[Ord. No. 98-3, 2/25/1998; as amended by Ord. No. 2007-03, 7/12/2007; and by Ord.
No. 2022-03, 10/25/2022]
1.
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.
2.
Easements shall be dedicated to the Township along all natural or man-made streams and watercourses (as described in § 8-223, Subsection 3) within a subdivision or land development. These easements should be of sufficient width to convey a 100-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 parkland crosses through the easement. 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.
F.
The landowner shall be responsible for all other maintenance and
repairs within this easement. For example the landowner must:
(1)
Mow the lawn.
(2)
Repair or replace fencing.
(3)
Repair or replace landscaping.
(4)
Repair sinkholes that may develop in the easement.
(5)
Keep the area free of obstructions, structures, vegetation or
accumulated sediment that may block or hinder the function and purpose
of the easement.
(6)
Keep the area free of litter or garbage.
3.
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.
4.
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.
5.
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.
6.
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.
7.
Low Point Drainage. 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. Underdrains
are required at a minimum for 50 feet upward from a road low point
along each approach road to the low point.
8.
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. Such detention facility
shall be designed in accordance with the following requirements:
A.
The detention facilities shall be designed to retard stormwater runoff rates after development to the peak runoff rate established for each district in Subpart C, § 8-222.
B.
Spillways shall be provided for possible overflows, and such spillways
shall be protected from erosion. Spillways shall be designed for the
100-year storm.
C.
Pipe outlet arrangements shall provide complete outletting of all
detained water, unless provisions for permanent ponding have been
approved.
D.
A detention basin, if utilized in an area of limestone geology, shall be lined with a synthetic impervious liner as more specifically described in Subsection 8J.
E.
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.
F.
To minimize the negative visual impact of detention basins, and avoid
the need for fencing, the basins shall be designed to the following
specifications:
(1)
Maximum depth of detained runoff shall be 24 inches for a ten-year
storm event; and
(2)
Maximum depth of detained runoff shall be 36 inches for a 100-year
storm event; and
(3)
Interior slopes shall not be steeper than a ratio of 4:1 horizontal
to vertical;
(4)
A water surface limit shall be no closer than 100 feet to any
residential building and no closer.
(5)
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.
G.
These depths 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:
(1)
A maximum depth of detained runoff shall be 24 inches for a
two-year storm event; and
(2)
A maximum depth of detained runoff shall be 36 inches for a
ten-year storm event; and
(3)
A maximum depth of detained runoff shall be 48 inches for a
100-year storm event; and
(4)
Interior side slopes shall not be steeper than a ratio of 5:1,
horizontal to vertical; and
(5)
A water surface limit no closer than 100 feet to any residential
building and no closer than 25 feet to any other type building.
I.
An access ramp of 10:1, 10 feet wide, shall be provided to allow
maintenance equipment to reach the basin floor.
J.
All detention/retention facilities, utilized in areas of limestone
geology, whether ultimately privately or publicly owned, shall be
lined with a synthetic impervious liner meeting the following minimum
requirements:
(1)
The minimum liner allowed is 30 mil PVC. Actual individual liner
specifications shall be provided by the manufactures for each individual
pond.
(2)
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.
(3)
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.
(4)
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.
(5)
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.
(6)
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.
(7)
The liner must be installed to a minimum height of the 100-year
floodwater elevation in the facility.
K.
The minimum slope of the bottom of a detention pond shall be 2% toward
the outlet structure.
9.
All streets shall be designed so as to provide for the discharge
of surface water from their rights-of-way.
10.
Design Criteria.
A.
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 Nonresidential Areas
|
100 year
|
|
Fixed Pipe
|
25
|
|
Total Conveyance
|
100-year
|
|
Culvert Crossings of Any Road
| |
|
In Culvert
|
25
|
|
Total Conveyance
|
100 year
|
B.
The preliminary plan or lot location plan shall indicate the areal
extent of the 100-year storm.
11.
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.
12.
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 shall run
with the land, and shall provide for municipal maintenance, assessment
of cost and penalties, in the case of lack of maintenance.
[Ord. No. 98-3, 2/25/1998; as amended by Ord. No. 2007-03, 7/12/2007; and by Ord.
No. 2022-03, 10/25/2022]
1.
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.
A.
Capacity. "Q" is the required capacity in cubic feet per second for
the collection system at the point of design.
B.
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 as an attachment to this chapter.
C.
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 Formula 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.
D.
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.
2.
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.
3.
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.
4.
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.
5.
Catch Basin Limits. Not more than two catch basins shall be interconnected
before being connected to a manhole or "access type" catch basin.
6.
Open Swales. Open swales shall be designed on the basis of Manning's
Formula as indicated for collection systems with the following considerations:
A.
Roughness Coefficient. The roughness coefficient shall be 0.040 for
earth swales, and 0.015 for paved swales.
B.
Bank Slopes. Slopes for swale banks shall not be steeper than one
vertical for three horizontal.
C.
Flow Velocity. Design velocity in grass or vegetated swales shall
not exceed four feet per second.
D.
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.
7.
General Design Standards.
A.
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. The collection capacity of curbed
inlets is to be determined using PennDOT standard efficiency charts
for the capture capacity of Type C inlets. All inlets shall be labeled
with an embedded plastic disk indicating a prohibition against pollutants.
B.
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.
D.
Minimum Pipe Size. Minimum pipe size shall be 15 inches.
E.
Inlet and Manhole Construction. Inlet and manhole castings and concrete
construction shall be equivalent to Pennsylvania Department of Transportation
Design Standards.
F.
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.
G.
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.
H.
Open pipe ends must be fitted with concrete end walls or wing walls.
I.
No open pipe shall be allowed to end within the Township road or
state road right-of-way, except in cases where new driveways must
cross existing deep road side swales adjacent to existing roads. In
the case of these exemptions to the standard, the pipe shall be located
as far off the edge of the pavement as possible (at least 14 feet
from the road center line), and shall be at least 12 inches in diameter.
J.
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.
K.
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.
L.
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.
M.
The minimum pipe slope allowed is 0.5%.
