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COAL <br />8 COMPANY G� <br />4 <br />T%.AX-OPLS PRODUCTIOT&E�£ <br />Colo wyo's Response: <br />When setting up a SEDCAD model, the first demarcation is usually the <br />drainage boundary. Next, if particular watershed has areas of constant runoff <br />characteristics (eg, a single reclamation status condition and therefore a single <br />CN), then that will likely become a candidate for a sub - watershed. It may be <br />one of several sub - watersheds tributary to a SEDCAD "structure'; or it may, be <br />the only sub - watershed tributary to that structure. The reason for this is that <br />the collection point (the SEDCAD "structure') is selected as the point at which <br />flow can arrive subject to the restriction that the flow path must generally <br />cross the contours at a perpendicular angle. In fact, that flow path is used by <br />SEDCAD to determine the time of concentration for that sub - watershed. <br />In the case of SubwatersbedL, it is entirely, reclaimed, all at 3-f years (CN =74). <br />Crossing the contours at right angles takes the flow down to Structure 39 as <br />overland flow, almost flowing parallel to Reach 2 of prospect Ditch, but <br />several hundred feet to the north. <br />Watersheds M and K are limited to the other side of the channel, but not <br />because they are different CN's; they are the same CN =74 for 3+ years of <br />vegetation growth as the land on Subwatershed L on the north side ofProspect <br />Ditch. However, looking at the contours it is clear that Sub - watershed K <br />drains directly into Pond PDI (perpendicular lines to the contours), while <br />Sub - watershed M must drop into the channel (Str. # 30) somewhere around <br />Station 5, again constrained by the requirement to cross contours at a right <br />angle as close as practicable. <br />It is recognized there is some judgment involved in building the model. But in <br />this case it would be unlikely than much of Subwatershed s runoff would <br />report to Str. 30 (channel from Pond PD] to Pond PD2) because it would have <br />to flow parallel to the contours to get th the channel, which violates the <br />physics). In fact, some small portion of the runoff form Sub - watershed L <br />probably does find its way into Reach 2, but the model is constrained by the <br />physics, which are controlled by the contours. <br />Current Division comments: Some of the sub - watershed areas are odd shapes <br />and do not, in fact, follow the restriction that flow paths must cross the <br />contours at a perpendicular angle. For example, for sub - watershed L the <br />eastern portion of this area appears to not drain to Structure 39, unless there is <br />a contour ditch that causes flows to deviate from the basic flow pattern. <br />Another example is sub - watershed K; the eastern portion of this area does not <br />appear to drain to Pond PD1, per the topography. Please indicate if contour <br />ditches are the reason for these odd shapes or if there is another explanation. <br />A mining property of Western Fuels- Colorado, A Limited Liability Company <br />