[Ord. No. 416, 9/29/2022]
1. For all regulated activities, unless preparation of an SWM site plan is specifically exempted in §
23-106:
A. Preparation and implementation of an approved SWM site plan is required.
B. No regulated activities shall commence until the municipality issues
written approval of an SWM site plan, which demonstrates compliance
with the requirements of this chapter.
2. The existing locations of concentrated drainage discharge onto adjacent
property shall not be altered without written approval of the affected
property owner(s).
3. Areas of existing diffused drainage discharge onto adjacent property
shall be managed such that, at minimum, the peak diffused flow does
not increase in the general direction of discharge, except as otherwise
provided in this chapter. If diffused flow is proposed to be concentrated
and discharged onto adjacent property, the developer must document
that there are adequate downstream conveyance facilities to safely
transport the concentrated discharge to the point of predevelopment
flow concentration, to the stream reach or otherwise prove that no
harm will result from the concentrated discharge. Areas of existing
diffused drainage discharge shall be subject to any applicable release
rate criteria in the general direction of existing discharge whether
they are proposed to be concentrated or maintained as diffused drainage
areas.
4. Where a site is traversed by watercourses other than those for which a 100-year floodplain is defined by the municipality, there shall be provided drainage easements conforming substantially with the line of such watercourses. The width of any easement shall be adequate to provide for unimpeded flow of storm runoff based on calculations made in conformance with §
23-307 for the 100-year return period runoff and to provide a freeboard allowance of 1/2 foot above the design water surface level. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations which may adversely affect the flow of stormwater within any portion of the easement. Also, periodic maintenance of the easement to ensure proper runoff conveyance shall be required. Watercourses for which the 100-year floodplain is formally defined are subject to the applicable municipal floodplain regulations.
5. When it can be shown that, due to topographic conditions, natural
drainage swales on the site cannot adequately provide for drainage,
open channels may be constructed conforming substantially to the line
and grade of such natural drainage swales. Capacities of open channels
shall be calculated using the Manning Equation.
6. Post-construction BMPs shall be designed, installed, operated and
maintained to meet the requirements of the Clean Streams Law, 35 P.S. § 691.1
et seq., and implemented regulations, including the established practices
in 25 Pa. Code Chapter 102, and the specifications of this chapter
as to prevent accelerated erosion in watercourse channels and at all
points of discharge.
7. No earth disturbance activities associated with any regulated activities
shall commence until approval by the municipality of a plan which
demonstrates compliance with the requirements of this chapter.
8. Techniques described in Appendix 23-E, "Low Impact Development," of this chapter are encouraged because they reduce the
costs of complying with the requirements of this chapter and the state
water quality requirements.
9. Infiltration for stormwater management is encouraged where soils and geology permit, consistent with the provisions of this chapter. Infiltration is encouraged for capturing and treating the water quality volume (as calculated in §
23-304), any part of the water quality volume or for otherwise meeting the purposes of this chapter.
10. SWM site plans approved by the municipality, in accordance with §
23-409, shall be on-site throughout the duration of the regulated activity.
11. The municipality may, after consultation with DEP, approve measures
for meeting the state water quality requirements other than those
in this chapter, provided that they meet the minimum requirements
of, and do not conflict with, state law including, but not limited
to, the Clean Streams Law.
12. For all regulated earth disturbance activities, erosion and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this chapter and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law. Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual4), No. 363-2134-008, as amended
and updated.
13. Impervious Area:
A. The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in stages.
B. For development taking place in stages, the entire development plan
must be used in determining conformance with this chapter.
C. For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter in accordance with §
23-106.
14. Concentrated stormwater flows onto adjacent property shall not be
created, increase, relocated, or otherwise significantly altered without
written notification to the adjacent property owner(s). Such stormwater
flows shall be subject to the requirements of this chapter.
15. All regulated activities shall include measures as necessary to:
A. Protect health, safety, and property.
B. Meet the water quality goals of this chapter by implementing measures
to:
(1)
Minimize disturbance to floodplains, wetland, and wooded areas.
(2)
Maintain or extend riparian buffers.
(3)
Avoid erosive flow conditions in natural flow pathways.
(4)
Minimize thermal impacts to waters of this commonwealth.
(5)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
C. Incorporate methods described in the Pennsylvania Stormwater Best
Management Practices Manual (BMP Manual3).
16. The design of all facilities over karst shall include an evaluation
of measures to minimize adverse effects.
17. Infiltration BMPs should be spread out, made as shallow as practicable,
and located to maximize use of natural on-site infiltration features
while still meeting the other requirements of this chapter.
18. Normally dry, open top, storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not less than 24 and not more than 72 hours from the end of
the design storm.
19. The design storm volumes to be used in the analysis of peak rates
of discharge should 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's Atlas 145 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/.
20. For all regulated activities, SWM BMPs 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, and the Storm Water Management Act.
21. Various BMPs and their design standards are listed in the BMP Manual.3
[Ord. No. 416, 9/29/2022]
1. The following permit requirements apply to certain regulated and
earth disturbance activities and must be met prior to commencement
of regulated and earth disturbance activities, as applicable:
A. All regulated and earth disturbance activities subject to permit
requirements by DEP under regulations at 25 Pa. Code Chapter 102.
B. Work within natural drainageways subject to permit by DEP under 25
Pa. Code Chapter 102.
C. Any stormwater management facility that would be located in or adjacent
to surface waters of the commonwealth, including wetlands, subject
to permit by DEP under 25 Pa. Code Chapter 105.
D. Any stormwater management facility that would be located on a state
highway right-of-way or require access from a state highway shall
be subject to approval by the Pennsylvania Department of Transportation
(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 DEP under 25 Pa. Code Chapter
105.
[Ord. No. 416, 9/29/2022]
1. No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of an erosion and
sediment control plan for construction activities. Written approval
by DEP or a delegated county conservation district shall satisfy this
requirement.
2. An erosion and sediment control plan is required by DEP regulations
for any earth disturbance activity of 5,000 square feet or more under
25 Pa. Code § 102.4(b).
3. A DEP NPDES Stormwater Discharges Associated with Construction Activities
Permit is required for regulated earth disturbance activities under
25 Pa. Code Chapter 92.
4. Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate DEP regional office or county conservation
district must be provided to the municipality before the commencement
of an earth disturbance activity.
5. A copy of the erosion and sediment control plan and any permit, as
required by DEP regulations, shall be available at the project site
at all times.
[Ord. No. 416, 9/29/2022]
1. No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of an SWM site plan
which demonstrates compliance with this chapter.
2. The water quality volume (WQv) shall be captured and treated. The
green infrastructure and low impact development practices provided
in the BMP Manual3 shall be utilized for
all regulated activities wherever possible. The WQv shall be calculated
two ways.
A. First, WQv shall be calculated using the following formula:
Where:
|
WQv
|
=
|
Water quality volume in acre-feet.
|
c
|
=
|
Rational Method post-development runoff coefficient for the
2-year storm.
|
P
|
=
|
1.25 inches.
|
A
|
=
|
Area in acres of proposed regulated activity.
|
B. Second, the WQv shall be calculated as the difference in runoff volume
from predevelopment to post development for the two-year return period
storm. The effect of closed depressions on the site shall be considered
in this calculation. The larger of these two calculated volumes shall
be used as the WQv to be captured and treated, except that in no case
shall the WQv exceed 1.25 inches of runoff over the site area.
(1)
Existing (predevelopment) nonforested pervious areas must be
considered meadow in good condition.
(2)
Twenty percent of existing impervious area, when present, shall
be considered meadow in good condition in the model for existing conditions.
3. The WQv shall be calculated for each post-development drainage direction
on a site for sizing BMPs. Site areas having no impervious cover and
no proposed disturbance during development may be excluded from the
WQv calculations and do not require treatment.
4. If an applicant is proposing to use a wet pond, constructed wetland
or other BMP that ponds water on the land surface and may receive
direct sunlight, the discharge from that BMP must be treated by infiltration,
a vegetated buffer, filter strip, bioretention, vegetated swale or
other BMP that provides a thermal benefit to protect any high-quality
waters of the Bushkill Creek, Martins/Jacoby Creeks and Delaware River
Sub-Basin 1 from thermal impacts.
5. Any stormwater runoff from the site as a result of the regulated activities must either be treated with infiltration or two acceptable BMPs such as those listed in §
23-304, Subsection
11.
6. Infiltration BMPs shall not be constructed on fill.
7. The applicant shall document the bedrock type(s) present on the site
from published sources. Any apparent boundaries between carbonate
and noncarbonate bedrock shall be verified through more detailed site
evaluations by a qualified geotechnical professional.
8. For each proposed regulated activity in the watershed, the applicant
shall conduct a preliminary site investigation on the portion of the
site that is judged to be the best candidate hydrogeologically for
possible infiltration, including gathering data from published sources,
a field inspection of the site, a minimum of one test pit and a minimum
of two percolation tests, as outlined in Appendix 23-F. This investigation will determine depth to bedrock, depth
to the seasonal high-water table, soil permeability and location of
special geologic features, if applicable. The location(s) of special
geologic features shall be verified by a qualified geotechnical professional.
9. The WQv shall be infiltrated unless the applicant demonstrates that it is infeasible to infiltrate the WQv for reasons of seasonal high-water table, permeability rate, soil depth or isolation distances. The preliminary site investigation described in §
23-304, Subsection
8, shall continue on different areas of the site until a suitable infiltration location is found or the entire site is determined to be infeasible for infiltration. For proposed infiltration areas, the additional site investigation and testing as outlined in Appendix 23-F shall be completed. The municipality may determine infiltration to be infeasible if there are known existing conditions or problems that may be worsened by the use of infiltration. The following conditions are suitable for infiltration:
A. Depth to bedrock below the invert of the BMP greater than or equal
to two feet.
B. Depth to seasonal high-water table below the invert of the BMP greater
than or equal to three feet. (If the depth to bedrock is between two
and three feet and the evidence of the seasonal high-water table is
not found in the soil, no further testing to locate the depth to seasonal
high-water table is required.)
C. Soil permeability greater than or equal to 0.5 inch per hour and
less than or equal to 12 inches per hour.
D. Setback distances or buffers as follows:
(1)
One hundred feet from water supply wells.
(2)
Ten feet downgradient or 100 feet upgradient from building foundations.
(3)
Fifty feet from septic system drainfields.
(4)
One hundred feet from the property line unless documentation
is provided to show that all setbacks from wells, foundations and
drainfields on neighboring properties will be met. If it is not feasible
to infiltrate the full WQv, the applicant shall infiltrate that portion
of the WQv that is feasible based on the site characteristics.
10. Site areas proposed for infiltration shall be protected from disturbance
and compaction except as necessary for construction of infiltration
BMPs.
11. If infiltration of the entire WQv is not proposed, the remainder
of the WQv shall be treated by two acceptable BMPs in series for each
discharge location. Sheet flow draining across a pervious area can
be considered as one BMP. Sheet flow across impervious areas and concentrated
flow shall flow through two BMPs. If sheet flow from an impervious
area is to be drained across a pervious area as one BMP, the length
of the pervious area must be equal to or greater than the length of
impervious area. In no case may the same BMP be employed consecutively
to meet this requirement. Acceptable BMPs are listed below along with
the recommended reference for design.
Best Management Practice
|
Design Reference
|
---|
Bioretention low
|
Impact Development Design Strategies, Prince George's County,
Md., June 1999
|
Capture/reuse
|
Texas Guide to Rainwater Harvesting, 2nd Edition. Texas Water
Development Board, Center for Maximum Potential Building Systems,
1997
|
Constructed wetlands
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment
|
Minimum disturbance/minimum maintenance practices
|
Conservation Design for Stormwater Management. Delaware Dept.
of Natural Resources and Brandywine Conservancy, September 1997
|
Oil/water separators
|
Georgia Stormwater Management Manual Volume 2 Technical Handbook,
August 2001
|
Sediment traps/catch basin sumps
|
U.S. Environmental Protection Agency's Post-Construction
Stormwater Management in New Development & Redevelopment BMP Fact
Sheet for "Catch Basins/Catch Basin Insert"
|
Significant reduction of existing impervious cover
|
N/A
|
Stormwater filters (sand, peat, compost, etc.)
|
Design of Stormwater Filtering Systems. Claytor, R. and Schueler,
T., Center for Watershed Protection, December 1996
|
Trash/debris collectors in catch basins
|
Pennsylvania Handbook of BMPs for Developing Areas or latest
PA Dept. of Environmental Protection Manual
|
Vegetated buffers/filter strips
|
Pennsylvania Handbook of BMPs for Developing Areas or latest
PA Dept. of Environmental Protection Manual
|
Vegetated roofs
|
Roof Gardens: History, Design, and Construction. Osintmdson,
T., W.W. Norton & Co., 1998
|
Vegetated swales/filter strips
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment
|
Water quality inserts for inlets
|
Pennsylvania Handbook of BMPs for Developing Areas or latest
PA Dept. of Environmental Protection Manual
|
Wet detention ponds
|
Pennsylvania Handbook of BMPs for Developing Areas or latest
PA Dept. of Environmental Protection Manual
|
12. Stormwater runoff from hot spot land uses shall be pretreated. In no case may the same BMP be employed consecutively to meet this requirement and the requirement in §
23-304, Subsection
11.
A. Acceptable methods of pretreatment are listed below:
Hot Spot Land Use
|
Pretreatment Method(s)
|
---|
Vehicle maintenance and repair
|
Oil/water separators
|
Facilities including auto parts stores
|
Use of drip pans and/or dry sweep material
|
|
Under vehicles/equipment
|
|
Use of absorbent devices to reduce liquid releases
|
|
Spill prevention and response program
|
Vehicle fueling stations
|
Oil/water separators
|
|
Water quality inserts for inlets
|
|
Spill prevention and response program
|
Storage areas for public works
|
Oil/water separators
|
|
Sediment traps/catch basin sumps
|
|
Water quality inserts for inlets
|
|
Use of drip pans and/or dry sweep material under vehicles/equipment
|
|
Use of absorbent devices to reduce liquid releases
|
|
Spill prevention and response program
|
|
Diversion of stormwater away from potential contamination areas
|
Outdoor storage of liquids
|
Spill prevention and response program
|
Commercial nursery operations
|
Vegetated swales/filter strips
|
|
Constructed wetlands
|
|
Stormwater collection and reuse
|
Salvage yards and recycling facilities
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Fleet storage yards and vehicle cleaning facilities
|
BMPs that are a part of a stormwater pollution Prevention Plan
under an NPDES permit
|
Facilities that store or generate regulated substances
|
BMPs that are a part of a Stormwater Pollution prevention plan
under an NPDES permit
|
Marinas
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Certain industrial uses (listed under NPDES)
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
B. Design references for the pretreatment methods, as necessary, are
listed below. The applicant may demonstrate that due to the site characteristics
the land use is not a hot spot land use.
Pretreatment Method
|
Design Reference
|
---|
Constructed wetlands
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment
|
Diversion of stormwater away from potential contamination areas
|
Pennsylvania Handbook of BMPs for Developing Areas or latest
PA Dept. of Environmental Protection Manual
|
Oil/water separators
|
Georgia Stormwater Management Manual Volume 2 Technical Handbook,
August 2001
|
Sediment traps/catch basin sumps
|
U.S. Environmental Protection Agency's Post-Construction
Stormwater Management in New Development & Redevelopment BMP Fact
Sheet for "Catch Basins/Catch Basin Insert"
|
Stormwater collection and reuse (especially for irrigation)
|
Texas Guide to Rainwater Harvesting, 2nd Edition, Texas Water
Development Board, Center for Maximum Potential Building Systems,
1997
|
Stormwater filters (sand, peat, compost, etc.)
|
Design of Stormwater Filtering Systems. Claytor, R. and Schueler,
T., Center for Watershed Protection, December 1996
|
Trash/debris collectors in catch basins
|
Pennsylvania Handbook of BMPs for Developing Areas or latest
PA Dept. of Environmental Protection Manual
|
Vegetated swales/filter strips
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment
|
Water quality inserts for inlets
|
Pennsylvania Handbook of BMPs for Developing Areas or latest
PA Dept. of Environmental Protection Manual
|
13. The use of infiltration BMPs is prohibited on hot spot land use areas.
14. Stormwater infiltration BMPs shall not be placed in or on a special
geologic feature(s). Additionally, stormwater runoff shall not be
discharged into existing sinkholes.
15. Applicants shall request, in writing, public water suppliers to provide the Zone I wellhead protection radius, as calculated by the method outlined in the Pennsylvania Department of Environmental Protection wellhead protection regulations, for any public water supply well within 400 feet of the site. In addition to the setback distances specified in Subsections
9 and
10, infiltration is prohibited in the Zone I radius as defined and substantiated by the public water supplier in writing. If the applicant does not receive a response from the public water supplier, the Zone I radius is assumed to be 100 feet.
16. The volume and rate of the net increase in stormwater runoff from
the regulated activities must be managed to prevent the physical degradation
of receiving waters from such effects as scour and streambank destabilization,
to satisfy state water quality requirements.
17. The municipality may, after consultation with DEP, approve alternative
methods for meeting the state water quality requirements other than
those in this chapter, provided that they meet the minimum requirements
of and do not conflict with state law, including but not limited to
the Clean Streams Law, 35 P.S. § 691.1 et seq.
18. The Simplified Method (CG-2 in the BMP Manual
3) provided below may be used as specified in §
23-106, Subsection 2A. This method is not applicable to regulated activities greater than one acre. For new impervious surfaces:
A. Stormwater facilities shall capture at least the first two inches
of runoff from all new impervious surfaces.
B. At least the first one inch of runoff from new impervious surfaces
shall be permanently removed from the runoff flow, i.e., it shall
not be released into the surface waters of this commonwealth. Removal
options include reuse, evaporation, transpiration, and infiltration.
C. Wherever possible, infiltration facilities should be designed to
accommodate infiltration of the entire permanently removed runoff;
however, in all cases at least the first 0.5 inch of the permanently
removed runoff should be infiltrated.
D. This method is exempt from the requirements of §
23-305 and §
23-306 rate controls.
[Ord. No. 416, 9/29/2022]
1. Mapping of Stormwater Management Districts. To implement the provisions
of the Bushkill Creek Watershed and Martins/Jacoby Creek Watershed
and Delaware River Sub-Basin 1 Stormwater Management Plans, the municipality
is hereby divided into stormwater management districts consistent
with the associated presented in the plan. The boundaries of the stormwater
management districts are shown on official maps which are available
for inspection at the municipal office. A copy of the official maps
at a reduced scale are included in Appendix 23-A for general reference.
2. Description of Stormwater Management Districts. Four types of stormwater
management districts may be applicable to the municipality, namely
provisional no-detention districts, conditional no-detention I districts,
conditional no-detention II districts and dual release rate districts
as described below.
A. Provisional No-Detention Districts (Bushkill Creek Watershed) and Conditional No-Detention I Districts (Martins/Jacoby Creek Watershed and Delaware River Sub-Basin 1). Within these districts, the capacity of the local runoff conveyance facilities (as defined in Part
2) must be calculated to determine if adequate capacity exists. For this determination, the developer must calculate peak flows assuming that the site is developed as proposed and that the remainder of the local watershed is in the existing condition. The developer must also calculate peak flows assuming that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified by this chapter. The larger of the two peak flows calculated will be used in determining if adequate capacity exists. If adequate capacity exists to safely transport runoff from the site to the main channel (as defined in Part
2), these watershed areas may discharge post-development peak runoff without detention facilities. If the capacity calculations show that the local runoff conveyance facilities lack adequate capacity, the developer shall either use a 100% release rate control or provide increased capacity of downstream elements to convey increased peak flows consistent with §
23-306, Subsection
16. Any capacity improvements must be designed to convey runoff from development of all areas tributary to the improvement consistent with the capacity criteria specified in §
23-306, Subsection
4. By definition, a storm drainage problem area associated with the local runoff conveyance facilities indicates that adequate capacity does not exist.
B. Conditional No-Detention II Districts (Martins/Jacoby Creeks and Delaware River Sub-Basin 1). Within these districts, the capacity of the local runoff conveyance facilities must be calculated in the same manner as in Subsection 2A above. In this case, however, adequate capacity must be demonstrated from the site to the Delaware River. After determining if adequate capacity exists, the developer shall use either no detention, a 100% release rate or provide capacity improvements as detailed in §
23-306, Subsection
16.
C. Dual Release Rate Districts. Within these districts, the two-year
post-development peak runoff must be controlled to 30% of the predevelopment
two-year runoff peak. Further, the ten-year, twenty-five-year and
100-year post-development peak runoff must be controlled to the stated
percentage of the predevelopment peak. Release rates associated with
the ten-year through 100-year events vary from 60% to 100% depending
upon location in the watershed.
D. For areas not covered by a release rate map from an approved Act
167 stormwater management plan, post-development discharge rates shall
not exceed the predevelopment discharge rates for the two-, two-,
five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour
storm events. If it is shown that the peak rates of discharge indicated
by the post-development analysis are less than or equal to the peak
rates of discharge indicated by the predevelopment analysis for one-,
two-, five-, ten-, twenty-five-, fifty-, and 100-year, twenty-four-hour
storms, then the requirements of this section have been met. Otherwise,
the applicant shall provide additional controls as necessary to satisfy
the peak rate of discharge requirement.
[Ord. No. 416, 9/29/2022]
1. Applicants shall provide a comparative pre- and post-construction
stormwater management hydrograph analysis for each direction of discharge
and for the site overall to demonstrate compliance with the provisions
of this chapter.
2. Any stormwater management controls required by this chapter and subject to a dual release rate criteria shall meet the applicable release rate criteria for each of the two-, ten-, twenty-five- and 100-year return period runoff events consistent with the calculation methodology specified in §
23-307.
3. The exact location of the stormwater management district boundaries
as they apply to a given development site shall be determined by mapping
the boundaries using the two-foot topographic contours provided as
part of the SWM site plan. The district boundaries as originally drawn
coincide with topographic divides or, in certain instances, are drawn
from the intersection of the watercourse and a physical feature such
as the confluence with another watercourse or a potential flow obstruction
(e.g., road, culvert, bridge, etc.). The physical feature is the downstream
limit of the subarea and the subarea boundary is drawn from that point
up slope to each topographic divide along the path perpendicular to
the contour lines.
4. Any downstream capacity 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 two-year return period event within
their banks at velocities consistent with protection of the channels
from erosion.
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 25 Pa. Code Chapter 105 regulations (if applicable) and,
at minimum, pass the increased twenty-five-year return period runoff.
5. For a proposed development site located within one release rate category
subarea, the total runoff from the site shall meet the applicable
release rate criteria. For development sites with multiple directions
of runoff discharge, individual drainage directions may be designed
for up to a 100% release rate so long as the total runoff from the
site is controlled to the applicable release rate.
6. For a proposed development site located within two or more release
category subareas, the peak discharge rate from any subarea shall
be the predevelopment peak discharge for that subarea multiplied by
the applicable release rate. The calculated peak discharges shall
apply regardless of whether the grading plan changes the drainage
area by subarea. An exception to the above may be granted if discharges
from multiple subareas recombine in proximity to the site. In this
case, peak discharge in any direction may be a 100% release rate,
provided that the overall site discharge meets the weighted average
release rate.
7. For a proposed development site located partially within a release
rate category subarea and partially within a provisional no-detention
district or conditional no-detention district, a significant portion
of the site area subject to the release rate control may not be drained
to the discharge point(s) located in the no-detention district except
as part of a no-harm or hardship waiver procedure.
8. No portion of a site may be regraded between the Bushkin Creek Watershed
and Martins/Jacoby Creeks and Delaware River Sub-Basin 1 Watershed
and any adjacent watershed except as part of a no-harm or hardship
waiver procedure.
9. Within a release rate category area, for a proposed development site which has areas which drain to a closed depression(s), the design release from the site will be the lesser of: (a) the applicable release rate flow assuming no closed depression(s); or (b) the existing peak flow actually leaving the site. In cases where (b) would result in an unreasonably small design release, the design discharge of less than or equal to the release rate will be determined by the available downstream conveyance capacity to the main channel calculated using Subsection
4 and the minimum orifice criteria.
10. Off-site areas which 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 using the capacity criteria in Subsection
4 and the detention criteria in §
23-307.
11. For development sites proposed to take place in phases, all detention
ponds shall be designed to meet the applicable release rate(s) applied
to all site areas tributary to the proposed pond discharge direction.
All site tributary areas will be assumed as developed, regardless
of whether all site tributary acres are proposed for development at
that time. An exception shall be sites with multiple detention ponds
in series where only the downstream pond must be designed to the stated
release rate.
12. Where the site area to be impacted by a proposed development activity
differs significantly from the total site area, only the proposed
impact area shall be subject to the release rate criteria. The impact
area includes any proposed cover or grading changes.
13. Development proposals which, through groundwater recharge or other
means, do not increase either the rate or volume of runoff discharged
from the site compared to predevelopment are not subject to the release
rate provisions of this chapter.
14. No-Harm Water Quantity Option. For any proposed development site not located in a provisional no-detention district or conditional no-detention (I or II) district, the developer has the option of using a less restrictive runoff control (including no detention) if the developer can prove that special circumstances exist for the proposed development site and that no harm would be caused by discharging at a higher runoff rate than that specified by the plan. Special circumstances are defined as any hydrologic or hydraulic aspects of the development itself not specifically considered in the development of the plan runoff control strategy. Proof of no harm would have to be shown from the development site through the remainder of the downstream drainage network to the confluence of the creek with the Delaware River. Proof of no harm must be shown using the capacity criteria specified in Subsection
4 if downstream capacity analysis is a part of the no-harm justification.
A. Attempts to prove no harm based upon downstream peak flow versus
capacity analysis shall be governed by the following provisions:
(1)
The peak flow values to be used for downstream areas for the
design return period storms (two-, ten-, twenty-five-, and 100-year)
shall be the values from the calibrated Penn State Runoff Model for
the Bushkill Creek study area or the Martins/Jacoby Creek and Delaware
River Sub-Basin 1 study area or as calculated by an applicant using
an alternate method acceptable to the municipality. The flow values
from the PSRM Model would be supplied to the developer by the municipality
upon request.
(2)
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).
(3)
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 consistent with Subsection
16.
B. Any no-harm justifications shall be submitted by the developer as
part of the SWM site plan submission per Part 4.
15. Regional Detention Alternatives. For certain areas within the study
area, 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 are the responsibility of
prospective developers. 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 based on
the required release rate at the point of discharge.
16. Capacity Improvements.
A. In certain instances, primarily within the provisional no-detention or conditional no-detention (I and II) areas, local drainage conditions may dictate more stringent levels of runoff control than those based upon protection of the entire watershed. In these instances, if the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then the capacity improvements could be provided by the developer in lieu of runoff controls on the development site. Peak flow calculations shall be done assuming that the local watershed is in the existing condition and then assuming that the local watershed is developed per current zoning and using the specified runoff controls. Any capacity improvements would be designed using the larger of the above peak flows and the capacity criteria specified in Subsection
4. All new development in the entire subarea(s) within which the proposed development site is located shall be assumed to implement the developer's proposed discharge control, if any.
B. Capacity improvements may also be provided as necessary to implement
any regional detention alternatives or to implement a modified no-harm
option which proposes specific capacity improvements to provide that
a less stringent discharge control would not create any harm downstream.
[Ord. No. 416, 9/29/2022]
1. Stormwater runoff from all development sites shall be calculated
using either the Rational Method or the Soil-Cover-Complex Methodology.
2. Sites with soil permeability greater than 12.0 inches per hour or
less than 0.5 inch per hour are not recommended for infiltration practices.
3. The design of any detention basin intended to meet the requirements
of this chapter shall be verified by routing the design storm hydrograph
through the proposed basin using the storage indication method or
other methodology demonstrated to be more appropriate. For basins
designed using the Rational Method technique, the design hydrograph
for routing shall be either the universal rational hydrograph or the
modified Rational Method trapezoidal hydrograph which maximizes detention
volume. Use of the Modified Rational hydrograph shall be consistent
with the procedure described in Section "PIPE.RAT" of the Users Manual
for the Penn State Urban Hydrology Model (1987). For basins designed
using the SCS method, the design hydrograph for routing shall be the
full TR-55 tabular hydrograph for a Type II rainfall distribution.
4. BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall be routed using the storage indication method.
5. BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall provide storage volume for the full WQv
below the lowest outlet invert.
6. Wet detention ponds designed to have a permanent pool for the WQv
shall assume that the permanent pool volume below the primary outlet
is full at the beginning of design event routing for the purposes
of evaluating peak outflows.
7. All stormwater detention facilities shall provide a minimum 1.0 foot
freeboard above the maximum pool elevation associated with the two-year
through twenty-five-year runoff events. A 0.5 foot freeboard shall
be provided above the maximum pool elevation of the 100-year runoff
event. The freeboard shall be measured from the maximum pool elevation
to the invert of the emergency spillway. The two-year through 100-year
storm events shall be controlled by the primary outlet structure.
An emergency spillway for each basin shall be designed to pass the
100-year return frequency storm peak basin inflow rate with a minimum
0.5 foot freeboard measured to the top of basin. The freeboard criteria
shall be met considering any off-site areas tributary to the basin
as developed, as applicable. The emergency spillway shall function
to control overflows in the event of a complete blockage of the basin
outlet system. If this detention facility is considered to be a dam
as per DEP 25 Pa. Code Chapter 105, the design of the facility must
be consistent with the Chapter 105 regulations, and may be required
to pass a storm greater than the 100-year event.
8. The minimum circular orifice diameter for controlling discharge rates
from detention facilities shall be three inches. Designs where a lesser
size orifice would be required to fully meet release rates may be
acceptable using a three-inch orifice, provided that as much of the
site runoff as practical is directed to the detention facilities.
9. Runoff calculations using the Soil-Cover-Complex Method shall use
the Natural Resources Conservation Service Type II twenty-four-hour
rainfall distribution. The twenty-four-hour rainfall depths for the
various return periods to be used consistent with this chapter may
be taken from NOAA Atlas 14, Volume 2, or the PennDOT Intensity-Duration-Frequency
Field Manual (PDT-IDF) (May 1986) for Region 4. The following values
are taken from the PDT-IDF Field Manual:
Return Period
|
24-Hour Rainfall Depth
(inches)
|
---|
1-year
|
2.40
|
2-year
|
3.00
|
5-year
|
3.60
|
10-year
|
4.56
|
25-year
|
5.52
|
50-year
|
6.48
|
100-year
|
7.44
|
A graphical and tabular presentation of the Type II 24-hour
distribution is included in Appendix 23-C.
|
10. Runoff calculations using the Rational Method shall use rainfall
intensities consistent with appropriate times of concentration and
return periods and the intensity-duration frequency curves as presented
in Appendix 23-C.
11. Runoff curve numbers (CNs) to be used in the Soil-Cover-Complex Method
shall be based upon the matrix presented in Appendix 23-C.
12. Runoff coefficients for use in the Rational Method shall be based
upon the table presented in Appendix 23-C.
13. All time of concentration calculations shall use a segmental approach
which may include one or all of the flow types below:
A. Sheet flow (overland flow) calculations shall use either the NRCS
average velocity chart (Figure 3-1, Technical Release-55, 1975) or
the modified kinematic wave travel time equation (equation 3-3, NRCS
TR-55, June 1986). If using the modified kinematic wave travel time
equation, the sheet flow length shall be limited to 50 feet for designs
using the Rational Method and limited to 150 feet for designs using
the Soil-Cover-Complex Method.
B. Shallow concentrated flow travel times shall be determined from the
watercourse slope, type of surface and the velocity from Figure 3-1
of TR-55, June 1986.
C. Open channel flow travel times shall be determined from velocities
calculated by the Manning Equation. Bankfull flows shall be used for
determining velocities. Manning "n" values shall be based on the table
presented in Appendix 23-C.
D. Pipe flow travel times shall be determined from velocities calculated
using the Manning Equation assuming full flow and the Manning "n"
values from Appendix 23-C.
14. If using the Rational Method, all predevelopment calculations for
a given discharge direction shall be based on a common time of concentration
considering both on-site and any off-site drainage areas. If using
the Rational Method, all post-development calculations for a given
discharge direction shall be based on a common time of concentration
considering both on-site and any off-site drainage areas.
15. The Manning Equation shall be used to calculate the capacity of watercourses.
Manning "n" values used in the calculations shall be consistent with
the table presented in Appendix 23-C or other appropriate standard
engineering "n" value resources. Pipe capacities shall be determined
by methods acceptable to the Township Engineer.
16. The Pennsylvania DEP 25 Pa. Code Chapter 105 rules and regulations,
apply to the construction, modification, operation or maintenance
of both existing and proposed dams, water obstructions and encroachments
throughout the watershed. Criteria for design and construction of
stormwater management facilities according to this chapter may not
be the same criteria that are used in the permitting of dams under
the dam safety program.