A.
Applicants proposing regulated activities in Coolbaugh Township which do not fall under the exemption criteria included in § 344-9 shall submit a drainage plan consistent with this chapter to the municipality for review. These criteria shall apply to the total proposed development even if development is to take place in stages.
B.
The applicant is required to perform an alternatives analysis to
find practicable alternatives to the surface discharge of stormwater,
the creation of impervious surfaces and the degradation of waters
of the commonwealth, and must maintain as much as possible the natural
hydrologic regime.
(1)
An alternative is practicable if it is available and capable of being
done after taking into consideration cost, existing technology and
logistics in light of overall project purposes.
(2)
All practicable alternatives to the discharge of stormwater are presumed
to have less adverse impact on quantity and quality of waters of the
commonwealth unless otherwise demonstrated.
C.
The drainage plan must be designed through an alternatives analysis consistent with the sequencing provisions of § 344-20 to ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with Article IV of this chapter.
D.
Stormwater drainage systems shall be provided in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this chapter.
E.
The existing points of concentrated drainage that discharge onto
adjacent property shall not be altered in any manner which could cause
property damage without permission of the affected property owner(s)
and shall be subject to any applicable discharge criteria specified
in this chapter.
F.
Areas of existing diffused drainage discharge shall be subject to
any applicable discharge criteria in the general direction of existing
discharge, whether proposed to be concentrated or maintained as diffused
drainage areas, except as otherwise provided by this chapter. If diffused
drainage discharge is proposed to be concentrated and discharged onto
adjacent property, the applicant must document that adequate downstream
conveyance facilities exist to safely transport the concentrated discharge,
or otherwise prove that no erosion, sedimentation, flooding or other
impacts will result from the concentrated discharge.
G.
Where a development site is traversed by existing watercourses, drainage
easements shall be provided conforming to the top of bank of such
watercourses. The terms of the easement shall prohibit any alterations
which may adversely affect the flow of stormwater within any portion
of the easement.
H.
Any stormwater management facilities regulated by this chapter that
would be located in the floodway of waters of the commonwealth or
wetlands shall be subject to approval by PADEP through the joint permit
application process, or, where deemed appropriate by PADEP, the general
permit process. When there is a question whether wetlands may be involved,
it is the responsibility of the applicant to show that the land in
question cannot be classified as wetlands; otherwise approval to work
in the area must be obtained from PADEP.
I.
Any stormwater management facilities regulated by this chapter that
would be located on state highway rights-of-way shall be subject to
approval by the Pennsylvania Department of Transportation (PennDOT).
J.
Infiltration of runoff through seepage beds, infiltration trenches, etc. where soil conditions permit, and minimization of impervious surfaces to the extent permitted by Chapter 400, Zoning, are required to reduce the size or eliminate the need for, detention facilities or other structural BMPs.
K.
In order to promote overland flow and infiltration, roof drains shall
not be connected to streets, or storm sewers or roadside ditches.
Direct connection of roof drains to storm sewers or roadside ditches
shall only be permitted by the Township on a case-by-case basis when
it is demonstrated that it is more advantageous to do so from an environmental
standpoint. It is recommended that roof runoff be directed to infiltration
BMPs. Considering potential pollutant loading, roof drain runoff will
not require pretreatment, in most cases.
L.
All stormwater runoff, other than roof runoff, shall be treated for
water quality prior to discharge to surface or groundwater.
M.
Adequacy of downstream facilities and effect of project on downstream
properties must be considered in the stormwater design.
The applicant shall demonstrate that the regulated activities
have been designed in the following sequence to minimize the increases
in stormwater runoff and impacts to water quality:
A.
Prepare an Existing Resource and Site Analysis Map (ERSAM), showing environmentally sensitive areas including, but not limited to, slopes in excess of 15%, ponds, lakes, streams, wetlands, hydric soils, vernal ponds, floodplains, buffer areas, hydrologic soil groups A and B (areas conducive to infiltration), any existing recharge areas and any other requirements outlined in Chapter 355, Subdivision and Land Development.
C.
Prepare a draft project layout avoiding earth disturbance in sensitive areas identified in Subsection A and minimizing total site earth disturbance as much as possible. The ratio of the disturbed area to the entire site area and measures taken to minimize earth disturbance shall be included on the ERSAM.
D.
Identify site specific predevelopment drainage areas, discharge points,
recharge areas to be preserved and hydrologic soil groups A and B
to be utilized for recharge.
G.
Satisfy groundwater recharge (infiltration) objective (§ 344-24) and provide for stormwater treatment prior to infiltration.
H.
Determine in which management district the site is located (Appendix
D),[1] and conduct a predevelopment runoff analysis.
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
I.
Prepare final project design to maintain predevelopment drainage
areas and discharge points, to minimize earth disturbance and impervious
surfaces, and to reduce runoff to the maximum extent possible.
J.
Conduct a post-development runoff analysis based on the final design and to meet the release rate, and in turn the overbank flow and extreme event requirements (§ 344-25).
K.
Manage any remaining runoff through treatment prior to discharge,
as part of detention, bioretention, direct discharge or other structural
control. All stormwater runoff, other than rooftop runoff, shall be
treated for water quality prior to discharge to surface or groundwater.
A.
Where required by 25 Pa. Code, Chapter 102, buffers shall be provided
accordingly.
B.
Where not specifically required by 25 Pa. Code, Chapter 102, buffers
shall be established adjacent to all wetlands, vernal ponds, lakes,
ponds, streams and natural watercourses, as required herein.
C.
Exemptions. Lots with an area of one acre or less within residential
subdivisions which were approved prior to the effective date of this
chapter shall be exempt from the requirements for the establishment
of buffers, except that this exemption shall not apply to parcels
on approved subdivision plans which may be considered remaining lands,
residual lands, reserved lands, recreation areas, or homeowners' association
lands.
D.
Where buffers along various water resources overlap, the more restrictive
requirements shall apply.
E.
One-hundred-fifty-foot inner buffers.
[Amended 8-2-2023 by Ord. No. 152-2023]
(1)
Inner buffers shall be established with a width of 150 feet from
the edge of any wetlands, vernal pond, lake, pond and from the top-of-bank
on both sides of any stream or natural watercourse (measured horizontally,
perpendicular or radial to such edge or top-of-bank).
(2)
Within the inner buffer, the following uses and activities are permitted,
provided that not more than 35% of the inner buffer on the parcel
shall be altered by grading, filling, construction or development:
(a)
Stormwater conveyances approved by the Township.
(b)
Maintenance and restoration of the buffer.
(c)
The correction of hazardous or dangerous conditions.
(d)
Stream crossings and encroachments permitted by the PADEP.
(e)
Unpaved, stable trails used for passive recreation.
(f)
In the case of an inner buffer adjacent to lake or pond, boat
docks are also permitted.
(g)
In the case of an inner buffer along a stream or natural watercourse,
fish hatcheries, wildlife sanctuaries and boat launches are also permitted,
provided they are constructed as not to alter the floodplain cross-section.
F.
One-hundred-fifty-foot outer buffers.
[Amended 8-2-2023 by Ord. No. 152-2023]
(1)
Except as otherwise required by 25 Pa. Code, Chapter 102, outer buffers
shall be established with a width of 150 feet from the inner buffer
(measured horizontally, parallel to and concentric with the inner
buffer), around the inner buffer of wetlands, vernal ponds, streams
and watercourses; no outer buffer is required around lakes and ponds.
(2)
Within the outer buffer, the following areas and activities are permitted,
provided that not more than 20% of the area of the outer buffer on
the parcel shall be altered by these uses and activities:
(a)
Any use or activity permitted in the inner buffer for the corresponding
water resource.
(b)
Access roads constructed to approximate existing grade.
(c)
Limited forestry activities that do not clear-cut the buffer
(e.g., selective regeneration harvest) conducted in accordance with
a forestry management plan.
(d)
Plant nurseries, provided no new buildings are constructed.
(e)
Parking lots constructed to approximate existing grade.
(f)
Additions to existing buildings.
(g)
Stormwater management facilities.
(h)
In the case of buffers along a stream or natural watercourse,
uses accessory to residential uses, outdoor athletic and passive sports
facilities, provided no building is constructed.
In addition to the performance standards and design criteria
requirements of this chapter, the applicant shall comply with the
following water quality requirements of this article.
A.
For water quality and stream bank erosion, the objective is to design
a water quality BMP to detain the proposed condition's two-year, twenty-four-hour
design storm to the existing condition's one-year flow using the SCS
Type II distribution. Additionally, provisions shall be made (such
as adding a small orifice at the bottom of the outlet structure) so
that the proposed condition's one-year storm takes a minimum of 24
hours to drain from the facility from a point where the maximum volume
of water from the one-year storm is captured (i.e., the maximum water-surface
elevation is achieved in the facility). This can be accomplished by
configuration of the outlet structure not to control the larger storms,
or by a bypass or channel to divert only the two-year flood into the
basin or divert flows in excess of the two-year storm away from the
basin. Where practicable, water quality controls shall meet the requirements
found in the Pennsylvania Stormwater BMP Manual. Release of water
can begin at the start of the storm (i.e., the invert of the water
quality orifice is at the invert of the facility). The design of the
facility shall consider and minimize the chances of clogging and sedimentation.
Orifices smaller than three inches in diameter are not recommended.
However, if the design professional can provide proof that smaller
orifices are protected from clogging by use of trash racks, etc.,
smaller orifices may be permitted.
B.
In selecting the appropriate BMPs or combinations thereof, the applicant
shall consider the following:
(1)
Total contributing area.
(2)
Permeability and infiltration rate of the site soils.
(3)
Slope and depth to bedrock.
(4)
Seasonal high water table.
(5)
Proximity to building foundations and well heads.
(6)
Erodibility of soils.
(7)
Land availability and configuration of the topography.
(8)
Peak discharge and required volume control.
(9)
Stream bank erosion.
(10)
Efficiency of the BMPs to mitigate potential water quality problems.
(11)
The volume of runoff that will be effectively treated.
(12)
The nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife habitat.
(15)
Recreational value.
C.
For areas within defined special protection subwatersheds which include
exceptional value (EV) and high-quality (HQ) waters, the temperature
and quality of water and streams shall be maintained through the use
of temperature-sensitive BMPs and stormwater conveyance systems.
D.
The applicant shall consider the guidelines found in the Pennsylvania
Stormwater BMP Manual, and other acceptable guidelines for constructed
wetlands, where proposed.
F.
Stream bank restoration projects shall include the following:
(1)
No restoration or stabilization projects may be undertaken without
examining the fluvial geomorphology of stable reaches above and below
the unstable reach.
(2)
Restoration project design must then consider maintenance of stability
in the adjacent stable reaches of the stream channel.
(3)
An erosion and sediment control plan approved by the Conservation
District must be provided by the applicant.
(4)
All applicable state and federal permits must be obtained.
G.
All wet basin designs shall incorporate biologic controls in accordance
with the West Nile Virus Guidance found in Appendix E.[1]
[1]
Editor's Note: Appendix E is included as an attachment to this chapter.
H.
To accomplish the above, the applicant shall submit original and
innovative designs to the municipality for review and approval. Such
designs may achieve the water quality objectives through a combination
of BMPs (best management practices).
I.
In the Wallenpaupack watershed, critical areas for control of post-development runoff quality have been defined based on the projected pollutant loading of the subwatersheds. In Coolbaugh Township, the Wallenpaupack M-WC subwatershed is defined as one of these critical areas. The control criteria for these critical areas are established as 0.13 mg/l for phosphorus (as total soluble phosphorous) and 65 mg/l for sediment (as total suspended solids). See § 344-23 for method of calculation of runoff pollutant parameters.
A.
The methods of computation used to determine total phosphorous and
sediment loads shall be one of the following methods or other method
approved by the Township in advance:
(1)
The application of the unit areal loading rates is presented at the
end of Appendix G for phosphorus and sediment loads. The total load
for a given pollutant at a development site is the summation of the
pollutant loads generated by each land use type for the site. The
individual land use loads are calculated by multiplying the land use
area (in acres) by the appropriate loading rate.
(2)
The simple method for phosphorus pollutant export as set forth in
the "A Framework for Evaluating Compliance with the 10% Rule in the
Criteria Area."
|
L = (P)(Pj)(Rv)/12*(C)(A)(2.72)
|
|
Where:
| |||
|
L
|
=
|
Phosphorus pollutant export (in pounds)
| |
|
P
|
=
|
Rainfall depth (in inches) for the year
| |
|
Pj
|
=
|
A factor that corrects P for storms that produce no runoff
| |
|
Rv
|
=
|
Runoff coefficient for the site which expresses the fraction
of rainfall that is converted into runoff
| |
|
C
|
=
|
The average storm concentration of phosphorus for the land use
(in mg/l)
| |
|
A
|
=
|
Total area of the site (in acres)
| |
|
2.72
|
=
|
Conversion factor to produce load in pounds
| |
(3)
The universal soil loss equation for sediment erosion.
|
A = (R)(K)(L)(C)(P)
|
|
Where:
| |||
|
A
|
=
|
Computed soil loss in tons/day for a given storm
| |
|
R
|
=
|
Rainfall energy factor
| |
|
K
|
=
|
Soil erodibility factor
| |
|
L
|
=
|
Slope length factor
| |
|
C
|
=
|
Vegetative cover factor
| |
|
P
|
=
|
Erosion control practice factor
| |
B.
Refer to Appendix G for a sample problem that describes the typical
procedure to be followed in selecting a control technique to control
runoff pollutants.[1]
[1]
Editor's Note: Appendix G is included as an attachment to this chapter.
Maximizing the ground water recharge capacity of the area being developed is required. The design shall be consistent with the measures listed in § 344-3 and take advantage of utilizing any existing recharge areas.
A.
Regulated activities will be required to recharge (infiltrate), where practicable based on suitability of soils and site conditions, a portion of the runoff created by the development, except as provided in Subsection B. The following criteria shall apply to recharge facilities:
(1)
Infiltration BMPs shall be selected based on suitability of soils
and site conditions. A detailed soils evaluation of the project site
performed by a qualified design professional shall be performed to
determine general areas of suitability for infiltration practices.
The evaluation shall include at a minimum, the following:
(a)
An analysis of the hydrologic soil groups as well as material
and man-made features within the watershed to determine general areas
of suitability for infiltration practices.
(b)
Depth to limiting zone, bedrock and water table and subgrade
stability.
(c)
Site-specific infiltration test results. The tests shall be
run at the elevation of the proposed infiltration surface and shall
be in accordance with ASTM Guide No. D5126 to determine the appropriate
hydraulic conductivity rate.
(d)
Infiltration rate to be used on the design based on the site
specific testing.
(2)
A minimum depth of 24 inches shall be maintained between the bottom
of the infiltration BMP and the limiting zone of the soil.
(3)
The infiltration rate of the soils as determined by field tests must
be sufficient to accept the additional stormwater load and drain completely.
(4)
The volume of runoff to be recharged shall be determined based on
the following equation:
|
Re (cu. ft.) = I (in) x Impervious area (sq. ft.) x (1 ft./12
in)
|
Eqn. 344-24.1
|
|
Where:
| |
|
Re is the required recharge volume
| |
|
I is the infiltration requirement
| |
|
The infiltration requirement (I) shall be determined based upon
the following:
|
(a)
NRCS Curve Number Equation.
|
I (in) = (200/CN) - 2
|
Eqn: 344-24.2
|
|
Where:
| |
|
I is the infiltration requirement
| |
|
CN is the NRCS curve number for the area contributing to the
recharge facility based on existing conditions.
| |
|
Equation 344-24.2 is displayed graphically in Figure 344-24.1
|
Figure 344-24.1
Infiltration requirement based upon NRCSA Curve Number
|
(b)
Annual recharge — water budget approach. It has been determined that infiltrating 0.6 inch of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of Subsection A(4) cannot be achieved due to soils limitations and/or site conditions, then the infiltration requirement (I) may be reduced to 0.6 when existing conditions curve numbers (CN) are less than 77.
(5)
The recharge facility shall be capable of completely infiltrating
the recharge volume with four days.
(7)
If individual on-lot infiltration structures are proposed, it must
be demonstrated that the soils are conducive to infiltration on those
lots.
B.
Stormwater hotspots.
(1)
A stormwater hotspot is defined as a land use activity that generates
higher concentrations of hydrocarbons, trace metals or toxicants than
are found in typical stormwater runoff, based on monitoring studies.
Table 344-24.1 provides samples of designated hotspots. If a site
is designated as a hotspot, it has important implications for how
stormwater is managed. First and foremost, untreated stormwater runoff
from hotspots cannot be allowed to infiltrate into groundwater where
it may contaminate water supplies. Therefore, the Rev requirement is not applied to development sites that fit into the
hotspot category (the entire WQv must still
be treated). Second, a greater level of stormwater treatment may be
needed at hotspot sites to prevent pollutant washoff after construction.
EPA's NPDES stormwater program requires some industrial sites to prepare
and implement a stormwater pollution prevention plan.
|
Table 344-24.1
Classification of Stormwater Hotspots
|
|---|
|
The following land uses and activities are samples of stormwater
hotspots:
|
|
Salvage yards and recycling facilities
|
|
Fleet storage areas (bus, truck, etc.)
|
|
Public works storage areas
|
|
Facilities that generate or store hazardous materials
|
|
Commercial gasoline and fuel oil sales
|
|
Vehicle fluid replacement facilities
|
|
Vehicle service stations, repair facilities and body repair
and painting facilities
|
|
Dry-cleaning and dyeing establishments and laundries that utilize
cleaning solvents
|
|
Printing and photo-processing establishments
|
|
Furniture and finish-stripping establishments
|
(2)
Extreme caution shall be exercised where salt or chloride would be
a pollutant since soils do little to filter this pollutant and it
may contaminate the groundwater. The qualified design professional
shall evaluate the possibility of groundwater contamination from the
proposed infiltration/recharge facility and perform a hydrogeologic
justification study if necessary. The infiltration requirement in
high quality/exceptional value waters shall be subject to the Department's
Chapter 93 Antidegradation Regulations. The municipality may require
the installation of an impermeable liner in detention basins where
the possibility of groundwater contamination exists. A detailed hydrogeologic
investigation may be required by the municipality.
(3)
The applicant shall provide safeguards against groundwater contamination
for uses which may cause groundwater contamination, should there be
a mishap or spill.
C.
Extreme caution shall be exercised where infiltration is proposed
in source water protection areas or that may affect a wellhead or
surface water intake.
D.
Recharge/infiltration facilities shall be used in conjunction with
other innovative or traditional BMPs, stormwater control facilities,
and nonstructural stormwater management alternatives.
A.
Runoff rates by watershed.
[Amended at time of adoption of Code (see Ch. 1, General
Provisions, Art. I)]
(1)
There are portions of four watersheds within Coolbaugh Township:
the Brodhead Creek watershed (as part of the Brodhead and McMichaels
Creek watershed), the Tobyhanna Creek watershed, the Wallenpaupack
Creek watershed, and the Lehigh River watershed. Act 167 Stormwater
Management Plans have been adopted for the Brodhead and McMichaels
Creek, the Tobyhanna Creek, and the Wallenpaupack Creek watersheds.
In these plans, the watersheds have been divided into stormwater management
districts as shown on the map of Act 167 Delineated Watersheds, in
Appendix D.[1]
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
(2)
Standards for managing runoff from each subarea in the various watersheds
are shown in Table 344-25.1. Proposed (post-development) stormwater
runoff rates of development sites must be controlled to the stormwater
runoff rates shown in Table 344-25.1 for the indicated design storms.
(3)
In addition to the requirements specified in Table 344-25.1 below, the stormwater quality (§ 344-22), groundwater recharge (§ 344-24), and erosion and sediment control (§ 344-28) requirements shall be implemented.
|
Table 344-25.1
Stormwater Runoff Release Rate Requirements
| |||
|---|---|---|---|
|
District
|
Proposed Conditions
|
(Reduce to)
|
Existing Conditions
|
|
Tobyhanna Creek Watershed
| |||
|
A
|
2-year
10-year
50-year
|
1-year
10-year
50-year
| |
|
B
|
2-year
10-year
50-year
|
1-year
2.33-year
10-year
| |
|
C*
|
2-year
|
1-year
| |
|
Brodhead Creek Watershed
| |||
|
B-1
|
2-year
5-year
10-year
25-year
100-year
|
1-year
2-year
5-year
10-year
50-year
| |
|
B-2
|
2-year
5-year
25-year
100-year
|
1-year
2-year
5-year
100-year
| |
|
Wallenpaupack Creek Watershed
| |||
|
M-TC
|
2-year
5-year
10-year
25-year
50-year
100-year
|
Lesser of
|
1-year or 90% of 2-year
90% of 5-year
90% of 10-year
90% of 25-year
90% of 50-year
90% of 100-year
|
|
M-WC
|
2-year
5-year
10-year
25-year
50-year
100-year
|
Lesser of
|
1-year or 70% of 2-year
70% of 5-year
70% of 10-year
70% of 25-year
70% of 50-year
70% of 100-year
|
|
Lehigh River Watershed
| |||
|
2-year
5-year
10-year
25-year
50-year
100-year
|
1-year
5-year
10-year
25-year
50-year
100-year
| ||
|
NOTES:
| |
|
*
|
Detention is not required if the increase in stormwater runoff
can be conveyed to a stream or watercourse in a safe manner. Otherwise,
District A regulations apply.
|
B.
General. Proposed (post-development) stormwater runoff rates from
any regulated activity shall not exceed the rates of stormwater runoff
indicated in Table 344-25.1 for the indicated design storms.
C.
District boundaries. The boundaries of the Stormwater Management
Districts are shown on the map of Act 167 Delineated Watersheds (Appendix
D).[2]
[2]
Editor's Note: Appendix D is included as an attachment to this chapter.
D.
Sites located in more than one district. For a proposed development
site located within two or more stormwater management district category
subareas, the peak discharge rate from any subarea shall be the existing
conditions peak discharge for that subarea. 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 by the municipalities
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.
E.
Off-site areas. Off-site areas that drain through a proposed development
site are not subject to release rate criteria when determining allowable
peak runoff rates. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site.
F.
Site areas. Where the site area to be impacted by a proposed development
activity differs significantly from the total site area, only the
proposed impact area utilizing stormwater management measures shall
be subject to the management district criteria. In other words, unimpacted
areas bypassing the stormwater management facilities would not be
subject to the management district criteria.
G.
"No harm" option. For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less restrictive runoff control (including no detention) if the applicant can prove that "no harm" would be caused by discharging at a higher runoff rate than that specified by the stormwater management plan. The "no harm" option is used when an applicant can prove that the proposed hydrographs can match existing hydrographs, or if it can be proved that the proposed conditions will not cause increases in peaks at all points downstream. Proof of "no harm" must be shown based upon the following "Downstream Impact Evaluation," which shall include a "downstream hydraulic capacity analysis" consistent with § 344-25H to determine if adequate hydraulic capacity exists. The applicant shall submit to the municipality this evaluation of the impacts due to increased downstream stormwater flows in the watershed.
(1)
The hydrologic regime of the site must be maintained.
(2)
The "Downstream Impact Evaluation" shall include hydrologic and hydraulic
calculations necessary to determine the impact of hydrograph timing
modifications due to the proposed development upon a dam, highway,
structure, natural point of restricted streamflow or any stream channel
section, established with the concurrence of the municipality.
(3)
The evaluation shall continue downstream until the increase in flow
diminishes due to additional flow from tributaries and/or stream attenuation.
(4)
The peak flow values to be used for downstream areas for the design
return period storms (two-, five-, ten-, twenty-five-, fifty-, and
one-hundred-year) shall be the values from the calibrated models for
the Brodhead/McMichaels watershed, the Tobyhanna watershed or the
Wallenpaupack watershed. These flow values can be obtained from the
original Act 167 watershed stormwater management plans.
(5)
Applicant-proposed conditions runoff controls which would generate increased peak flow rates at storm drainage problem areas would, by definition, are precluded from successful attempts to prove "no-harm," except in conjunction with proposed capacity improvements for the problem areas consistent with § 344-25H.
(6)
A financial distress shall not constitute grounds for the municipality
to approve the use of the "no-harm" option.
(7)
Downstream capacity improvements may be provided as necessary to
achieve the "no harm" option.
H.
Downstream hydraulic capacity analysis. Any downstream hydraulic
capacity analysis conducted in accordance with this chapter shall
use the following criteria for determining adequacy for accepting
increased peak flow rates:
(1)
Existing 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. Acceptable velocities shall be based upon criteria
included in the DEP Erosion and Sediment Pollution Control Program
Manual.
(2)
Existing natural or man-made channels or swales must be able to convey
increased twenty-four-year return period runoff without creating any
hazard to persons or property.
I.
Hardship option. The stormwater management plans and their standards
and criteria are designed to maintain existing conditions peak flows
and volumes throughout the watersheds as the watersheds becomes developed.
There may be certain instances, however, where the standards and criteria
established are too restrictive for a particular applicant. The existing
drainage network in some areas may be capable of safely transporting
slight increases in flows without causing a problem or increasing
flows elsewhere. If an applicant cannot meet the stormwater standards
due to lot conditions or if conformance would become a hardship to
an applicant, the hardship option may be applied. A financial distress
shall not constitute grounds for the municipality to approve the use
of the hardship option. The applicant would have to plead his/her
case to the Board of Supervisors with the final determination made
by the municipality. Any applicant's pleading the "hardship option"
will assume all liabilities that may arise due to exercising this
option. A financial distress shall not constitute grounds for the
municipality to approve the use of the "no-harm" option.
A.
Stormwater runoff from all development sites shall be calculated
using a generally accepted calculation technique that is based on
the NRCS Soil-Cover-Complex Method. Table 344-26.1 summarizes acceptable
computation methods and the method selected by the design professional
shall be based on the individual limitations and suitability of each
method for a particular site. The municipality may allow the use of
the Rational Method to estimate peak discharges from drainage areas
that contain less than 200 acres. The Soil-Cover-Complex Method shall
be used for drainage areas greater than 200 acres.
|
Table 344-26.1
Acceptable Computation Methodologies for Stormwater Management
Plans
| ||
|---|---|---|
|
Method
|
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 within limitations described
in TR-55
|
|
HEC-1/HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of full hydrologic computer model is desirable
or necessary
|
|
PSRM
|
Penn State University
|
Applicable where use of a hydrologic computer model is desirable
or necessary; simpler than TR-20 or HEC-1
|
|
Rational Method
(or commercial computer package based on Rational Method)
|
Emil Kuichling (1889)
|
For sites less than 200 acres, or as approved by the municipality
and/or Municipal Engineer
|
|
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
and/or Municipal Engineer
|
B.
All calculations consistent with this chapter using the Soil-Cover-Complex
Method shall use the appropriate design rainfall depths for the various
return period storms according to the region in which they are located
as presented in Table B-1 in Appendix B of this chapter.[1] If a hydrologic computer model such as PSRM or HEC-1 is
used for stormwater runoff calculations, then the duration of rainfall
shall be 24 hours. The SCS 'S' curve shown in Figure B-1, Appendix
B, of this chapter, shall be used for the rainfall distribution.
[1]
Editor's Note: Appendix B is included as an attachment to this chapter.
C.
Times-of-concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). Times-of-concentration for channel and pipe flow shall be computed using Manning's Equation.
D.
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times-of-concentration and return periods from the NOAA Charts for the appropriate PennDOT region (from PennDOT Pub 584, Chapter 7) (Appendix B).
E.
Runoff Curve Numbers (CN) for both existing and proposed conditions
to be used in the Soil-Cover-Complex Method shall be obtained from
Table B-2 in Appendix B of this chapter, except as noted in G and
H, below.
G.
For the purposes of existing conditions flow rate determination,
undeveloped land shall be considered as "meadow" in good condition,
unless the natural ground cover generates a lower curve number or
Rational "C" value, as listed in Table B-2 or B-3 in Appendix B of
this chapter.[2]
[2]
Editor's Note: Appendix B is included as an attachment to this chapter.
H.
The designer shall consider that the runoff from proposed sites graded
to the subsoil will not have the same runoff conditions as the site
under existing conditions, even after topsoiling or seeding. The designer
shall increase his proposed condition "CN" or "C" to better reflect
proposed soil conditions.
I.
Where uniform flow is anticipated, the Manning Equation shall be
used for hydraulic computations, and to determine the capacity of
open channels, pipes, and storm sewers. Values for Manning's roughness
coefficient (n) shall be consistent with Table B-4 in Appendix B of
this chapter.
J.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this chapter using any generally
accepted hydraulic analysis technique or method.
K.
The design of any stormwater detention facilities intended to meet
the performance standards of this chapter shall be verified by routing
the design storm hydrograph through these facilities using the Storage-Indication
Method. For drainage areas greater than 200 acres in size, the design
storm hydrograph shall be computed using a calculation method that
produces a full hydrograph. The Township may approve the use of any
generally accepted full hydrograph approximation technique that uses
a total runoff volume that is consistent with the volume from a method
that produces a full hydrograph.
L.
Existing conditions runoff calculations must consider natural or
man-made features or structures that may limit existing runoff including
such features as existing culverts that may restrict flow and natural
or man-made depressions.
A.
Any stormwater management facility (i.e., BMP, detention basin) designed to store runoff and requiring a berm or earthen embankment required or regulated by this chapter shall be designed to provide an emergency spillway to handle flow up to and including the one-hundred-year proposed conditions. Emergency spillways shall be constructed on undisturbed ground and shall not be constructed on embankment fill. The height of embankment must provide a minimum 1.0 foot of freeboard above the maximum pool elevation computed when the facility functions for the one-hundred-year proposed conditions inflow. Should any stormwater management facility require a dam safety permit under PADEP Chapter 105, the facility shall be designed in accordance with Chapter 105, which may require facilities to pass storms larger than the one-hundred-year event.
B.
Any other drainage conveyance facility (e.g., culverts, bridges, outfalls of stream enclosure) that does not fall under PADEP Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of the roadway.
C.
Any drainage conveyance facility and/or channel not governed by PADEP Chapter 105 regulations, must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm. Conveyance facilities to or exiting from stormwater management facilities (i.e., detention basins) shall be designed to convey the design flow to or from that structure. Roadway crossings located within designated floodplain areas must be able to convey runoff from a one-hundred-year design storm.
D.
Storm sewers must be able to convey proposed conditions runoff from
a twenty-five-year design storm without surcharging inlets, where
appropriate.
E.
Stormwater conveyance facilities must be designed to convey the design
storms to the stormwater facilities.
F.
The design of all stormwater management facilities shall incorporate
sound engineering principles and practices. The municipality reserves
the right to disapprove any design that would result in the creation
of or continuation of a stormwater problem area.
G.
A fifteen-foot wide access easement to and around all stormwater
management facilities is required to provide ingress and egress from
a public right-of-way.
A.
Any earth disturbance must be conducted in conformance with Pa. Code
Title 25, Chapter 102, "Erosion and Sediment Control."
B.
Additional erosion and sediment control design standards and criteria
to be applied where infiltration BMPs are proposed shall include the
following:
(1)
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity.
(2)
Infiltration BMPs shall not be constructed nor receive runoff until
the entire contributory drainage area to the infiltration BMP has
achieved final stabilization.
All regulated activities located within the Brodhead Creek Watershed
shall submit a "Consumptive Use Tracking Report" (CUTR), which shall
be developed in accordance with Appendix F as follows:[1]
A.
Residential development or redevelopment. The CUTR shall be submitted
to the Monroe County Conservation District along with the erosion
and sedimentation control plan.
B.
Commercial/industrial development or redevelopment. The CUTR shall
be submitted to the Monroe County Conservation District during the
land development plan approval process.
[1]
Editor's Note: Appendix F is included as an attachment to this chapter.
