1043.14 STORM SEWER SYSTEM DESIGN.
(a) The storm sewer system shall be designed to meet the more restrictive of the following standards:
(1) To collect stormwater at any point where three to five cubic feet per second is accumulated during the design storm; and/or
(2) Inlets/manholes shall not be spaced more than 300 feet apart on pipe sizes up to twenty-four inches in diameter and not more than 400 feet apart on greater sizes.
(b) Inlets, manholes, grates, covers, frames and the like shall conform to the Pennsylvania Department of Transportation Roadway Construction Standards (Publication No. 72) and Form 408 Specifications, and all amendments, revisions or updates thereof.
(Ord. 644. Passed 8-17-88.)
1043.15 BRIDGE/CULVERT/CHANNEL DESIGN.
(a) Bridges and culverts shall have ample waterways to carry expected flows, based on a minimum storm frequency of twenty-five years and/or the requirements of the Pennsylvania Department of Environmental Resources. All culverts shall be provided with concrete end sections unless approved otherwise by the Township.
(b) All drainage channels shall be designed to carry a flow rate equal to a 100-year, twenty-four hour storm.
(c) All drainage channels shall be designed to prevent the erosion of the bed and bank areas. The flow velocity in all vegetated drainage channels shall not exceed the maximum permissible velocity to prevent erosion. Suitable bank stabilization shall be provided where required to prevent erosion of the drainage channels. Where storm sewers discharge into existing drainage channels at an angle greater than thirty degrees from parallel with the downstream channel flow, the far side bank shall be stabilized by the use of rip-rap, masonry and/or concrete walls, The stabilization shall be designed to prevent erosion and frost heave under and behind the stabilizing media.
(d) Any vegetated drainage channel requiring mowing of the vegetation shall have a maximum slope of three horizontal to one vertical on those areas to be mowed.
(e) The design of all channels shall, as a minimum, conform to the design procedures outlined in:
| (1) | U.S. Department of Transportation | ||
| Federal Highway Administration | |||
| Roadside Drainage Channels | |||
| Hydraulic Design Series No. 4 | |||
| (2) | U.S. Department of Transportation | ||
| Federal Highway Administration | |||
| Design Charts for Open Channel Flow | |||
| Hydraulic Design Series No. 3 | |||
| (3) | Standards and Specifications for Soil Erosion and Sediment Control in Developing Areas, U.S. Department of Agriculture, Soil Conservation Service, College Park, Maryland. |
(Ord. 644. Passed 8-17-88.)
An overflow system shall be provided to carry flow to the detention basin when the capacity of the storm drain pipe system is exceeded. The overflow system shall be of sufficient capacity to carry the difference between the 100-year and the ten-year peak flow rates. (Ord. 644. Passed 8-17-88.)
All inlets must be designed to accommodate the ten-year peak flow rate, except at low points, where they shall accommodate the twenty-five year peak flow rate. The capacity of Type C, M or S inlets shall be determined from the following source:
Commonwealth of Pennsylvania,
Design Manual, Part 2,
Highway Design, August 1981 (or the most recent revision thereof)
Chapter 10
The capacity of each inlet shall be indicated on the stormwater drainage plan. All stormwater management plans shall indicate that inlet grades be installed in such a manner that the roadway stormwater will be directed into the inlet and away from the roadway. At curbed street/driveway intersections, inlets shall be placed on the tangent section and not in the curved portion of the curbing. (Ord. 644. Passed 8-17-88.)
1043.18 STRAIGHT PIPE SECTIONS PREFERRED.
Wherever possible, all storm sewers shall be designed to follow straight courses. No angular deflections of storm sewer pipe sections in excess of five degrees shall be permitted. No vertifical curves shall be permitted in the storm sewer system. (Ord. 644. Passed 8-17-88.)
1043.19 MINIMUM GRADE AND SIZE OF PIPES.
All storm drain pipes shall be designed to maintain a minimum grade of one percent. All storm sewer pipes shall have a minimum inside diameter of fifteen inches. (Ord. 644. Passed 8-17-88.)
The capacity of all pipe culverts shall, as a minimum, provide the required carrying capacity as determined by the following sources:
| (1) | U.S. Department of Transportation | |
| Federal Highway Administration | ||
| Hydraulic Engineering Circular No. 6 | ||
| Hydraulic Charts for the Selection of Highway Culverts | ||
| (2) | U.S. Department of Transportation | |
| Federal Highway Administration | ||
| Hydraulic Design Series No. 3 | ||
| Design Charts for Open-Channel Flow | ||
| (3) | United States Department of Transportation | |
| Bureau of Public Roads | ||
| Hydraulic Engineering Circular No. 10 | ||
| Capacity Charts for the Hydraulic Design of Highway Culve |
(Ord. 644. Passed 8-17-88.)