The Township finds that:
A.
Inadequate management of accelerated stormwater runoff resulting
from development throughout a watershed increases flood flows and
velocities contributes to erosion and sedimentation, overtaxes the
carrying capacity of existing streams and storm sewers, greatly increases
the cost of public facilities to convey and manage stormwater, undermines
floodplain management and flood reduction efforts in upstream and
downstream communities, reduces groundwater recharge, and threatens
public health and safety.
B.
A comprehensive program of stormwater management, including reasonable
regulation of development and activities causing accelerated erosion,
is fundamental to the public health, safety, welfare, and the protection
of the people of the Township and all the people of the Commonwealth,
their resources, and the environment.
C.
Inadequate planning and management of stormwater runoff resulting
from land development and redevelopment throughout a watershed can
also harm surface water resources by changing the natural hydrologic
patterns; accelerating stream flows (which increase scour and erosion
of streambeds and stream banks thereby elevating sedimentation); destroying
aquatic habitat; and elevating aquatic pollutant concentrations and
loadings such as sediments, nutrients, heavy metals, and pathogens.
Groundwater resources are also impacted through loss of recharge.
D.
Stormwater can be an important water resource by providing groundwater
recharge for water supplies and base flow of streams, which also protects
and maintains surface water quality.
E.
Public education on the control of pollution from stormwater is an
essential component in successfully addressing stormwater issues.
F.
Federal and state regulations require certain townships to implement
a program of stormwater controls. These townships are required to
obtain a permit for stormwater discharges from their separate storm
sewer systems under the National Pollutant Discharge Elimination System
(NPDES).
G.
Nonstormwater discharges to municipal separate storm sewer systems
can contribute to pollution of waters of the Commonwealth by the Township.
The purpose of this Part is to promote health, safety, and welfare within the Township and its watersheds, by minimizing the harms and maximizing the benefits described in § 22-601 of this Chapter through provisions designed to:
A.
Manage accelerated runoff and erosion and sedimentation problems
at their source, by regulating activities that cause these problems.
B.
Utilize and preserve the existing natural drainage systems as much
as possible.
C.
Encourage infiltration of stormwater, where appropriate, to maintain
groundwater recharge, to prevent degradation of surface and groundwater
quality, and to otherwise protect water resources.
D.
Maintain existing flows and quality of streams and watercourses in
the Township and the Commonwealth.
E.
Preserve and restore the flood-carrying capacity of streams and prevent,
scour and erosion of stream banks and streambeds.
F.
Provide proper operations and maintenance of all temporary and permanent
stormwater management facilities and BMPs that are constructed and
implemented in the Township.
G.
Provide performance standards and design criteria for watershed-wide
stormwater management and planning.
H.
Manage stormwater impacts close to the runoff source, with a minimum
of structures and a maximum use of natural processes.
I.
Meet legal water quality requirements under state law, including
regulations at 25 Pennsylvania Code Chapter 93.4a to protect and maintain
existing uses and maintain the level of water quality to support those
uses in all streams and to protect and maintain water quality in special
protection streams.
J.
Provide a mechanism to identify controls necessary to meet the NPDES
permit requirements.
K.
Implement an illegal discharge detection and elimination program
to address nonstormwater discharges into the Township's separate storm
sewer system.
L.
Permit the unimpeded flow of natural watercourses.
M.
Ensure the drainage of all low points along the streets and other
applicable areas.
N.
Intercept, retain, or detain surface water runoff in a manner reasonably
related to the extent and grade of the area drained.
O.
Provide positive drainage away from buildings.
1.
The Township is empowered to regulate land use activities that affect
runoff by the authority of the Act of October 4, 1978, 32 P.S., P.L.
864 (Act 167), Section 680.1 et seq., as amended, the "Storm Water
Management Act."
2.
The Township also is empowered to regulate land use activities that
affect runoff by the authority of the Act of July 31, 1968, P.L. 805,
No. 247, The Pennsylvania Municipalities Planning Code, as amended
by Act 170 of December 21, 1988, and Act 131 of December 14, 1992.
3.
Chapter 102 of the Rules and Regulations of the Department of Environmental
Protection, Subpart C, Protection of Natural Resources, Article II,
Water Resources, imposes requirements on earthmoving activities which
create accelerated erosion or a danger of accelerated erosion and
which require planning and implementation of effective soil conservation
measures.
1.
This Chapter shall apply to any regulated activity within the Township,
and all stormwater runoff entering into the Township's separate storm
sewer system from lands within the boundaries of the Township.
2.
Earth disturbance activities and associated stormwater management
controls are also regulated under existing state law and implementing
regulations. This Chapter shall operate in coordination with those
parallel requirements; the requirements of this Chapter shall be no
less restrictive in meeting the purposes of this Chapter than state
law.
3.
The following activities are defined as regulated activities and
shall be regulated by this Chapter:
A.
Land development.
B.
Subdivision.
C.
Land/earth disturbance activities.
D.
Construction of new or additional impervious or semi-pervious surfaces
(driveways, parking lots, etc.).
E.
Construction of new buildings or additions to existing buildings.
F.
Diversion or piping of any natural or man-made stream channel.
G.
Installation of stormwater management facilities or appurtenances
thereto.
H.
Mining operations.
I.
Nursery, forest or agriculture operations.
J.
Other activities, which would cause an increase in stormwater runoff.
Any ordinance or ordinance provision(s) of the Township inconsistent
with any of the provision(s) of this Chapter is hereby repealed to
the extent of the inconsistency only.
Should a court of competent jurisdiction declare any section(s)
or provision(s) of this Section invalid, such decision shall not affect
the validity of any of the remaining section(s) or provision(s) of
this Chapter.
1.
Approvals issued pursuant to this Chapter do not relieve the applicant
of the responsibility to comply with or to secure required permits
or approvals for activities regulated by any other applicable codes,
rules, statutes, or ordinances. To the extent that this Chapter imposes
more rigorous or stringent requirements for stormwater management,
the specific requirements contained in this Chapter shall be followed.
2.
Nothing in this Chapter shall be construed to affect any of the Township's
requirements regarding stormwater matters which do not conflict with
the provisions of this Chapter, such as local stormwater management
design criteria (e.g., inlet spacing, inlet type, collection system
design and details, outlet structure design, etc.). Conflicting provisions
in other Township ordinances or regulations shall be construed to
retain the requirements of this Chapter addressing State water quality
requirements.
The degree of stormwater management sought by the provisions
of this Chapter is considered reasonable for regulatory purposes.
This Chapter shall not create liability on the part of the Township,
any appointed or elected official of the Township, the Dauphin County
Conservation District or any officer, engineer or employee thereof
for any erosion, sedimentation or flood damages or flood damages that
result from reliance on this Chapter or any administrative decision
lawfully made there under.
Notwithstanding any provision(s) of this Chapter, including
exemptions, any landowner or any person engaged in the alteration
or development of land which may affect stormwater runoff characteristics
shall implement such measures as are reasonably necessary to prevent
injury to health, safety, or other property. Such measures also shall
include actions as are required to manage the rate, volume, direction,
and quality of resulting stormwater runoff in a manner which otherwise
adequately protects health, property, and water quality.
1.
All regulated activities in the Township, which are not granted an exemption under § 22-611, shall submit a drainage plan consistent with this Chapter to the Township for review. These criteria shall apply to the total proposed development even if development is to take place in stages. Impervious cover shall include, but not be limited to: additional indoor living space, decks, patios, garages, storage sheds and similar structures, roofs, parking or driveway areas, and any new streets and sidewalks. Any areas designed to initially be gravel or crushed stone shall be assumed to be impervious. The Drainage Plan shall be approved prior to the final approval of the regulated activity.
2.
All regulated activities within the Township shall be designed, implemented,
operated, and maintained to meet the purposes of this Chapter, through
these three elements:
3.
No earth disturbance activities within the Township associated with
any regulated activities shall commence until the requirements of
this Chapter are met.
4.
All BMPs used to meet the requirements of this Chapter shall be designed,
installed, operated, and maintained to conform to the State water
quality requirements, the requirements of the Clean Streams Law and
implementing regulations, and any more stringent requirements as determined
by the Township.
5.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this Chapter.
6.
The existing points of concentrated drainage that discharge onto
adjacent property shall not be altered without permission of the altered
property owner(s) and shall be subject to any applicable discharge
criteria specified in this Chapter.
7.
Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this Chapter. If diffused
flow is proposed to be concentrated and discharged onto adjacent property,
the developer must document that adequate downstream conveyance facilities
exist to safely transport the concentrated discharge, or otherwise
prove that no erosion, sedimentation, flooding, or other harm will
result from the concentrated discharge.
8.
Where watercourses traverse a development site, drainage easements
shall be provided conforming to the line of such watercourses. The
terms of the easement shall prohibit excavation, the placing of fill
or structures, and any alterations that may adversely affect the flow
of stormwater within any portion of the easement. Also, maintenance,
including mowing of vegetation within the easement may be required,
except as approved by the appropriate governing authority.
9.
All natural streams, channels, swales, drainage systems and surface
water concentrations shall be maintained in their existing condition
unless an alteration is approved by the Township and all encroachment
activity shall comply with the requirements of Chapter 105 (Dam Safety
and Waterway Management) of Pa. Title 25, Environmental Protection.
Any stormwater management facility intended to meet the requirements
of this Chapter that constitutes an encroachment or enclosure, as
described in Chapter 105, will require a DEP permit.
10.
Any stormwater management facilities regulated by this Chapter that
will be located in or adjacent to waters of the Commonwealth (including
wetlands) shall be subject to approval by DEP under regulations at
25 Pennsylvania Code Chapter 105 through the joint permit application
process, or, where deemed appropriate by DEP, the general permit process.
When there is a question whether wetlands may be involved, it is the
responsibility of the developer or his agent to show that the land
in question cannot be classified as wetlands; otherwise, approval
to work in the area must be obtained from DEP.
A.
Where no wetlands will be impacted by the proposed subdivision or
land development the applicant shall provide the certification on
the plan:
"I, (signature of consultant and date), hereby certify that
there are no wetlands on the subject property, the proposed project
will not impact off-site wetlands, and wetland permits are not required
from the state or federal government."
|
11.
Culverts, bridges, storm sewers, or any other facilities which must
pass or convey flows from the tributary area and any facility which
may constitute a dam are subject to permit by DEP under regulations
at 25 Pennsylvania Code Chapter 105.
12.
All earth disturbance activities are subject to permit requirements
by DEP under regulations at 25 Pennsylvania Code Chapter 102.
13.
Any stormwater management facilities regulated by this Chapter that
will be located on State highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
14.
Minimization of impervious surfaces and infiltration of runoff through
seepage beds, infiltration trenches, etc., are encouraged, where soil
conditions permit, to reduce the size or eliminate the need for detention
facilities.
15.
Developers are encouraged to incorporate designs to take advantage
of the stormwater credits presented in the Spring or Paxton Creek
Act 167 Stormwater Management Plans.
16.
Special Conditions for Areas Falling within Defined Exceptional Value
and High Quality Sub-Watersheds. The temperature and quality of water
and streams that have been declared as exceptional value and high
quality is to be maintained as defined in Chapter 93, Water Quality
Standards, Title 25, of Pennsylvania Department of Environmental Protection
Rules and Regulations. Temperature sensitive BMPs and stormwater conveyance
systems are to be used and designed with storage pool areas and supply
outflow channels and should be shaded with trees. This will require
modification of berms for permanent ponds and relaxation of restrictions
on planting vegetation within the facilities, provided that the capacity
for volumes and rate controls is maintained. At a minimum, the southern
half on pond shorelines will be planted with shade or canopy trees
within 10 feet of the pond shoreline. In conjunction with this requirement,
the maximum slope allowed on the berm area to be planted is 10 to
one. This will lessen the destabilization of berm soils due to root
growth. A long-term maintenance schedule and management plan for the
thermal control BMPs is to be established and recorded for all development
sites.
18.
Infiltration for stormwater management is encouraged where soils
and geology permit, consistent with the provisions of this Chapter
and, where appropriate, infiltration is encouraged for capturing and
treating any part of the water quality volume or for otherwise meeting
the purposes of this Chapter.
19.
The Township may, after consultation with DEP, approve alternative
methods for meeting the State water quality requirements other than
those in this Section, provided that they meet the minimum requirements
of, and do not conflict with, State law, including, but not limited
to, the Clean Streams Law.
20.
All developments that create impervious surface or change the existing topography, except for exemptions provided in § 22-611, shall demonstrate that adequate capacity will be provided to contain the ground water recharge and to treat the water quality requirements, as described under §§ 22-617 and 22-618 of this Chapter.
21.
If a regulated activity by this Chapter is to be performed by any
individual, firm, contractor or other entity other than that which
submitted the Drainage Plan, such entity shall, by signature, acknowledge
awareness of the plan requirements before the start of the regulated
activity.
22.
Although there are no stormwater control methods restricted from
or required for use, the following considerations apply to the selection
and use of any method:
A.
The Township may approve or disapprove those methods based on geologic,
topographic, hydrologic, soil, aesthetic, safety, health or other
considerations.
B.
The following is a list of methods which may be used for stormwater
control. The choice of control method is not limited to these methods
and any method selected should be carefully suited to the requirements
of the project and the characteristics of the site:
(1)
Detention basins.
(2)
Roof-top storage.
(3)
Parking lot storage.
(4)
Infiltration structures.
(5)
Porous pavement.
(6)
Grassed channels.
(7)
Underground storage.
(8)
Cisterns.
NOTE: For further description of those and other
methods, see the Pennsylvania Stormwater Best Management Practices
Manual.
|
1.
Two exemptions (Exemption 1, Release Rates, Water Quality Volume,
Channel Protection Volume, and Drainage Plan Submission; and Exemption
2, Ground Water Recharge) from this Chapter may be granted at the
discretion of the Township. The applicant must demonstrate that the
following BMPs are being utilized to the maximum extent practicable
to receive consideration for either of the two exemptions:
A.
Design around and limit disturbance of floodplains, wetlands, natural
slopes over 15%, existing native vegetation, and other sensitive and
special value features;
B.
Clearly show limits of disturbance on construction plans;
C.
Maintain riparian and forested buffers;
D.
Limit grading and maintain non-erosive flow conditions in natural
flow paths;
E.
Maintain existing tree canopies near impervious areas;
F.
Minimize soil disturbance and reclaim disturbed areas with topsoil
and vegetation;
G.
Direct runoff to pervious areas;
H.
Utilize stormwater credits presented in the Spring or Paxton Creek
Act 167 Stormwater Management Plans; and
I.
Utilize guidance listed in the Pennsylvania Stormwater Best Management
Practices Manual.
2.
Exemption 1: Release Rates, Water Quality Volume, Channel Protection
Volume, and Drainage Plan Submission. An exemption of these requirements
contained within this Chapter for all regulated activities within
the Township may be granted at the discretion of the Township in accordance
with the following:
A.
An exemption of Release Rates, Water Quality Volume, Channel Protection
Volume, and Drainage Plan Submission may be granted in accordance
with Table 611.1 to determine the maximum additional impervious area
(and associated minimum separation distance) that can be placed on
a development site. This exemption shall be granted only if the Township
determines that proposed development/additional impervious area will
not adversely impact the following:
B.
Development that is planned to occur in stages or phases will be
considered in its entirety for the purposes of determining the exemption.
Table 611.1
Exemption Criteria
| |||
---|---|---|---|
Parcel Size*
(acres)
|
Minimum Separation Distance
(feet)
|
Maximum Additional Impervious Area — Since The Date
of Adoption of This Chapter
(square feet)
| |
0.5
|
10
|
2,700
| |
1.0
|
50
|
4,600
| |
1.5
|
100
|
6,200
| |
2.0
|
125
|
7,600
| |
2.5
|
150
|
9,000
| |
3.0
|
175
|
10,300
| |
3.5
|
200
|
11,500
| |
4.0
|
225
|
12,700
| |
4.5
|
250
|
13,800
| |
5.0
|
275
|
15,000
| |
>5.0
|
300
|
15,000
|
*
|
NOTE: Parcel size to be rounded to the nearest
half-acre for the purpose of utilizing Table 611.1.
|
3.
Exemption 2: Ground Water Recharge. An exemption of this requirement
for all regulated activities within the Township may be granted at
the discretion of the Township in accordance with the following:
A.
An exemption of Ground Water Recharge may be granted if the maximum
additional impervious coverage is 2,000 square feet or less. Development
sites that generate greater than 2,000 square feet of new impervious
cover are not eligible for this exemption based on additional impervious
coverage. The 2,000 square foot maximum additional impervious cover
applies to the total amount of additional impervious cover to be placed
on a development site whether the project is a single phase or will
occur in multiple phases. It does not include existing impervious
cover placed on a development site prior to the adoption of this Chapter.
B.
An exemption of Ground Water Recharge may be granted if the Township,
based upon data provided by the applicant, determines that the Ground
Water Recharge requirements are not suitable in the following areas:
(1)
High groundwater table (need minimum of three feet from bed
of infiltration facility to seasonal high groundwater elevation).
(2)
Shallow depth to bedrock (need minimum of two feet from bed
of infiltration facility to top of bedrock).
(3)
High risk of sinkhole development, to be determined on a case-by-case
basis.
4.
At the discretion of the Township, the applicant may be required
to provide a detailed geotechnical evaluation.
1.
The Township is hereby divided into stormwater management districts
in accordance with the Paxton Creek Stormwater Management Plan, the
Paxton Creek Release Rate Map, the Spring Creek Stormwater Management
Plan and the Spring Creek Release Rate Map. The official release rate
district maps are available for inspection at the Township office.
All areas within the districts are subject to the specified release
rates. The two-, ten-, and twenty-five-year design storms are all
subject to the specified release rates.
2.
If the developer can show that the post-development hydrograph matches
the predevelopment hydrograph for peak flows and volume, for all design
storms, then meeting the requirements of the release rates are not
required.
3.
Specific Watershed Requirements:
A.
Paxton Creek Watershed: Specified Release Rate Districts. For all
districts in this category, the future runoff must be controlled to
the specified release rate. That is, the post-development runoff rate
must be less than or equal to the predevelopment rate multiplied by
the specified release rate for that district.
B.
Paxton Creek Watershed: Provisional No Detention Districts. These watershed areas may discharge post-development peak runoff without detention facilities. However, the developer must prove that the "local" runoff conveyance facilities which transport runoff from the site to the main channel have adequate capacity to safely transport unattenuated increased peak flows for a twenty-five-year storm in accordance with § 22-613(3). If there is inadequate capacity, the developer shall either use 100% release rate control or provide increased capacity of downstream drainage facilities to convey increase peak flows consistent with § 22-613(3). When determining if adequate capacity exists in the local watershed drainage network, the developer must assume that the entire local watershed is developed per current zoning and that all new development will use the least restrictive runoff controls specified by this Section.
C.
Spring Creek Watershed: Specified Release Rate Districts. For all
districts in this category, the future runoff must be controlled to
the specified release rate. That is, the post-development runoff rate
must be less than or equal to the predevelopment rate multiplied by
the specified release rate for that district.
D.
Areas Not Within the Paxton Creek or Spring Creek Watershed. For
all areas within the Township but outside the Paxton Creek or Spring
Creek Watersheds, the future peak rate of runoff for the two-, ten-
and twenty-five-year design storms must be controlled to the existing
rate.
E.
The exact location of any given development site, or activity regulated
by this Chapter relative to the release rate district boundaries shall
be determined by mapping the release rate district boundaries using
two foot topographic contour mapping provided as part of the Drainage
Plan.
F.
For the proposed development site located entirely within one release
rate district, the total runoff from the site shall meet the required
release rate criteria. For sites with multiple discharge points, any
individual point may be designed to a 100% release rate, provided
that the total runoff from the site is controlled to the applicable
release rate for that district.
G.
For a proposed development site which is located within two or more
release rate districts, the maximum runoff discharged at any point
shall be equal to the release rate for the district in which the discharge
point is located. In the event that a portion of the site is located
in a provisional no detention area, no runoff from portions of the
site located in areas subject to release rate controls may be drained
to or through the provisional no detention area.
H.
Each development site shall be considered separately and shall conform
to the criteria of the district in which it is located. In no case
may the release rate for an area be exceeded as credit for a reduction
below the criteria or any other restrictions on a separate site.
I.
Regional detention facilities will be permitted, provided that adequate
conveyance is available or provided from the site to the facility.
The acceptability and discharge characteristics of the facility will
be determined on a case by case basis, by the Township Engineer, using
the calibrated model developed for the Paxton Creek Act 167 Plan or
Spring Creek Act 167 Plan, as applicable.
1.
Off-Site Areas. Off-site areas that drain through a proposed development
site are not subject to release rate criteria when determining allowable
peak runoff rates. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site.
2.
No-Harm Option. For any proposed development site, the developer has the option of using a less restrictive runoff control (including no detention) if the developer can prove that no harm would be caused by discharging at a higher runoff rate than existing conditions. The no-harm option is used when a developer can prove that the post-development hydrographs can match pre-development hydrographs, or if it can be proven that the post-development conditions will not cause increases in peak flows at all points downstream. Proof of no harm would have to be shown based upon a downstream impact evaluation which shall include a downstream hydraulic capacity analysis consistent with § 22-613(3) to determine if adequate hydraulic capacity exists. The developer shall submit this evaluation of the impacts due to increased downstream stormwater flows in the watershed to the Township.
A.
The downstream impact evaluation shall include hydrologic and hydraulic
calculations necessary to determine the impact of hydrograph timing
modifications due to the proposed development upon a dam, highway,
structure, natural point of restricted stream flow, or any stream
channel section, established with the concurrence of the Township.
B.
Proof of no harm must be shown from the point of discharge through
entire downstream network to the mouth of Paxton Creek or Spring Creek,
as applicable, at the Susquehanna River. For those areas outside of
the Paxton Creek and Spring Creek Watersheds, proof of no harm must
be shown through the entire downstream network to the ultimate discharge
point at the Susquehanna River.
C.
The peak flow values to be used for downstream areas for the design
return period storms (two-, ten-, and twenty-five-year) shall be the
values from the calibrated model for the Paxton Creek or Spring Creek
Watershed Act 167 Plans. These flow values can be obtained from the
watershed plan.
D.
Developer-proposed runoff controls which would generate increased
peak flow rates at storm drainage problem areas would, by definition,
be precluded from successful attempts to prove no harm, except in
conjunction with proposed capacity improvements for the problem areas.
E.
A financial distress shall not constitute grounds for granting a
no-harm exemption.
F.
Capacity improvements may be provided as necessary to implement the
no-harm option, which proposes specific capacity improvements to demonstrate
that a less stringent discharge control would not create any harm
downstream.
G.
Any available capacity in the downstream conveyance system as documented
by a developer may be used by the developer only in proportion to
his development site acreage relative to the total upstream undeveloped
acreage from the identified capacity (i.e., if his site is 10% of
the upstream undeveloped acreage, he may use up to 10% of the documented
downstream available capacity).
H.
Any municipality approving a no-harm option shall notify all downstream
municipalities of such approval. The approving municipality shall
make all relevant information used to prove a no-harm option available
upon request to any municipality with the Paxton Creek Watershed and
the Spring Creek Watershed.
I.
Any no-harm justifications shall be submitted by the developer as
part of the Drainage Plan submission. The burden of proof shall rest
on the developer.
3.
Downstream Hydraulic Capacity Analysis. Any downstream capacity hydraulic
analysis conducted in accordance with this Chapter shall use the following
criteria for determining adequacy for accepting increased peak flow
rates:
A.
Natural or man-made channels or swales must be able to convey the
increased runoff associated with a twenty-five-year return period
event within their banks at velocities consistent with protection
of the channels from erosion. Acceptable velocities shall be based
upon criteria included in the DEP Erosion and Sediment Pollution Control
Program Manual.
B.
Natural or man-made channels or swales must be able to convey the
increased twenty-five-year return period runoff without creating any
hazard to persons or property.
C.
Culverts, bridges, storm sewers, or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with DEP, Chapter 105 regulations (if applicable), and, at a minimum,
pass the increased twenty-five-year return period runoff, except for
facilities located within a designated floodplain area which must,
at a minimum, conform to FEMA and local floodplain ordinance requirements.
4.
Regional Detention Alternatives. For certain areas within the watershed,
it may be more cost-effective to provide one control facility for
more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives is the responsibility of
prospective developer(s). The design of any regional control basins
must incorporate reasonable development of the entire upstream watershed.
The peak outflow of a regional basin would be determined on a case-by-case
basis using the hydrologic model of the watershed consistent with
protection of the downstream watershed areas. "Hydrologic model" refers
to the calibrated model as developed for the Paxton Creek Stormwater
Management Plan.
5.
Capacity improvements may be provided as necessary to permit direct
discharge in a provisional no detention district, to implement any
regional or subregional detention alternatives, or to implement a
no-harm option which proposes specific capacity improvements to document
the validity of less stringent discharge control which would not create
any harm downstream.
1.
Stormwater runoff from all development sites shall be calculated
using either the Rational Method or a Soil-Cover-Complex methodology.
A.
Any stormwater runoff calculations involving drainage areas greater
than 20 acres, including on- and off-site areas, shall use a generally
accepted calculation technique that is based on the NRCS Soil Cover
Complex Method. Table 614.1 summarizes acceptable computation methods.
It is assumed that all methods will be selected by the design professional
based on the individual limitations and suitability of each method
for a particular site.
B.
The Township may approve the use of the Modified Rational Method
to estimate peak discharges from drainage areas that contain less
than 20 acres. However, the Modified Rational Method may not be used
to compute the volume of stormwater runoff.
C.
The Township may approve the use of any generally accepted full hydrograph
approximation technique that shall use a total runoff volume that
is consistent with the volume from a method that produces a full hydrograph.
D.
All calculations consistent with this Chapter using the Soil Cover
Complex Method shall use the appropriate design rainfall depths for
the various return period storms presented in Table A-1 in Appendix
A[1] of this Chapter. If a hydrologic computer model is used
for stormwater runoff calculations, then the duration of rainfall
shall be 24 hours along with a Soil Conservation Service Type II rainfall
distribution.
[1]
Editor's Note: Appendix A is included as an attachment to
this Chapter.
E.
For the purpose of predevelopment flow rate determination, undeveloped
land shall be considered as "meadow" good condition, or "range" unless
the natural ground cover generates a lower Rational "C" value or curve
number (i.e. forest).
F.
For the purpose of post-development flow rate determination, the
proposed ground cover shall be used to determine the Rational "C"
value or curve number.
G.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times of concentration for overland flow
and return periods from the Intensity Duration Frequency (IDF) Curves
from the Pennsylvania Department of Transportation, latest version.
H.
Times of concentration for overland flow may be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS), for developed sites. Times of concentration for channel and pipe flow shall be computed using the Manning equation.
(1)
The length of the flow path for sheet flow shall not exceed
150 feet and the length of the flow path for shallow concentrated
flow shall not exceed 1,000 feet.
I.
Times of concentration for undeveloped sites may also be computed
using the SCS equation for lag time:
Time of Concentration = Tc = [(Tlag/.6) * 60] (minutes)
|
Where:
| ||||
Tlag
|
=
|
Lag time (hours)
| ||
L
|
=
|
Hydraulic length of watershed (feet)
| ||
Y
|
=
|
Average overland slope of watershed (percent)
| ||
S
|
=
|
Maximum retention in watershed as defined by:
| ||
S
|
=
|
[(1,000/CN) - 10]
| ||
CN
|
=
|
SCS curve number for watershed as defined by the SCS Loss Method
|
J.
Runoff coefficients (C) for both existing and proposed conditions
for use in the Rational Method shall be obtained from Table A-3 in
Appendix A of this Chapter.
K.
Runoff curve numbers (CN) for both existing and proposed conditions
to be used in the Soil Cover Complex Method shall be obtained from
Table A-2 in Appendix A of this Chapter.
L.
Where uniform flow is anticipated, the Manning equation shall be
used for hydraulic computations and to determine the capacity of open
channels, pipes, and storm sewers. Values for Manning roughness coefficient
"n" shall be consistent with Table A-4 in Appendix A of this Chapter.
Manning equation should not be used for analysis of pipes under pressure
flow or for analysis of culverts.
M.
The design of any stormwater detention facilities intended to meet
the performance standards of this Chapter shall be verified by routing
the future two-, ten-, twenty-five- and one-hundred-year hydrographs
through these facilities using the Storage-Indication Method or Modified
Puls Method. For drainage areas greater than 20 acres in size, the
design storm hydrograph shall be computed using a calculation method
that produces a full hydrograph.
N.
The Township has the authority to require that computed existing
runoff rates be reconciled with field observations and conditions
and site history. If the designer can substantiate, through actual
physical calibration, that more appropriate runoff and time of concentration
values should be utilized at a particular site, then appropriate variations
may be made upon review and recommendation of the Township.
O.
Principal outlet structures for stormwater management facilities
shall be designed to meet the performance standards of this Chapter
using any generally accepted hydraulic analysis technique or method.
Table 614.1 — Acceptable Computation Methodologies
for Stormwater Management Plans
| |||
---|---|---|---|
Method*
|
Method Developed By
|
Applicability
| |
TR-20 or Commercial Package Based on TR-20
|
USDA — NRCS
|
When use of full model is desirable or necessary
| |
TR-55 Or Commercial Package Based on TR-55
|
USDA — NRCS
|
Applicable for plans within the models limitations
| |
HEC — HMS
|
U.S. Army Corps of Engineers
|
When full model is desirable or necessary
| |
PSRM
|
Penn State University
|
When full model is desirable or necessary
| |
Rational Method or Commercial Package based on Rational Method
|
Emil Kuiching (1889)
|
For sites less than 20 acres
| |
Other Methods
|
Various
|
As approved by the Municipal Engineer
|
*
|
NOTE: Successors to the above methods are also
acceptable. These successors include Win TR55 for TR-55 and Win TR20
for TR-20.
|
1.
No earth disturbance activities within the Township shall commence
until approval by the Dauphin County Conservation District of an Erosion
and Sediment Control Plan for construction activities.
2.
When 5,000 square feet or more of earth disturbance activities are
proposed, an Erosion and Sedimentation Control Plan must be submitted
to the Dauphin County Conservation District and the Township in accordance
with 25 Pennsylvania Code § 102.4(b). In addition, a letter
from the Dauphin County Conservation District approving the Erosion
and Sedimentation Control Plan must be obtained.
3.
DEP has regulations, under 25 Pa. Code Chapter 92, that a DEP NPDES
Construction activities permit is required and must be obtained from
the Dauphin County Conservation District and or DEP for earth disturbance
activities.
4.
Evidence of any necessary permit(s) for earth disturbance activities
from the Southcentral Regional DEP office or Dauphin County Conservation
District must be provided to the Township.
5.
A copy for the Erosion and Sediment Control Plan and any required
permit, as required by DEP regulations, shall be available at the
project site at all times.
6.
Design Criteria for Erosion Control Facilities. All erosion control
facilities shall be designed at a minimum to meet the design standards
and specifications of the latest revision of the Erosion and Sediment
Pollution Control Program Manual, published by DEP. Grassed waterways
allow recharge of groundwater. The usage of grassed waterways is not
recommended in areas of year-round or seasonally high groundwater
tables unless provision is made to handle long duration flows, for
example by means of subsurface drainage or stone centered waterways.
7.
Construction Standards for Erosion Control Facilities. Construction
standards for erosion control facilities shall be in accordance with
the approved plans and accompanying specifications. The construction
standards for erosion control facilities outlined in the latest revision
of the Erosion and Sediment Pollution Control Program Manual published
by DEP shall be considered the minimal acceptable standard. Controls
shall be installed at initial stages of earthmoving and otherwise
as outlined in the staging of earthmoving activities section of the
soil erosion and sediment control plan.
8.
Maintenance Criteria for Erosion Control Practices. Maintenance is
an essential part of the successful functioning of an erosion control
system.
A.
Maintenance during development of a project shall be the responsibility
of the developer and/or landowner and shall usually include, but not
be limited to:
(1)
Removal of silt from all debris basins, traps or other structures
or measures when capacity of those structures is reached. (See DEP's
Erosion and Sediment Pollution Control Program Manual, current edition.).
(2)
Periodic maintenance of temporary control facilities such as
replacement of straw bale dikes, straw filters or similar measures.
(3)
Establishment or reestablishment 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 design frequencies.
(5)
The contractor or developer shall be responsible for removal
of all temporary measures and installation of permanent measures upon
completion of the project.
B.
After dedication of facilities to the Township, except in cases where
agreements to the contrary have been previously executed, maintenance
shall be the responsibility of the Township and shall include:
(1)
Mowing to maintain adequate stands of grass and to control weeds.
Chemical weed control may be used if State and local regulations are
met. Selection of seed mixtures should reflect the type of maintenance
desired by the Township.
(2)
Removal of silt from all permanent structures which trap silt
or sediment is essential to keep this material from building up in
grassed waterways and reducing their capacity.
(3)
It shall be the responsibility of the Township to inspect all
permanent facilities and to see that corrective action is taken where
necessary.
1.
No regulated earth disturbance activities within the Township shall
commence until approval by the Township of a plan which demonstrates
compliance with State water quality requirements after construction
is complete.
2.
The BMPs must be designed, implemented, and maintained to meet State
water quality requirements, and any other more stringent requirements
as determined by the Township.
3.
To control post-construction stormwater impacts from earth disturbance
activities, State water quality requirements can be met by a variety
of BMPs, including site design, which provide for replication of pre-construction
stormwater infiltration and runoff conditions, so that post-construction
stormwater discharges do not degrade the physical, chemical or biological
characteristics of the receiving waters. As described in the DEP Comprehensive
Stormwater Management Policy (#392-0300-002, September 28, 2002),
this may be achieved by the following:
A.
Groundwater Recharge/Infiltration: replication of pre-construction
stormwater infiltration conditions;
B.
Water Quality Treatment: use of water quality treatment BMPs to ensure
filtering out of the chemical and physical pollutants from the stormwater
runoff; and
C.
Stream Bank and Streambed Protection: management of volume and rate
of postconstruction stormwater discharges to prevent physical degradation
of receiving waters (e.g., from scouring).
4.
DEP has regulations that require the Township to ensure design, implementation,
and maintenance of BMPs that control runoff from new development and
redevelopment after earth disturbance activities are complete. These
requirements include the need to implement post-construction stormwater
BMPs with assurance of long-term operations and maintenance of those
BMPs.
1.
The ability to retain and maximize the ground water recharge capacity
of the area being developed or redeveloped is encouraged. Design of
the infiltration/recharge stormwater management facilities shall give
consideration to providing ground water recharge to compensate for
the reduction in the percolation that occurs when the ground surface
is paved and roofed over. These measures are encouraged, particularly
in hydrologic soil groups A and B and shall be utilized wherever feasible.
2.
The annual recharge volume requirement shall be specified for a site
as follows:
A.
Percent Volume Method
Rev = [(S)(Rv)(A)] / 12
| ||||
Where:
| ||||
Rev
|
=
|
Groundwater Recharge Volume (ac-ft)
| ||
S
|
=
|
Soil Specific Recharge Factor
| ||
Rv
|
=
|
0.05 + 0.009(I)
| ||
I
|
=
|
Percent Impervious Cover (i.e., use I = 20 when there is 20%
impervious cover)
| ||
A
|
=
|
Site area (acres)
|
B.
Percent Area Method
Rev=(S)(Ai)
| ||||
Where:
| ||||
Rev
|
=
|
Groundwater Recharge Volume (ac-ft)
| ||
S
|
=
|
Soil Specific Recharge Factor
| ||
Ai
|
=
|
Measured impervious cover (acres)
|
Hydrologic Soil Group
|
Soil Specific Recharge Factor
(S)
| |
---|---|---|
A
|
0.39
| |
B
|
0.26
| |
C
|
0.14
| |
D
|
0.07
|
C.
The recharge volume is considered part of the total water quality
volume WQv that must be provided at a site
and can be achieved either by a structural practice (e.g., infiltration,
bioretention), a nonstructural practice (e.g., buffers, disconnection
of rooftops), or a combination of both.
D.
Drainage areas having no impervious cover and no proposed disturbance
during development may be excluded from the Rev calculations. Designers are encouraged to use these areas as nonstructural
practices for Rev treatment.
E.
Note: Rev and WQv are
inclusive. When treated separately, the Rev may be subtracted from the WQv when sizing
the water quality BMP.
3.
Basis for Determining Recharge Volume.
A.
Developers are encouraged to incorporate designs to take advantage
of the stormwater credits presented in the Spring or Paxton Creek
Act 167 Stormwater Management Plans.
B.
If more than one HSG is present at a site, a composite soil-specific
recharge factor shall be computed based on the proportion of total
site area within each HSG. The recharge volume provided at the site
shall be directed to the most permeable HSG available.
C.
The "Percent Volume" method is used to determine the Rev treatment requirement when structural practices are
used to provide recharge. These practices must provide seepage into
the ground and may include infiltration and exfiltration structures
(e.g., infiltration, bioretention, dry swales or sand filters with
storage below the under drain). Structures that require impermeable
liners, intercept groundwater, or are designed for trapping sediment
(e.g., forbays) may not be used. In this method, the volume of runoff
treated by structural practices shall meet or exceed the computed
recharge volume.
D.
The "Percent Area" method is used to determine the Rev treatment requirements when nonstructural practices are used. Under
this method, the recharge requirements are evaluated by mapping the
percent of impervious area that is effectively treated by an acceptable
nonstructural practice and comparing it to the minimum recharge requirements.
E.
Acceptable nonstructural practices include filter strips that treat
rooftop or parking lot runoff, sheet flow discharge to stream buffers,
and grass channels that treat roadway runoff.
F.
The recharge volume criterion does not apply to any portion of a
site designated as a stormwater hotspot or any project considered
as redevelopment. In addition, the Township Board of Commissioners
may alter or eliminate the recharge volume requirement if the site
is situated on unsuitable soils (e.g., marine clays, karst, or in
an urban redevelopment area). In this situation, nonstructural practices
(Percent Area Method) shall be implemented to the maximum extent practicable
and the remaining or untreated Rev included
in the WQv treatment.
G.
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase, as to maintain their
maximum infiltration capacity.
H.
If Rev is treated by structural or non-structural
practices separate and upstream of the WQv treatment,
the WQv is adjusted accordingly.
4.
Soils Evaluation.
A.
A detailed soils evaluation of the project site shall be performed
to determine the suitability of recharge facilities. The evaluation
shall be performed by a qualified professional, and at a minimum,
address soil permeability, depth of bedrock, susceptibility to sinkhole
formation, and subgrade stability, hydrologic soil groups and natural
and man-made features.
(1)
Soil percolation or infiltration rates must be based on actual
field tests and may not be assumed from data contained within the
Dauphin County Soils Survey.
B.
Extreme caution shall be exercised where infiltration is proposed
in geologically susceptible areas such as strip mine or limestone
areas. Extreme caution shall also be exercised where salt or chloride
would be pollutant since soils do little to filter this pollutant
and it may contaminate the groundwater. It is also extremely important
that the design professional evaluate the possibility of groundwater
contamination from the proposed infiltration/recharge facility and
recommend a hydrogeologic justification study be performed if necessary.
Whenever a basin will be located in an area underlain by limestone,
a geological evaluation of the proposed location shall be conducted
to determine susceptibility to sinkhole formations. The design of
all facilities over limestone formations shall include measures to
prevent groundwater contamination and, where necessary, sinkhole formation.
C.
The Township may require the installation of an impermeable liner
in detention basins. A detailed hydrogeologic investigation may be
required by the Township. The Township may require the developer to
provide safeguards against groundwater contamination for uses which
may cause groundwater contamination, should there be a mishap or spill.
D.
It shall be the developer's responsibility to verify if the site
is underlain by limestone. The following note shall be attached to
all Drainage Plans and signed and sealed by the developer's engineer/surveyor/landscape
architect/geologist: "I, ____________________, certify that the proposed
detention basin (circle one) is/is not underlain by limestone."
E.
Where pervious pavement is permitted for parking lots, recreational
facilities, non-dedicated streets, or other areas, pavement construction
specifications shall be noted on the plan.
F.
Recharge/infiltration facilities may be used in conjunction with
other innovative or traditional BMPs, stormwater control facilities,
and nonstructural stormwater management alternatives.
G.
All recharge/infiltration facilities shall be designed to completely
drain within 72 hours from the end of the storm.
H.
Infiltration structures shall be designed for required storm volume
based on field-determined capacity at the elevation of the proposed
infiltration surface.
1.
In addition to the general standards and design criteria requirements
of this Chapter, the land developer shall comply with the following
water quality requirements unless otherwise exempted by provisions
of this Chapter.
A.
The size of the water quality facility shall be based upon the following
equation:
WQv = [(P)(Rv)(A)]
/ 12
| ||||
Where:
| ||||
WQv
|
=
|
Water Quality Volume (ac-ft)
| ||
P
|
=
|
1.1 inches of rainfall
| ||
Rv
|
=
|
0.05 + 0.009(I)
| ||
I
|
=
|
Percent Impervious Cover (i.e., use I = 20 when there is 20%
impervious cover)
| ||
A
|
=
|
Site Area (acres)
|
B.
Treatment of the WQv shall be provided at
all developments where stormwater management is required. A minimum
WQv of 0.2 acre-inches shall be met at sites
or in drainage areas that have less than 15% imperious cover.
C.
Drainage areas having no impervious cover and no proposed disturbance
during development may be excluded from the WQv calculations. Designers are encouraged to maximize the use of these
areas as nonstructural practices for WQv treatment.
D.
The design of the facility shall consider and minimize the chances
of clogging and sedimentation potential. Orifices smaller than three
inches diameter are not recommended. However, if the design engineer
can provide proof that the smaller orifices are protected from clogging
by use of trash racks, etc., smaller orifices may be permitted.
E.
Developers are encouraged to incorporate designs to take advantage
of the stormwater credits presented in the Spring or Paxton Creek
Act 167 Stormwater Management Plans.
F.
To comply with the requirements of § 22-618, the developer may submit original and innovative designs to the Township for review and approval. Such designs may achieve the water quality objectives through a combination of BMPs.
G.
In selecting the appropriate BMPs or combinations thereof, the developer
shall consider the following:
H.
The following additional factors should be considered when evaluating
the suitability of BMPs used in control water quality at a given development
site:
1.
Stream bank protection, including riparian buffer, shall be considered
in implementing performance standards. If a stormwater storage facility
needs to be constructed then, to protect channels from erosion, the
outflow structure shall be designed to provide the twenty-four-hour
extended detention of the one-year twenty-four-hour storm event. The
method for determining the Channel Protection Storage Volume (Cpv) requirement is detailed in Appendix C[1] of this Chapter.
[1]
Editor's Note: Appendix C is included as an attachment to
this Chapter.
2.
Basis for Determining Channel Protection Storage Volume, Cpv:
A.
The models HEC-HMS, TR-55 and TR-20 (or an equivalent approved by
the Township) shall be used for determining peak discharge rates.
B.
Rainfall depth for the one-year, twenty-four-hour storm event in
Dauphin County is 2.5 inches.
C.
Off-site areas shall be modeled as present land use in good condition
for the one-year storm event.
D.
The Cpv is not required at sites where the
one-year post-development peak discharge (qi) is less than or equal
to 2.0 cfs. A Cpv office diameter (do) of less than three inches is subject to approval by
the Township and is not recommended unless an internal control for
orifice protection is used.
E.
Cpv shall be addressed for the entire site.
If a site consists of multiple drainage areas, Cpv may be distributed proportionately to each drainage area.
F.
Extended detention storage provided for the Cpv does not meet the WQv requirement (i.e.,
Cpv and WQv shall be
treated separately).
G.
The stormwater storage needed for the Cpv may
be provided above the WQv storage in stormwater
ponds and wetlands thereby meeting all storage criteria except Rev in a single facility with appropriate hydraulic control
structures for each storage requirement.
H.
Infiltration is not recommended for Cpv control
because of large storage requirements.
1.
The existing points of natural drainage discharge onto adjacent property
shall not be altered without the written approval of the affected
landowners.
2.
Stormwater runoff or natural drainage water shall not be diverted
so as to overload existing drainage systems, or create flooding or
the need for additional drainage structures on other private properties
or public lands, without approved provisions being made by the applicant
for properly handling such conditions.
3.
Where a watercourse runs across or through a subdivision, a drainage
easement, which conforms with the line of such watercourse shall be
provided.
4.
Storm drainage facilities, as required, shall be placed in front
of the curb line when located in a street right-of-way. When located
in undedicated land, they shall be placed within an easement, as approved
by the Township, who may require additional width of easement as circumstances
warrant.
5.
Retention/Detention Basin Criteria:
A.
Where a stormwater detention basin is proposed, the plan shall include
a proposal to prevent such basin from becoming a safety hazard or
public nuisance and for regular perpetual maintenance of the basin
to insure its continuous effectiveness.
B.
All controls designed to meet the requirements of this Chapter shall
meet the applicable release rate criteria for the two-, ten- and twenty-five-year
return period storms.
C.
Any stormwater management facility (i.e., detention basin) designed
to store runoff and requiring a berm or earthen embankment, required
or regulated by this Chapter, shall be designed to provide an emergency
spillway to handle flow up to and including the one-hundred-year post-development
conditions. The height of embankment must be set as to provide a minimum
one-foot of freeboard above the maximum pool elevation computed when
the facility functions for the one-hundred-year post-development inflow.
Soils used for the construction of basins shall have low-erodibility
factors ("K" factors). Any facility that constitutes a dam, as defined
in DEP Chapter 105 regulations, may require a permit under dam safety
regulations.
D.
Any facilities that constitute water obstructions (e.g., culverts,
bridges, outfalls, or stream enclosures) and any work involving wetlands
as directed in DEP Chapter 105 regulations (as amended or replaced
from time to time by DEP) shall be designed in accordance with Chapter
105 and will require a permit from DEP. Any water obstruction that
does not fall under Chapter 105 regulations must be able to convey,
without damage to the drainage structure or roadway, runoff from the
twenty-five-year design storm with a minimum one-foot of freeboard
measured below the lowest point along the top of the roadway.
E.
The design of all stormwater management facilities shall incorporate
sound engineering principles and practices. The Township shall reserve
the right to disapprove any design that would result in the occupancy
or continuation of an adverse hydrologic or hydraulic condition within
the watershed.
F.
Basins which are not designed to release all stormwater shall be
specifically identified as retention basins or permanent pond basins.
All other basins shall have provisions for dewatering, particularly
the bottom, and shall not create swampy and/or unmaintainable conditions.
Sod-lined or stone lowflow channels may be used to dewater the bottom
of a basin. The minimum slope of any surface on the bottom of the
pond shall be 1.5%.
G.
Retention basins and/or detention basins which are designed with
earth fill embankments shall incorporate the following standards:
(1)
The minimum top width of embankments up to eight feet in height
shall be equal to 2/3 of the embankment height, but in no case shall
the top width be less than five feet.
(2)
The side slopes of the earth fill shall not be less than three
horizontal to one vertical.
(3)
A cut off trench and key trench of impervious material shall
be provided under all embankments exceeding four feet in height.
(4)
All pipes and culverts through embankments shall be fitted with
properly spaced and sized cut off collars.
(5)
No outlet structure from a detention basin or swale shall discharge
directly onto a Township or State road, but may discharge into a culvert
under a Township or State road.
(6)
Any basin may be required to be fenced with a minimum of four-foot-high
fence of a material acceptable to the Township. Gates shall be provided
where required. The Board of Commissions shall make the decision to
require fencing based on potential hazards at the site such as detention
versus retention capability, slope, depth of water and length of detention
time.
(7)
All facilities shall have access roads and easements where necessary.
6.
General Requirements for Stormwater Collection.
A.
The design criteria for storm sewers and man-made channels (i.e.,
swales) shall be the ten-year frequency storm, unless more restrictive
frequencies are required by Chapter 105 of the Department of Environmental
Protection regulations, with intensities based on the times of concentration
for PennDOT Intensity Duration Frequency (IDF) curves, and runoff
coefficients based on land use for each drainage area. A minimum time
of concentration of five minutes shall be used. Computation methods
shall be based on the Rational Method or Soil Cover Complex Method.
The Township, pursuant of recommendations of the Township Engineer,
may require a design storm of higher intensity be used when on site
or surrounding conditions, such as history of flooding downstream
or the capacity of the receiving stream or stormwater system indicate
such a variation to be necessary.
B.
Storm drainage systems shall be provided to allow unimpeded flow
of natural watercourses except as modified by stormwater detention
facilities or open channels consistent with this Section.
C.
Storm drainage facilities and appurtenances shall be so designed
and constructed as to minimize erosion at discharge points and in
watercourse channels. Adequate erosion protection shall be provided
along all open channels and at all points of discharge.
D.
When connecting to an existing storm sewer system, the applicant
must demonstrate that the proposed system will not exacerbate any
existing stormwater problems.
E.
Pipe Design.
(1)
Pipes shall be designed so as to provide a minimum velocity
of 2 1/2 feet per second when flowing full.
(2)
At a minimum, pipe capacities shall be computed using both the
Manning Equation for full flow capacity and the Inlet Control Nomographs
in Hydraulic Design Series 5 by the Federal Highway Administration,
dated September 1985. For inlets, the maximum headwater elevation
must be less than the top of grate. Outlet control calculations shall
be required for special circumstances such as high tailwater conditions,
long runs of pipe, excessive bends and other losses, etc. Alternate
methods of headwater computation may be accepted at the discretion
of the Municipal Engineer.
(3)
All pipe shall conform to and be constructed in conformance
with the specifications set forth in the Pennsylvania Department of
Transportation, Publication 408, as amended and as shown on approved
drawings.
(4)
Pipe sizes, lengths and slopes shall be shown on the approved
drawings.
F.
Inlets.
(1)
Storm drainage inlets shall be provided at all low points and
hydraulically intermediate points on a system. Location and spacing
of inlets shall be based on the hydraulic capacity of each inlet related
to the flow received and amount of flow bypassed from upstream inlets,
but shall not be greater than 600 feet. Inlets shall be placed so
street drainage shall not cross intersections or street crowns.
(2)
The maximum allowable spread of water on streets is 1/2 of a
travel lane. Computations should be provided which demonstrate compliance
with this spread requirement.
(3)
All street inlet tops shall be the combination curb and gutter
inlet referred to as PennDOT Type "C," with a ten-inch curb reveal
to allow an automatic two-inch depressed condition to existing when
used on an eight-inch curb. All inlet tops shall be precast concrete
with heavy-duty bicycle-safe steel grating. Weep holes shall be provided
on all inlet tops at the appropriate elevations to completely drain
the sub grade prior to placing the base course and surface course.
In private parking areas, streets and yard areas with no curbing,
Type M inlet tops shall be used.
(4)
Inlets shall be constructed in accordance with the specifications
as set forth in the Pennsylvania Department of Transportation, Publication
408, as amended, and as detailed on the Roadway Construction Standard
drawing (RC-34).
(5)
Inlet foundations shall be a minimum of eight inches of plain
concrete. Inlet walls shall be precast concrete. All pipes entering
or existing inlets shall be cut flush with the inlet wall.
(6)
Inlets must be sized to accept the specified pipe sizes without
knocking out of any inlet corners.
(7)
Any inlets or junction boxes over five feet in depth shall be
equipped with ladder rings.
(8)
Inlets shall not have a sump condition in the bottom. Pipes
shall be flush with the bottom of the box or concrete channels shall
be poured. Sumped inlets may be permitted where specifically utilized
for water quality purposes.
H.
Roof Leaders, Foundation Drains, Springs and Sump Pumps.
(1)
In order to promote overland flow and infiltration/percolation
of stormwater where it is advantageous to do so, roof drains, foundation
drains, sump pumps, etc., shall not be connected to streets, sanitary
sewers, or storm sewers. When it is more advantageous to connect directly
to streets or storm sewers, the Township shall permit it on a case-by-case
basis.
(2)
Roof drains and sump pumps shall discharge to infiltration areas
or vegetative BMPs to the maximum extent practicable.
(3)
Stormwater roof drains shall not discharge water directly over
a sidewalk.
(4)
Stabilized outlets shall be provided for footer drains, flood
drains, and downspouts.
(5)
All underground or surface springs encountered during or after
construction of roadways or buildings shall be adequately piped or
drained to the nearest storm drainage system. The Township Roadway
Inspector or Township Engineer shall be contacted when a spring is
encountered. The Inspector or Engineer may make a site investigation
and make written recommendations to the developer for correcting the
problem. Such recommendations shall be binding on the developer unless
the Board of Commissioners, upon the request of the developer, agree
to permit an alternative solution.
(6)
Subbase drains shall be provided at all low points in cut areas,
toe of slope areas and other areas as dictated by proven engineering
principles and design judgment. Subbase drains shall be designed and
constructed in accordance with the Pennsylvania Department of Transportation
Design Criteria and Publication 408 Specifications. All drains shall
be connected to a storm drainage system.
(7)
All land development projects shall be designed and constructed
in order to provide proper drainage of stormwater runoff with minimal
impact on adjoining properties, unless an area specifically designed
for stormwater detention is provided.
7.
Compliance with Department of Environmental Protection (DEP) Chapter
105 Regulations.
A.
The design criteria in this Chapter are intended for usage in conjunction
with the Chapter 105 Regulations of DEP, entitled "Dam Safety and
Waterway Management." All information and regulations contained in
Chapter 105 shall be considered to be incorporated into this Chapter
as if reproduced in full.
B.
DEP permit in accordance with Chapter 105 shall be required for any
obstruction or encroachment in the regulated waters of the Commonwealth
prior to the approval of the final plan. In the event any question
or conflict arises between this Section and the DEP Chapter 105 Regulations,
the design criteria contained in the DEP regulations shall govern.
8.
Compliance with Pennsylvania Department of Transportation Publication
408 Specifications.
A.
All materials, workmanship and methods of work shall comply with
the Pennsylvania Department of Transportation Publication 408 Specifications,
as accepted and commonly used by the Township, and such specifications
shall be considered to be incorporated into this Section as if copied
in full. In the event a conflict arises between the requirements and
specifications of this Section and the Publication 408 Specifications,
the Township Engineer shall resolve the difference, and his opinion
shall be binding.