mine contours for the Trapper Mine are given on Map M12. These contours <br />are similar to the pre-mine contours. Profiles of Johnson, No Name, Coyote and <br />Buzzard Gulches are presented on Map M14. The ends of each profile are shown on <br />Map M12 for location. Drainage densities following mining will be approximately <br />the same as before mining. A discussion of criteria to be followed for drainage <br />reconstruction is found in Section 3.5.3. <br />G~~~l <br />~~`"~~.r <br />4-179 ~ a ~, ~ ti <br />