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to the extent possible, using the best technology currently available. Appropriate sediment <br />control measures for these diversions may include, but not be limited to, maintenance of <br />appropriate gradients, channel lining, revegetation, roughness structures, and detention basins. <br />No diversion will be located so as to increase the potential for landslides. When no longer <br />needed, each temporary diversion will be removed and the affected land regraded, topsoiled, and <br />revegetated in accordance with 4.06, 4.14, and 4.15. If the temporary diversion was for an <br />ephemeral stream, the channel will be reestablished to functionally blend with the undisturbed <br />drainage above and below the area to be reclaimed. Diversion design will incorporate the <br />following: <br />a. Most ditches will not need to be lined; however, any stretch of collection ditch <br />which has a velocity above 5.5 feet per second will be lined. Channel linings, <br />including channel riprap, will be designed using standard engineering practices to <br />pass safely the design velocities. These velocities assume the typical silty loam <br />soil conditions on site. If better conditions exist, the velocities will be allowed to <br />increase without lining. If worse conditions exist, lining may be needed for lower <br />velocities. <br />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. Many of the ditches, culverts and diversions will be temporary. For these <br />structures, peak flows will be designed for a minimum 10 -year, 24-hour storm <br />event of 2.0 inches. However, some of the ditches, culverts and diversions will be <br />permanent. These structures have been designed using a 100 -year, 24-hour storm <br />event of 3.0 inches. These designs 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. Desiins for All Ditches in the Permit Area <br />Designs for all ditches were accomplished in the following steps: <br />Section 2.05.3(3) Page 3 April 2017 (MR -104) <br />