(A) The minimum pipe diameter will be 12 and made of reinforced concrete or other material if approved by the Director of Public Services. Drains specifically intended for roof drainage, sump dis- charge, and footings may be of smaller size. Minimum and maximum grades allowable for any pipe are as follows:
Pipe Diameter
|
Minimum Pipe Grades
|
Maximum Pipe Grades
|
Pipe Diameter
|
Minimum Pipe Grades
|
Maximum Pipe Grades
|
12 | 0.32 | 4.88 |
15 | 0.24 | 3.62 |
18 | 0.20 | 2.84 |
21 | 0.16 | 2.30 |
24 | 0.14 | 1.94 |
30 | 0.10 | 1.44 |
36 | 0.08 | 1.12 |
42 | 0.06 | 0.92 |
(B) Catch basins with a 2 sump will be used for all storm inlets. The minimum internal diameter catch basin will be 4, have mastic joints or O-ring joints, have a bituminous sealant between casting and pave- ment, and be built to meet ASTM C 478. Manholes or catch basins will be set at every intersection of pipe larger than 8, change in grade, change in direction, or at a maximum distance of 350. Proprietors shall contact the Public Services Department to obtain a list of current castings to be used.
(C) Storm conveyance networks will be designed to provide for the ten-year peak discharge as calculated by § 55.35 of this chapter. The method necessary to analyze pipe or channel hydraulics will be based on Manning's Equation as given below:
Q = A*1.486/n*(R)^(2/3)*(S)^1/2
where:
Q = Cumulative flow from ten-year storm event
A = Cross sectional area of pipe or channel
R = Hydraulic radius
S = Slope of hydraulic grade line based on ten-year storm event
n = Manning's coefficient taken from table below
Typical Manning's Coefficients
Concrete pavement 0.011
Concrete pipe 0.012
Cast iron 0.012
Vitrified clay 0.014
Channel lined with asphalt 0.015
Earth, clean 0.018
Gravel 0.023
Corrugated metal 0.024
Earth with grass and weeds 0.030
Earth with dense weeds and brush 0.080
(D) Storm conveyance channels will be designed to ensure that the elevation of the hydraulic grade line will not permit uncontrolled flooding. If surcharging of manholes will be required to meet the anticipated ten-year storm event, the hydraulic line must be included in the profile view of submitted plans. Calculations supporting drainage requirements for the Director of Public Service's review will also be necessary.
(Ord. 420-4-97, passed 4-21-97)