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APPENDIX 12-9 Culvert and Ditch Design Introduction A meeting was held in the field between the Colorado Division of Minerals and Geology (CMDG) and Hayden Gulch Terminal, Inc. (HGTI) personnel ae part of assigning the Loadout facility permit to HGTI. It was agreed at this meeting that existing (installed during the construction oP the Loadout facility in 1980) hydrologic structures required designs. It mss further agreed that those designs would be limited to hydrologic structures within the immediate facilities area (i.e., crusher, conveyor, tipple, etc.) and not extend the entire length of the railroad track. Although numerous culverts extended beneath the railroad embankment, these were constructed (in 1980) for flood control and not to route runoff through the transportation network or to sedimentation ponds. However, two of the existing railroad ditches (Ditches 7 and 8) were included in the design process. She existing culverts and ditches have been in place for a number of years (since the facility was built in 1960). This design effort is, therefore, a verification that these structures will continue to function properly. Existing ditch shapes and sizes were derived from aerial photography, surveying and topographic maps. This information was used in the SE DCAD+ computer analysis. Although ditch shapes may not be consistent throughout the entire length, the cross-sectional area is more than adequate due to the largely insignificant drainage areas. Design Considerations Most design information is found in the computer analysis outputs. All ditches and culverts were designed to safely pass surface runoff from the 10- year, 24-hour precipitation event. Only two different curve number (CN) values were"used: - • Rangeland: CN = 89 • Dirt Roads: CN = 89 \J Areas, slopes and land use categories are as stated. ~/ TR-06 12-4.1 Revised 11/09