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Peabody Sage Creek Mine — Drainage and Sediment Control Plan <br />Channel Slope: Channel slope is a sensitive parameter. The steeper the slope grade the <br />lower the allowable velocity. The channel slopes were determined by direct measurement <br />from the mine permit maps. <br />Channel Geometry: Existing channels (constructed prior to 2007, as part of the Seneca II <br />Mine reclamation plan) were generally evaluated assuming a triangular, or V- shaped, <br />configuration, with a 3H:1V side slope. In certain situations, several postmine channel <br />designs incorporated a trapezoidal shaped channel with a bottom width of either three (3) or <br />ten (10) feet and 4H: IV side slopes. <br />Retardance Class: The reclamation seed mixture used in the reclamation plan results in a <br />mixed grass community. Consequently, the vegetation type selected as the model input is <br />mixed grass. <br />The flow resistance varies by grass type and length. Retardance classes have been divided <br />into five (5) classes designated by A, B, C, D, and E. SCS (1979) developed guidance for <br />selection of vegetation Retardance classes and they are outlined in Table 2.05.3 -E2 -8, <br />Guide to Retardance Class Selection. <br />Under short grass conditions, the channel is more prone to being eroded than with tall grass <br />conditions. Consequently, stability is evaluated under short grass conditions. Retardance <br />classes of D and E are typically used for stability analysis of vegetated channels. <br />Tall grass conditions are used to determine channel capacity. The tall grass affords a great <br />deal of resistance to channel flow as a function of stem basal area and by laying over during <br />high flows. The higher the resistance, the higher the elevation of flowing water in the <br />channel. Retardance classes of A through C (especially A and B) are used for capacity <br />analysis. SCCC used Retardance values of Class D for stability and Class B for capacity. <br />TABLE 2.05.3 -E2 -8 <br />Guide to Retardance Class Selection <br />Stand <br />Length of Ve etation in. <br />Retardance Class <br />Good <br />>30 <br />A <br />11 -24 <br />B <br />6 -10 <br />C <br />2 -6 <br />D <br /><2 <br />E <br />Fair <br />>30 <br />B <br />11 -24 <br />C <br />6 -10 <br />D <br />2 -6 <br />D <br /><2 <br />E <br />TR -01 2.05.3 -E2.18 Revised 04/12 <br />4 <br />