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Whet.!EtoqI7e,J <br />Associatesw Technical Memorandum <br />meet the requirement of 0.5 -ft minimum freeboard. Several channel segments are rock <br />lined, rather than earthlined, and therefore are more resistant to scour and capable of <br />conveying flow at velocities in excess of 5 ft /sec. A figure has been added from the DDP <br />showing the soil types mapped by the Natural Resources Conservation Service (NRCS). <br />The length of the OPWRD channel has been mapped as rock outcrop, confirming that <br />the existing channel is rock -lined rather than earthen -lined along the OPWRD_Div2 <br />reach. <br />iii. Erosion protection details ... Please see new comments below <br />Cotter response: Erosion protection details have been provided in the engineering <br />drawings in the revised DDP. <br />New Comments: <br />3. Section 4.1 and Figure 10. A peak design flow of 75.94 cfs is diverted from subbasin NG to <br />undefined channel. Please discuss impact of additional 76 cfs from "Pit Diversion East" <br />discharge point to the natural drainage (—I, 200 ft) in basin B4. <br />Cotter response: The Pit Diversion East structure has been in place since <br />approximately 1990. Stormwater runoff from subbasin NG (132.9 acres) enters <br />adjacent subbasin B4 (677.9 acres) and flows northeast and east into the natural <br />ephemeral channel as shown on the satellite image in Figure 1. The channel is routed <br />through a culvert (CV4) under the access road (County Road EE17). The 19.5% <br />increase in area for the entire subbasin would result in double the flow volume at the <br />CV4 location and an overall increase in runoff of approximately 19.5% for the entire <br />B4 subbasin. Montrose County maintains the access road and the culvert, and the <br />access road has remained intact, although routine maintenance is generally required on <br />all roads and culverts. <br />4149A.140207 5 <br />