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• <br />Volume II -Appendix M <br />Rational: <br />Calculation Rational and Results Summary <br />Silt Fence Design <br />Office Area, Construction Material Stockpile & Topsoil Stockpile <br />Calculated using SEDCADT"' 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 arid 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 Peak Flow (cfs) Length of Silt Fence <br />Office Area ~ 0.35 16-feet <br />Construction Material 0.14 14-feet <br />Topsoil Stockpile 0.18 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 di <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 />a~o' James E. St~v~r, P.E. Date <br />'AC~Pagistered Pr~c~~csional Engineer <br />°.~kRte.of ~aal'~afo No. 19230 <br />M-2 <br />1 /02 <br />