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The following is an outline of the general design procedures used in the design of culverts: <br />1. Identify the need for a structure from topographic maps, and a visit to the site; <br />2. Determine the size and hydrology of the watershed in question; <br />3. Perform SEDCAD, or other acceptable software, computer run to determine the <br />peak runoff from a 10 -year, 24 -hour precipitation event; <br />4. Using SEDCAD, or other acceptable software, computer run to determine the <br />proper size of culvert to handle the peak runoff from a 10 -year, 24 hour <br />precipitation event. SEDCAD design runs can be found in Appendix 2.05.3(3) -1 <br />Other applicable methods of culvert design include the use of charts developed by the Federal <br />Highway Administration, published in Hydrologic Engineering Circular HEC -5 (FHA, 1980), <br />and Hydrologic Design Series HDS -3 (FHA, 1980). <br />Charts published in HEC -10 (FHA, 1978) are also used; however, exit velocities must then be <br />determined by other methods. Headwater conditions are typically examined by using HEC -5 <br />inlet control nomograph. To be conservative and to allow for adequate freeboard, WFC usually <br />uses "projecting" conditions. <br />As virtually all culverts have free outfalls, inlet control assumptions can be verified by the "Pipe <br />Flow Charts" in HDS -3. If flow in the culvert has a free surface, entrance control exists and exit <br />velocity can be approximated by using the greater of normal or critical velocity determined by <br />the "Pipe Flow Charts" in HDS -3. <br />Maintenance Haul roads will be inspected on a daily work basis at the NHN Mine. If, upon <br />inspection, it is determined that repairs are needed, appropriate repairs such as, but not limited to, <br />grading, filling of potholes, replacement of the road surfaces, revegetation of side slopes and <br />watering for dust control, will be conducted as necessary. Magnesium Chloride solution may be <br />utilized to control fugitive dust. The solution of Magnesium Chloride will be applied by a <br />commercial company specializing in this product and will be dispensed from a truck with <br />approximate 16 foot spray bars. One -two applications are anticipated per year. <br />Restoration Unless WFC requests retention of haul roads for postmining land use and the <br />DRMS approves such request, immediately after the road is no longer needed for operations, <br />reclamation, or monitoring: <br />a. The road will be closed to vehicular traffic; <br />b. The natural- drainage patterns will be restored; <br />C. All culverts will be removed; <br />d. Roadbeds will be ripped, plowed and scarified; <br />Section 2.05.3(3) Page 8 October 2013 (TR -05) <br />E: \New Horizon \DRMS \NHN Permit \04 Technical Revisions TR \TR -05 \Documents from Cason \2.05.3(3) Mine Facilities_TR- 05.docx <br />