Proper engineering calculations shall be used to determine pipe, culvert, trench, orifice and inlet control devices sizing.
(a) Mannings equation may be used to size pipes, culverts and trenches, as follows:
Q = (1.49/n) AR 2/3 S1/2
Where: Q = discharge (cfs).
n = Manning's roughness coefficient
A = Cross-sectional area (ft2)
R = the hydraulic radius
Note: R = wetted perimeter/cross-sectional area
S = Slope of the channel or pipe (ft/ft)
(b) The size of storm lines shall be determined on the basis of the hydraulic gradient to provide adequate capacity of the computed run-off, using n=0.015 for vitrified clay and concrete pipe, bituminous paved corrugated metal pipe plan 0.024, paved invert 0.020, asphalt spun 0.013, and brick sewers and n = 0.013 for monolithic concrete sewers. In no case shall the size of the lines be less than twelve inches in diameter.
(c) Minimum depth for storm sewers shall be planned to provide clearance for all utilities and to permit inlet leads to be laid on not less than one percent slope.
(d) All on-site storm sewers shall be designed on a ten-year storm curve with the exception of the retention/detention outlet.
(Ord. 4360. Passed 4-18-94.)