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juniper grass cover of 55 percent density is considered <br />• conservative for the drainage basin. A listing of the soil series <br />and groups is shown on Table 1, Soil Series and Groups. <br />b. How was the equivalent peak flow of 600 cfs/in determined? <br />Response: The equivalent peak flow 600 of cfs is estimated from <br />Figure S-lA of Procedures for Determining Peak Flows in Colorado, <br />Soil Conservation Service, U.S. Department of Agriculture, March <br />1980. <br />The estimate of peak flow from Figure S-lA was determined by <br />extending the log chart to include approximately 1,600 acres. <br />c. Based upon the size of riprap designed for this channel, the <br />roughness coefficient is too small. <br />• Response: Evaluation of the riprap size nd corresponding roughness <br />coefficient has been completed. From page 190 of Applied Hydrology <br />and Sedimentology for Disturbed Areas by Barfield, Warner & Haan, <br />1981, Manning's n for D50 riprap of 1.7 feet to 2.5 feet ranges <br />from 0.043 to 0.046 respectively. Given the riprap size of 5.33 <br />feet and 1.58 feet, Manning's n of 0.045 is more applicable than <br />0.025. In the steep portion of the channel, using a Manning's n of <br />0.045 with 0.3 feet of freeboard, the channel has a capacity of <br />approximately 839 cfs. A freeboard of 1.5 feet provides adequate <br />capacity to pass the design flow. <br />d. Please indicate the reference used in the riprap design <br />method. It is not clear what size riprap will be ultimately <br />utilized, how this riprap will be placed, and what protective <br />measures will be utilized on the side slopes and at bends in <br />the channel. In addition, the Division feels that the channel <br />slope of Segment 1 could be lessened by re-designing the <br />• channel to maintain a consistent slope for its entire length. <br />Peerless should investigate this passibility. <br />-2- <br />