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• <br />Volume II - Appendix M <br />Calculation Rational and Results Summary <br />Silt Fence Design <br />Office Area, Construction Material Stockpile & Topsoil Stockpile <br />Rational: <br />Calculated using SEDCADTm 4 for Windows <br />Areas, slopes and flow paths obtained from Figure 2.2-3 Surface Water Controls <br />Systems. <br />The soil type in the study area is Glendive sandy loam, B -soil group. <br />The following CN was used in the calculations: <br />80 - B soil group, sage -grass with poor cover. <br />Table 2-2d Runoff curve numbers for and and semiarid rangelands <br />Other curve numbers considered were, from Table 2-2c - Runoff curve number for other <br />agricultural lands - Farmsteads -Buildings, lanes, driveways, and surrounding lots which <br />would have a curve number of 74 for a B soil group and 82 for a C soil group. Also <br />considered was roads (dirt) with which would have a curve number of 82 with a B soil <br />group. <br />10 year 24 hour storm event of 1.7" used in calculations to be conservative. <br />Results: <br />Area <br />Peak Flow (cfs) <br />Length of Silt Fence <br />Office Area <br />0.35 <br />16 -feet <br />Construction Material <br />0.14 <br />14 -feet <br />Topsoil Stockpile <br />0.18 <br />16 -feet <br />Triangular ditch design is based on the peak flow of 0.35 cfs at the office complex and it <br />will be applied to all areas. Applying a 2% slope and the 0.35 cfs flow will generate a <br />conservative flow depth. Page M-4xxiii presents the required flow depth of 0.6 -feet which <br />includes 0.3 -feet freeboard. <br />The SEDCAD calc <br />prepared by me dt <br />correct to the best <br />TR -11 <br />presented on pages M-2 through M-4xxiii were <br />y 2002, and the information presented is true and <br />U-0 V James E. St�vr, P. E. Date <br />'AMistered Pr�cc sional Engineer <br />te.of ral'afo No. 19230 <br />IkyjW <br />1/02 <br />