1. Collection and Conveyance Facilities.
A. The design of stormwater management collection and conveyance facilities that service drainage areas within the site shall be based upon the peak flow from a 25- year storm frequency event.
B. All developments shall include design provisions that allow for the overland conveyance of the post-development 100-year peak flows through the site without damage to any private or public property.
C. Method of Calculations. Runoff calculations for on-site stormwater conveyance facilities shall be based upon the Rational Method or an acceptable engineering design method, subject to Borough approval.
D. Criteria, Methodology and Assumptions. Appropriate values for runoff coefficients, time of concentration, and rainfall intensity shall be from the latest edition of the Commonwealth of Pennsylvania, Department of Transportation Design Manual, Part 2, Highway Design, Chapter 10. Use of other criteria, methodology, assumptions, references, calculation methods and/or computer modeling may be accepted, provided detailed design information and programming with references are submitted and approved by the Borough.
2. Stormwater Basins.
A. The peak discharges and volumes of runoff may be determined by using the latest version of Technical Release No. 55, Urban Hydrology for Small Watersheds, or an acceptable engineering method, subject to Borough approval.
B. Retention basins and detention basins shall be designed with a minimum one-foot freeboard above the design elevation of the 100-year water surface at the emergency spillway. Additionally, basins shall be designed to safely discharge the full 100-year peak discharge of a post-development storm event through an emergency spillway in a manner which will not damage the integrity of the basin. Basins shall not be located over any existing or proposed utility line. Infiltration facilities with a depth of 18 inches or less shall not be subject to this requirement.
C. Stormwater basins located in known sinkhole-prone areas are required to be lined to prevent infiltration into the ground, unless intended to be infiltration facilities.
D. Basins shall be constructed and maintained to ensure the design capacity after sedimentation has taken place.
E. Basin discharge outlets shall be designed to release runoff in a condition which reflects pre-development characteristics.
F. Basins which are not designed to release all stormwater shall be specifically identified as retention basins or permanent pond basins. All surface basins shall have provisions for de-watering, particularly the bottom, and shall not create swampy and/or unmaintainable conditions.
G. Discharge structures shall be designed to eliminate the possibility of blockage during operation.
H. Basins which are located in or adjacent to a residential zone and viewed by the Borough as a potential hazard to the public safety shall be completely surrounded by a fence or wall of not less than four feet in height.
I. Earth Fill Dams. Basins which are designed with earth fill dams shall be designed by a registered professional engineer with experience in earth-filled dams and shall incorporate the following minimum standards:
(1) The maximum water depth (measured from the base to the crest of the emergency spillway) shall not exceed six feet, unless approved by waiver of the Borough.
(2) The minimum top width of all dams shall be five feet, unless approved by waiver of the Borough.
(3) The side slopes of earth fill dams shall not be steeper than three horizontal to one vertical on both sides of the embankment.
(4) Basins without restricted access shall have impoundment areas with side slopes no greater than five horizontal to one vertical.
(5) A cutoff trench of impervious material shall be provided under all dams.
(6) All pipes and culverts through dams shall be reinforced concrete or HDPE and have properly spaced concrete cutoff collars.
(7) All outlet structures shall be reinforced concrete.
(8) Minimum floor elevations for all structures that would be affected by a basin, other temporary impoundments, or open conveyance systems where ponding may occur shall be two feet above the 100-year water surface elevation and/or one foot above the 500-year water surface elevation. If basement or underground facilities are proposed, detailed calculations addressing the effects of stormwater ponding on the structure and water-proofing and/or flood-proofing design information shall be submitted for approval.
J. The Borough may, upon recommendation of the Borough Engineer, impose additional requirements on earth fill dams for the safety and welfare of the Borough.
3. Pipe and Swale Design.
A. The capacity of gutters, inlets, culverts, outlet structures and swales shall consider all possible hydraulic conditions. The following are minimum design standards.
(1) Grass swales and roadside gutters shall consider both the channel velocity and stability.
(2) The “n” factors to be used for paved or rip-rap swales or gutters shall be based on the latest edition of the Pennsylvania Department of Transportation Design Manual, Part 2, Highway Design, Chapter 10.
(3) The “n” factors for corrugated metal pipe shall be based upon the manufacturer's standard.
(4) The velocity to be used in the design of any piped stormwater conveyance system shall be a minimum of two and one-half feet per second.
(5) Inlets, culverts, and basin discharge systems shall be designed for the worst case condition. Inlet capacity shall be based on design standards provided by the latest edition of the Pennsylvania Department of Transportation's Design Manual, Part 2, Highway Design, Chapter 10. If acceptable information is not available, inlets in non-ponding areas shall be designed for a maximum capacity of five cubic feet per second. Where ponding occurs, inlet capacity shall be based on accepted engineering design practices. Culvert design shall consider either inlet/outlet control or a combination of hydraulic losses through the system, whichever is greater. Basin discharge systems shall be designed to the same standards as culverts. If it cannot be readily determined which hydraulic condition controls, the basin discharge rate shall be based on the highest possible discharge rating curve, with the basin capacity sized to store the excessive storm runoff, based on the lowest possible discharge rating curve.
B. Stormwater Flow Along Streets and Access Drives. Inlets shall be along the curb line and are not permitted along the curb radius at an intersection. When possible, inlets shall be located away from the side lot property line to avoid conflicts with driveways. For the purpose of inlet placement, curb, gutter, or roadside swale, flow depths for a ten- year storm frequency with a five minute duration shall not exceed three inches in a swale condition, two inches in a gutter condition, and one-half inch across intersections and travel lanes. In no case shall inlets be spaced more than 600 feet apart and function at less than 65% efficiency based on the criteria in the PennDOT Design Manual.
C. Manhole Locations. Manholes shall not be spaced more than 500 feet apart. Additionally, manholes shall be placed at points of changes in the horizontal or vertical direction of storm sewers. Inlets may be substituted for manholes where they will serve a useful purpose.
D. Alignment Requirement. If less than a 48-inch diameter, curves in pipes or box culverts without an inlet or manhole are prohibited. T-joints, elbows, and wyes are always prohibited on piping 12 inches or greater.
E. Minimum Pipe Size. Stormwater management pipe collection and conveyance systems shall have a minimum diameter of 15 inches.
F. Material Specifications. All materials and installations must be approved for use by the Borough Engineer and comply with the Borough Specification Manual.
G. Surface Flow Characteristics.
(1) The maximum swale, gutter, or curb velocity of stormwater runoff shall be maintained at levels which result in a stable condition both during and after construction. The following are considered characteristics of a stable condition:
(a) It neither aggrades nor degrades beyond tolerable limits.
(b) The channel banks do not erode to the extent that the channel cross section is changed appreciably.
(c) Sediment bars do not develop.
(d) Erosion does not occur around culverts and bridges or elsewhere.
(e) Gullies do not form or enlarge due to the entry of uncontrolled stormwater runoff.
(f) Grass-lined channels shall be considered stable if the calculated velocity does not exceed the allowable velocities shown below:
1) Three feet per second where only sparse vegetation can be established and maintained because of shade or soil condition.
2) Four feet per second where normal growing conditions exist and vegetation is to be established by seeding.
3) Five feet per second where a dense, vigorous sod can be quickly established or where water can be temporarily diverted during establishment of vegetation. Netting and mulch or other equivalent methods for establishing vegetation shall be used.
4) Six feet per second where there exists a well-established sod of good quality.
(2) Where swale bends occur, the allowable velocities listed above shall be divided by the following factors:
Degree of Bend | Velocity |
0 to 30 | 1.50 |
30 to 60 | 1.75 |
60 to 90 | 2.00 |
90 and over | 2.50 |
(3) The above grass-lined channel flows may be exceeded if the designer can provide acceptable supportive design criteria as proof of erosion prevention.
H. Where the velocity of stormwater runoff exceeds the allowable velocity, erosion protection must be provided. The method of erosion protection proposed must be supported by the appropriate design information and/or references.
I. Sump pump discharges and roof drains will be directed to lawn areas away from residences, into areas that will surface drain to conveyance structures (e.g., swales and storm sewer collection systems).
4. Erosion and Sedimentation.
A. All land disturbance facilities shall conform to the requirements of the Perry County Conservation District and the Pennsylvania Department of Environmental Protection, and with the following provisions.
B. A Pennsylvania Department of Environmental Protection “NPDES Construction Activities” permit in compliance with 25 Pa. Code Chapter 92 is required for any earth disturbance of one acre regardless of the planned runoff (hereinafter collectively referred to as “Regulated Earth Disturbance Activities”). This includes earth disturbance on any portion of, part of, or during any stage of, a larger common plan of development.
C. Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or County Conservation District must be provided to the Borough. The issuance of an NPDES construction permit (or permit coverage under the statewide General Permit (PAG-2)) satisfies the requirements of this Section.
D. A copy of the erosion and sediment control plan and any required permit, as required by DEP regulations, shall be always available at the project site.
E. The following principles shall be applied to the design plan and construction schedule to minimize soil erosion and sedimentation: a) Stripping of vegetation, grading, or other soil disturbance shall be done in a manner which will minimize soil erosion. b) Whenever feasible, natural vegetation shall be retained and protected. c) The extent of the disturbed area and the duration of its exposure shall be kept to a minimum, within practical limits. d) Either temporary seeding, mulching, or other suitable stabilization measures shall be used to protect exposed critical areas during construction. e) Drainage provisions shall accommodate the stormwater runoff both during and after construction. f) Soil erosion and sedimentation facilities shall be installed prior to any on-site grading. g) The design plan and construction schedule shall incorporate measures to minimize soil erosion and sedimentation. h) Retention and/or detention basins and water carrying facilities shall be stabilized in accordance with current engineering and soil conservation service practices.
F. Floodplain. All stormwater management plans shall conform with the floodplain standards specified in latest ordinance as amended.
G. Easements. When considered appropriate, easements shall be provided where stormwater or surface water drainage facilities are existing or proposed, whether located within or beyond the boundaries of the property. Easements for maintenance of pipes and culverts shall run from outlet to inlet. Normal lot grading will not require easements. Swales which receive runoff from more than one other lot must be provided with an easement. Easements shall have a minimum width of 20 feet and shall be adequately designed to provide area for (a) the collection and discharge of water; (b) the maintenance, repair, and reconstruction of the drainage facilities; and (c) the passage of machinery for such work. When considered appropriate, easements shall include a description of an ownership and maintenance program, in a recordable form, that clearly sets forth responsibility for all temporary and permanent stormwater management facilities.
5. Ownership and Maintenance of Stormwater Management Facilities.
A. The intent of these regulations is to provide private ownership and maintenance of stormwater management facilities, erosion and sedimentation control facilities and floodplain control facilities. Under no circumstances does the Borough intend to accept dedication of erosion control and sedimentation basins. The Borough does not encourage the dedication of stormwater management facilities that are located outside public street rights-of-way. Where the stormwater management plan proposes that the Borough own or maintain a stormwater management facility, a description of the methods, procedures, and the extent of maintenance shall be described in such an offer.
B. Maintenance of all stormwater management facilities during development shall be the sole responsibility of the developer and shall include, but not be limited to:
(1) Removal of silt from all basins, traps or other structures or measures when 30% of capacity is filled with silt;
(2) Periodic maintenance of temporary control facilities as described in the soil erosion and sedimentation control plan such as replacement of silt fencing, straw filters or similar measures;
(3) Establishment or re-establishment of vegetation by seeding and mulching or sodding of scoured areas or areas where vegetation has not successfully been established;
(4) Installation of necessary controls to correct unforeseen problems caused by storm events within designed frequencies;
(5) Removal of all temporary measures and installation of permanent measures upon completion of the project; and
(6) Requirements of the Pennsylvania Department of Environmental Protection, Chapter 102 Regulations.
C. Ownership of all stormwater management facilities after construction shall be the sole responsibility of the developer or the private landowner as set forth in the plan. The only stormwater management facilities which are to be controlled by the Borough shall be those facilities which have been offered for dedication and accepted for dedication by the Borough. Future offers for dedication can only be made for facilities which meet current Borough specifications.
(Ord. 643, 10/10/2022)