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b. Freeboard will be a minimum of 0.3 feet. Protection will be provided for <br />transition of flows and for critical areas such as swales and curves when excessive <br />velocities are anticipated. <br />c. Excess excavated material not necessary for diversion channel geometry or <br />regrading of the channel will be disposed of in accordance with 4.09. <br />d. Topsoil will be handled in compliance with 4.06. <br />e. 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, CI I, C 12, 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 Carlson Software, 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 Carlson Software 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 />Section 2.05.3(3) Page 3 February 2017 (TR -78) <br />