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I • <br />Minc Wafer Cowol Plm~ <br />to accrue flow time for overland flow and channel flow according to ]and use. Three <br />categories of overland flow were utilized: forest with heavy ground cover (1), short grass <br />pasture (3), and bare ground (5). One category of sheet flow on paved areas and small <br />upland gullies was used (7). Two categories of channel flow were employed: grassed <br />waterways (6) and large gullies, diversions, and low flowing streams (8). these assumptions <br />may be reviewed in the Detailed Subwatersbed Input/output tables. <br />Canopy cover was broken up into several discrete sections. Each of these units were for <br />direct input into the SEDCAD+ model. The units used to best represent the West Elk <br />mine were tall weeds with short grass with 35 - 45 percent cover to an area bulldozed across <br />slope with no ground cover. <br />Pond MB-1 and MB-2R were designed to pass the 100-year 24-hour event through the <br />emergency spillways due to dam height. All other emergency spillways were designed to <br />pass the 25-year, 24-hour event. <br />Numeric Labeling of the Drainage System <br />The mine water control plan is composed of five sepazate retention ponds (Map 54). Ponds <br />;,. are label MB-1 through MB-5. Each pond has its own ditch collection system that collects <br />water from watersheds and transfers the water to the pond. To alleviate confusion of which <br />ditch flows to which ponds, the ditches have been identified to correspond to their respective <br />ponds. For an example, Ditch D2-1 is the first ditch that flows into pond MB-2R. As the <br />last number increases, the ditch is usually farther away from the pond or a tnbutary to a <br />second ditch flowing into the pond. The addition of several ditches to the system has <br />resulted in the use of suffixes (-a, -b, etc.) to maintain the original ordering system. <br />The same type of numbering designation has been assigned to the culverts. An example of <br />the culverts would Cl-4. This culvert carries water that flows into pond MB-1 and is farther <br />away from the pond then Cl-2 or Cl-3. A summary table of culverts and ditches are <br />presentation in Table 44. <br />Discharge <br />• <br />Peak discharge analyses were projected using SEDCAD+ for three design events. The <br />10-yeaz 24-hour event was used to calculate the required storage volume and to verify the <br />primary outlet works. The 25-year 24-hour event was used to determine the minimum size <br />of each emergency spillway for pond MB-3 through MB-6 and the 100-year 24-hour event <br />J <br />6 <br />