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Mr. Michael Cunningham <br />CDRMS <br />April 22, 2014 <br />riprap typically range between 0.035 (stability) and 0.045 (capacity). The Division's erodibility <br />and revetment considerations are as follows: <br />a. In general, earth -lined channels with a flow velocity greater than 5.0 feet per <br />second (fps) will require revetment such as riprap to reduce the potential for <br />scouring. <br />b. Revetment, when required, should be sized for each reach /segment using industry <br />accepted methods. Sizing methodology and calculations should be included in the <br />submittal. The Division can suggest various methods appropriate for different <br />conditions. <br />Response: <br />The Manning's n values have been revised for riprap -lined channels to the values <br />indicated by the CDRMS. 0.035 will be used for stability checks on riprap -lined <br />channels, and 0.045 will be used for capacity checks on riprap -lined channels. Riprap <br />will be installed on all channels with flow velocities greater than 5 fps. Riprap was sized <br />using the FHA's Design of Roadside Channels with Flexible Linings Hydraulic <br />Engineering Circular Number 15, Third Edition, 2005. <br />3. Appendix B, West Diversion, max slope. The maximum slope is identified as 62.5 percent. <br />Even though the peak flow is very low, riprap will not stand at this slope. A 40 percent slope is <br />typically the highest recommended slope from available research and publications. As the <br />topography may make it impractical to flatten the slope to 40 percent, the Division <br />recommends diverting this small flow to the east at the outfall /design point for Basin OS1 <br />towards the east where Basins OS2 and OS3 are diverted. Please provide a revised design <br />for the West Diversion that is on a slope less than or equal to 40 percent or revise the <br />direction of the diversion. <br />Response: <br />Per the Division's recommendation, the flows from Basin OS1 above the property have <br />been directed to Basin OS2. The peak flows in Basin OS2 have been revised to include <br />the additional runoff from OS1. Basin OS1 has been eliminated from the drainage plan. <br />4. Page 6, Second Paragraph: The response indicates the upland diversion "will handle a 200 <br />year, 24 -hr rainfall event ". The precipitation depth (2.47) and statements earlier in the <br />response suggest this should be the 100 -year, 24 -hour event. Please clarify which design <br />storm is intended. <br />Response: <br />The hydraulic analyses have been revised to reflect the proposed linings of the individual <br />channels depending on the proposed linings. All channels with flows greater than 5 feet <br />per second are riprap - lined, and channels with flows less than 5 feet per second are <br />earth - lined. <br />5. Appendix B, South TSF Contact. The hydraulic analyses for this channel indicate the bottom <br />width is five feet. There are no details on Drawing DR -2 with a trapezoidal section. Please <br />revise the analyses to match a proposed channel section or add a trapezoidal section to <br />drawing DR 2. <br />