(A) Pipe size.
(1) Storm sewer pipes shall be sized to handle the anticipated stormwater run-off flows. Stormwater pipe size shall be sized based on the flow equation below. However, in no case shall the minimum stormwater drainage pipe be 15 inches.
(2) Manning formula. Q= (1.468/n) * A * R2/3 * S1/2. | |
(3) Values of “n.” | |
(a) Plastic | 0.009 |
(b) Concrete | 0.012 |
(c) Corrugated Steel | See Chart C |
(4) Minimum size. | 15 inches |
(5) Minimum cover. | 2 feet (from top of pipe) |
(6) Minimum slope (inlet lead). | 1% |
(7) Minimum mean velocity. | 3.0 fps desired |
(8) Maximum mean velocity. | 10.0 fps |
(9) Maximum manhole spacing. | 400 ft. (36 inches and under) |
(B) Manhole placement.
(1) Intersections, termini of sewers, changes in size and/or slope, changes in alignment (36 inches and under), places where inlet leads are to be connected.
(2) Drop manholes are required at stream entrances for storm sewer outfalls if the difference between stream and pipe inverts is greater than 12 inches. The manhole outlet pipe shall be directed to the flow of stream (not counter to the flow).
(C) Inlet spacing (for each side of street).
(1) Stormwater drainage inlet spacing shall be at all low spots, where the street grade changes to a flatter slope, dead end of descending streets, at P.C. or P.T. of all intersection radius curves where the curb and gutter grade descends toward radius curve (locate on property line extended or at mid-lot). Stormwater inlets shall be located as outlined below:
(a) Flat (0.3% - 1.0%) | 150-200 feet (normal conditions*) |
(b) Normal (1.0% - 5.0%) | 250 feet (normal conditions) |
(c) Steep (5% plus) | 250-300 feet(normal conditions*) |
* Spacing shall be governed by a two inch allowable depth of gutter flow based upon a ten minute time of concentration and a ten year design storm if it would be less than the above spacing. | |
(2) Unless otherwise approved by the City Engineer, catch basins shall be 30 inches in width by 30 inches in length inside to inside measurement. They shall either be precast or built of solid concrete block. The inside edge of the rear wall shall be in line with the back or curb. The foundation shall consist of six inches class concrete on six inches gravel subgrade. Neenah R-3246-AL, "V" grate or approved equal frame and grates shall be used with the curb box set to five inches of opening. All grates shall be bicycle safe. Neenah R-3246-AL, "V" grate or approved equal frame and grates shall be used with the curb box set to five inches of opening shall be used if the curb grade is 2% or greater.
(D) Outlet protection.
(1) < 5 fps | Sodded ditch |
(2) 5 fps to 12 fps | Dump rock |
(3) Over 12 fps | Special outlet protection |
(Ord. - -, passed - -03; Am. Ord. 16-2020, passed 12-7-20)
Editor’s note:
Chart C can be found in Exhibit "A" attached to Ordinance 16-2020.