(A) All stormwater runoff collection or conveyance facilities, whether storm sewers or other open or closed channels, shall be designed in accordance with the following basic standards.
(1) All sites shall be graded to provide drainage away from and around the structure in order to prevent any potential flooding damage.
(2) Lots located on the high side of streets shall extend roof and French drains to the curb line storm sewer (if applicable). Low side lots shall extend roof and french drains to a stormwater collection/conveyance/control system or natural watercourse in accordance with the approved stormwater management plan for the development site.
(3) Collection/conveyance facilities should not be installed parallel and close to the top or bottom of a major embankment to avoid the possibility of failing or causing the embankment to fail.
(4) All collection/conveyance facilities shall be designed to convey the 25-year storm peak flow rate from the contributing drainage area and to carry it to the nearest suitable outlet such as a stormwater control facility, curbed street, storm sewer or natural watercourse without damage to the drainage structure or roadway, with runoff from the 25-year design storm at a minimum one foot of freeboard measured below the lowest point along the top of the roadway. Roadway crossings Located within designated floodplain areas must be able to convey runoff from a 100-year design storm with a minimum of one-foot freeboard measured below the lowest point along the top of the roadway. When it can be shown that, due to topographic conditions, natural drainage ways on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainage ways. Work within natural drainage ways shall be subject to approval by PADEP through the joint permit application process, or, where appropriate by PADEP, through the general permit process.
(5) Where drainage swales or open channels are used, they shall be suitably lined to prevent erosion and designed to avoid excessive velocities.
(6) Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities or open channels consistent with this chapter.
(7) Existing points of concentrated drainage that discharge onto adjacent property shall not be altered without permission of the altered property owner(s) and shall be subject to any applicable discharge criteria specified in this chapter.
(8) Areas of existing diffused drainage discharge shall be subject to any applicable discharge criteria in the general direction of existing discharge, whether proposed to be concentrated or maintained as diffused drainage areas, except as otherwise provided by this chapter. If diffused flow is proposed to be concentrated and discharged onto adjacent property, the developer must document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding or other harm will result from the concentrated discharge.
(9) Where a development site is traversed by watercourses, drainage easements shall be provided conforming to the line of such watercourses. The terms of the easements shall prohibit excavation, the placing of fill or structures, and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Also maintenance, including mowing of vegetation within the easement shall be prohibited, except as approved by the appropriate governing authority.
(10) Any stormwater management facilities regulated by this chapter that would be located in or adjacent to waters of the commonwealth or wetlands shall be subject to approval by PADEP through the joint permit application process, or, where deemed appropriate by PADEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the developer or his or her agent to show that the land in question cannot be classified as wetlands, otherwise approval to work in the area must be obtained by PADEP.
(11) Any stormwater management facilities regulated by this chapter that would be located on state highway rights-of-way shall be subject to approval by the State Department of Transportation.
(12) In order to promote overland flow and infiltration/percolation of runoff where it is advantageous to do so, roof drains must not be connected to streets, sanitary or storm sewers, or roadside ditches. When it is more advantageous to connect directly to streets or storm sewers, then it shall be permitted on a case-by-case basis by the municipality.
(B) Wherever storm sewers are proposed to be utilized, they shall comply with the following criteria.
(1) Where practical, designed to traverse under seeded and planted areas. If constructed within ten feet of road paving, walks or other surfaced areas, drains shall have a narrow trench and maximum compaction of backfill to prevent settlement of the superimposed surface or development.
(2) Preferably installed after excavating and filling in the area to be traversed is completed, unless the drain is installed in the original ground with a minimum of three feet cover and/or adequate protection during the fill construction.
(3) Designed: with cradle when traversing fill areas of indeterminate stability; with anchors when gradient exceeds 20%; and with encasement or special backfill requirements when traversing under a paved area.
(4) Designed to adequately handle the anticipated stormwater flow and be economical to construct and maintain. The minimum pipe size shall be 15 inches in diameter.
(5) Drain pipe, trenching, bedding and backfilling requirements shall conform to the requirements of the municipality and/or applicable PennDOT Specifications, Form 408.
(6) Storm inlets and structures shall be designed to be adequate, safe, self-cleaning and unobtrusive and consistent with municipal standards.
(7) Approved grates shall be designed for all catch basins, stormwater inlets and other entrance appurtenances.
(8) Manholes shall be designed so that the top shall be at finished grade and sloped to conform to the slope of the finished grade. Top castings of structures located in roads or parking areas shall be machined or installed to preclude “rattling”.
(9) Where a proposed storm sewer connects with an existing storm sewer system, the applicant shall demonstrate that sufficient capacity exists in the downstream system to handle the additional flow.
(10) Storm sewer outfalls shall be equipped with energy dissipation devices to prevent erosion and conform with applicable requirements of the State DEP for stream encroachments (25 Pa. Code Chapter 105).
(Ord. 4-2011, passed 10-8-2011)