Laserfiche WebLink
• 4. CULVERT DESIGNS <br />Culverts have been designed using the corrugated metal type, with a Manning's n of 0.024, slopes of <br />1.5% and peak flows of either 10, 25 or 100 year return intervals, depending upon the life of the <br />structure. Standard Federal Highway Administration techniques were used to size the culverts in all <br />locations. Culverts mitered to conform to the slope was used with a tCe of 0.70, although culverts <br />projecting from fill forthe HW/D ratios used here also produce almost the same results.The data on the <br />following pages shows the designs for 18", 24", 36" and 42" CMP's. Along the BB Road detour, 13" x <br />17" CMP's were used as drainage culverts for the road. These do not have any significant drainage <br />basins since Ditch C1 parallels the road on the south side and captures any significant runoff that would <br />normally drain to the road. For this reason, the capacity of these culverts far exceeds any peak flows <br />that could occur in the minor basins and no designs are shown for these culverts (Culverts 119 through <br />128}. <br />The allowed height of water above each culvert is shown on each of the following charts (from FHA), <br />which are used in determining the headwater to diameter ratio (HW/D} and consequently, the capacity <br />• of the culvert. <br />Many culverts have the same basin designs as ditches described earlier. If this is the case, no new <br />design is shown, the table simply refers to that ditch design. <br />Given the above parameters, the following pages show that the capacities of the culverts are as follows: <br />18" 9.5 cfs <br />24" 18.4 cfs <br />30" 30.0 cfs <br />36" 47.0 cfs <br />42" 70.0 cfs <br />48" 82.0 cfs <br />• REVISED MARCH2O06 Attachment 2.05.3(3)-1-58 <br />