A.
All regulated activities in the municipality shall
be subject to the stormwater management requirements of this ordinance.
B.
Storm drainage systems shall be provided to permit
unimpeded flow in natural watercourses, except as modified by stormwater
detention facilities, recharge facilities, water quality facilities,
pipe systems or open channels consistent with this ordinance.
C.
The existing locations of concentrated drainage discharge
onto adjacent property shall not be altered without written approval
of the affected property owner(s).
D.
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 ordinance. If diffused flow is
proposed to be concentrated and discharged onto adjacent property
{including flows from detention basin emergency spillways), the developer's
engineer must document and certify 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. It is recommended that the developer obtain written permission
from the downstream property owner(s) for the proposed discharges.
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.
E.
Where a site is traversed by watercourses, swales, ditches, etc, there shall be provided drainage easements conforming substantially with the line of such watercourses swales, ditches, etc. The width of any easement shall be adequate to provide for unimpeded flow of postdevelopment storm runoff based either on calculations completed by the developer in conformance with § 158-17 for the one-hundred-year return period runoff, Bushkill Creek Watershed and Fry's Run Study Area Act 167 one-hundred-year return period flows, or Federal Emergency Management Agency (FEMA) one-hundred-year frequency flood flows and to provide a freeboard allowance of 0.5 foot above the design water surface level. In all areas, the flow rate to be utilized shall be the maximum rate identified through either developer's calculations, the Bushkill Creek Watershed and Fry's Run Study Area Act 167 or (if applicable) FEMA study flows. In areas where the Act 167 flow rate is the maximum rate, this rate shall be used unless a reduced flow rate is determined by the Lehigh Valley Planning Commission to take precedence over the Act 167 flow rate. This maximum flow rate shall be used to determine the one-hundred-year flood elevations with HEC-RAS modeling (or other modeling method as approved by the municipality). 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 in the postdevelopment condition. Also, periodic maintenance of the easement to ensure proper runoff conveyance shall be required. Watercourses for which the one-hundred-year floodplain is formally defined by FEMA studies are also subject to the applicable municipal floodplain regulations. All proposed buildings within or adjacent to a floodplain as defined by FEMA studies shall have first floor elevations at least 1.5 feet above the one-hundred-year frequency flood elevation. The one-hundred-year flood elevation to be used to establish the first floor elevation shall be determined using the maximum flow rate between FEMA study flows, Act 167 flows or calculated flows as identified above.
F.
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.
G.
Postconstruction BMPs shall be designed, installed,
operated and maintained to meet the requirements of the Clean Streams
Law[1] and implementing regulations, including the established practices in 25 Pa. Code Chapter 102 and the specifications of this ordinance, so as to prevent accelerated erosion in watercourse channels and at all points of discharge.
[1]
Editor's Note: See 35 P.S. § 691.1
et seq.
H.
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
ordinance.
J.
Infiltration for stormwater management is encouraged
where soils and geology permit, consistent with the provisions of
this ordinance and, where appropriate, the Recommendation Chart for
Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix
D.[3]
[3]
Editor's Note: Appendix D is on file in the
Township offices.
K.
Within areas containing soils identified by the Soil
Conservation Service to be sinkhole prone, permanent detention basins
shall be lined with a material, which after installation, attains
a maximum permeability rate as determined by the Township Geotechnical
Engineer.
L.
Groundwater recharge methods shall not be permitted
without written approval of the Township Geotechnical Engineer.
M.
Parking lot ponding depth shall not exceed two inches
in areas of anticipated pedestrian traffic, and six inches in all
other areas for a twenty-five-year frequency storm.
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 the DEP under regulations at 25 Pa. Code
Chapter 102.14.
C.
Any stormwater management facility that would be located
in or adjacent to surface waters of the commonwealth, including wetlands,
subject to permit by the 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 the DEP under 25 Pa.
Code Chapter 105.
A.
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 the DEP or a delegated County Conservation District
shall satisfy this requirement.
B.
An erosion and sediment control plan is required by
DEP regulations for any earth disturbance activity of 5,000 square
feet or more under Pa. Code § 102.4(b).
C.
A DEP NPDES stormwater discharges associated with
construction activities permit is required for regulated earth disturbance
activities under Pa. Code Chapter 92.
D.
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.
E.
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.
A.
No regulated earth disturbance activities within the
municipality shall commence until approval by the municipality of
a plan which demonstrates compliance with this ordinance. DEP has
determined that this ordinance meets state water quality requirements.
Therefore, any approvals under this ordinance would satisfy the postconstruction
stormwater management requirements associated with an NPDES permit
for stormwater discharges associated with construction activities.
B.
The water quality volume (WQv) shall be captured and
treated. The WQv shall be calculated two ways.
(2)
Second, the WQv shall be calculated as the difference
in runoff volume from predevelopment to postdevelopment 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 be required to exceed 1.25 inches of
runoff over the site area. This standard does not limit the volume
of infiltration an applicant may propose for purposes of water quantity/peak
rate control.
C.
The WQv shall be calculated for each postdevelopment
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.
D.
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 the
high quality waters of the Bushkill Creek and/or Fry's Run Study Area
from thermal impacts.
E.
The WQv for a site as a result of the regulated activities must either be treated with infiltration or two acceptable BMPs such as those listed in § 158-14O except for minor areas on the periphery of the site that cannot reasonably be drained to an infiltration facility or other BMP.
F.
Infiltration BMPs shall not be constructed on fill
unless the applicant demonstrates that the fill is stable and otherwise
meets the infiltration BMP standards of this ordinance.
G.
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 geo-professional.
H.
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 G.[1] 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 geo-professional.
Additionally, the Township Geotechnical Engineer or its authorized
representative shall be notified of the soil testing in order to observe
any such testing as determined to be necessary.
[1]
Editor's Note: Appendix G is on file in the
Township offices.
I.
Sites where applicants intend to use infiltration
BMPs must meet the following criteria:
(1)
Depth to bedrock below the invert of the BMP greater
than or equal to two feet.
(2)
Depth to seasonal high water table below the invert
of the BMP greater than or equal to three feet; except for infiltration
of residential roof runoff where the seasonal high water table must
be below the invert of the BMP(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.)
(3)
Soil permeability (as measured by the adapted 25 PA
Code § 73.15 percolation test in Appendix G) greater than
or equal to 0.5 inch per hour and less than or equal to 12 inches
per hour.
(4)
Setback distances or buffers as follows:
(a)
One hundred feet from water supply wells.
(b)
Fifteen feet downgradient or 100 feet upgradient
from building foundations, except for residential development where
that required setback is 15 feet downgradient or 40 feet upgradient
from building foundations.
(c)
Fifty feet from septic system drainfields, except
for residential development where the required setback is 25 feet
from septic system drainfields and should be located downstream from
the septic system where practical.
(d)
Fifty feet from a geologic contact with carbonate
bedrock unless a preliminary site investigation is done in the carbonate
bedrock to show the absence of special geologic features within 50
feet of the proposed infiltration area.
(e)
One hundred feet from the property line unless
documentation is provided to show that all setbacks from existing
or potential future wells, foundations and drainfields on neighboring
properties will be met, except for one- and two-family residential
dwellings where the required setback is 40 feet unless documentation
is provided to show that all setbacks from existing or potential future
wells, foundations and drainfields on neighboring properties will
be met.
J.
For entirely noncarbonate sites, the recharge volume (REv) shall be infiltrated unless the applicant demonstrates that it is infeasible to infiltrate the REv for reasons of seasonal high water table, permeability rate, soil depth or setback distances; or except as provided in § 158-14U.
(1)
The REv shall be calculated as follows:
REv = (0.25) * (I)/12
| |||
Where
| |||
REv
|
=
|
Recharge volume in acre-feet.
| |
I
|
=
|
Impervious area in acres.
|
(2)
The preliminary site investigation described in § 158-14H is required and shall continue on different areas of the site until a potentially suitable infiltration location is found or the entire site is determined to be infeasible for infiltration. For infiltration areas that appear to be feasible based on the preliminary site investigation, the additional site investigation and testing as outlined in Appendix G[2] shall be completed.
[2]
Editor's Note: Appendix G is on file in the
Township offices.
(3)
If an applicant proposes infiltration, 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.
(5)
If it is not feasible to infiltrate the full REv, the applicant shall infiltrate that portion of the REv that is feasible based on the site characteristics. If none of the REv can be infiltrated, REv shall be considered as part of the WQv and shall be captured and treated as described in § 158-14O.
(6)
If REv is infiltrated, it may be subtracted from the
WQv required to be captured and treated.
K.
Entirely carbonate areas.
(1)
In entirely carbonate areas, where the applicant intends to use infiltration BMPs, the preliminary site investigation described in § 158-14H shall be conducted. For infiltration areas that appear feasible based on the preliminary site investigation, the applicant shall conduct the additional site investigation and testing as outlined in Appendix G. The soil depth, percolation rate and proposed loading rate, each weighted as described in Section 307, along with the buffer from special geologic features shall be compared to the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D[3] to determine if the site is recommended for infiltration. In addition to the recommendation from Appendix D, the conditions listed in § 158-14I are required for infiltration in carbonate areas.
[3]
Editor's Note: Appendix D is on file in the
Township offices.
(2)
Applicants are encouraged to infiltrate the REv, as calculated in § 158-14J but are not required to use infiltration BMPs on a carbonate site even if the site falls in the recommended range on the chart in Appendix D. Any amount of volume infiltrated can be subtracted from the WQv to be treated by noninfiltration BMPs. If infiltration is not proposed, the full WQv shall be treated by two acceptable BMPs, as specified in § 158-14O.
L.
If a site has both carbonate and noncarbonate areas, the applicant shall investigate the ability of the noncarbonate portion of the site to fully meet this ordinance to meet the requirements for REv for the whole site through infiltration. If that proves infeasible, infiltration in the carbonate area as described in § 158-14K or two other noninfiltration BMPs as described in § 158-140 must be used. No infiltration structure in the noncarbonate area shall be located within 50 feet of a boundary with carbonate bedrock, except when a preliminary site investigation has been done showing the absence of special geologic features within 50 feet of the proposed infiltration area.
M.
If infiltration BMPs are proposed in carbonate areas,
the postdevelopment two-year runoff volume leaving the site shall
be 80% or more of the predevelopment runoff volume for the carbonate
portion of the site to prevent infiltration of volumes far in excess
of the predevelopment infiltration volume.
N.
Site areas proposed for infiltration shall be protected
from disturbance and compaction except as necessary for construction
of infiltration BMPs.
O.
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 Reference3
| |
---|---|---|
Bioretention1
|
4, 5, 11, 16
| |
Capture/reuse2
|
4, 14
| |
Constructed wetlands
|
4, 5, 8, 10, 16
| |
Dry extended detention ponds
|
4, 5, 8, 10, 16
| |
Minimum disturbance/minimum maintenance practices
|
1, 9
| |
Impervious cover
|
N/A
| |
Stormwater filters1 (sand, peat, compost, etc.)
|
4, 5, 10, 16
| |
Vegetated buffers/filter strips
|
2, 3, 5, 11, 16, 17
| |
Vegetated roofs
|
4, 13
| |
Vegetated swales
|
2, 3, 5, 11, 16, 17
| |
Water quality inlets4
|
4, 7, 15, 16, 19
| |
Wet detention ponds
|
4, 5, 6, 8
|
NOTES:
| ||
1
|
This BMP could be designed with or without an
infiltration component. If infiltration is proposed, the site and
BMP will be subject to the testing and other infiltration requirements
in this ordinance.
| |
2
|
If this BMP is used to treat the entire WQv
then it is the only BMP required because of this BMP's superior water
quality performance.
| |
3
|
See table below.
| |
4
|
Water quality inlets include such BMPs as oil/water
separators, sediment traps/catch basin sumps, and trash/debris collectors
in catch basins.
|
Design References
| ||
---|---|---|
Number
|
Design Reference Title
| |
1
|
"Conservation Design For Stormwater Management
— A Design Approach to Reduce Stormwater Impacts From Land Development
and Achieve Multiple Objectives Related to Land Use," Delaware Department
of Natural Resources and Environmental Control, The Environmental
Management Center of the Brandywine Conservancy, September 1997
| |
2
|
"A Current Assessment of Urban Best Management
Practices: Techniques for Reducing Nonpoint Source Pollution in the
Coastal Zone," Schueler, T. R., Kumble, P. and Heraty, M., Metropolitan
Washington Council of Governments, 1992.
| |
3
|
"Design of Roadside Channels with Flexible Linings,"
Federal Highway Administration, Chen, Y. H. and Cotton, G. K., Hydraulic
Engineering Circular 15, FHWA-IP-87-7, McLean Virginia, 1988.
| |
4
|
"Draft Stormwater Best Management Practices
Manual," Pennsylvania Department of Environmental Protection, January
2005.
| |
5
|
"Evaluation and Management of Highway Runoff
Water Quality," Federal Highway Administration, FHWA-PD-96-032, Washington,
D.C., 1996.
| |
6
|
"Evaporation Maps of the United States," U.S.
Weather Bureau (now NOAA/National Weather Service) Technical Paper
37, Published by Department of Commerce, Washington D.C., 1959.
| |
7
|
"Georgia Stormwater Manual," AMEC Earth and
Environmental, Center for Watershed Protection, Debo and Associates,
Jordan Jones and Goulding, Atlanta Regional Commission, Atlanta, Georgia,
2001.
| |
8
|
"Hydraulic Design of Highway Culverts," Federal
Highway Administration, FHWA HDS 5, Washington, D.C., 1985 (revised
May 2005).
| |
9
|
"Low Impact Development Design Strategies An
Integrated Design Approach, Prince Georges County, Maryland Department
of Environmental Resources, June 1999.
| |
10
|
"Maryland Stormwater Design Manual," Maryland
Department of the Environment, Baltimore, Maryland, 2000.
| |
11
|
"Pennsylvania Handbook of Best Management Practices
for Developing Areas," Pennsylvania Department of Environmental Protection,
1998.
| |
12
|
"Recommended Procedures for Act 167 Drainage
Plan Design," LVPC, Revised 1997.
| |
13
|
"Roof Gardens History, Design, and Construction,"
Osmundson, Theodore. New York: W.W. Norton & Company, 1999.
| |
14
|
"The Texas Manual on Rainwater Harvesting,"
Texas Water Development Board, Austin, Texas, Third Edition, 2005.
| |
15
|
"VDOT Manual of Practice for Stormwater Management,"
Virginia Transportation Research Council, Charlottesville, Virginia,
2004.
| |
16
|
"Virginia Stormwater Management Handbook," Virginia
Department of Conservation and Recreation, Richmond, Virginia, 1999.
| |
17
|
"Water Resources Engineering," Mays, L. W.,
John Wiley & Sons, Inc., 2005.
| |
18
|
"Urban Hydrology for Small Watersheds," Technical
Report 55, US Department of Agriculture, Natural Resources Conservation
Service, 1986.
| |
19
|
US EPA, Region 1 New England web site (as of
August 2005) http://www.epa.gov/NE/assistance/ceitts/stormwater/techs/html.
|
P.
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 § 158-14O.
(1)
Acceptable methods of pretreatment are listed below.
Hot Spot Land Use
|
Pretreatment Method(s)
| |
---|---|---|
Vehicle maintenance and repair facilities including
auto parts stores
|
Oil/water separators
| |
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
|
NOTES:
| |
*Regulated under the NPDES Stormwater Program.
|
(2)
Design references for the pretreatment methods, as
necessary, are listed below. If the applicant can demonstrate to the
satisfaction of the municipality that the proposed land use is not
a hot spot, then the pretreatment required would not apply.
Pretreatment Method
|
Design Reference1
| |
---|---|---|
Constructed wetlands
|
4, 5, 8, 10, 16
| |
Diversion of stormwater away from potential
contamination areas
|
4, 11
| |
Stormwater collection and reuse (especially
for irrigation)
| ||
Stormwater filters (sand, peat, compost, etc.)
|
4, 5, 10, 16
| |
Vegetated swales
|
2, 3, 5, 11, 16, 17
| |
Water quality inlets
|
4, 7, 15, 16, 19
|
NOTES:
| |
---|---|
1These numbers refer to the Design Reference Title Chart in § 158-14O above.
|
Q.
The use of infiltration BMPs is prohibited on hot
spot land use areas.
R.
Stormwater infiltration BMPs shall not be placed in
or on a special geologic feature(s). Additionally, stormwater runoff
shall not be discharged into existing on-site sinkholes.
S.
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 §§ 158-14I 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.
T.
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
by controlling the two-year postdevelopment runoff to a release rate
of 30%.
U.
The municipality may, after consultation with the
DEP, approve alternative methods for meeting the state water quality
requirements other than those in this section, provided that they
meet the minimum requirements of and do not conflict with state law,
including, but not limited to, the Clean Streams Law.[4]
[4]
Editor's Note: See 35 P.S. § 691.1
et seq.
A.
Mapping of stormwater management districts. To implement
the provisions of the Bushkill Creek Watershed and Fry's Run Study
Area Stormwater Management Plans, the municipality is hereby divided
into stormwater management districts consistent with the Bushkill
Creek and Fry's Run Study Area Release Rate Maps presented in the
plans. The boundaries of the stormwater management districts are shown
on an official map which is available for inspection at the municipal
office. A copy of the official map at a reduced scale is included
in Appendix A[1] for general reference.
[1]
Editor's Note: Appendix A is on file in the
Township offices.
B.
Description of stormwater management districts. Four
types of stormwater management districts may be applicable to the
municipality, namely Conditional No Detention I Districts, Conditional
No Detention II Districts, Provisional No Detention Areas and Dual
Release Rate Districts, as described below.
(1)
Conditional No Detention I Districts, Fry's Run Study Area. Within these districts, the capacity of the local runoff conveyance facilities (as defined in Article II) 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 ordinance. 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 Article II), these watershed areas may discharge postdevelopment peak runoff without detention facilities. The Township reserves the right to require one-hundred-percent release rate controls irrespective of the adequacy of the downstream capacity where the uncontrolled release could adversely impact downstream properties. If the capacity calculations show that the local runoff conveyance facilities lack adequate capacity, the developer shall either use a one-hundred-percent release rate control or provide increased capacity of downstream elements to convey increased peak flows consistent with § 158-16Q. 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 § 158-16D. By definition, a storm drainage problem area associated with the local runoff conveyance facilities indicates that adequate capacity does not exist.
(2)
Conditional No Detention II Districts, Fry's Run Study
Area. Within these districts, the capacity of the local runoff conveyance
facilities must be calculated in the same manner as the Conditional
No Detention I Districts. In this case, however, adequate capacity
must be demonstrated from the site to the Delaware River or Lehigh
River, as applicable. After determining if adequate capacity exists,
the developer shall use either no detention, a one-hundred-percent
release rate or provide capacity improvements as one-hundred-percent-release-rate
controls irrespective of the adequacy of the downstream capacity where
the uncontrolled release could adversely impact downstream properties.
(3)
Provisional No Detention Districts, Bushkill Creek. These watershed areas may discharge postdevelopment peak runoff without detention facilities without adversely affecting the watershed peak flow. In certain instances however, the local runoff conveyance facilities, which transport runoff from the site to the main channel, may not have adequate capacity to safely transport increased peak flows associated with not providing detention for a proposed development. In these instances, the developer shall either use a one-hundred-percent release control or provide increased capacity of downstream drainage elements to convey increased peak flows consistent with § 158-16Q. The Township reserves the right to require one-hundred-percent release-rate controls irrespective of the adequacy of the downstream capacity where the uncontrolled release could adversely impact downstream properties. In determining if adequate capacity exists in the local watershed drainage network, the developer must assume that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified by this ordinance. Similarly, any capacity improvement must be designed to convey runoff from development of all areas tributary to the improvement consistent with the capacity criteria specified in § 158-16D.
(4)
Dual Release Rate Districts, Bushkill Creek and Fry's
Run Study Area. Within this district, the two-year postdevelopment
peak runoff must be controlled to 30% of the predevelopment two-year
runoff peak. Further, the ten-year, twenty-five-year and one-hundred-year
postdevelopment peak runoff must be controlled to the stated percentage
of the predevelopment peak. Release rates associated with the ten-
through one-hundred-year events vary from 50% to 100% depending upon
location in the watershed.
A.
Applicants shall provide a comparative pre- and postconstruction
stormwater management hydrograph analysis for each direction of discharge
and for the site overall to demonstrate compliance with the provisions
of this ordinance.
B.
Any stormwater management controls required by this ordinance and subject to a dual release rate criteria shall meet the applicable release rate criteria for each of the two-, ten-, twenty-five- and one-hundred-year return period runoff events consistent with the calculation methodology specified in § 158-17.
C.
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 drainage 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.
D.
Any downstream capacity analysis conducted in accordance
with this ordinance shall use the following criteria for determining
adequacy for accepting increased peak flow rates:
(1)
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.
(2)
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.
(3)
Culverts, bridges, storm sewers or any other facilities
which must pass or convey flows from the tributary area must be designed
in accordance with DEP Chapter 105 regulations (if applicable) and,
at minimum, pass the increased twenty-five-year return period runoff.
E.
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 one-hundred-percent release rate so long
as the total runoff from the site is controlled to the applicable
release rate.
F.
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 one-hundred-percent
release rate, provided that the overall site discharge meets the weighted
average release rate.
G.
For a proposed development site located partially
within a release rate category subarea and partially within a conditional
no detention subarea, 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 subarea except as part of a no harm or
hardship waiver procedure.
H.
No portion of a site may be regraded to redirect runoff
onto adjacent property, except as part of a no harm or hardship waiver
procedure:or unless runoff peak flow rate and volume controls are
proposed which limit postdevelopment peak flow rate and volume discharges
to predevelopment levels.
I.
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 § 158-16D and the minimum orifice criteria.
J.
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 § 158-16D and the detention criteria in § 158-17.
K.
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.
L.
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.
M.
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 ordinance.
N.
In any stormwater management district, the Township
reserves the right to require a more stringent design release rate
and/or volume control for a development site or other amendments to
a drainage plan to address problems in the local runoff conveyance
system downstream of the site. Such problems include existing flooding
problems, inadequate conveyance capacity, poorly defined or poorly
stabilized downstream conveyance systems or other factors,
O.
No harm water quantity option. For any proposed development site not located in a conditional no detention 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 or Lehigh River, as applicable. Proof of no harm must be shown using the capacity criteria specified in § 158-16D if downstream capacity analysis is a part of the no harm justification.
(1)
Attempts to prove no harm based upon downstream peak
flow versus capacity analysis shall be governed by the following provisions:
(a)
The peak flow values to be used for downstream
areas for the design return period storms (two-, ten-, twenty-five-
and one-hundred-year) shall be the values from the calibrated Penn
State Runoff Models for the Bushkill Creek or the Fry's Run Study
Area or as calculated by an applicant using an alternate method acceptable
to the municipality. These flow values would be supplied to the developer
by the Lehigh Valley Planning Commission upon request.
(b)
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).
(c)
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 § 158-16Q.
P.
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 on a case-by-case
basis using the hydrologic model of watershed consistent with protection
of the downstream watershed areas. "Hydrologic model" refers to the
calibrated version of the Penn State Runoff Model as developed for
the stormwater management plan.
Q.
Capacity improvements. In certain instances, primarily within the conditional no detention 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 § 158-16D. 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. 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.
R.
Compatibility with NPDES requirements. Any proposed
regulated activity for which a permanent stormwater quality control
detention basin is required under the NPDES regulations shall use
the more stringent runoff control criteria between this ordinance
and the NPDES requirements.
S.
In any stormwater management district, storm sewer piping, swales and inlet systems shall be designed for a twenty-five-year return period storm, or a one-hundred-year return period storm where the system is designed to convey one-hundred-year storm flows to a detention facility. Bridges and culverts along roadways shall be designed to convey the one-hundred-year return period storm. Flows from off-site upstream areas shall be determined in accordance with the procedure identified in § 158-11E.
A.
Stormwater runoff from all development sites shall
be calculated using either the Rational Method or the Soil-Cover-Complex
Methodology. The following requirements apply unless otherwise approved
by the municipality:
C.
Soil thickness.
(1)
Soil thickness is to be measured from the bottom of
any proposed infiltration system. The effective soil thickness in
the Recommendation Chart for Infiltration Stormwater Management BMPs
in Carbonate Bedrock in Appendix D is the measured soil thickness
multiplied by the thickness factor based on soil permeability (as
measured by the adapted 25 PA Code § 73.15 percolation test
in Appendix G[2]), as follows:
Permeability Range*
(inches/hour)
|
Thickness Factor
| |
---|---|---|
6.0 to 12.0
|
0.8
| |
2.0 to 6.0
|
1.0
| |
1.0 to 2.0
|
1.4
| |
0.75 to 1.0
|
1.2
| |
0.5 to 0.75
|
1.0
|
NOTE:
| |
*If the permeability rate (as measured by the
adapted 25 PA Code § 73.15 percolation test in Appendix
G) falls on a break between two thickness factors, the smaller thickness
factor shall be used.
|
[2]
Editor's Note: Appendix G is on file in the
Township offices.
(2)
Sites with soil permeability greater than 12.0 inches
per hour or less than 0.5 inch per hour, as measured by the adapted
25 PA Code § 73.15 percolation test in Appendix G, are not
recommended for infiltration.
D.
The design of any detention basin intended to meet
the requirements of this ordinance 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 the Universal Rational Hydrograph
or as otherwise reviewed by the municipality.
E.
BMPs designed to store or infiltrate runoff and discharge
to surface runoff or pipe flow shall be routed using the Storage Indication
Method.
F.
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.
G.
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. All wet detention ponds
shall be subject to review by the Township Geotechnical Engineer.
H.
All stormwater detention facilities shall provide
a minimum freeboard of 1.0 foot above the maximum pool elevation associated
with the two- through twenty-five-year runoff events. A freeboard
of 0.5 foot shall be provided above the maximum pool elevation of
the one-hundred-year runoff event. The freeboard shall be measured
from the maximum pool elevation to the invert of the emergency spillway.
The two- through one-hundred-year storm events shall be controlled
by the primary outlet structure. An emergency spillway for each basin
shall be designed to pass the one-hundred-year return frequency storm
peak basin inflow rate with a minimum freeboard of 0.5 foot 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.
If this detention facility is considered to be a dam as per DEP 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 one-hundred-year event.
I.
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 shall be acceptable, provided that as much of the site runoff
as practical is directed to the detention facilities. The minimum
three-inch diameter does not apply to the control of the WQv.
J.
Runoff calculations using Soil-Cover-Complex Method.
(1)
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 ordinance may
be taken from NOAA Atlas 14, Volume 2.1, 2004 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
(years)
|
24-Hour Rainfall Depth
(inches)
| |
---|---|---|
1
|
2.40
| |
2
|
3.00
| |
5
|
3.60
| |
10
|
4.56
| |
25
|
5.52
| |
50
|
6.48
| |
100
|
7.44
|
K.
Runoff calculations using the Rational Method shall
use rainfall intensities consistent with appropriate times of concentration
and return periods and NOAA Atlas 14, Volume 2.1, 2004 or the Intensity-Duration-Frequency
Curves as presented in Appendix C.
L.
Runoff curve numbers (CN's) to be used in the Soil-Cover-Complex
Method shall be based upon the matrix presented in Appendix C.
M.
Runoff coefficients for use in the Rational Method
shall be based upon the table presented in Appendix C.
N.
All time of concentration calculations shall use a
segmental approach which may include one or all of the flow types
below:
(1)
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.
(2)
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.
(3)
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 C.
(4)
Pipe flow travel times shall be determined from velocities
calculated using the Manning Equation assuming full flow and the Manning
'n' values from Appendix C.
O.
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 postdevelopment 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.
P.
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 C or other
appropriate standard engineering 'n' value resources. Pipe capacities
shall be determined by methods acceptable to the municipality.
Q.
The Pennsylvania DEP, 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 ordinance may not
be the same criteria that are used in the permitting of dams under
the Dam Safety Program.