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ACCESS ROAD DRAINAGE DITCH AND CULVERT DESIGN <br />Peabody Energy Twentymile Coal Company (TCC) proposes to construct approximately <br />7,125 feet of access road from an existing road to the new Fish Creek bleeder shaft <br />facility within the Twentymile Coal-Foidel Creek Mine located in Routt County, <br />Colorado. The purpose of this analysis is to model the access road hydrology to <br />determine the sizing of up-gradient runoff drainage ditches along the cut slope of the <br />road, and to determine the number, sizes and locations of road culverts required to <br />intercept drainage ditch flows. The hydrologic and hydraulic modeling was conducted <br />using SEDCAD*" 4 (Build Date 2000.09.07). Watershed soil and cover information were <br />taken from site photos and a soil investigation report (Habitat Management, Inc. October, <br />2003. Fish Creek Shaft & Access Road Soil Investigation, Routt County, Colorado, <br />Twentymile Coal Company Permit #82056). Information on the material that would be <br />exposed in the road cut drainage ditches was taken from exploratory test-hole data from <br />10 different holes drilled along the proposed centerline of the access road alignment <br />(Northwest Colorado Consultants, Inc. December 23, 2003. Geotechnical/Pavement <br />Design Investigation, Proposed Intake and Bleeder Shaft Pads and Access Roads, <br />Twentymile Coal-Foidel Creek Mine, Routt County, Colorado). The access road, <br />watershed, drainage ditch and culvert locations are shown on Figure 1. Supporting <br />SEDCAD"' 4 modeling results (including input data and final reports) are attached. A <br />typical road drainage ditch design is provided on Figure 2. Six (6) culverts are required <br />to remove the flow from runoff ditches to limit runoff velocities in the ditches to less than <br />• or equal to 3.75 feet per second (fps). This will ensure that the ditches remain stable with <br />no channel scour or degradation during the peak flow event. Although modeling results <br />indicate that small culverts (less than 12 inches in diameter) will adequately pass the <br />flow, it is recommended that culverts with a minimum diameter of 18 inches be used so <br />that culverts remain operational should debris deposition or icing occur. Following is the <br />summary of road drainage ditch and culvert design parameters and results: <br />Road Drainage Ditch and Culvert Design Parameters and Results <br />Road Drainage Ditch 1 <br />Design Parameters: <br />Precipitation: <br />Use 10-year, 24-hour storm precipitation depth = 1.8 in <br />Land Use: <br />Undistwbed area = 43.73 ac with CN = 63 (Sagebrush - Hyd. Soil Gp. C) <br />Road surface (gravel) = 0.95 ac with CN = 89 <br />Maximum road grade = 8.4 <br />Ditch length = 1,656 feet <br />Ditch design =triangular ditch with 3:1 side slopes (see Figure 2) <br />Ditch surface material is alluvial silts colloidal <br />Limiting ditch velocity = 3.75 fps <br />Results: <br />Peak flow = 0.88 cfs <br />Peak velocity = 3.73 fps <br />• <br /> <br />