Laserfiche WebLink
velocities. These velocities assume the typical silty loam soil conditions on site. If better <br /> conditions exist, the velocities will be allowed to increase without lining. If worse <br /> conditions exist, lining may be needed for lower velocities. <br /> b. Freeboard will be a minimum of 0.3 feet.Protection will be provided for transition of flows <br /> and for critical areas such as swales and curves when excessive velocities are anticipated. <br /> c. Excess excavated material not necessary for diversion channel geometry or regrading of <br /> the channel will be disposed of in accordance with 4.09. <br /> d. Topsoil will be handled in compliance with 4.06. <br /> e. Many of the ditches, culverts and diversions will be temporary. For these structures, peak <br /> flows will be designed for a minimum 10-year, 24-hour storm event of 2.0 inches. <br /> However, some of the ditches, culverts and diversions will be permanent. These structures <br /> have been designed using a 100-year, 24-hour storm event of 3.0 inches. These designs <br /> also satisfy Montrose County regulations. <br /> As shown on Map 2.05.3(3)-1, the permit area contains many collection ditches and culverts, <br /> which are labeled as either temporary or permanent. Many of the culverts are needed to convey <br /> drainage from disturbed areas under roads to the downstream collection 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 or SEDCAD, the time of <br /> concentration was 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 or SEDCAD using the SCS graphical method. <br /> 5. Using the maximum velocities stated earlier, ditch slopes, depth and bottom width geometry <br /> 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. In order to standardize culverts, a few culvert sizes were selected for all situations <br /> although, in some cases, the culvert is over designed. <br /> Section 2.05.3(3) Page 5 July 2020 (TR-99) <br />