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minute period. Therefore, the flood would have been produced by <br /> storm having a recurrence interval of something greater than 100 <br /> years according to this method. <br /> t ' Figure 3 shows the 25-year and 50-year peak discharges versus <br /> ! <br /> drainage areas computed by the SCS method for the Road Systems Area <br /> and the Rational Method for the Plant Preparation Area. The scatter <br /> of values obtained using the SCS method is due to the variation of <br /> 1 soil conditions in the drainage areas. The comparative values <br /> obtained by the CWCB method for the Road Systems Area and the <br /> observed July 24, 1977 flood discharge are also shown on this graph. <br /> is <br /> i , <br /> Culvert Installations. The existing drainage facilities for the Road <br /> Systems Area consist of culverts at the locations shown on Plate I <br /> 4! ' and road drain ditches along the uphill sides of the roads. The <br /> t <br /> culverts convey the runoff from the drainage sub-basins intercepted by <br /> the roads to the downhill side of the roads. The existing culverts <br /> are circular corrugated metal pipes (CMP) of the diameters shown in <br /> Column 9 of Table 2. The culvert installations conform to the <br /> applicable specifications of the Colorado Department of Highways (9) . <br /> �s The slopes of the culverts and their .outfall channels are suffi- <br /> ciently steep so that the culverts will all operate under inlet <br /> control. In this situation, the amount of flow a culvert will carry <br /> is dependent on the condition of the culvert entrance and the depth <br /> ! 43 <br />