[Ord. 691, 9/10/2009]
1.
The standards contained in this Part 4 shall apply as minimum design
standards; however, federal, state, and other Warminster Township
regulations may impose additional standards subject to their jurisdiction.
A.
All regulated activities within the municipality shall be designed,
implemented, operated, and maintained to meet the purposes of this
Part 4, through these two elements:
B.
No regulated earth disturbance activities within the municipality
shall commence until the requirements of this Part 4 are met.
E.
All best management practices (BMPs) used to meet the requirements
of this Part 4 shall conform to the state water quality requirements
and any more stringent requirements as set forth by the municipality.
F.
Techniques described in Appendix D (Low-Impact Development) of this Part 4[1] shall be considered because they reduce the costs of complying
with the requirements of this Part 4 and the state water quality requirements.[2]
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
2.
Where applicable, stormwater management facilities or programs shall
comply with the requirements of Chapter 102, Erosion and Sediment
Control, Chapter 105, Dam Safety and Waterway Management, and Chapter
106, Floodplain Management, of Title 25, Rules and Regulations, of
the DEP.
[Amended by Ord. 737, 1/19/2017]
3.
Stormwater management facilities which involve a state highway shall
be subject to the approval of PennDOT.
4.
Stormwater management facilities located within or affecting the
floodplain of any watercourse shall also be subject to the requirements
of any Warminster Township ordinance which regulates construction
and development within areas which are subject to flooding.
5.
Access to facilities shall be provided for maintenance and operation.
This access shall be a cleared access that is a minimum of 10 feet
wide. Proximity of facilities to public rights-of-way shall be encouraged
in order to minimize the length of accessways. Multiple accesses shall
be encouraged for major facilities.
6.
Additional studies and higher levels of control than the minimum
provided in the requirements and criteria of this Part 4 may be required
by the Board of Supervisors to ensure adequate protection to life
and property.[3]
7.
Requirements for erosion and sediment control. No regulated earth disturbance activities within Warminster Township shall commence until approval has been granted by the Township of an erosion and sediment control plan in accordance with § 26-427.
8.
Post-construction stormwater runoff controls for new development
and redevelopment, including operations and maintenance of stormwater
BMPs. Post-construction runoff control requirements:
A.
No regulated earth disturbance activities within Warminster Township
shall commence until approval has been granted by the Township of
a plan which demonstrates compliance with the state water quality
requirements after construction is complete.
B.
The BMPs (best management practices) must be designed to protect
and maintain existing uses (e.g., drinking water use; cold water fishery
use) and maintain the level of water quality necessary to protect
those uses in all streams, and to protect and maintain water quality
in special protection streams, as required by statewide regulations
at 25 Pa. Code Chapter 93 (collectively referred to herein as "state
water quality requirements").
C.
To control post-construction stormwater impacts from regulated earth
disturbance activities, state water quality requirements can be met
by BMPs, including site design, which provide for replication of preconstruction
stormwater infiltration and runoff conditions, so that post-construction
stormwater discharges do not degrade the physical, chemical or biological
characteristics of the receiving waters. As described in the DEP Comprehensive
Stormwater Management Policy (No. 392-0300-002, September 28, 2002),
this may be achieved by the following:
(1)
Infiltration: replication of preconstruction stormwater infiltration
conditions.
(2)
Treatment: use of water quality BMPs to ensure filtering out
of chemical and physical pollutants from the stormwater runoff.
(3)
Streambank and streambed protection: management of volume and
rate of post-construction stormwater discharges to prevent physical
degradation of receiving waters (e.g., from scouring and erosion).
D.
DEP has regulations that require municipalities to ensure design,
implementation and maintenance of BMPs that control runoff from new
development and redevelopment (hereinafter "development") after regulated
earth disturbance activities are complete. These requirements include
the need to implement post-construction stormwater BMPs with assurance
of long-term operations and maintenance of those BMPs.
E.
Evidence of any necessary permits for regulated earth disturbance activities from the appropriate DEP regional office or the Bucks County Conservation District must be provided to the Township. The issuance of an NPDES Construction Permit [or permit coverage under the statewide General Permit (PAG-2)] satisfies the requirements of Subsection 8A.
9.
Stormwater
flows onto adjacent property shall not be created, increased, decreased,
relocated, or otherwise altered without written notification to the
adjacent property owner(s). Such stormwater flows shall be subject
to the requirements of this Part 4.
[Added by Ord. No. 769, 9/8/2022]
[Ord. 691, 9/10/2009]
1.
No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of a plan which
demonstrates compliance with state water quality requirements post
construction has been granted.
2.
The BMPs shall be designed, implemented, and maintained to meet state
water quality requirements, and any other more stringent requirements
as determined by the municipality.
3.
The volume of additional stormwater runoff to be captured, stored,
and treated is called the water quality volume (WQv).
A.
The formula for determining WQv (in acre-feet)
is:
|
WQv = [P x Rv x
A]/12
| |||
|
Where:
| |||
|
1.
|
P
|
=
|
Rainfall depth in inches, using first flush rainfall amount,
1.5 inches
|
|
2.
|
A
|
=
|
Project area in acres
|
|
3.
|
Rv, volume runoff coefficient = (0.05
+ 0.009 x I]) where I is the impervious surface percentage (impervious
area ÷ total project area) x 100%
| ||
B.
In special protection watersheds, as described in 25 Pa. Code Chapter
93, this volume is required to remain on site through infiltration
and other methods to protect water quality. Guidance can be obtained
from PADEP "Pennsylvania Stormwater Best Management Practices Manual,"
latest edition.
4.
The following factors must be considered when evaluating the suitability
of BMPs used to control water quality at a given development site:
A.
Total contributing drainage area.
B.
Permeability and infiltration rate of the site soils.
C.
Slope and depth to bedrock.
D.
Seasonal high water table.
E.
Proximity to building foundations and well heads.
F.
Erodibility of soils.
G.
Land availability and configuration of the topography.
H.
Peak discharge and required volume control.
I.
Streambank erosion.
J.
Efficiency of the BMPs to mitigate potential water quality problems.
K.
Volume of runoff that will be effectively treated.
L.
Nature of the pollutant being removed.
M.
Maintenance requirements.
N.
Creation/protection of aquatic and wildlife habitat.
O.
Recreational value.
P.
Enhancement of aesthetic and property value.
|
To accomplish the above, the applicant shall submit original
and innovative designs for review. Such designs may achieve the water
quality objectives through a combination of BMPs.
|
5.
The applicant may, subject to approval of Warminster Township, use
any of the following nonstructural stormwater credits in computing
the required water quality volume.
|
Stormwater Credit
|
Description
|
|---|---|
|
Natural area conservation
|
Conservation of natural areas, such as forest, wetlands, or
other sensitive areas, in a protected easement thereby retaining their
predevelopment hydrologic and water quality characteristics. Using
this credit, a designer may subtract conservation areas from the total
site area when computing the required water quality volume.
|
|
Vegetated roof
|
Credit may be given for water quality and volume benefits for
vegetated roof covers where vegetation is grown on, and completely
covers, an otherwise flat or pitched roof (less than or equal to thirty-degree
slope). Green roof, if adequately designed, may be counted as lawn
for runoff calculations.
|
|
Disconnection of rooftop runoff
|
Credit may be given when rooftop runoff is disconnected and
then directed over a pervious area where it may either infiltrate
into the soil or filter over it. Credit is typically obtained by grading
the site to promote overland flow or by providing bioretention on
single-family residential lots. If a rooftop area is adequately disconnected,
the impervious area may be deducted from the total impervious cover.
|
|
Disconnection of non-rooftop runoff
|
Credit may be given for practices that disconnected surface
impervious cover by directing it to pervious areas where it may either
infiltrate into the soil or filter over it. As with rooftop runoff,
if area is adequately disconnected, the impervious area may be deducted
from the total impervious cover.
|
|
Stream buffer credit
|
Credit may be given when a stream buffer effectively treats
stormwater runoff. Effective treatment constitutes capturing runoff
from pervious and impervious areas adjacent to the buffer and treating
runoff through overland flow across a grass or forested area. Areas
treated in this manner may be deducted from total site area.
|
|
Grass channel/open section roads
|
Credit may be given when open grass channels are used to reduce
the volume of runoff and pollutants during smaller storms. If designed
according to appropriate criteria, these channels may meet water quality
criteria for certain types of residential development. Curbs may be
eliminated where adequately designed swales or bioretention facilities
are located in or adjacent to parking areas.
|
|
Environmentally sensitive rural development
|
Credit may be given when a group of environmental site design
techniques are applied to low density or rural residential development.
This credit eliminates the need for structural practices to address
water quality volume.
|
|
Removal of additional impervious areas
|
Credit may be given when existing impervious areas are removed
and restored to lawn or other landscape areas representing a net reduction
in impervious cover. The stormwater volume reduction resulting from
the restoration may be counted toward water quality and recharge volume
requirements.
|
|
For design and applicability of nonstructural BMPs refer to Chapter 5 of the "Pennsylvania Stormwater Best Management Practices Manual," December 2006 or latest edition. For the nonstructural BMPs proposed, the applicant shall utilize and submit appropriate checklists included in Chapter 8, Section 8.8, of said manual to demonstrate that the BMPs are applicable to the project an to determine the amount of volume or peak rate credit applicable.
|
6.
The volume and rate of any stormwater discharges allowed under this
Part 4 shall be managed to prevent the physical degradation of receiving
waters, such as by streambank scour and erosion. If a detention facility
is proposed which is part of the BMPs approved for the project, the
facility(ies) shall be designed to provide for a twenty-four-hour
extended detention of the one-year, twenty-four-hour storm event as
measured from the time of peak inflow to the facility to zero outflow.
[Ord. 691, 9/10/2009]
1.
Prevention of excess stormwater runoff is a key objective of state
water quality requirements because runoff can change the physical,
chemical, and biological integrity of water bodies thereby impacting
water quality.
2.
The project plan shall describe how water quality protection requirements with regard to volume control will be met. Infiltration BMPs shall be evaluated and utilized to the maximum extent possible to manage the net change in stormwater runoff generated so that post-construction discharges do not degrade the physical, chemical or biological characteristics of the receiving waters. These BMPs may be used to satisfy all or part of the requirements in § 26-422. For project areas equal to or less than one acre that do not require hydrologic routing to design the stormwater facilities, this Part 4 establishes no preference for either methodology; therefore, the applicant may select either methodology on the basis of economic considerations, the intrinsic limitations on applicability of the analytical procedures associated with each methodology and other factors.
[Amended by Ord. No. 769, 9/8/2022]
3.
Post-construction stormwater infiltration of runoff shall replicate
preconstruction infiltration of runoff to the maximum extent possible.
4.
In calculating the volume of runoff that can be infiltrated at a
site, the following methodology shall be used:
A.
Methodology:
|
Rev = [S x Rv x
A]/12
| |||
|
Where:
| |||
|
Rev
|
=
|
Recharge Volume (acre-feet)
| |
|
A
|
=
|
Site area contributing to the recharge facility (acres)
| |
|
Rv
|
=
|
Volumetric runoff coefficient = 0.05 + 0.009 x I where I is
the impervious surface percentage (impervious area ÷ total
project area) x 100%
| |
|
S
|
=
|
Soil specific recharge factor (inches) based on the hydrologic
soil group as provided in the table below:
| |
|
Hydrologic Soil Group
|
Recharge Factor, S
|
|---|---|
|
A
|
0.38
|
|
B
|
0.26
|
|
C
|
0.14
|
|
D
|
0.07
|
|
If more than one hydrologic soil group (HSG) is present at a
site, a composite recharge volume shall be computed based upon the
proportion of total site area within each HSG.
|
B.
In selecting the appropriate infiltration BMPs, the applicant shall
consider the following:
(1)
Permeability and infiltration rate of the site soils.
(2)
Slope and depth to bedrock.
(3)
Seasonal high water table and groundwater elevation.
(4)
Proximity and elevation relative to building foundations, basements,
and well heads. Infiltration BMPs should be located downgrade of these
structures.
(5)
Erodibility of soils.
(6)
Land availability, configuration, and topography.
(7)
Peak discharge and required volume control.
(8)
Streambank erosion.
(9)
Efficiency of the BMPs to mitigate potential water quality problems.
(10)
Volume of runoff that will be effectively treated.
(11)
Nature of the pollutant being removed.
(12)
Maintenance requirements.
(13)
Creation/protection of aquatic and wildlife habitat.
(14)
Recreational value.
(15)
Enhancement of aesthetic and property value.
C.
The recharge volume provided at the site shall be directed to the
most permeable HSG available, except where other considerations apply
to the use of groundwater recharge on the site.
[Amended by Ord. 737, 1/19/2017]
D.
The plan shall include safeguards against groundwater contamination
for uses which may cause groundwater contamination should there be
a mishap or spill. The Township may require installation of mitigative
layer or an impermeable liner in BMPs where the possibility exists.
A detailed hydrogeologic investigations study may be required by the
Township.
E.
The requirements for volume control are applied to all disturbed
areas, even if they are ultimately to be a pervious or permeable land
use given the extent to which development-related disturbance leads
to compaction of the soils and reduces their infiltrative capacity.
[Ord. 691, 9/10/2009]
1.
Location.
A.
Mapping of stormwater runoff peak districts. In order to implement
the provisions of the Neshaminy Creek Watershed Stormwater Management
Plan, which includes the Little Neshaminy Creek Watershed, and the
Pennypack Creek Stormwater Management Plan, Warminster Township is
hereby divided into stormwater runoff peak rate districts consistent
with said plans. The boundaries of the districts are shown on an official
Stormwater Runoff Peak Rate Districts Map which is available for inspection
at the Warminster Township Municipal Building.
[Amended by Ord. 737, 1/19/2017]
B.
The exact location of the stormwater runoff peak rate district boundaries
as they apply to a given development site may also be determined by
mapping the boundaries using the two-foot or five-foot topographic
contours provided as part of the stormwater management plan developed
for the site in accordance with the technical reports. 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 (road, culvert, bridge, etc.) to the
topographic divide consistent with topography. The location of the
stormwater management district boundary on a stormwater management
plan shall be reviewed and verified by the Township Engineer.
2.
Description of stormwater runoff peak rates.
[Amended by Ord. 737, 1/19/2017]
A.
Release rates. These watershed areas require that the post-development
peak rate of storm runoff be controlled to the stated predevelopment
peak rate of storm runoff for design storms greater than one-year,
twenty-four-hour storm in order to protect downstream watershed areas.
The release rate districts and their respective release rate control
design criteria for peak flow are as follows:
|
Neshaminy and Little Neshaminy Creek
|
Release Rate
|
|---|---|
|
2-year storm event, post development
|
1-year storm event, predevelopment
|
|
5-year storm event, post development
|
2-year storm event, predevelopment
|
|
10-year storm event, post development
|
5-year storm event, predevelopment
|
|
25-year storm event, post development
|
10-year storm event, predevelopment
|
|
50-year storm event, post development
|
25-year storm event, predevelopment
|
|
100-year storm event, post development
|
50-year storm event, predevelopment
|
|
Pennypack Creek
|
Release Rate
|
|---|---|
|
2-year storm event, post development
|
1-year storm, predevelopment
|
|
5-year storm event, post development
|
5-year storm event, predevelopment
|
|
10-year storm event, post development
|
10-year storm event, predevelopment
|
|
25-year storm event, post development
|
25-year storm event, predevelopment
|
|
50-year storm event, post development
|
50-year storm event, predevelopment
|
|
100-year storm event, post development
|
100-year storm event, predevelopment
|
[Ord. 691, 9/10/2009]
1.
Design storms.
A.
Any stormwater management controls required by this Part 4 and subject to the water quality requirement (§ 26-422), recharge volume requirement (§ 26-423), and the stormwater runoff peak rate requirements (§ 26-424, Subsection 2) shall meet the applicable water quality and peak rate requirements for the one-, two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year return period runoff events (design storms) consistent with the calculation methodology specified in § 26-426. Provisions must also be made for safely passing the runoff greater than that occurring from the largest design storm.
B.
Runoff volume standard. Post-development stormwater runoff volume
being discharged from any regulated activity shall not exceed predevelopment
stormwater runoff volume being discharged for up to the two-year design
storm for each watershed or design point on the site.
2.
For a proposed development site located within a single release district (§ 26-424, Subsection 2A), the total runoff from the site shall meet the applicable release criteria. For development sites within a single release rate district with multiple points of concentrated runoff discharge, individual drainage points may be designed for up to one-hundred-percent release rate so long as the total runoff from the site is controlled to the applicable release rate. All points of concentrated discharge, however, must meet the applicable water quality requirement (§ 26-422) for the specific drainage areas of the site draining to the discharge points.
3.
Runoff control measures or best management practices (BMPs).
[Amended by Ord. 737, 1/19/2017]
A.
Stormwater runoff which may result from regulated activities listed in § 26-405 shall be controlled by permanent stormwater runoff BMPs that will provide the required standards within §§ 26-422, 26-423, and 26-424. The methods of stormwater control or best management practices (BMPs) which may be used to meet the required standards are described in § 22-520 of Chapter 22, Subdivision and Land Development, of the Code of the Township of Warminster and "Pennsylvania Stormwater Best Management Practices Manual," December 2006, as amended. The choice of BMPs is not limited to the ones appearing in Chapter 22, Subdivision and Land Development, and/or the Manual; however, any selected BMP must meet or exceed the required water quality, recharge volume, and runoff peak rate requirements of this Part 4.
[Ord. 691, 9/10/2009]
1.
To calculate the potential increase in total runoff and peak flow
rate resulting from a proposed site development, the Cover Complex
Method will be used as outlined in "Urban Hydrology for Small Watersheds,"
U.S. Department of Agriculture, Natural Resources Conservation Service,
Technical Release 55 (NTIS PB87-101580) and following mathematical
analyses described in Computer Program for Project Formulation-Hydrology
(SCS Technical Release 20, 1983).
2.
Where the initial condition of the site is undeveloped land, the
land use shall be considered as meadow for modeling purposes unless
the natural land cover is proven to generate a lower curve number
or Rational "c" value, such as forested lands.
[Amended by Ord. 737, 1/19/2017]
3.
Impervious surfaces of a site used for modeling purposes which are
in excess of the maximum impervious cover allowance in the existing
condition (refer existing nonconformity) shall be considered meadow
in the predevelopment cover conditions when developing the necessary
Cover Complex calculations.
4.
The Natural Resources Conservation Service Type II twenty-four-hour
rainfall distribution shall be used in the soil-cover complex calculations.
The twenty-four-hour rainfall depths for the return periods used in
the Soil-Cover Complex Methods shall be according to the National
Oceanic and Atmospheric Administration (NOAA) Atlas 14, Volume 2,
Version 3, rain data corresponding to the Doylestown rain gage for
the precipitation depth data and the partial duration time series
using the upper bound of the ninety-percent confidence interval for
the various return period storms. If a hydrologic computer model,
such as PSRM or HEC-1/HEC-HMS, is used for stormwater runoff calculations,
then the duration of rainfall shall be 24 hours. This data may also
be directly retrieved from the NOAA Atlas 14 website: hdsc.nws.noaa.gov/hdsc/pfds/orb/pa
pfds.html and are found below:
[Amended by Ord. 737, 1/19/2017]
|
Precipitation Frequency
(inches)
| |
|---|---|
|
Design Storm
(years)
|
24 Hours
|
|
1
|
2.94
|
|
2
|
3.54
|
|
5
|
4.45
|
|
10
|
5.20
|
|
25
|
6.29
|
|
50
|
7.21
|
|
100
|
8.21
|
5.
The design of any stormwater management facility intended to meet
the requirements of this Part 4 shall be verified by routing the design
storm hydrographs through the proposed facility.
6.
Rational Method may be used to calculate runoff and peak flow rates
for drainage areas less than 10 acres or as approved by the Township
Engineer.
[Amended by Ord. 737, 1/19/2017]
A.
Runoff coefficients for existing and proposed conditions for use
in the Rational Method are noted in Table A-2 in Appendix A.[1]
[1]
Editor's Note: Appendix A is included as an attachment to this chapter.
B.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times of concentration for overland flow
and return periods from NOAA Atlas 14, Volume 2, Version 3, rain data
corresponding to the Doylestown rain gage for the precipitation intensity
data and the partial duration time series using the upper bound of
the ninety-percent confidence interval as follows:
|
Precipitation Intensity (inches/hour)
| ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|
|
Design Storm
(years)
|
5 min.
|
10 min.
|
15 min.
|
30 min.
|
60 min.
|
120 min.
|
3 hrs.
|
6 hrs.
|
12 hrs.
|
24 hrs.
|
|
1
|
4.45
|
3.55
|
2.96
|
2.03
|
1.27
|
0.76
|
0.56
|
0.35
|
0.21
|
0.12
|
|
2
|
5.29
|
4.24
|
3.55
|
2.45
|
1.54
|
0.92
|
0.67
|
0.42
|
0.26
|
0.15
|
|
5
|
6.23
|
4.99
|
4.21
|
2.99
|
1.92
|
1.15
|
0.85
|
0.53
|
0.32
|
0.19
|
|
10
|
6.91
|
5.53
|
4.66
|
3.37
|
2.20
|
1.33
|
0.98
|
0.61
|
0.38
|
0.22
|
|
25
|
7.72
|
6.15
|
5.20
|
3.85
|
2.56
|
1.57
|
1.16
|
0.73
|
0.46
|
0.26
|
|
50
|
8.29
|
6.61
|
5.58
|
4.20
|
2.84
|
1.76
|
1.30
|
0.83
|
0.53
|
0.30
|
|
100
|
8.86
|
7.04
|
5.93
|
4.54
|
3.13
|
1.95
|
1.45
|
0.94
|
0.60
|
0.34
|
|
NOAA's Atlas 14 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/
|
C.
Times of concentration for overland flow shall be calculated using
the segmental approach presented in Chapter 3 of Urban Hydrology for
Small Watersheds, NRCS, TR-55 (as amended). Times of concentration
for channel or pipe flow shall be computed using Manning's equation.
Roughness coefficients for overland flow and channel flow shall be
consistent with Table A-1 in Appendix A.
7.
The Township has the authority to require that computed existing
runoff rates be reconciled with field observations and conditions.
If the design professional engineer can substantiate through actual
physical calibration that more appropriate runoff and time-of-concentration
values should be utilized at a particular site, then appropriate variations
may be made upon review and recommendations of the Township Engineer.
Calibration shall require detailed gauge and rainfall data for the
particular site in question.
[Ord. 691, 9/10/2009; as amended by Ord. 737, 1/19/2017]
The owner, developer, or subdivider shall install erosion and
sediment control measures for any site improvements in accordance
with an approved erosion and sediment control plan. The measures shall
be shown on a plan in accordance with current Township ordinances
and Bucks County Conservation District Standards. All required permits
shall be obtained from the Bucks County Conservation District prior
to approval by the Township.
[Ord. 691, 9/10/2009]
The following permit requirements may apply to certain regulated
earth disturbance activities and must be met prior to commencement
of regulated earth disturbance activities, as applicable:
A.
All regulated 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 105.
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.
