2012-06-20_PERMIT FILE - C2010089A (15)

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The following is an outline of the general design procedures used in the design of culverts: 1. Identify the need for a structure from topographic maps, and a visit to the site; 2. Determine the size and hydrology of the watershed in question; 3. Perform SEDCAD, or other acceptable software, computer run to determine the peak runoff from a 10 -year, 24 -hour precipitation event. 4. Using SEDCAD, or other acceptable software, computer run to determine the proper size of culvert to handle the peak runoff from a 10 -year, 24 hour precipitation event. SEDCAD design runs can be found in Appendix 2.05.3(3) -1 Other applicable methods of culvert design include the use of charts developed by the Federal Highway Administration, published in Hydrologic Engineering Circular HEC -5 (FHA, 1980), and Hydrologic Design Series HDS -3 (FHA, 1980). Charts published in HEC -10 (FHA, 1978) are also used; however, exit velocities must then be determined by other methods. Headwater conditions are typically examined by using HEC -5 inlet control nomograph. To be conservative and to allow for adequate freeboard, WFC usually uses "projecting" conditions. As virtually all culverts have free outfalls, inlet control assumptions can be verified by the "Pipe Flow Charts" in HDS -3. If flow in the culvert has a free surface, entrance control exists, and exit velocity can be approximated by using the greater of normal or critical velocity determined by the "Pipe Flow Charts" in HDS -3. Maintenance. Haul roads will be inspected on a daily work basis at the NHN Mine. If, upon inspection, it is determined that repairs are needed, appropriate repairs such as, but not limited to, grading, filling of potholes, replacement of the road surfaces, revegetation of side slopes and watering for dust control, will be conducted as necessary. Magnesium Chloride solution may be Section 2.05.3(3) Page 9 November 2011