Township of Crescent, PA
Allegheny County
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Table of Contents
Table of Contents
GENERAL REFERENCES
Subdivision and land development — See Ch. 440.
Stormwater management — See Ch. 445.
Sanitary sewers — See Ch. 630.

§ 446.01 Stormwater performance standards.

[Amended 12-11-2014 by Ord. No. 556]
A. 
Applicants are encouraged to design conveyance systems that encourage infiltration and improve water quality wherever practicable.
B. 
Wherever conveyance channels are necessary, drainage shall be maintained by an open channel with landscape banks designed to carry the one-hundred-year, twenty-four-hour stormwater runoff from upstream contributory areas. If the runoff from stormwater collection and conveyance facilities would drain over land to a stormwater detention facility, the twenty-five-year frequency storm event may be used. The Township Engineer with the approval of the Township may increase the design storm, as conditions require. All open channels shall be designed with one foot of freeboard above the design water surface elevation of the design runoff condition.
C. 
Flood relief channels shall be provided and designed to convey the runoff from the one-hundred-year, twenty-four-hour storm, such that a positive discharge of this runoff is to a natural drainagecourse with a defined bed and bank.
D. 
Manholes and/or inlets shall not be spaced more than 300 feet apart for pipe sizes up to 24 inches in diameter and not more than 450 feet apart for larger pipe sizes.
E. 
Where drainage swales are used in lieu of or in addition to storm sewers, they shall be designed to carry the required runoff without erosion and in a manner not detrimental to the properties they cross. Drainage swales shall provide a minimum grade of 1% but shall not exceed a grade of 9%. Drainage swales used strictly for conveyance are not the same as open vegetated channels.
F. 
Street curbing for the purpose of stormwater conveyance is discouraged. On streets that must contain curbing, storm sewers shall be placed in front of the curbing. To the greatest extent possible, storm sewers shall not be placed directly under curbing. At curbed street intersections, storm inlets shall be placed in the tangent section of the road.
G. 
Use of grassed swales or open vegetated swales in lieu of curbing to convey, infiltrate and/or treat stormwater runoff from roadways is encouraged. Inlets shall be placed at the center of the shoulder swale draining the street and shall be located no closer than four feet from the edge of the cartway.
H. 
When requested by the Township the developers shall obtain or grant a minimum twenty-foot-wide drainage easement over all storm sewers, drainage swales, channels, etc., that are a component of the stormwater management system when located within undedicated land. All permanent detention basins and/or other stormwater management facilities providing stormwater control for other than a single residential lot shall be located within a defined drainage easement that allows proper legal access and maintenance vehicle access.
I. 
No property owner shall obstruct or alter the flow, location or carrying capacity of a stream, channel or drainage swale to the detriment of any other property owner, whether upstream or downstream. All subdivision and/or land development plans containing streams, channels, drainage swales, storm sewers or other conveyance systems that cross property boundaries, existing or proposed, or whose discharge crosses such boundaries shall contain a note stating the above.
J. 
Water quality inlets. Storm drainage systems that collect runoff from parking areas and/or loading areas exceeding 5,000 square feet of impervious coverage and discharge to stormwater management systems, including surface, or subsurface infiltration systems, shall have a minimum of one water quality inlet per each acre of drainage area. The purpose of water quality inlets is to remove oil, grease, and heavy particulates or total suspended solids, hydrocarbons and other floating substances from stormwater runoff; methods other than water quality inlets may be permitted if the applicant demonstrates to the Township's satisfaction that any such alternative will be as effective and as easily maintained. Periodic cleaning of these systems shall be addressed in the operation and maintenance plan submitted to the Township.
K. 
Suitable drainage structures, culverts, storm sewers, swales and related installations shall be provided along roads to ensure removal of stormwater from all gutters, at all low points and at intervals elsewhere not exceeding 600 feet, such that the width of stormwater flow in any gutter does not exceed 1/4 of the total cartway width.
L. 
No stormwater pipe (public or private) shall be less than 15 inches in diameter that conveys surface runoff. All stormwater pipes shall be concrete unless otherwise approved by the Township. The minimum pipe slope shall be such that a minimum of two ft/sec velocity is maintained. Where a culvert or pipe is used to replace a stream, the cross-sectional area shall be at least as large as the original stream channel. All stormwater BMPs shall be constructed in accordance with the Township's "standard details." Minimum pipe cover shall conform to the manufacturer's recommendations. Stormwater conveyance pipes utilized in BMPs shall have a pipe size of four-inch diameter or larger.
M. 
Where open watercourses for stormwater drainage are used the following standards shall apply:
1. 
Artificial channels shall be of trapezoidal cross section, with the channel width at the bottom at least 10 times the maximum water depth which would be produced by the one-hundred-year design storm and with rough, permeable and flexible sides and bottom. No artificial channel shall be used to replace a natural stream.
2. 
At all points in the drainage system the velocity shall be less than the erosion threshold of the conveyance material, including at the outlet from the construction area or subdivision site.
N. 
All stormwater collection and conveyance facilities (pipes, swales, and structures) shall be designed for a one-hundred-year design storm event, unless the runoff would naturally drain overland to a stormwater detention facility, in which case a twenty-five-year design storm event may be used. All drainage facilities shall be designed to contain the energy grade line for the peak flow rate for the design storm within the structures a minimum of two feet below surface elevation. The hydraulic grade line must be within the pipe. Swales and channels shall provide at least one foot of freeboard above the energy grade line. Backwater effects of pipes discharging under surcharge conditions shall be included in the calculations.
O. 
All workmanship and materials shall conform to the Township's construction standards. In addition, all workmanship and materials shall conform to the latest edition of PennDOT Form 408 and be supplied by manufacturers of suppliers listed in PennDOT's Bulletin 15.
P. 
All connections to existing storm sewer pipes shall be made by construction of a suitable junction box (inlet or manhole) to provide access for cleanout. No blind connections shall be permitted.
Q. 
All pipe outlets shall discharge onto a stone riprap blanket to prevent erosion of soil. Riprap shall be sized considering pipe exit velocities.
R. 
The discharge of stormwater runoff shall be to a well-defined drainagecourse, which has a defined bed and bank. If stormwater runoff cannot be discharged to a defined drainagecourse, documentation of written permission from each downstream property owner shall be provided for all properties between the source of discharge and the defined drainagecourse.
S. 
Inlets of each type shown in the Township construction standards shall be installed. Inlets at street intersections shall be placed on the tangent and not on the curved portion of the intersection radii.
T. 
Manhole and inlet castings shall conform to the Pennsylvania Department of Transportation Form 408 and PennDOT Standards for Roadway Construction. Inlet grates shall be bicycle safe. Frames and grates shall be cast iron or structural steel. Concrete frames shall not be permitted.
U. 
All roof drains shall discharge to an on-lot sump, or to a storm sewer system which is controlled by a detention pond. Outlets from roof drain sumps shall not discharge directly to fill slopes. Outlets shall not discharge directly to the gutter line of any street. All pipes from roof drains shall be a minimum four-inch Schedule 40 ABS, PVC or SDR 26 pipe. Four-inch Schedule 40 PVC or ABS pipe is required for a distance of 10 feet from the foundation of the dwelling. No stormwater drainage system shall be permitted to be constructed through any curbing on any public street. Minimum pipe size for sump stormwater piping is four inches.
V. 
All bridges and culverts shall be designed to support expected loads and to carry expected flows and shall be designed to meet current standards of the Pennsylvania Department of Transportation. All bridges and culverts shall be subject to all permits required by the Pennsylvania Department of Environmental Protection, Bureau of Dams and Waterways.
W. 
Disposal of stormwater from roof and driveway drains:
1. 
Unless otherwise approved by the Township, no stormwater from roofs or driveway drains shall be discharged to the street surface or curb underdrain.
2. 
Acceptable methods of disposal include properly designed dry sumps, grassed or other round surfaces with adequate consideration being given to erosion protection, storm sewers, or any other method approved by the Township.

§ 446.02 Manholes.

For pipe sizes of 24 inches or less, manholes shall be spaced at a maximum of 400 feet and for larger pipe sizes, the maximum distances between manholes shall be 600 feet. In addition, manholes shall be installed at all points of changes in horizontal alignment and vertical grade. Inlets may be substituted for manholes where practical.

§ 446.03 Inlets.

Inlets of the type shown in the Township Construction Standards shall be installed. Inlets at street intersections shall be placed on the tangent and not on the curved portions.

§ 446.04 Castings.

Manholes and inlet castings shall conform to the Pennsylvania Department of Transportation (PennDOT) Form 408 and PennDOT Standards for Roadway Construction. Inlet grates shall be bicycle safe. Frames and grates shall be cast iron or structural steel. Concrete frames shall not be permitted.

§ 446.05 Stormwater roof drains.

All roof drains shall discharge to an on-lot sump or to a storm sewer system which is controlled by a detention pond. Outlets from roof drain sumps shall not discharge directly onto fill slopes. Outlets shall not discharge directly to the gutter line of any street.
All pipes from roof drains shall be a minimum four-inch Schedule 40 ABS, PVC or SDR 35 pipe. Four-inch Schedule 40 PVC or ABS pipe is required for a distance of 10 feet from the foundation of the dwelling. No stormwater drainage system shall be permitted to discharge into any sanitary sewer system. No pipes shall be permitted to be constructed through any curbing on any public street.

§ 446.06 Unnatural drainage.

All points of concentrated flow discharge shall outlet directly to a well-defined drainage channel, with a defined bed and bank. Whenever construction stops or concentrates the natural flow of storm drainage in such a way as to affect adjoining properties, approval of the owners shall be obtained in writing. Approval of plans by the Township shall not authorize or sanction drainage affecting adjoining properties.

§ 446.07 Watercourses.

Open watercourses shall not be permitted within the rights-of-way of streets. The stopping, filling up, confining or other interference with, or changing the course of, drains, ditches, streams and watercourses in the Township shall not be permitted unless approval in writing is obtained from the Board of Commissioners. A permit must be obtained from the Department of Environmental Protection (DEP) of the Commonwealth of Pennsylvania for construction or changes in a watercourse subject to the regulations of the Pennsylvania Department of Environmental Protection.

§ 446.08 Bridges and culverts.

All bridges and culverts shall be designed to support expected loads and to carry expected flows and shall be designed to meet current standards of the Pennsylvania Department of Transportation. All bridges and culverts shall be subject to all permits required by the Pennsylvania Department of Environmental Protection, Bureau of Dams and Waterways.

§ 446.09 Intersections of private driveways and public streets.

[Ord. No. 509, passed 9-12-2007; amended 12-11-2014 by Ord. No. 556]
Stormwater drainage facilities shall be placed where each private driveway intersects with a public street. The design shall be approved by the Township and shall meet the following requirements:
A. 
The facility shall be placed to maintain the flow line of the stormwater drainage facility in the public street.
B. 
Where an apron gutter is to be utilized, said apron gutter shall be designed and constructed in accordance with the Township construction standards.
C. 
Where reinforced concrete, metal or tile pipe is to be used beneath the driveway, said pipe shall not be less than 15 inches in diameter and shall extend across the full width of the driveway and beyond the driveway for a distance determined by the Township. The pipe shall be installed with flared end sections and shall be designed to support H-15 loading and any other imposed loadings necessary without structurally damaging the system. The installation of the pipe shall be in accordance with the Township construction standards.

§ 446.10 Testing.

[Amended 12-11-2014 by Ord. No. 556]
All construction materials used in storm sewers shall be tested by a qualified testing laboratory, if required by the Township. The cost for such tests shall be borne by the developer.