Township of Hanover, PA
Northampton County
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Table of Contents
Table of Contents

§ 152-10 General requirements.

A. 
Any proposed storm drainage plans which affect the drainage basin of any river or stream shall be approved by the Division of Dams and Waterway Management of the Pennsylvania Department of Environmental Protection if the affected drainage area is more than 100 acres.
B. 
Easements shall be dedicated to the Township along all natural or man-made streams and watercourses (as described in § 152-8C) and/or detention basin areas within a subdivision or land development. These easements should be of sufficient width to convey a one-hundred-year design storm, assuming the upstream drainage basin to be fully developed. Easements shall also be provided where storm drainage swales, culverts or other structures traverse, enter or discharge onto private property. On private property the entire easement area and fencing and landscaping (if any) shall be maintained by the property owner and the Township shall not maintain and/or repair any improvements within that easement, unless stormwater runoff from public roads or public park land crosses through the easement.
(1) 
If stormwater runoff from public roads or public lands crosses through the easement the Township shall, upon satisfactory installation of improvements as specified in a developer's improvement agreement and maintenance agreement, maintain and repair only the structural stormwater management improvements within the easement such as:
(a) 
Piping.
(b) 
Inlets.
(c) 
Outlet, headwalls.
(d) 
Energy dissipation structures or facilities.
(e) 
Detention basin control structures.
(2) 
The landowner shall be responsible for all other maintenance and repairs within this easement. For example, the landowner must:
(a) 
Mow the lawn.
(b) 
Repair or replace fencing.
(c) 
Repair or replace landscaping.
(d) 
Repair sinkholes that may develop in the easement.
(e) 
Keep the area free of obstructions, structures, vegetation or accumulated sediment that may block or hinder the function and purpose of the easement.
(f) 
Keep the area free of litter or garbage.
(g) 
Repair erosion and restore vegetation as necessary to keep the easement in good repair.
C. 
Storm sewers, culverts, and related installations shall be provided to permit the flow of natural watercourses, to ensure the drainage of all low points on the subdivided lots or developed land areas and along the line of streets, and to intercept stormwater runoff along streets at intervals related to the extent and grade of the area drained. The system shall also be designed to accommodate or receive and discharge all runoff from adjacent upstream properties, as if the upstream properties were developed. Where adequate existing storm sewers are readily accessible, the developer must connect new stormwater facilities to the existing system.
D. 
Flood protection. No stormwater runoff or natural drainage water shall be so diverted as to overload existing drainage systems, or create flooding or the need for additional drainage structures on other private properties or public lands, without proper and approved provisions being made for taking care of these conditions.
E. 
When the runoff is increased, due to development, the developer must secure written approval from the downstream property owners. In lieu of such written approval, the developer shall follow the other requirements of this chapter, in particular, the sections dealing with detention basins and downstream facilities, and shall provide the Township with a notarized statement satisfactory to the Township Solicitor, stating that the Township shall be held harmless against any claim of damage from the downstream property owners that may result from the proposed development.
F. 
Scour and erosion prevention. In areas in which street curbs are not required by any ordinance of the Township, drainage may be accomplished by natural or artificial swales and culverts. Special structures such as check dams, drop-outlets, or other energy dissipating structures or riprap may be required to prevent scour or erosion in locations with large runoff quantities or steep slopes. In no case may a change be made in the existing topography which would result in a slope exceeding the normal angle of slippage of the material involved. No paved swales will be allowed without the approval of the Township.
G. 
Fixed pipe collection system. The Township may require a fixed pipe collection system with catch basins. Such fixed pipe collection system with catch basins shall be used in all areas with street curbs and gutters, when required. The Township may require foundation pipe underdrains.
H. 
Low point drainage.
(1) 
Developer shall grade and install all necessary drainage facilities to insure the drainage of all low points on subdivided lots or within the subdivision or developed land areas.
(2) 
Underdrains are required at a minimum for 50 feet upward from a road low point along each approach road to the low point.
I. 
Storm runoff detention facilities. Where the topography of the tract being developed or the character of the downstream storm sewer indicate, as determined by the Township, storm sewer detention facilities shall be provided within the subdivision proposed. This provision may be required even if downstream property owners have given written approval. Such detention facility shall be designed in accordance with the following requirements:
(1) 
The detention facilities shall be designed to retard stormwater runoff rates after development to the peak runoff rate established for each district in Article III, § 152-7.
(2) 
Spillways shall be provided for possible overflows, and such spillways shall be protected from erosion. Spillways shall be designed for the one-hundred-year storm.
(3) 
Pipe outlet arrangements shall provide complete outletting of all detained water, unless provisions for permanent ponding have been approved.
(4) 
A detention basin, if utilized, shall be lined with a synthetic impervious liner, as more specifically called out in Subsection I(9).
(5) 
The detention facility shall be planted with low-maintenance grass or a substitute satisfactory to the Township. Detention basins shall be planted with ground cover in accordance with Township standards.
(6) 
To minimize the visual impact of detention basins, any required basin shall be designed to avoid the need for safety fencing. To meet this requirement, basins shall be designed to the following specifications:
(a) 
Maximum depth of detained runoff shall be 24 inches for a ten-year storm event; and
(b) 
Maximum depth of detained runoff shall be 36 inches for a one-hundred-year storm event; and
(c) 
Interior slopes shall not be steeper than a ratio of 4:1 horizontal to vertical; and
(d) 
A water surface limit shall be no closer than 100 feet to any residential building and no closer than 25 feet to any other type of building.
(7) 
These depths and slopes may be exceeded by permission of the Board of Supervisors of the Township, on a case-by-case basis if lot runoff, topography, and/or existing downstream systems make the required pond area unreasonably large. In such a case a deeper depth may be allowed if the basin is designed to the following specifications:
(a) 
A maximum depth of detained runoff shall be 24 inches for a two-year storm event; and
(b) 
A maximum depth of detained runoff shall be 36 inches for a ten-year storm event; and
(c) 
A maximum depth of detained runoff shall be 48 inches for a one-hundred-year storm event; and
(d) 
Interior side slopes shall not be steeper than a ratio of 5:1, horizontal to vertical; and
(e) 
A water surface limit no closer than 100 feet to any residential building and no closer than 25 feet to any other type building.
(8) 
An access ramp of 10:1, 10 feet wide, shall be provided to allow maintenance equipment to reach the basin floor.
(9) 
All detention/retention facilities, whether ultimately privately or publicly owned, shall be lined with a synthetic impervious liner meeting the following minimum requirements:
(a) 
The minimum liner allowed is 30 mil PVC. Actual individual liner specifications shall be provided by the manufacturer for each individual pond.
(b) 
The liner must be placed on a layer of fine grained soil that has been rolled with a smooth drum roller in both directions to produce a smooth level base for the liner. The soil may not contain sharp angular rock or other debris which could puncture the liner, and must meet all manufacturer's specifications for a liner bedding. All vegetation, roots, and grass must be removed and any cracks or voids shall be filled.
(c) 
If rock is encountered in the bedding area, this rock must be excavated to a depth of six inches below the liner and backfilled with a fine grained soil. This area should then be covered with geotextile fabric, extending three feet beyond the limits of the rock outcrop before placing the pond liner.
(d) 
Installation of the liner may only take place when the ambient temperature is within the manufacturer's recommended range. Installation and testing shall be in accordance with manufacturer's specifications. The number of field seams shall be minimized by requiring factory fabrication of large panels. Any field seams performed must be in accordance with the manufacturer's specifications.
(e) 
All structures (i.e., headwalls, pipes, outlet structures) which come in contact with the liner must have a waterproof seal installed to prevent leaks around the structure. These seals shall be installed per manufacturer's recommendations.
(f) 
A minimum of 12 inches of earth cover shall be placed over the lining. Soil containing sharp jagged rocks, roots, debris, or any other material which may puncture the liner shall not be used as cover material.
(g) 
The liner must be installed to a minimum height of the one-hundred-year floodwater elevation in the facility.
(10) 
The minimum slope of the bottom of a detention pond shall be 2% toward the outlet structure.
J. 
All streets shall be designed so as to provide for the discharge of surface water from their rights-of-way.
K. 
Design criteria.
(1) 
Unless a more conservative design is required by another regulation, or is required because of conditions particular to an individual development, the following storm criteria shall be used to design storm collection and conveyance systems:
Area
Design Storm Return
(years)
Residential areas
Fixed pipe
10
Total conveyance
100
Nonresidential areas
Fixed pipe
25
Total conveyance
100
Culvert crossings of any road
In culvert
25
Total conveyance
100
(2) 
The preliminary plan or lot location plan shall indicate the areal extent of the one-hundred-year storm.
L. 
Design preparation. Designs of storm drainage systems shall be prepared by a licensed professional engineer. Complete detail calculations shall be submitted to the Township for approval. Calculations shall cover the entire drainage basin involved, including consideration of areas outside the proposed subdivision or developed land areas. All designs must be approved by the Township.
M. 
The developer shall provide written assurance, satisfactory to the Township, that the detention pond will be properly maintained. Such assurances shall be in a form to act as a covenant that will follow with the land, and shall provide Township maintenance in case of default, and further provide for assessment of costs and penalties in case of default in Township takeover.
N. 
As an alternate to the above Subsection M, the Township may, at its own option, assume responsibility of the pond and require dedication of the pond by the developer. If the detention basin is dedicated or offered to the Township for long-term maintenance, the following regulations shall apply:
(1) 
The dedicated area shall not be considered part of the open space and recreation dedication requirements as required in Chapter 159, Subdivision and Land Development.
(2) 
The detention basin berm top shall be a minimum width of eight feet.
(3) 
The developer shall provide for the special financial burden the Township will be accepting if the Township accepts the detention basin maintenance. To help mitigate this future financial burden the developer shall give to the Township a cash payment in the amount of $60,000 per acre, on a pro-rata basis, for any detention basin site or area dedicated to the Township and being accepted by the Township. This requirement is minimum and can be modified by a resolution of the Board of Supervisors, as necessary, to reflect actual long-term costs of detention basin maintenance in the Township.
[Amended 2-12-2002 by Ord. No. 02-01]
O. 
The design, construction and maintenance of all stormwater management facilities required by this chapter shall be provided in accordance with Chapter 67, Construction Standards, as amended.

§ 152-11 Collection system design.

A. 
The collection system shall be designed by the Rational Method of Design in accordance with American Society of Civil Engineers Manual No. 37 except where noted, using the formula Q = CiA, unless otherwise approved by the Township.
(1) 
Capacity: "Q" is the required capacity in cubic feet per second for the collection system at the point of design.
(2) 
Runoff coefficient: "C" is the runoff coefficient applicable to the entire drainage area. It shall be based on consideration of soil conditions, average slope of the drainage area and the ultimate development of the entire drainage area according to comprehensive plans. For the various types of ultimate development, the runoff coefficient shall be taken from the table in Appendix C,[1] unless sufficient engineering data has been presented to the Township Engineer by the developer which information in the judgment of the Township Engineer and the Board of Supervisors is sufficient to warrant the use of an alternate runoff coefficient.
[1]
Editor's Note: Appendix C is included at the end of this chapter.
(3) 
Rainfall intensity formula: "i" is the rainfall intensity in inches per hour and shall be determined from rainfall intensity charts for this area, based on time of concentrations, including overland flow time, Manning's formulae for channelized flow time and pipe flow time. The design rainfall frequency shall be taken from the PennDOT Intensity-Duration-Frequency Field Manual, Region 4, as presented in Appendix C.
(4) 
Drainage area: "A" is the drainage area, in acres, tributary to the point of design, and shall include areas tributary from outside sources as well as from within the subdivision or developed land area itself.
B. 
Flow velocity. Storm drains shall be designed to produce a minimum velocity of 3.0 feet per second when flowing full. The maximum permissible velocity shall be 15.0 feet per second.
C. 
Manholes. Manholes shall be spaced at intervals not exceeding 300 feet, and shall be located wherever branches are connected or sizes are changed, and wherever there is a change in alignment or grade. For drainage lines of at least 36 inches diameter, manholes may be spaced at intervals greater than 300 feet with the approval of the Township.
D. 
Drain line location. Drain lines shall be located between the center line of the street and the curbline, and shall parallel the center line of the street as far as practical.
E. 
Catch basin limits. Not more than two catch basins shall be interconnected before being connected to a manhole or access-type catch basin.
F. 
Open swales. Open swales shall be designed on the basis of Manning's formula as indicated for collection systems with the following considerations:
(1) 
Roughness coefficient. The roughness coefficient shall be 0.040 for earth swales, and 0.015 for paved swales.
(2) 
Bank slopes. Slopes for swale banks shall not be steeper than one vertical for three horizontal.
(3) 
Flow velocity. Design velocity in grass or vegetated swales shall not exceed four feet per second.
(4) 
Right-of-way. A swale right-of-way of sufficient minimum width to include a ten-foot access strip, in addition to the width of the swale from bank top, shall be shown as an easement for drainage purposes. The Township may, under unusual conditions, require a wider swale right-of-way.
G. 
General design standards.
(1) 
Curb inlets. Curb inlets shall be located at curb tangents on the uphill side of street intersections. Design and location of curb inlets shall be approved by the Township.
(2) 
State approvals. Drainage structures that are located on state highway rights-of-way shall be approved by the Pennsylvania Department of Transportation, and a letter from that office indicating such approval shall be directed to the Township.
(3) 
Pipe materials. All storm piping shall be Class III reinforced concrete piping with "O" ring joints. Piping shall be saw-cut at ends, as needed, and not hammered or broken.
(4) 
Minimum pipe size. Minimum pipe size shall be 15 inches.
(5) 
Inlet and manhole construction. Inlet and manhole castings and concrete construction shall be equivalent to Pennsylvania Department of Transportation design standards.
(6) 
Roof drainage. Stormwater roof drains and pipes shall not discharge water over a sidewalk, driveway or paved area. Where accessible, roof drains can be connected with a storm drain system.
(7) 
Discharge structures shall be designed to minimize the impact of development on downstream properties. Flow retarding and dissipating facilities are required to meet this goal. Such structures shall be no closer than 20 feet to downstream off-site properties or drainage easement boundaries.
(8) 
Open pipe ends must be fitted with concrete end walls or wing walls.
(9) 
No open pipe shall be allowed to end within the existing or proposed Township road or state road right-of-way.
(10) 
Any riprap dissipation area or riprap swale area shall be constructed with mixed stone sizes in accordance with PennDOT criteria for riprap and all such areas shall be lined with PennDOT approved geotextile fabric.
(11) 
A maximum of five cubic feet per second (cfs) will be permitted along the curb or roadside swale, prior to discharge away from the street surface by way of roadside swale or underground piping.
(12) 
All pipe endwalls or wingwalls and all detention basin intake and discharge structures shall be protected from frost-related movement and scour activity by the construction of a concrete footer with a minimum depth of 30 inches below ground level.
(13) 
The minimum pipe slope is 0.5%
(14) 
All inlets shall be labeled with an embedded plastic disk indicating a prohibition against pollutants.
[Added 4-10-2007 by Ord. No. 07-07]

§ 152-12 Storm sewer interceptor construction.

A. 
In accordance with the standards of this chapter, the developer shall provide throughout his development, and adjacent to his development, storm sewer facilities adequate to handle the expected storm flows. This requirement pertains to collector systems or interceptor systems.
B. 
The developer is required to install or improve the Township interceptor system, either on-site, off-site, or both, by the value of at least:
(1) 
Twelve dollars and fifty cents per lineal foot of new streets in developments for single-family detached building lots; or
(2) 
One dollar and eighty cents per square yard of impervious cover for all other developments or subdivisions.
C. 
In those cases where the developer cannot make all or a portion of such required improvements as outlined in Subsection B, the Township shall accept money in lieu of improvements. Such money shall be in an amount equal to the difference between the minimum required improvement value; no credit shall be due the developer from the Township.