A.
Applicants proposing regulated activities in the Township which are not exempt under § 178-6 shall submit a stormwater management site plan (SWM site plan) to the Township for review and approval in accordance with Articles III and IV. SWM site plans approved by the Township shall be on site throughout the duration of the regulated activity.
B.
The stormwater management and runoff control criteria and standards
in this chapter shall apply to the total proposed regulated activity,
even if it is to take place in stages. The measurement of impervious
surfaces shall include all of the impervious surfaces in the total
proposed regulated activity even if the development is to take place
in stages.
C.
No regulated activity within the Township shall commence until:
(1)
The Township issues approval of a SWM site plan, which demonstrates
compliance with the requirements of this chapter; and
(2)
The applicant has received a letter of adequacy or approval for the
erosion and sediment control plan review by the Township and the Conservation
District (if required), and has received all other local, state and
federal permit approvals required for the project involving the regulated
activity.
D.
Neither submission of a SWM site plan under the provisions herein
nor compliance with the provisions of this chapter shall relieve any
person from responsibility for damage to any person or property otherwise
imposed by law.
E.
The applicant shall design the site to minimize disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall apply the procedures set forth in § 178-18 for the overall site design and for selection, location and design of features and BMPs to be used to comply with the requirements of this chapter.
F.
To the maximum extent practicable, postconstruction stormwater shall
be discharged within the drainage area of the same stream or water
body receiving the runoff prior to construction of the proposed regulated
activity.
G.
Existing drainage peak rate discharges up to and including the 100-year
storm and the volume of runoff up to and including the two-year storm
onto or through adjacent property(ies) or downgradient property(ies),
including diffuse drainage discharge, shall not be altered in any
manner by regulated activities under this chapter without written
permission from, and, where applicable as determined by the Township
an easement and agreement with, the affected landowner(s) for conveyance
of discharges onto or through their property(ies). Altered stormwater
discharges shall be subject to any applicable discharge criteria specified
in this chapter.
H.
Areas located outside of the site (i.e., areas outside of the regulated activity) that drain through a proposed site are not subject to water quality and volume control, infiltration, stream channel protection, or peak flow rate control requirements (as presented in §§ 178-19, 178-20, 178-21, and 178-22). Drainage facilities located on the site shall be designed to safely convey flows from outside of the site through the site.
I.
If site conditions preclude capture of runoff from limited portions
of the disturbed area for achieving water quality volume control standards,
stream channel protection standards, and the two-year, five-year and
ten-year storm event peak runoff rate reduction standards for new
development required by this chapter, the applicant shall propose
alternate methods to mitigate the bypass of the BMPs, subject to the
approval of the Township Engineer. In no case shall resulting peak
rate be greater than the predevelopment peak rate for the equivalent
design storm.
J.
For all regulated activities, erosion and sediment control BMPs shall
be designed, implemented, operated, and maintained during the regulated
activities (i.e., during construction) as required to meet the purposes
and requirements of this chapter, to meet the erosion and sediment
control requirements of the Township, if applicable, and to meet all
requirements under Title 25 of the Pa. Code and the Clean Streams
Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
K.
For all regulated activities, permanent BMPs and conveyances shall
be designed, implemented, operated, and maintained to meet the purposes
and requirements of this chapter and to meet all requirements under
Title 25 of the Pennsylvania Code, the Clean Streams Law,[2] and the Stormwater Management Act.[3]
L.
The design of all BMPs and conveyances shall incorporate sound engineering
principles and practices in a manner that does not aggravate existing
stormwater problems as identified by the Township. The Township reserves
the right to disapprove any design that would result in construction
in an area affected by existing stormwater problem(s) or continuation
of an existing stormwater problem(s).
M.
Existing wetlands, either on the site or on an adjacent property,
shall not be used to meet the minimum design requirements for stormwater
management or stormwater runoff quality treatment. Stormwater discharges
to existing wetlands shall not degrade the quality or hydrologic integrity
of the wetland.
N.
Hotspots runoff controls. Specific structural or pollution prevention
practices may be required, as determined to be necessary by the Township
Engineer, to pretreat runoff from hotspots prior to infiltration.
Following is a list of examples of hotspots:
(1)
Vehicle salvage yards and recycling facilities;
(2)
Vehicle fueling stations;
(3)
Vehicle service and maintenance facilities;
(4)
Vehicle and equipment cleaning facilities;
(5)
Fleet storage areas (bus, truck, etc.);
(6)
Industrial sites based on Standard Industrial Classification Codes;
(7)
Marinas (service and maintenance areas);
(8)
Outdoor liquid container storage;
(9)
Outdoor loading/unloading facilities;
(10)
Public works storage areas;
(11)
Facilities that generate or store hazardous materials;
(12)
Commercial container nursery;
(13)
Contaminated sites/brownfields;
(14)
Other land uses and activities as designated by the Township.
O.
Contaminated and brownfield sites. Where BMPs may contribute to the
migration of contaminants in groundwater, the water quality and runoff
volume, stream channel protection, and peak rate control standards
shall be met; however, at the Township Engineer's discretion, the
minimum infiltration requirement may be reduced or eliminated commensurate
with the contaminated area and the required water quality and runoff
control measures may be increased to mitigate the reduced infiltration
requirement for the contaminated area.
P.
Additional water quality requirements. The Township may require additional
stormwater control measures for stormwater discharges to special management
areas including, but not limited to:
(1)
Water bodies listed as "impaired" by PADEP.
(2)
Any water body or watershed with an approved total maximum daily
load (TMDL).
(3)
Areas of known existing flooding problems.
(4)
Critical areas with sensitive resources (e.g., state-designated special
protection waters, cold water fisheries, carbonate geology or other
groundwater recharge areas that may be highly vulnerable to contamination,
drainage areas to water supply reservoirs, etc.).
Q.
Applicants shall utilize the Pennsylvania Stormwater Best Management
Practices Manual (PA BMP Manual), as amended, or other sources acceptable
to the Township Engineer, for testing and design standards for BMPs,
and where there is a conflict with the provisions of this chapter,
the most restrictive applies.
R.
For areas underlain by karst or carbonate geology that may be susceptible
to the formation of sinkholes and other karst features, the location,
type, and design of infiltration BMPs shall be based on a site evaluation
conducted by a qualified licensed professional and based on the PA
BMP Manual (as amended) or other design guidance acceptable to the
Township Engineer.
S.
All regulated activities located within a special flood hazard area designated by the Federal Emergency Management Agency (FEMA) shall comply with Article VI of the Zoning Ordinance[4] of Pocopson Township and shall be designed to maintain
the flood-carrying capacity of the floodway such that the base flood
elevations are not increased, either upstream or downstream. The natural
conveyance characteristics of the site and the receiving floodplain
shall be incorporated into the stormwater management practices proposed
for the site.
T.
Disturbance of existing ground cover during construction of the proposed regulated activity is prohibited within riparian buffer areas, as defined in § 250-6 of the Zoning Ordinance, except for activities otherwise approved by state or local agencies (e.g., stream restoration projects, road crossings, subsurface utility projects, etc.). At the Township Engineer's discretion, and with Conservation District and PADEP approval where necessary, the nondisturbance buffer may be reduced because of setback or other site constraints, but never be less than 10 feet.
The following permit or other regulatory requirements may apply
to certain regulated activities and shall be met prior to (or as a
condition of) final approval by Pocopson Township of the SWM site
plan and prior to commencement of any regulated activities, as applicable:
A.
All regulated activities subject to permit or regulatory requirements
by PADEP under regulations at Title 25 Pennsylvania Code, Chapter
102, or erosion and sediment control requirements of the Township.
B.
Work within natural drainageways subject to permit by PADEP under
Title 25 Pennsylvania Code, Chapter 105.
C.
Any BMP or conveyance that would be located in or adjacent to surface
waters of the commonwealth, including wetlands, subject to permit
by PADEP under Title 25 Pennsylvania Code, Chapter 105.
D.
Any BMP or conveyance that would be located on or discharge to a
state highway right-of-way, or require access to or from a state highway
and be subject to approval by PennDOT.
E.
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 subject to permit by PADEP under Title 25 Pennsylvania
Code, Chapter 105.
A.
No regulated activity within the Township shall commence until:
(1)
The Township receives documentation that the applicant has received:
(a)
A "letter of adequacy" from the Conservation District or other
approval from PADEP in compliance with Title 25, Chapter 102, of the
Pennsylvania Code of an erosion and sediment control plan for construction
activities for projects where the area of disturbance exceeds one
acre, where pond dredging is involved, or when the disturbance is
associated with activities described under Title 25, Chapter 105,
of the Pennsylvania Code permits;
(b)
A PADEP NPDES Permit for Stormwater Discharges Associated with
Construction Activities as required under Title 25 Pennsylvania Code,
Chapter 92a, if applicable;
(c)
Evidence of any other permit(s) or approvals required for the
regulated activities; and
B.
A copy of the erosion and sediment control plan and any required
permit(s), as required by PADEP regulations, shall be available on
the site at all times.
The applicant shall design the site to minimize the disturbances to land, site hydrology, and natural resources, and to maintain the natural hydrologic regime, drainage patterns and flow conditions. The applicant shall demonstrate in its SWM site plan (as required in § 178-27C) that the design sequence, objectives and techniques described below were applied to the maximum extent practicable in the site design of the regulated activity while complying with all other requirements of this chapter. The site design shall:
A.
First, identify and delineate all existing natural resources and natural and man-made hydrologic features listed in § 178-27B(8), and in § 250-87B(8) that are located within the site, or receive discharge from, or may be impacted by the proposed regulated activity.
B.
Second, provide a prioritized listing of these resources and features
to identify:
(1)
Those to be incorporated into the site design in a manner that provides
protection from any disturbance or impact from the proposed regulated
activity;
(2)
Those to be protected from further disturbance or impact but for
which the proposed regulated activity will provide improvement to
existing conditions;
(3)
Those that can be incorporated into and utilized as components of
the overall site design in a manner that protects or improves their
existing conditions while utilizing their hydrologic function within
the limits of their available capacity (e.g., for infiltration, evapotranspiration,
or reducing pollutant loads, runoff volume or peak discharge rates,
etc.) to reduce the need for or size of constructed BMPs; and
(4)
Those that may be considered for alteration, disturbance or removal.
C.
Third, develop the site design to achieve the following:
(1)
Recognize and incorporate the priorities identified in § 178-18B as the basis for the proposed site layout, grading, construction, and permanent ground cover design;
(2)
Minimize earth disturbance (both surface and subsurface);
(3)
Maximize protection of or improvement to natural resources and special
management areas;
(4)
Minimize the disturbance of natural site hydrology, in particular
natural drainage features and patterns, discharge points and flow
characteristics, natural infiltration patterns and characteristics,
and natural channel and floodplain conveyance capacity;
(5)
Incorporate natural hydrologic features and functions identified in § 178-18B into the site design to protect and utilize those features and their hydrologic functions to reduce the need for or size of constructed BMPs;
(6)
Maximize infiltration and the use of natural site infiltration features,
patterns and conditions, and evapotranspiration features;
(7)
Apply selective grading design methods to provide final grading patterns
or preserve existing topography in order to evenly distribute runoff
and minimize concentrated flows;
(8)
Minimize the cumulative area to be covered by impervious surfaces,
and:
(9)
Minimize the volume and peak discharge rates of stormwater generated;
(10)
Avoid or minimize stormwater runoff pollutant loads and receiving
stream channel erosion;
(13)
For flow volumes requiring conveyance from the source of generation
to a BMP for management, give preference to open channel conveyance
techniques that provide infiltration and water quality benefits, and
landscaped-based management in common open space areas, where practicable;
and
(14)
Consider additional guidance for incorporating natural hydrology into the site and BMP designs, methods and techniques that support the objectives of § 178-18B and C. Appendix B[1] presents additional discussion of conservation design
and low-impact development.
[1]
Editor's Note: Appendix B is included as an attachment to
this chapter.
To control postconstruction stormwater impacts from regulated
activities and meet state water quality requirements, BMPs shall be
provided in the site design that replicate predevelopment stormwater
infiltration and runoff conditions, such that postconstruction stormwater
discharges do not degrade the physical, chemical, or biological characteristics
of the receiving waters. The green infrastructure and low-impact development
(LID) practices provided in the PA BMP Manual, as well as the guidance
on green infrastructure, LID and conservation design (CD) provided
in Appendix B,[1] shall be utilized for all regulated activities wherever
possible. The applicant shall comply with the following water quality
and runoff volume requirements for all regulated activities, including
all new development and redevelopment activities:
A.
The postconstruction total runoff volume shall not exceed the predevelopment
total runoff volume for all storms equal to or less than the two-year,
twenty-four-hour duration precipitation (design storm). The water
quality and runoff volume to be managed shall consist of any runoff
volume generated by the proposed regulated activity over and above
the predevelopment total runoff volume and shall be captured and permanently
retained or infiltrated on the site. Permanent retention options may
include, but are not limited to, reuse, evaporation, transpiration,
and infiltration.
B.
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 178-23D of this chapter.
C.
The design of the stormwater management facility outlet shall provide
for protection from clogging and unwanted sedimentation.
D.
BMPs that moderate the temperature of stormwater shall be used to
protect the temperature of receiving waters. The applicant shall fulfill
the requirements of the PADEP "Thermal Impact Analysis" for the "PAG-02
Stormwater Discharges Associated with Construction Activities, NOI
for Coverage under General or Individual Permit" if they cannot meet
the volume control requirements.
E.
Water quality improvement shall be achieved in conjunction with achieving the infiltration requirements of § 178-20. The infiltration volume required under § 178-20 may be included as a component of the water quality volume. If the calculated water quality and runoff volume is greater than the volume infiltrated, then the difference between the two volumes shall be managed for water quality and runoff volume control through other techniques or practices but shall not be discharged from the site.
F.
Runoff from the disturbed area shall be treated for water quality
prior to entering existing waterways or water bodies. If a stormwater
management practice does not provide water quality treatment, then
water quality BMPs shall be utilized to provide pretreatment prior
to the runoff entering the stormwater management practice.
G.
The Township may require additional water quality and runoff control measures for stormwater discharging to special management areas such as those listed in § 178-15P.
H.
When the regulated activity contains or is divided by multiple drainage
areas, the water quality and runoff volume shall be separately addressed
for each drainage area.
I.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
J.
Areas located outside of the site (i.e., areas outside of the regulated
activity) may be excluded from the calculation of the water quality
and runoff volume requirements.
K.
Water quality and volume control practices shall be selected and designed to meet the criteria of § 178-18C that apply to water quality and volume control.
L.
Evapotranspiration may be quantified and credited towards meeting
volume requirements according to the PADEP Post Construction Stormwater
Management (PCSM) Spreadsheet and Instructions (December 2020) or
the most recent guidance from PADEP.
[1]
Editor's Note: Appendix B is included as an attachment to
this chapter.
Providing for infiltration consistent with the natural hydrologic
regime is required to compensate for the reduction in the recharge
that occurs when the ground surface is disturbed or impervious surface
is created or expanded. The applicant shall achieve the following
infiltration requirements:
A.
For regulated activities involving both new development and redevelopment, infiltration should be designed to accommodate the entire water quality and runoff volume required in § 178-19. Infiltration BMPs should be consistent with the design and infiltration period guidelines included in the PA BMP Manual or other PA DEP design guidance. If the runoff volume required by § 178-19 cannot be infiltrated, then alternative methods consistent with the PA BMP Manual (as amended) or other PA DEP guidance, such as the Managed Release Concept, may be used to manage this volume with approval from the Township Engineer.
B.
For regulated activities involving both new development and redevelopment,
the volume of a minimum of one inch of runoff from all regulated impervious
surfaces shall be infiltrated.
C.
If the requirements of § 178-20A or B cannot be physically accomplished, then the applicant shall be responsible for demonstrating with data or calculations to the satisfaction of the Township Engineer why this infiltration volume cannot be physically accomplished on the site (e.g., shallow depth to bedrock or limiting zone, open voids, steep slopes, etc.) and what alternative volume can be infiltrated;
E.
If site conditions preclude capture of runoff from portions of the
impervious surfaces, the infiltration volume for the remaining area
shall be increased an equivalent amount to offset the loss.
F.
When a project contains or is divided by multiple watersheds, the
infiltration volume shall be separately addressed for each watershed.
G.
Existing impervious surfaces located in areas outside of the site
(i.e., outside of the regulated activity) may be excluded from the
calculation of the required infiltration volume.
H.
A detailed soils evaluation of the site shall be conducted by a qualified
professional and at a minimum shall address soil permeability, depth
to bedrock, and subgrade stability. The general process for designing
the infiltration BMP shall be conducted by a qualified licensed professional
and shall be consistent with the PA BMP Manual (as amended) (or other
guidance acceptable to the Township Engineer) and in general shall:
(1)
Analyze hydrologic soil groups as well as natural and man-made features
within the site to determine general areas of suitability for infiltration
practices. In areas where development on fill material is under consideration,
conduct geotechnical investigations of subgrade stability; infiltration
may not be ruled out without conducting these tests.
(2)
Provide field tests such as double ring infiltrometer or other hydraulic
conductivity tests (at the elevation of the proposed infiltration
surface) to determine the appropriate hydraulic conductivity rate.
Standard septic/sewage percolation tests are not acceptable for design
purposes.
(3)
Design the infiltration facility for the required retention (infiltration)
volume based on field-determined infiltration capacity (and apply
safety factor as per applicable design guidelines) at the elevation
of the proposed infiltration surface.
(4)
On-lot infiltration features are encouraged; however, it shall be
demonstrated to the Township Engineer that the soils are conducive
to infiltration on the identified lots.
I.
Infiltration BMPs shall be selected based on suitability of soils
and site conditions and shall be constructed on soils that have the
following characteristics:
(1)
A minimum depth of 24 inches between the bottom of the BMP and the top of the limiting zone. Additional depth may be required in areas underlain by karst or carbonate geology (see § 178-20M).
(2)
An infiltration rate sufficient to accept the additional stormwater
volume and drain completely as determined by field tests conducted
by the applicant.
(3)
The infiltration facility shall completely drain the retention (infiltration)
volume within three days (72 hours) from the end of the design storm.
J.
All infiltration practices shall:
(2)
Be set back at least 15 feet from all buildings and features with
subgrade elements (e.g., basements, foundation walls, etc.), and 10
feet from property or right-of-way lines, unless otherwise approved
by the Township Engineer;
(3)
For any infiltration practice that collects runoff from shared or
multiple features and that is located within 25 feet of a building
or feature with subgrade elements (e.g., basements, foundation walls,
etc.), the bottom elevation shall be set below the elevation of the
subgrade element.
K.
Infiltration facilities shall, to the maximum extent practicable,
be located to avoid introducing contaminants to groundwater:
(1)
When a hotspot is located in the area draining to a proposed infiltration
facility, an evaluation of the potential of groundwater contamination
from the proposed infiltration facility shall be performed, including
a hydrogeologic investigation (if requested by the Township Engineer)
by a qualified licensed professional to determine what, if any, pretreatment
or additional design considerations are needed to protect groundwater
quality.
(2)
When located within a "wellhead protection area" of a public water
supply well, infiltration practices shall be in conformance with the
applicable approved source water protection assessment or source water
protection plan.
(3)
The applicant shall provide appropriate safeguards against groundwater
contamination for land uses that may cause groundwater contamination
should there be a mishap or spill.
L.
During site construction, all infiltration practice components shall
be protected from compaction due to heavy equipment operation or storage
of fill or construction material. Infiltration areas shall also be
protected from sedimentation. Areas that are accidentally compacted
or graded shall be remediated to restore soil composition and porosity.
Adequate documentation to this effect shall be submitted to the Township
Engineer for review. All areas designated for infiltration shall not
receive runoff until the contributory drainage area has achieved final
stabilization.
M.
Where sediment transport in the stormwater runoff is anticipated
to reach the infiltration system, appropriate permanent measures to
prevent or collect sediment shall be installed prior to discharge
to the infiltration system.
N.
Where roof drains are designed to discharge to infiltration practices,
they shall have appropriate measures to prevent clogging by unwanted
debris (for example, silt, leaves and vegetation). Such measures shall
include but are not limited to leaf traps, gutter guards and cleanouts.
O.
All infiltration practices shall have appropriate positive overflow
controls.
P.
No sand, salt or other particulate matter may be applied to a porous
surface material for winter ice conditions.
Q.
The following procedures and materials shall be required during the
construction of all subsurface facilities:
(1)
Excavation for the infiltration facility shall be performed with
equipment that will not compact the bottom of the seepage bed/trench
or like facility.
(2)
The bottom of the bed and/or trench shall be scarified prior to the
placement of aggregate.
(3)
Only clean aggregate with documented porosity, free of fines, shall
be allowed.
(4)
The tops, and sides of all seepage beds, trenches, or like facilities
shall be covered with drainage fabric. Where the seepage bed, trench
or like facility will be subject to vehicular traffic, the bottom
of the bed may be required to be covered with fabric as well. Fabric
shall be nonwoven fabric acceptable to the Township Engineer.
(5)
Stormwater shall be distributed throughout the entire seepage bed/trench
or like facility and provisions for the collection of debris shall
be provided in all facilities.
For regulated activities involving new development with one
or more acres of earth disturbance, the applicant shall comply with
the following stream channel protection requirements to minimize stream
channel erosion and associated water quality impacts to the receiving
waters:
A.
The peak flow rate of the postconstruction two-year, twenty-four-hour
design storm shall be reduced to the predevelopment peak flow rate
of the one-year, twenty-four-hour duration precipitation, using the
SCS Type II distribution.
B.
To the maximum extent practicable, and unless otherwise approved
by the Township Engineer, the postconstruction one-year, twenty-four-hour
storm flow shall be detained for a minimum of 24 hours and a maximum
not to exceed 72 hours from a point in time when the maximum volume
of water from the one-year, twenty-four-hour storm is stored in a
proposed BMP (i.e., when the maximum water surface elevation is achieved
in the facility). Release of water can begin at the start of the storm
(i.e., the invert of the orifice is at the invert of the proposed
BMP).
C.
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 178-23D of this chapter.
D.
The minimum orifice size in the outlet structure to the BMP shall
be three inches in diameter unless otherwise approved by the Township
Engineer, and a trash rack shall be installed to prevent clogging.
For sites with small drainage areas contributing to the BMP that do
not provide enough runoff volume to allow a twenty-four-hour attenuation
with the three-inch orifice, the calculations shall be submitted showing
this condition.
E.
When the calculated orifice size is below three inches, gravel filters
(or other methods) are recommended to discharge low-flow rates subject
to the Township Engineer's satisfaction. When filters are utilized,
maintenance provisions shall be provided to ensure filters meet the
design function.
F.
All proposed stormwater management facilities shall make use of measures
to extend the flow path and increase the travel time of flows in the
facility.
G.
When a regulated activity contains or is divided by multiple drainage
areas, the peak flow rate control shall be separately addressed for
each drainage area.
The applicant shall comply with the following peak flow rate
control requirements for all regulated activities including those
that involve new development and redevelopment.
A.
Postconstruction peak flow rates from any regulated activity shall
not exceed the predevelopment peak flow rates as shown for each of
the design storms specified in Table 178-22.1.
|
Table 178-22.1
Peak Rate Control Standards
| ||
|---|---|---|
|
(Peak Flow Rate of the Postconstruction Design Storm Shall Be
Reduced to the Peak Flow Rate of the Corresponding Predevelopment
Design Storm Shown in the Table)
| ||
|
Postconstruction Design Storm Frequency
(24-Hour Duration)
|
Predevelopment Design Storm
| |
|
New Development Regulated Activities
|
Redevelopment Regulated Activities
| |
|
2-year
|
1-year
|
2-year
|
|
5-year
|
2-year
|
5-year
|
|
10-year
|
2-year
|
10-year
|
|
25-year
|
25-year
|
25-year
|
|
50-year
|
50-year
|
50-year
|
|
100-year
|
100-year
|
100-year
|
B.
For modeling purposes, the predevelopment ground cover conditions shall be determined using the corresponding ground cover assumptions presented in § 178-23D of this chapter.
C.
For regulated activities involving only redevelopment, no peak flow rate controls are required when and only if the total regulated impervious surface area is at least 20% less than the total existing impervious surface area to be disturbed by the regulated activity. In all cases where this requirement is not met, the redevelopment regulated activity shall achieve the peak flow rate controls presented in Table 178-22.1, using the redevelopment ground cover assumptions presented in § 178-23D. This design criterion for redevelopment is only permitted with approval of Township Engineer. It shall result in no impact on downstream properties.
D.
Only the area of the proposed regulated activity shall be subject
to the peak flow rate control standards of this chapter. Undisturbed
areas for which the discharge point has not changed are not subject
to the peak flow rate control standards.
E.
Areas located outside of the site (i.e., areas outside of the regulated
activity) that drain through a proposed site are not subject to peak
flow rate control requirements. Drainage facilities located on the
site shall be designed to safely convey flows from outside of the
site through the site.
F.
When a regulated activity contains or is divided by multiple drainage
areas, the peak flow rate controls shall be separately addressed for
each drainage area.
G.
The effect of structural and nonstructural stormwater management
practices implemented as part of the overall site design may be taken
into consideration when calculating total storage volume and peak
flow rates.
A.
Stormwater runoff from all regulated activity sites with a drainage
area of greater than five acres shall be calculated using a generally
accepted calculation technique(s) that is based on the NRCS Soil Cover
Complex Method. Table 309.1 summarizes acceptable computation methods.
The method selected for use shall be based on the individual limitations
and suitability of each method for a particular site. The use of the
Rational Method to estimate peak discharges for drainage areas greater
than five acres shall be permitted only upon approval by the Township
Engineer.
|
Table 178-23.1
Acceptable Computation Methodologies for SWM Site Plan
| ||
|---|---|---|
|
Method
|
Developed By
|
Applicability
|
|
TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of full hydrology computer model is desirable
or necessary
|
|
TR-55 (or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans where limitations described
in TR-55 are met
|
|
HEC-1/HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of a full hydrologic computer model is
desirable or necessary
|
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For sites up to 5 acres, or as approved by the Township
|
|
Other methods
|
Varies
|
Other computation methodologies approved by the Township
|
B.
All calculations using the Soil Cover Complex Method shall use the
appropriate design rainfall depths for the various return period storms
consistent with this chapter. Rainfall depths used shall be obtained
from the latest version of the Precipitation-Frequency Atlas of the
United States, National Oceanic and Atmospheric Administration (NOAA),
National Weather Service, Hydrometeorological Design Studies Center,
Silver Spring, Maryland (NOAA Atlas 14), values consistent with a
partial duration series. When stormwater calculations are performed
for routing procedures or infiltration, water quality and runoff volume
functions, the duration of rainfall shall be 24 hours.
C.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times-of-concentration (duration) and
storm events with rainfall intensities obtained from NOAA Atlas 14
partial duration series estimates, or the latest version of the PennDOT
Drainage Manual (PDM Publication 584). Times-of-concentration shall
be calculated based on the methodology recommended in the respective
model used. Times of concentration for channel and pipe flow shall
be computed using Manning's equation.
D.
The applicant shall utilize the following ground cover assumptions
for all predevelopment water quality and runoff volume, infiltration
volume and peak flow rate calculations:
(1)
For regulated activities involving new development, the following
ground cover assumptions shall be used:
(2)
For regulated activities involving redevelopment, the following ground
cover assumptions shall be used:
(a)
For areas that are woods (as defined in Article II of this chapter), predevelopment calculations shall assume ground cover of "woods in good condition."
(b)
For areas that are not woods or not impervious surfaces, predevelopment
calculations shall assume ground cover of "meadow."
(c)
For areas that are impervious surfaces, predevelopment calculations
shall assume at least 20% of the existing impervious surface area
to be disturbed as "meadow" ground cover.
(3)
The applicant shall determine which stormwater standards apply to
the proposed regulated activity as follows:
(a)
Stormwater standards for new development shall apply to all
proposed regulated activities that involve only new development activities
as defined in this chapter.
(b)
Stormwater standards for redevelopment shall apply to all proposed
regulated activities that involve only redevelopment activities as
defined in this chapter.
(c)
At the discretion of the Township Engineer, regulated activities
that involve a combination of both new development and redevelopment
activities, as defined in this chapter, may either:
[1]
Apply the stormwater standards (redevelopment or new development)
that are associated with the activity that involves the greatest amount
of land area; or
[2]
Apply the redevelopment and new development stormwater standards
to the corresponding redevelopment and new development portions of
the proposed regulated activity.
G.
Weighted averaging of runoff coefficients shall not be used for manual
computations or input data for water quality and runoff volume calculations.
H.
Hydraulic computations to determine the capacity of pipes, culverts,
and storm sewers shall be consistent with methods and computations
contained in the Federal Highway Administration Hydraulic Design Series
Number 5 (Publication No. FHWA-NHI-01-020 HDS No. 5, as amended).
Hydraulic computations to determine the capacity of open channels
shall be consistent with methods and computations contained in the
Federal Highway Administration Hydraulic Engineering Circular Number
15 (Publication No. FHWA-NHI-05-114 HEC 15, as amended). Values for
Manning's roughness coefficient (n) shall be consistent with Table
C-3 in Appendix C[3] of the chapter.
[3]
Editor's Note: Appendix C is included as an attachment to
this chapter.
A.
Any BMP intended to hold standing water for four days or longer shall
be designed to incorporate biologic controls consistent with the West
Nile Guidance found in Appendix D,[1] PADEP document 363-0300-001 "Design Criteria - Wetlands
Replacement/Monitoring" (as amended) (or contact the Pennsylvania
State Cooperative Wetland Center or the Penn State Cooperative Extension
Office for design information).
[1]
Editor's Note: Appendix D is included as an attachment to
this chapter.
B.
Any stormwater basin required or regulated by this chapter designed
to store runoff and requiring a berm or earthen embankment shall be
designed to provide an emergency spillway to safely convey flow up
to and including the 100-year proposed conditions. The height of embankment
shall provide a minimum one foot of freeboard above the maximum pool
elevation computed when the facility functions for the 100-year proposed
conditions inflow. Should any BMP require a dam safety permit under
Pa. Code Chapter 105 regulations, the facility shall be designed in
accordance with and meet the regulations of Pa. Code Chapter 105 concerning
dam safety. Pa. Code Chapter 105 may require the safe conveyance of
storms larger than 100-year event.
C.
Any drainage conveyance facility and/or channel not governed by Pa.
Code Chapter 105 regulations shall be designed to convey, without
damage to the drainage facility or roadway, runoff from the twenty-five-year
storm event. Larger storm events (fifty-year and 100-year storms)
shall also be safely conveyed in the direction of natural flow without
creating additional damage to any drainage facilities, nearby structures,
or roadways.
D.
Conveyance facilities to or exiting from stormwater management facilities
(i.e., detention basins) shall be designed to convey the 100-year
design flow to or from the facility.
E.
Roadway crossings or structures located within designated floodplain
areas shall be able to convey runoff from a 100-year design storm
consistent with Federal Emergency Management Agency National Flood
Insurance Program floodplain management requirements.
F.
Any stormwater management facility located within a PennDOT right-of-way
shall comply with PennDOT minimum design standards and permit submission
and approval requirements.
G.
Adequate erosion protection and energy dissipation shall be provided
along all open channels and at all points of discharge. Design methods
shall be consistent with the Federal Highway Administration Hydraulic
Engineering Circular Number 11 (Publication No. FHWA-IP-89-016, as
amended) and the PADEP Erosion and Sediment Pollution Control Program
Manual (Publication No. 363-2134-008, as amended), or other design
guidance acceptable to the Township Engineer.
A.
Open vegetated channels.
(1)
Open vegetated channels are primarily applicable for land uses such
as roads, highways, residential developments and pervious areas.
(2)
Open vegetated channels shall be designed to meet the following minimum
standards:
(a)
The channel shall be designed to safely and nonerosively convey
the ten-year frequency storm event, with a freeboard of at least 12
inches. "Freeboard" is the difference between the water surface elevation
of the design flow in the channel and the top elevation of the side
bank of the channel.
(b)
The longitudinal slope shall be no greater than 6%, and no less
than 1%, unless an underdrain is provided.
(c)
Channels shall be trapezoidal in cross section. The minimum
bottom width shall be two feet. The maximum bottom width shall be
eight feet.
(d)
Channels shall be designed with moderate side slopes of no greater
than four horizontal to one vertical. Flatter side slopes may be necessary
under certain circumstances.
(e)
Landscape specifications shall address the grass species, wetland
plantings (if applicable), soil amendment, and hydric conditions present
along the channel.
(f)
Accumulated sediment within the channel bottom shall be removed
when it has reached three inches deep. This requirement shall be included
in the O&M plan.
(g)
The use of low ground pressure (less than four psi) equipment
for construction is required where infiltration credit will be sought.
B.
Retention and detention basins.
(1)
Basins intended to hold water for more than four days shall be designed to create a healthy ecological community with sufficient circulation of water to prevent the growth of unwanted vegetation and mosquitoes. Care should be taken to landscape retention basins in accordance with § 178-25D. Detention basins, also known as dry basins, are generally discouraged as a stormwater management practice and should only be used where infiltration of stormwater is not possible, and then only for street runoff, or, as a last resort, where no other management facility is practical.
(3)
The outlet structure of any basin designed with a permanent pool
shall include a gate valve designed to allow complete drainage of
the pond for maintenance.
(4)
The design of a retention basin shall include the determination of
the proposed site's ability to support a viable permanent pool. The
design shall take into account such factors as the available and required
rate and quality of dry weather inflow, the stormwater inflow, seasonal
and longer-term variations in groundwater table, freeboard, and impacts
of potential pollutant loadings.
(5)
A clay core, keyed into the in situ soil, shall be required in embankments.
(6)
Sediment storage volume equal to at least 20% of the volume of the
permanent pool shall be provided.
(7)
"Freeboard" is the difference between the water surface elevation
of the design flow in the emergency spillway and the top elevation
of the settled basin embankment (that is, top of berm). The minimum
freeboard shall be one foot.
(8)
A sediment forebay with a hardened bottom shall be provided at each
inlet into a basin. The forebay storage capacity shall, at minimum,
be 10% of the two-year volume discharged from that inlet. The forebay
shall be designed to allow for access by maintenance equipment for
periodic cleaning.
(9)
Emergency spillways shall be sized and located to permit the safe
passage of stormwater flows from a 100-year storm. The maximum velocities
in vegetated spillways, excavated in otherwise undisturbed soil, shall
be analyzed based upon the velocity of peak flow in the emergency
spillway during an assumed clogged primary outlet condition. Where
maximum velocities exceed design standards contained in the Engineering
Field Manual for Conservation Practices (USDA, SCS, July 1984), suitable
lining shall be provided. All emergency spillways placed on fill materials
shall be lined, regardless of flow velocities or depths. Suitable
linings include grass pavers, riprap (comprised of native stone if
possible) and permanent turf reinforcing mats.
(10)
Existing ponds or basins can be used for stormwater management,
provided that it can be demonstrated that the ponds are structurally
sound and meet the design requirements herein.
(11)
Inlet structures and outlet structures shall be separated to
the greatest extent possible in order to maximize the flow path through
the basin. Inlets shall discharge into areas of the basin that slope
toward the outlet structure, but be adequately separated to ensure
predischarge sediment deposition. Low-flow channels, constructed of
concrete or asphalt, are not permitted. Where low-flow channels are
necessary, they shall be composed of a natural or bioengineered material
or riprap. Low-flow channels shall be designed to improve water quality
and slow the rate of flow through the basin. Low-flow channels may
also be designed to infiltrate, where practical.
(12)
Basins shall be designed to provide a length-to-width ratio
of no greater than 3L:1W as measured in plan view (for example, a
ratio of 4L:1W is too narrow).
(13)
For ponds with a permanent pool, the basin depth shall average
three feet to six feet, with no area shallower than three feet, with
the exception of side slopes or benches. In residential areas, ponds
shall be equipped with management practices that reduce the potential
for unauthorized entry and use of the pond by the general public.
Special measures are particularly desirable where a deep pond is not
very visible from a public road or residence.
(14)
All areas of the basin that are deeper than four feet shall
have two safety benches, totaling 15 feet in width. One bench shall
start at the normal water surface (permanent pool) and extend up the
pond's side slopes at a maximum slope of 10%. The other shall extend
down from the normal water surface into the pond to a maximum depth
of 18 inches, also at a slope no greater than 10%.
(15)
Any side slopes below the permanent water surface level shall
not exceed five horizontal to one vertical (5H:1V). Side slopes above
the permanent water surface level shall not exceed three horizontal
to one vertical (3H:1V). For detention basins, where used, the inside
side slopes shall be no steeper than three horizontal to one vertical
(3H:1V). The minimum slope for the basin bottom is 2%. A level bottom
is acceptable, provided the designer demonstrates to the Township
Engineer's satisfaction that the basin bottom will be landscaped with
appropriate wetland vegetation. In addition, detention basins of sufficient
size and slope may serve other functions as well, including recreational
uses, which do not hinder or conflict with the function of the detention
basin.
(16)
Proper stabilization structures, including stilling basins,
energy dissipaters, and channel lining, shall be constructed at the
outlets of all basins and emergency spillways. The stabilization structures
shall control water to avoid erosion, reduce velocities of released
water, and direct water so that it does not interfere with downstream
activities.
(17)
An access ramp, with a slope no greater than 20% and an access
easement 20 feet in width, shall be provided to each basin to facilitate
cleanout.
(18)
Energy dissipaters and/or level spreaders shall be installed
to prevent erosion and/or initiate sheet flow at points where pipes
or drainageways discharge to or from basins. Energy dissipaters shall
comply with criteria in Hydraulic Engineering Circular No. 15, Design
for Stable Channels with Flexible Linings (USDOT, FHWA, 1986), or
the Engineering Field Manual for Conservation Practices (USDA, SCS,
July 1984) or the latest revised versions thereof. Such facilities
shall be both functional and harmonious with the surrounding environment.
For example, native rock (not quarried riprap) from the site may be
used in constructing dissipaters where practical.
(19)
The minimum distance between a proposed basin discharge point
(including the energy dissipater, etc.) and a downstream property
boundary shall in no case be less than 30 feet. Where there is discharge
onto, or through, adjacent properties prior to release to a stream,
designers shall demonstrate how downstream properties are to be protected.
The Township Engineer may require that the setback distance be increased
based upon factors such as topography, soil conditions, the size of
structures, the location of structures, and discharge rates. A drainage
easement may also be required.
(20)
Outlet structures shall meet the following specifications:
(a)
For storms up to, and including, the two-year storm, normal
overflow, after development, shall be through a siphon structure,
which draws cooler water from just above the bottom of the basin,
and discharges at the intended level of the permanent water surface
of the retention basin, to a concrete or rock apron or level spreader
on the downstream slope and toe of the basin, possibly in conjunction
with the discharge structure for larger storms.
(b)
For storms greater than the two-year storm, a concrete principal
outlet structure shall be built, using reinforced concrete with watertight
construction joints.
(c)
Discharges shall be to level spreaders or energy dissipaters.
The point of discharge shall be a point where the discharge will spread
out in shallow sheet flow to level ground or to slopes of less than
5%.
(d)
To minimize clogging and to facilitate cleaning and inspecting,
outlet pipes used to drain the pond and used for discharges to maintain
pond levels after construction shall have an internal diameter of
at least 18 inches and a minimum grade of 1%.
(e)
Concrete antiseep collars shall be provided on all outlet pipes
within a constructed berm.
(f)
The use of architecturally treated concrete, stucco, or stone
facade treatment shall be considered for enhancing the outlet structure.
Such facilities shall be both functional and harmonious in design
with the surrounding environment.
(g)
Outlet pipes through a basin berm shall be constructed of reinforced
concrete with rubber gaskets in conformance with AASHTO M170, M198
and M207. For siphon structures, pipe materials shall be reinforced
concrete, Schedule 80 PVC or other material acceptable to the Township
Engineer.
(h)
Basin outlet structures shall have childproof, nonclogging,
trash racks, fabricated from stainless steel. The bars in the trash
rack shall be spaced such that a four-inch-diameter sphere cannot
pass through any opening in the trash rack. Periodic cleaning of debris
from trash racks shall be included in the operation and maintenance
plan.
(i)
Antivortex devices, consisting of a thin vertical plate, shall
be provided at the top of all circular risers or standpipes.
C.
Conveyance systems (open channels, drainageways, and storm sewers).
(1)
Applicants are encouraged to design conveyance systems that encourage
infiltration and improve water quality wherever practicable.
(2)
Wherever conveyance channels are necessary, drainage shall be maintained
by an open channel with landscaped banks designed to carry the fifty-year,
twenty-four-hour stormwater runoff from upstream contributory areas
without erosion. The Township Engineer may require a higher design
storm, as conditions require. All open channels shall be designed
with one foot of freeboard above the water surface elevation of the
design runoff condition.
(3)
Flood relief channels shall be provided and designed to convey the
runoff from the 100-year, twenty-four-hour storm, such that a positive
discharge of this runoff to an adequate receiving stream or conveyance
system occurs without allowing this runoff to encroach upon other
properties. The intent is to ensure that runoff can reach its designated
management facility or receiving conveyance or stream, even if the
site conveyance becomes blocked or otherwise nonfunctional.
(4)
The Board of Supervisors may require that open channels along existing
roadways be enclosed if PennDOT standards for safety and maintenance
cannot be satisfied. All drainage structures shall conform to the
latest edition of Form 408, PennDOT specifications.
(5)
Manholes and/or inlets shall not be spaced more than 300 feet apart
for pipe sizes up to 24 inches in diameter and not more than 450 feet
apart for larger pipe sizes.
(6)
Stormdrain pipes shall be reinforced concrete pipe with gasketed
joints, or smooth lined corrugated polyethylene pipes with gasketed
joints. No mortar joint concrete pipes are permitted.
(7)
Inlet tops shall be sealed to boxes with a preformed concrete joint
sealant material (such as RAM-NEK® or
equivalent).
(8)
Storm manhole covers and inlet grates shall have the phrase "No dumping,
drains to waterway." cast into them, and shall meet all applicable
PennDOT specifications.
(9)
Where vegetated swales are used in lieu of, or in addition to, storm
sewers, they shall be designed to carry the ten-year flow without
erosion. Drainage swales shall be designed with a minimum grade of
1% and a maximum grade of 6%, unless underdrains or check dams are
provided.
(10)
Storm drainage systems collecting runoff from streets or parking
areas and discharging to detention basins shall, to the maximum extent
possible, allow runoff to flow through a series of one or more depressions
containing wetland vegetation in order to reduce the level of pollutants.
(11)
Utilizing street curbing for the purpose of stormwater conveyance
is discouraged. On streets that must contain curbing, storm sewers
shall be placed in front of the curbing. To the greatest extent possible,
storm sewers shall not be placed directly under curbing. At curbed
street intersections, storm inlets shall be placed in the tangent
sections of the road.
(12)
The use of open vegetated swales, in lieu of curbing, to convey,
infiltrate, and/or treat stormwater runoff from roadways is encouraged
in areas with slopes less than 6%. Inlets shall be placed at the center
of the shoulder swale, draining the street, and shall be located no
less than four feet from the edge of the cartway.
(13)
The Township (and the party responsible for maintenance, if
applicable) shall be granted a minimum twenty-foot-wide drainage easement
over all storm sewers, drainage swales, channels, etc., that are a
component of the stormwater management system, when located within
undedicated land. All permanent retention or detention basins, and/or
other stormwater management facilities providing stormwater control
for other than a single residential lot, shall be located within a
defined drainage easement that allows proper legal access and maintenance
vehicle access by the Township personnel.
(14)
No property owner shall obstruct or alter the flow, location,
or carrying capacity of a stream, channel, or drainage swale to the
detriment of any other property owner, whether upstream or downstream.
All subdivision and/or land development plans containing streams,
channels, drainage swales, storm sewers, or other conveyance systems
that cross property boundaries, existing or proposed, or whose discharge
crosses such boundaries, shall contain a note stating the above.
(15)
Water quality inlets. Storm drainage systems that collect runoff
from parking areas and/or loading areas exceeding 10,000 square feet
of impervious coverage and that discharge to stormwater management
systems, including surface or subsurface infiltration systems, shall
have a minimum of one water quality inlet per each acre of drainage
area. The purpose of water quality inlets is to remove oil, grease,
and heavy particulates or total suspended solids, hydrocarbons, and
other floating substances from stormwater runoff.
(16)
Oil-separation devices; runoff from streets or parking lots;
cleaning.
(a)
Any inlet or manhole in a storm drainage collection system which
discharges runoff from a street with lot or building frontages of
less than 100 feet or from a parking lot to a surface or subsurface
infiltration system shall have an oil-separation device installed
at the outlet of the manhole or inlet. The oil-separation device will
be maintained by the Township if the contributing flow is from a Township-owned
street, and the oil-separation device will be maintained by the property
owner or homeowners' association if the contributing flow is from
a parking lot or private street or driveway. The structure containing
the oil separator will be constructed with a ring foundation with
an open floor, consisting of a bed of clean three-quarter-inch stone
with a minimum depth of eight inches. The floor of the inlet structure
shall be a minimum of 18 inches below the outlet elevation. The Township
Engineer may also require structures to capture suspended solids or
permit other oil- and/or trash-separation devices, or methods, if
the applicant can prove that such alternative devices will be effective
and easily maintained.
(b)
Storm drainage systems receiving runoff from street or parking
lots and discharging to retention/detention basins or at points of
interest shall, to the maximum extent possible, flow through a series
of one or more depressions containing wetland vegetation in order
to reduce the level of pollutants leaving the property. The variety
of vegetation in wetlands created for this purpose shall be specified
on the plan and provided in the construction sequence. Wetland area
plantings shall be maintained and protected from invasive or inappropriate
species.
(c)
Periodic cleaning of these systems shall be addressed in the
operation and maintenance plan submitted to the Township.
(17)
All storm drainage pipes greater than 15 inches in diameter
shall incorporate grill-or grate-type measures, at headwalls and end
sections, to prevent children or small animals from entering the pipes.
The bars in the grill or grate shall be spaced such that a four-inch-diameter
sphere cannot pass through any opening. Periodic cleaning of debris
from grills and/or grates shall be included in the operation and maintenance
plan.
(18)
Box or arch culverts under roadways shall be designed for a
fifty-year storm and shall have a natural stream bottom, except when
under a road providing the only means of access to a property, also
known as a "single access street." For a single-access street, a 100-year
storm shall be used. A culvert for a driveway shall be designed for
a 100-year storm if the driveway provides the only means of access
to the property.
(19)
Structures, such as box culverts, arch culverts, or bridges,
shall be provided with wing walls with deep footings and shall be
constructed for the full width of the right-of-way. Where possible,
a natural stream channel, using river cobbles, or similar treatment,
shall be maintained under the structure to allow the passage of wildlife.
Measures such as toe walls, or similar methods, shall be provided
to prevent scouring. The cartway area over the bridge shall be as
wide as the widest road connecting with the bridge, or if the character
of the road is expected to change for future planning, the cartway
of the bridge shall be made to anticipate this condition. On either
side of the cartway, the bridge railing must be at least five feet
back from the edge of the final cartway width so this five feet may
be used to place sidewalks/bikeways, present or future. Where no increased
vehicle traffic is possible, a six-foot-wide sidewalk/bikeway shall
be provided on one side to connect to existing or planned sidewalks/bikeways.
(20)
If necessary, due to the configuration of a crossing requiring
the construction of headwalls, and/or wing walls or similar structures
outside of the right-of-way, additional right-of-way, encompassing
the structure, shall be provided.
(21)
Any point where a stormdrain pipe discharges to grade shall
be protected with rock outlet protection designed for the maximum
pipe capacity, as determined by Manning's equation. Additional measures
may be required where such pipes discharge to areas of greater than
5% slope.
(22)
Inlets along streets shall be arranged so that 95% of gutter
flow will be captured by each inlet.
D.
Landscaping of stormwater management practices. Stormwater management
practices shall be landscaped in accordance with the following standards.
Landscape plans shall be prepared by a professional landscape architect,
licensed in the Commonwealth of Pennsylvania.
(1)
Landscaping shall be required in and around all constructed stormwater
management practices, with a minimum surface area of 1,000 square
feet, for the purposes of:
(2)
A planting plan and planting schedule shall be submitted in accordance
with the following:
(a)
Wet meadows, including floors of stormwater management practices.
[1]
Wet meadows and floors of stormwater management practices shall
be planted with native wildflowers and nonaggressive grasses, the
intent being to create a mixed meadow of such plantings, where appropriate.
Selection of plantings shall be based on whether the area in question
is usually well drained or permanently wet and whether the area will
be used for recreation purposes. No woody plants shall be planted
within the saturated zone (phreatic line) of a stormwater management
practice or on a berm constructed for impounded water.
[2]
Seeding by drills, corrugated rollers, cyclone or drop seeders
or hand seeding of such areas is preferred. However, subject to approval
of the Township Engineer, hydroseeding, followed by hydromulching,
can be used.
[3]
Fertilizers, as a nutrient supplement, shall not be used unless
it is documented that soil conditions warrant such use and nutrient
applied does not exceed plant uptake. Soil for planting of wildflowers
shall contain not less than 3% or more than 10% organic matter, as
determined by an agricultural chemist, with certification of the test
before planting.
[4]
Seeding shall take place either between April 1 and May 15 or
between September 1 and October 15. Planting areas shall be soaked
to maintain a consistent level of moisture for at least four weeks
to six weeks after planting.
[5]
A maintenance plan shall be submitted for the stormwater management
practice(s) proposed, listing mowing frequency, weeding, aerating,
and any other required maintenance activities.
(b)
Wet edges that remain wet all or most of the year shall be planted
with native wildflowers, grasses, and shrubs. Plants to be located
on rims or banks which remain dry most of the year shall be planted
with species tolerant of dry soil conditions.
(c)
Wooded areas.
[1]
Where stormwater management practices adjoin wooded areas, native
trees and shrubs shall be selected and planted outside the practice,
so as to blend with existing surroundings.
[2]
Plantings in such areas shall be of sufficient density to eliminate
the need for mowing.
[3]
After construction, clusters of trees and shrubs shall be planted
in cleared areas around stormwater management facilities, but well
away from outfalls and any constructed berms.
[4]
Vegetation shall be planted during appropriate times of the
year, predominantly between late March and mid-May or from early October
until evidence of ground freezing, depending upon the species selected.
Most deciduous trees and shrubs can be planted in either spring or
fall. Evergreens are best planted in late summer or early fall.
(d)
Slopes.
[1]
On slopes of less than 20%, a mixture of native meadow grasses
and wildflowers (for wet meadows) shall be planted.
[2]
On slopes equal to or greater than 20% dense spreading shrubs,
tolerant of dry soils, shall be planted. Heavy mat mulch shall be
used during the period of establishment.
[3]
No woody plant materials or trees shall be located on a constructed
or natural berm acting as the impoundment structure of a stormwater
management practice. Trees shall be located downstream of an impoundment
berm a sufficient distance from the toe of the constructed slope to
assure that the toe of the slope is outside the future projected mature
dripline of the species planted, but in no case less than 15 feet.
[4]
In cases where stormwater management practices are to be located
in proximity to wetlands or waterways, the applicant's planting plan
and schedule shall consider the sensitive conditions existing therein
and be modified accordingly to reflect existing flora.
[5]
Stormwater management practices shall be screened in a manner
which complements the existing landscape and provides sufficient access
for maintenance.
