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• For Culverts A through F, Tables 1 and 2 provide a listing of the relative percentage of various <br />vegetative communities and associated drainage areas for each culvert. These vegetative <br />communities are shown on Sheet 2 of Map 25E. As noted in Table 2, most of the culverts also <br />have some contribution from direct runoff from the road surface as well. <br />Two SEDCAD analyses are attached. These are both based on a 10 year, 24 hour design event. <br />By inspection, it can been seen that the largest runoff volumes from these twenty small <br />watersheds would be expected to occur at culverts D and N, as these have the largest drainage <br />area and somewhat higher curve numbers. As shown of the attached SEDCAD analyses, the D <br />culvert installation shows that a 10 inch culvert is suggested, while the N installation <br />recommends a 24 inch culvert. All other culvert installations would be expected to predict <br />similar or smaller culvert installations. As a conservative design element, all culverts A through <br />T will be 36 inches in diameter. This size will ensure better results should future cleaning or <br />maintenance be required. <br />All 36 inch culverts shall be galvanized steel with 2 2/3" x % " corrugations and have a <br />galvanized thickness of 0.079 inches (14 gage). <br />Culvert installation lengths will vary as shown on the plans but typically range from 165 feet to <br />335 feet. Invert and outlet locations and elevations shall be as staked in the field by the field <br />engineer but in all cases the installed slope and minimum cover requirements described below <br />shall be followed. <br />All culverts shall have riprap erosion protection at the outlet points. All culverts shall be <br />installed at a minimum barrel slope of 1.5 percent. Minimum cover over the top of all pipes shall <br />be at least 4.0 feet. <br />• <br />Exh. 24 -1 -2 Revision Date: 03/25/10 <br />Revision No.: PR -03 <br />