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f. All ditches, culverts and diversions will be temporary; therefore peak flows will <br />be designed for the 10 year 24 hour event of 2.0 inches. The exceptions to this are <br />Ditches Cl, C2, C4, C5, CII, C12, C13, C14, C17, C19, C20, C23, C24, and <br />C29, which are permanent. Also, Culverts 117, 119, 120, 121, 122, 123, 124, and <br />129 are permanent and have been designed for the 100 year 24 hour event. These <br />designs also satisfy County regulations. <br />As shown on Map 2.05.3(3)-1, the permit area has been divided into many collection ditch and <br />culvert basins. All ditches, culverts and their respective watershed basins are labeled on the map. <br />Most of the culverts are needed to get disturbed areas under roads to the downstream collection <br />ditch or sediment pond. <br />D. Designs for All Ditches in the Permit Area <br />Designs for all ditches were accomplished in the following steps: <br />1. Using a 3D grid of the watershed, the actual area and average land slope was developed. <br />2. A long flow line was drawn from the top of each watershed to the bottom of the ditch. <br />3. Using the SCS Method provided within SURVCADD, the time of concentration was <br />developed for each watershed. <br />4. Using the Time of Concentration and a worst case curve number, the peak flow was also <br />developed within SURVCADD using the SCS graphical method. <br />5. Using the maximum velocities stated earlier, ditch slopes, depth and bottom width <br />geometry were then calculated for the channels. <br />Designs for all culverts were done in a similar manner except that once the peak flows for the <br />culvert watersheds were calculated, the standard FHA procedures were used to properly size the <br />culvert. For all culverts, a corrugated metal pipe was used with inlet control. In order to <br />standardize culverts, a few culvert sizes were selected for all situations although, in some cases, <br />the culvert is over designed. Although WFC commits to maintaining the culverts in good <br />condition, we only commit to the cross-sectional area needed to pass the design peak flow, not <br />the entire area of the culvert. <br />E. Sedimentation Pond 007 <br />Other ponds design details are discussed in Attachments 2.05.3(3)-4, 2.05.3(3)-5, 2.05.3(3)-6 and <br />2.05.3(3)-11. In accordance with 4.05.2 and the approved NPDES permit, WFC will use Pond <br />Page 2.05.3(3)-4 October 2015 (TR -69) <br />