Each land subdivision and/or land development, whether residential, commercial or industrial in nature or use, shall provide and implement a water drainage plan and stormwater management plan so as to prevent any damage or injury to health, safety or property from stormwater runoff or groundwater. The water drainage plan shall be in accordance with this article and shall be prior approved by the Township. The stormwater management plan shall be as required by Township ordinances or as directed by the Township Engineer.
All drainage management measures shall include such actions as are required to manage the quantity, velocity and direction of resulting ground water and/or stormwater runoff in a manner which protects health and property from injury.
Natural runoff flow characteristics shall be maintained either by augmenting natural infiltration processes or by physically controlling the release of development-related stormwater flow increases through structural means.
Purpose of stormwater system.
Positive drainage is required in all areas of development. The stormwater system shall be planned and designed to direct stormwater runoff away from all public roads, structures, buildings and development areas. The stormwater drainage system shall provide drainage facilities at all points along public streets and sidewalks, including other access and circulation systems.
Underdrainage shall be provided in all areas where springs, wet weather springs, or where poor soil drainage conditions exist or result from the development. During construction of any improvement, if springs or any other poor drainage conditions are encountered, or when construction of any improvement has or will alter the natural groundwater flow, the Township shall be notified. Underdrainage shall be provided by the owner/developer, as directed by the Township, to correct said poor drainage condition.
The stormwater system, including downspouting and other forms of rainware which are utilized upon any structure within the land subdivision and/or land development, and the underdrainage system shall be designed to convey, contain, store, absorb and/or use the surface or underground waters without damage to life or property and to minimize disruption of land usage.
All on-site storm drains (downspouts, area drains, foundation drains, etc.) shall include all pipe required to convey runoff water directly to storm sewers or the stormwater management facility. No runoff water shall be allowed to discharge into the street/road.
To the maximum extent possible, the stormwater drainage system and underground drainage system shall be designed to convey stormwater runoff through a conveyance system directly to a natural watercourse and prevent the discharge of stormwater or underground water onto adjacent facilities or properties.
Natural drainage routing shall be preserved where feasible. No discharge of on-site stormwater or underground water runoff into a natural drainage routing shall be permitted when such discharge will damage adjacent or downstream property.
No stormwater drainage system or underground drainage system shall be permitted to discharge into any sanitary sewer system.
The storm sewer system shall be designed to intercept and convey the peak rate of runoff from the twenty-five-year return storm.
Stormwater runoff and design calculations to meet this requirement shall be submitted to the Township for approval prior to preliminary plan approval. Hydraulic computation presenting invert elevations, pipe size, "n," capacity, velocity, hydraulic and energy grade line shall be submitted.
Stormwater runoff and design calculations shall be prepared by a qualified Pennsylvania-registered engineer or land surveyor. Computational method shall be Rational Method, Penn State Runoff Model or other generally accepted procedure approved by the Township Engineer.
Additional analysis, calculations and design criteria may be required for both the on-site and off-site stormwater systems where it has been determined by the Township that further study is necessary.
Upon Township request, stormwater runoff calculations shall be made available for the outlet and inlet sides of all stormwater drainage and storage facilities and structures; at points in a public street with a change of grade; or where water from a proposed structure, facility or vehicular way is to enter an existing public street, existing storm sewer, existing drainage ditch, or existing stormwater storage facility.
Design to consider adjacent and future upstream development. The stormwater drainage system for the land subdivision and land development and, where required, the underdrainage system for a land subdivision and/or land development shall be designed for compatibility with the watershed stormwater management system and any Township or adjacent municipality planned or proposed change to the system.
The design shall anticipate and provide for the effects of all tributary area and upstream development.
The design shall anticipate and provide for impact(s) on downstream flow conditions and water quality.
Off-site stormwater drainage and underdrainage facilities and improvement shall be provided by the applicant/owner of the proposed land subdivision and/or land development where needed and where requested by the Township.
Where required, the Pennsylvania Department of Environmental Protection approval, including permits as required, shall be obtained by the applicant/owner of the land subdivision and/or land development and evidence of same provided to the Township.
Identification of responsibilities for stormwater systems.
The installation, ownership, and maintenance responsibilities after completion of the development for all stormwater drainage and storage facilities and all underdrainage facilities shall be identified on the preliminary plans and exhibits.
All stormwater drainage or storage facilities or underdrainage facilities to be publicly dedicated shall be located in a right-of-way, a drainage easement, or in a location as required by the Township.
Designs and plans for all facilities.
The design for all stormwater drainage and storage facilities shall be in accordance with the requirements of the Pennsylvania Department of Transportation Design Manual, Part 2, latest edition, and of this article.
Plan and profile drawings to suitable scale shall be provided prior to preliminary plan approval. Plan and cross-section drawings, catalog cuts and specifications shall be provided showing complete construction details for all stormwater drainage storage facilities and appurtenances prior to final plan approval.
The access control for any storage facility shall be approved by the Township prior to preliminary plan approval.
The design of all retention facilities shall be subject to the review and approval of the Township Engineer and, where applicable, by the Pennsylvania Department of Environmental Protection.
Where open stormwater drainage and/or storage facilities are to be constructed, the access control measures, erosion control measures, capacity protection measures, flood protection measures, stagnant water control measures, and appearance control measures shall be presented for Township approval with the preliminary plans and exhibits.
Stormwater retention facilities shall have sufficient capacity to store the ten-year return storm at a minimum, except where a lesser return frequency (e.g., twenty-five-, fifty- or one-hundred-year) is determined to be appropriate at the sole discretion of the Township Engineer or where required by watershed studies. A minimum of two feet of freeboard shall be provided. The primary outlet structure shall be designed to control the two-, five- and ten-year return storms. An emergency spillway shall be designed to convey the twenty-five-, fifty- or one-hundred-year return storms, as appropriate. All dike embankments shall be a minimum of four feet wide at their crest.
Design of facilities to correlate with public street design. The design of stormwater drainage and storage facilities shall be closely correlated with the design of public streets.
Stormwater inlets. Stormwater inlets shall be spaced a maximum of 300 feet apart where pipe sizes of 24 inches or less are used and not over 450 feet where larger pipe sizes are installed. Sufficient inlets shall be provided to intercept all surface runoff.
Manholes. Manholes shall be spaced a maximum of 300 feet apart where pipe sizes of 24 inches or less are used and not over 450 feet where larger pipe sizes are installed. Design of manholes shall be as per Standard Drawing 2-4. If approved by the Township, inlets may be substituted for manholes.
Editor's Note: The Standard Drawings 2-4a and b of precast concrete manholes are included at the end of this chapter.
Drainage of street intersections. Enclosed stormwater drainagecourses shall be required at intersecting streets and elsewhere, as may be deemed necessary by the Township. Stormwater shall be collected in stormwater culverts or similar enclosed components.
Stormwater culverts, bridges and similar structures serving public streets, access drives or any other vehicular right-of-way, as may be designated by the Township, shall be designed to support HS-20 loading and any other imposed loadings necessary without structurally damaging the drainage system. The stormwater culverts, bridges and similar structures shall be constructed to the full width of the right-of-way plus any additional length as deemed necessary by the Township Engineer to satisfy a local drainage pattern.
Stormwater culverts in areas other than those noted above shall be designed to support the necessary loading (existing and potential) and any other imposed loadings without structurally damaging the pipe or affecting its capacity for drainage. Said design shall be approved by the Township Engineer.
Conduit size of culverts or other enclosed components of a stormwater drainage system shall be based on computed hydrologic and hydraulic data, and computations shall be approved by the Township Engineer.
Minimum size of any enclosed structure to be maintained by the Township shall be 15 inches in diameter.
Minimum size of any enclosed structure to be privately maintained shall be 15 inches in diameter unless design calculations are provided that can justify a lesser size. Design calculations shall be approved by the Township Engineer.
The design of the enclosed drainagecourse shall provide a minimum cleaning velocity of three feet per second. When the design provides for a maximum velocity greater than 10 feet per second, the enclosed components shall be lined or protected to prevent scour.
Pipe materials used shall be reinforced concrete pipe (RCCP), Class III minimum.
Storm sewers 36 inches in diameter or less shall be constructed to line and grade.
The pipe zone of storm sewers shall be installed in natural, virgin ground unless otherwise approved. The pipe zone shall be defined as the area outside the pipe diameter six inches below, six inches on either side and 12 inches above the pipe. No storm sewer pipe shall be constructed in fill materials.
Energy dissipaters shall be required at the outlet side of all enclosed culverts or similar components and shall be designed to reduce the velocity of flow sufficient to prevent damage to downstream areas.
No stormwater facility shall be enclosed or covered over until the Township has inspected and approved said facility.
Water velocity limitations for open drainagecourses. Open stormwater drainagecourses shall be designed for a maximum velocity not to exceed 10 feet per second and a minimum velocity of five feet per second. A minimum velocity of three feet per second may be permitted where a greater slope cannot be achieved to permit the standard required minimum velocity. An open stormwater drainagecourse shall include a lining (rip-rap, concrete, bituminous) to prevent erosion. Any required approval of the Allegheny County Soil Conservation Service shall be obtained by the applicant.
[Amended 8-14-1989 by Ord. No. 16-1989]
Any person violating any provision of this article shall, upon conviction thereof, be sentenced to pay a fine of not more than $600 and costs or, in default of payment thereof, shall be subject to imprisonment for a term not to exceed 30 days, provided that each violation of any provision of this article and each day the same is continued shall be deemed a separate offense.
In the event of the violation of the provisions of this article by any individual or corporation and when the Township deems it necessary to correct any storm sewers constructed and/or installed contrary to the provisions of this article, the Township may, at its discretion, immediately repair or cause to be repaired or reconstructed any storm sewer at the expense of the violator thereof, and said expenses shall be collected by the Township in any suit at law for correction of the same. In addition, the Township may institute appropriate action at law or equity to restrain, correct or abate threatened or continued violations of this article.