2019-12-13_REVISION - M1980244 (55)

Home Browse Search

Newmont Goldcorp ■ VLF/OSA Closure Stormwater Analysis NewFields Project No.475.0106.035 November 8,2019 Channel Channel Channel Depth Closure Peak Flow Bottom with ift of Surface Watershed Channel Name (cfs) Width Freeboard 500yr,24hr (ft) (ft) Schist South Schist Island Channel 3 62 0 4 Stack Schist Island Channel 4 106 4 3.5 Northwest 1 VLF2 Channel 5 206 12 3.5 2 VLF2 Channel 4 879 12 5.5 3b, 3c VLF2 Channel 4 879 12 5.5 4b VLF2 Channel 3 26 2 3 VLF2 5b VLF2 Channel 2 17 0 3.5 6b VLF2 Channel 1(13) 37 2 3.5 7b VLF2 Channel 1(13) 37 2 3.5 8 VLF2 Channel 1(A) 139 2 4.5 North1 VLF1 Channel 4 121 2 3.5 North2 VLF1 Channel 3 46 0 3 Northeast VLF1 Channel 5 428 8 5 VLF1 East VLF1 Channel 6 93 0 5.25 Southeast VLF1 Channel 1 325 6 5.5 West VLF1 Channel 2 357 4 5.75 A detailed summary of this analysis can be found in Appendix B. All perimeter channels have side slopes of 2.51-1:1V and were modeled as either triangular or trapezoidal cross sections, with exception of the sections of the channels that require concrete baffles. The proposed channel geometry was determined by HEC-RAS and Flowmaster and the final channel depth included a minimum 1 foot of freeboard. Depending on the length of the channel and the contributing watershed area, certain channels have several different cross sections to allow for the upstream portions to be smaller and require less earthworks and lining materials. The channels will either be unarmored (vegetation only) or armored to prevent erosion. The armored channels will be lined with reinforced turf matting, riprap, grouted riprap, or concrete. The requirement for the more durable armoring is based on the velocity of the flow in the channel. The channel erosion protection materials and design dimensions can be referenced on Drawings 520 and 525 in Appendix C. An overall plan of the proposed routing of surface water can be referenced on Figure 1 and plan and profiles of each channel are presented in Appendix C. Page 4