Each land subdivision and/or land development, whether residential,
commercial or industrial in nature or use, shall provide and implement
a water drainage plan and stormwater management plan so as to prevent
any damage or injury to health, safety or property from stormwater
runoff or groundwater. The water drainage plan shall be in accordance
with this article and shall be prior approved by the Township. The
stormwater management plan shall be as required by Township ordinances
or as directed by the Township Engineer.
A. Runoff characteristics.
(1) All drainage management measures shall include such actions as are
required to manage the quantity, velocity and direction of resulting
ground water and/or stormwater runoff in a manner which protects health
and property from injury.
(2) Natural runoff flow characteristics shall be maintained either by
augmenting natural infiltration processes or by physically controlling
the release of development-related stormwater flow increases through
structural means.
B. Purpose of stormwater system.
(1) Positive drainage is required in all areas of development. The stormwater
system shall be planned and designed to direct stormwater runoff away
from all public roads, structures, buildings and development areas.
The stormwater drainage system shall provide drainage facilities at
all points along public streets and sidewalks, including other access
and circulation systems.
(2) Underdrainage shall be provided in all areas where springs, wet weather
springs, or where poor soil drainage conditions exist or result from
the development. During construction of any improvement, if springs
or any other poor drainage conditions are encountered, or when construction
of any improvement has or will alter the natural groundwater flow,
the Township shall be notified. Underdrainage shall be provided by
the owner/developer, as directed by the Township, to correct said
poor drainage condition.
(3) The stormwater system, including downspouting and other forms of
rainware which are utilized upon any structure within the land subdivision
and/or land development, and the underdrainage system shall be designed
to convey, contain, store, absorb and/or use the surface or underground
waters without damage to life or property and to minimize disruption
of land usage.
(4) All on-site storm drains (downspouts, area drains, foundation drains,
etc.) shall include all pipe required to convey runoff water directly
to storm sewers or the stormwater management facility. No runoff water
shall be allowed to discharge into the street/road.
(5) To the maximum extent possible, the stormwater drainage system and
underground drainage system shall be designed to convey stormwater
runoff through a conveyance system directly to a natural watercourse
and prevent the discharge of stormwater or underground water onto
adjacent facilities or properties.
(6) Natural drainage routing shall be preserved where feasible. No discharge
of on-site stormwater or underground water runoff into a natural drainage
routing shall be permitted when such discharge will damage adjacent
or downstream property.
(7) No stormwater drainage system or underground drainage system shall
be permitted to discharge into any sanitary sewer system.
C. Design standards.
(1) The storm sewer system shall be designed to intercept and convey
the peak rate of runoff from the twenty-five-year return storm.
(2) Stormwater runoff and design calculations to meet this requirement
shall be submitted to the Township for approval prior to preliminary
plan approval. Hydraulic computation presenting invert elevations,
pipe size, "n," capacity, velocity, hydraulic and energy grade line
shall be submitted.
(3) Stormwater runoff and design calculations shall be prepared by a
qualified Pennsylvania-registered engineer or land surveyor. Computational
method shall be Rational Method, Penn State Runoff Model or other
generally accepted procedure approved by the Township Engineer.
(4) Additional analysis, calculations and design criteria may be required
for both the on-site and off-site stormwater systems where it has
been determined by the Township that further study is necessary.
(5) Upon Township request, stormwater runoff calculations shall be made
available for the outlet and inlet sides of all stormwater drainage
and storage facilities and structures; at points in a public street
with a change of grade; or where water from a proposed structure,
facility or vehicular way is to enter an existing public street, existing
storm sewer, existing drainage ditch, or existing stormwater storage
facility.
D. Design to consider adjacent and future upstream development. The
stormwater drainage system for the land subdivision and land development
and, where required, the underdrainage system for a land subdivision
and/or land development shall be designed for compatibility with the
watershed stormwater management system and any Township or adjacent
municipality planned or proposed change to the system.
(1) The design shall anticipate and provide for the effects of all tributary
area and upstream development.
(2) The design shall anticipate and provide for impact(s) on downstream
flow conditions and water quality.
(3) Off-site stormwater drainage and underdrainage facilities and improvement
shall be provided by the applicant/owner of the proposed land subdivision
and/or land development where needed and where requested by the Township.
(4) Where required, the Pennsylvania Department of Environmental Protection
approval, including permits as required, shall be obtained by the
applicant/owner of the land subdivision and/or land development and
evidence of same provided to the Township.
E. Identification of responsibilities for stormwater systems.
(1) The installation, ownership, and maintenance responsibilities after
completion of the development for all stormwater drainage and storage
facilities and all underdrainage facilities shall be identified on
the preliminary plans and exhibits.
(2) All stormwater drainage or storage facilities or underdrainage facilities
to be publicly dedicated shall be located in a right-of-way, a drainage
easement, or in a location as required by the Township.
F. Designs and plans for all facilities.
(1) The design for all stormwater drainage and storage facilities shall be in accordance with the requirements of the Pennsylvania Department of Transportation Design Manual, Part
2, latest edition, and of this article.
(2) Plan and profile drawings to suitable scale shall be provided prior
to preliminary plan approval. Plan and cross-section drawings, catalog
cuts and specifications shall be provided showing complete construction
details for all stormwater drainage storage facilities and appurtenances
prior to final plan approval.
(3) The access control for any storage facility shall be approved by
the Township prior to preliminary plan approval.
(4) The design of all retention facilities shall be subject to the review
and approval of the Township Engineer and, where applicable, by the
Pennsylvania Department of Environmental Protection.
(5) Where open stormwater drainage and/or storage facilities are to be
constructed, the access control measures, erosion control measures,
capacity protection measures, flood protection measures, stagnant
water control measures, and appearance control measures shall be presented
for Township approval with the preliminary plans and exhibits.
(6) Stormwater retention facilities shall have sufficient capacity to
store the ten-year return storm at a minimum, except where a lesser
return frequency (e.g., twenty-five-, fifty- or one-hundred-year)
is determined to be appropriate at the sole discretion of the Township
Engineer or where required by watershed studies. A minimum of two
feet of freeboard shall be provided. The primary outlet structure
shall be designed to control the two-, five- and ten-year return storms.
An emergency spillway shall be designed to convey the twenty-five-,
fifty- or one-hundred-year return storms, as appropriate. All dike
embankments shall be a minimum of four feet wide at their crest.
G. Design of facilities to correlate with public street design. The
design of stormwater drainage and storage facilities shall be closely
correlated with the design of public streets.
(1) The depth of flow in gutters and allowable spread across the pavement
shall be approved by the Township Engineer.
(2) Free flow of stormwater runoff shall not be permitted onto the cartway
of any public street from a private driveway, access drive or any
other vehicular right-of-way.
H. Stormwater inlets. Stormwater inlets shall be spaced a maximum of
300 feet apart where pipe sizes of 24 inches or less are used and
not over 450 feet where larger pipe sizes are installed. Sufficient
inlets shall be provided to intercept all surface runoff.
(1) Grate inlets shall be depressed below the plane of the gutter.
(2) Curb inlets/openings shall have a maximum permitted height of six
inches unless otherwise provided with a protective barrier.
(3) Design of inlets shall be as required by runoff calculations.
I. Manholes. Manholes shall be spaced a maximum of 300 feet apart where
pipe sizes of 24 inches or less are used and not over 450 feet where
larger pipe sizes are installed. Design of manholes shall be as per
Standard Drawing 2-4. If approved by the Township, inlets may be substituted
for manholes.
J. Drainage of street intersections. Enclosed stormwater drainagecourses
shall be required at intersecting streets and elsewhere, as may be
deemed necessary by the Township. Stormwater shall be collected in
stormwater culverts or similar enclosed components.
(1) Stormwater culverts, bridges and similar structures serving public
streets, access drives or any other vehicular right-of-way, as may
be designated by the Township, shall be designed to support HS-20
loading and any other imposed loadings necessary without structurally
damaging the drainage system. The stormwater culverts, bridges and
similar structures shall be constructed to the full width of the right-of-way
plus any additional length as deemed necessary by the Township Engineer
to satisfy a local drainage pattern.
(2) Stormwater culverts in areas other than those noted above shall be
designed to support the necessary loading (existing and potential)
and any other imposed loadings without structurally damaging the pipe
or affecting its capacity for drainage. Said design shall be approved
by the Township Engineer.
(3) Conduit size of culverts or other enclosed components of a stormwater
drainage system shall be based on computed hydrologic and hydraulic
data, and computations shall be approved by the Township Engineer.
(a)
Minimum size of any enclosed structure to be maintained by the
Township shall be 15 inches in diameter.
(b)
Minimum size of any enclosed structure to be privately maintained
shall be 15 inches in diameter unless design calculations are provided
that can justify a lesser size. Design calculations shall be approved
by the Township Engineer.
(4) The design of the enclosed drainagecourse shall provide a minimum
cleaning velocity of three feet per second. When the design provides
for a maximum velocity greater than 10 feet per second, the enclosed
components shall be lined or protected to prevent scour.
(5) The headwall and endwall structures for enclosed stormwater facilities
shall be as per the requirements of Standard 2-6 and approved by the Township Engineer.
(6) Pipe materials used shall be reinforced concrete pipe (RCCP), Class
III minimum.
(7) Storm sewers 36 inches in diameter or less shall be constructed to
line and grade.
(8) The pipe zone of storm sewers shall be installed in natural, virgin
ground unless otherwise approved. The pipe zone shall be defined as
the area outside the pipe diameter six inches below, six inches on
either side and 12 inches above the pipe. No storm sewer pipe shall
be constructed in fill materials.
(9) Energy dissipaters shall be required at the outlet side of all enclosed
culverts or similar components and shall be designed to reduce the
velocity of flow sufficient to prevent damage to downstream areas.
(10)
No stormwater facility shall be enclosed or covered over until
the Township has inspected and approved said facility.
K. Water velocity limitations for open drainagecourses. Open stormwater
drainagecourses shall be designed for a maximum velocity not to exceed
10 feet per second and a minimum velocity of five feet per second.
A minimum velocity of three feet per second may be permitted where
a greater slope cannot be achieved to permit the standard required
minimum velocity. An open stormwater drainagecourse shall include
a lining (rip-rap, concrete, bituminous) to prevent erosion. Any required
approval of the Allegheny County Soil Conservation Service shall be
obtained by the applicant.
[Amended 8-14-1989 by Ord. No. 16-1989]
A. Any person violating any provision of this article shall, upon conviction
thereof, be sentenced to pay a fine of not more than $600 and costs
or, in default of payment thereof, shall be subject to imprisonment
for a term not to exceed 30 days, provided that each violation of
any provision of this article and each day the same is continued shall
be deemed a separate offense.
B. In the event of the violation of the provisions of this article by
any individual or corporation and when the Township deems it necessary
to correct any storm sewers constructed and/or installed contrary
to the provisions of this article, the Township may, at its discretion,
immediately repair or cause to be repaired or reconstructed any storm
sewer at the expense of the violator thereof, and said expenses shall
be collected by the Township in any suit at law for correction of
the same. In addition, the Township may institute appropriate action
at law or equity to restrain, correct or abate threatened or continued
violations of this article.