[Ord. 2005-5, 7/14/2005, § 301; as amended by Ord. No. 2020-02, 1/6/2020]
1. For all regulated activities, unless preparation of an SWM Site Plan is specifically exempt in §
17-106:
A. Preparation
and implementation of an approved SWM Site Plan is required.
B. No regulated
activities shall commence until the municipality issues written approval
of an SWM Site Plan, which demonstrates compliance with the requirements
of this chapter.
2. SWM Site Plans approved by the municipality, in accordance with §
17-408, shall be on site throughout the duration of the regulated activity.
3. The municipality
may, after consultation with DEP, approve measures for meeting state
water quality requirements other than those in this chapter, provided
that they meet the minimum requirements of, and do not conflict with,
state law, including but not limited to the Clean Streams Law.
4. For all
regulated earth disturbance activities, erosion and sediment control
BMPs shall be designed, implemented, operated, and maintained during
the earth disturbance activities (e.g., during construction) to meet
the purposes and requirements of this chapter and to meet all requirements
under Title 25 of the Pennsylvania Code and the Clean Streams Law.
Various BMPs and their design standards are listed in the Erosion
and Sediment Pollution Control Manual (E&S Manual), No. 363-2134-008,
as amended and updated.
5. Impervious
areas.
A. The measurement
of impervious areas shall include all of the impervious areas in the
total proposed development even if the development is to take places
in stages.
B. For development
taking place in stages, the entire development plan must be used in
determining conformance with this chapter.
C. For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter; except that the volume controls in §
17-308 and the peak rate controls of §
17-305 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
6. 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 chapter.
7. All regulated
activities shall include such measures as necessary to:
A. Protect
health, safety, and property.
B. Meet
the water quality goals of this chapter by implementing measures to:
(1) Minimize disturbance to floodplains, wetlands, and wooded areas.
(2) Maintain or extend riparian buffers.
(3) Avoid erosive flow conditions in natural flow pathways.
(4) Minimize thermal impacts to the waters of this commonwealth.
(5) Disconnect impervious surfaces by directing runoff to pervious areas,
wherever possible.
C. Incorporate
methods described in the Pennsylvania Stormwater Best Management Practices
Manual (BMP Manual). If methods other than green infrastructure and
LID methods are proposed to achieve volume and rate controls required
under this chapter, the SWM Site Plan must include a detailed justification
demonstrating that the use of LID and green infrastructure is not
practicable.
8. The design
of all facilities over karst shall include an evaluation of measures
to minimize adverse effects.
9. Infiltration
BMPs should be spread out, made as shallow as practicable, and located
to maximize use of natural on-site infiltration features while still
meeting the other requirements of this chapter.
10. Normally
dry, open top, storage facilities should completely drain both the
volume control and rate control capacities over a period of time not
less than 24 hours and not more than 72 hours from the end of the
design storm.
11. The
design storm volumes to be used in the analysis of peak rates of discharge
should be obtained from the latest version of the Precipitation -
Frequency Atlas of the United States, National Oceanic and Atmospheric
Administration (NOAA), National Weather Service, Hydrometeorological
Design Studies Center, Silver Spring, Maryland. NOAA's Atlas 14 can
be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
12. For
all regulated activities, SWM BMPs shall be designed, implemented,
operated, and maintained to meet the purposes and requirements of
this chapter and to meet all requirements under Title 25 of the Pennsylvania
Code, the Clean Streams Law, and the Storm Water Management Act.
13. Various
BMPs and their design standards are listed in the BMP Manual.
14. Where a site is traversed by watercourses other than those for which a one-hundred-year floodplain is defined by the municipality, there shall be provided drainage easements conforming substantially with the line of such watercourses. The width of any easement shall be adequate to provide for unimpeded flow of storm runoff based on calculations made in conformance with §
17-307 for the one-hundred-year return period runoff and to provide a freeboard allowance of 1/2 foot above the design water surface level. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations which may adversely affect the flow of stormwater within any portion of the easement. Also, periodic maintenance of the easement to ensure proper runoff conveyance shall be required. Watercourses for which the one-hundred-year floodplain is formally defined are subject to the applicable municipal floodplain regulations.
15. 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.
16. Techniques described in Appendix F (Low-Impact Development) of this
chapter are encouraged because they reduce the costs of complying
with the requirements of this chapter and the state water quality
requirements.*
17. Infiltration for stormwater management is encouraged where soils
and geology permit, consistent with the provisions of this chapter
and, where appropriate, the Recommendation Chart for Infiltration
Stormwater Management BMPs in Carbonate Bedrock in Appendix D. Infiltration is encouraged for capturing and treating the water quality volume (as calculated in §
17-304), any part of the water quality volume or for otherwise meeting the purposes of this chapter.
[Ord. 2005-5, 7/14/2005, § 302]
1. The following permit requirements apply to certain regulated and
earth disturbance activities and must be met prior to commencement
of regulated and earth disturbance activities, as applicable:
A. All regulated and earth disturbance activities subject to permit
requirements by DEP under regulations at 25 Pa. Code Chapter 102.
B. Work within natural drainageways subject to permit by DEP under 25
Pa. Code Chapter 102.
C. Any stormwater management facility that would be located in or adjacent
to surface waters of the commonwealth, including wetlands, subject
to permit by DEP under 25 Pa. Code Chapter 105.
D. Any stormwater management facility that would be located on a state
highway right-of-way or require access from a state highway shall
be subject to approval by the Pennsylvania Department of Transportation
(PennDOT).
E. Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area, and any facility which
may constitute a dam subject to permit by DEP under 25 Pa. Code Chapter
105.
[Ord. 2005-5, 7/14/2005, § 303]
1. No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of an erosion and
sediment control plan for construction activities. Written approval
by DEP or a delegated county conservation district shall satisfy this
requirement.
2. A written erosion and sediment control plan is required by DEP regulations
for any earth disturbance activity of 5,000 square feet or more under
25 Pa. Code § 102.4(b).
[Amended by Ord. No. 2021-05, 5/6/2021]
3. A DEP NPDES stormwater discharges associated with construction activities
permit is required for regulated earth disturbance activities under
Pa. Code Chapter 92.
4. Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate DEP regional office or county conservation
district must be provided to the municipality before the commencement
of an earth disturbance activity.
5. A copy of the erosion and sediment control plan and any permit, as
required by DEP regulations, shall be available at the project site
at all times.
[Ord. 2005-5, 7/14/2005, § 304]
1. No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of a plan which
demonstrates compliance with this chapter.
[Amended by Ord. No. 2020-02, 1/6/2020]
2. The water quality volume (WQv) shall be captured and treated. The
WQv shall be calculated two ways.
A. First, WQv shall be calculated using the following formula:
Where
|
|
WQv
|
=
|
water quality volume in acre-feet
|
|
c
|
=
|
Rational Method post-development runoff coefficient for the
2-year storm
|
|
P
|
=
|
1.25 inches
|
|
A
|
=
|
Area in acres of proposed regulated activity
|
B. Second, the WQv shall be calculated as the difference in runoff volume
from predevelopment to post-development for the two-year return period
storm. The effect of closed depressions on the site shall be considered
in this calculation. The larger of these two calculated volumes shall
be used as the WQv to be captured and treated, except that in no case
shall the WQv be permitted to exceed 1.25 inches of runoff over the
site area.
3. The WQv shall be calculated for each post-development drainage direction
on a site for sizing BMPs. Site areas having no impervious cover and
no proposed disturbance during development may be excluded from the
WQv calculations and do not require treatment.
4. If an applicant is proposing to use a wet pond, constructed wetland
or other BMP that ponds water on the land surface and may receive
direct sunlight, the discharge from that BMP must be treated by infiltration,
a vegetated buffer, filter strip, bioretention, vegetated swale or
other BMP that provides a thermal benefit to protect the waters of
the Little Lehigh Creek and Jordan Creek from thermal impacts.
[Amended by Ord. No. 2020-02, 1/6/2020]
5. Any stormwater runoff from the site as a result of the regulated activities must either be treated with infiltration or two acceptable BMPs such as those listed in Section 14 of §
17-304
6. Infiltration BMPs shall not be constructed on fill.
7. The applicant shall document the bedrock type(s) present on the site
from published sources. Any apparent boundaries between carbonate
and noncarbonate bedrock shall be verified through more detailed site
evaluations by a qualified geotechnical professional.
8. For each proposed regulated activity in the watershed, the applicant
shall conduct a preliminary site investigation on the portion of the
site that is judged to be the best candidate hydrogeologically for
possible infiltration, including gathering data from published sources,
a field inspection of the site, a minimum of one test pit and a minimum
of two percolation tests, as outlined in Appendix G. This investigation will determine depth to bedrock, depth
to the seasonal high-water table, soil permeability and location of
special geologic features, if applicable. The location(s) of special
geologic features shall be verified by a qualified geotechnical professional.
The requirements of this section are not required for the carbonate
areas shown on the Upper Macungie Township Carbonate Overlay Map if
no infiltration is proposed.
9. For entirely noncarbonate sites, the WQv shall be infiltrated unless the applicant demonstrates that it is infeasible to infiltrate the WQv for reasons of seasonal high-water table, permeability rate, soil depth or isolation distances; or except as provided in Subsection
20 of this §
17-304. The preliminary site investigation described in Subsection
8 of this §
17-304 shall continue on different areas of the site until a suitable infiltration location is found or the entire site is determined to be infeasible for infiltration. For proposed infiltration areas, the additional site investigation and testing as outlined in Appendix G shall be completed. The municipality may determine infiltration to be infeasible if there are known existing conditions or problems that may be worsened by the use of infiltration.
A. The following conditions are suitable for infiltration in noncarbonate
areas:
(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. (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 greater than or equal to 0.5 inches/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)
Ten feet downgradient or 100 feet upgradient from building foundations.
(c)
Fifty feet from septic system drainfields.
(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 wells, foundations and
drainfields on neighboring properties will be met.
B. If it is not feasible to infiltrate the full WQv, the applicant shall
infiltrate that portion of the WQv that is feasible based on the site
characteristics.
10. In entirely carbonate areas, if infiltration is proposed, in addition to the testing required in Subsection
8 of this §
17-304, the preliminary site investigation shall include an assessment of the remainder of the site for possible infiltration based on required isolation distances from special geologic features and the likely soil depth and permeability based on published data or other site data available. Where infiltration BMPs are proposed, 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 §
17-307, 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 to determine if the site is recommended for infiltration. If at any point in the preliminary site investigation the data (e.g., location of Karst features on the site or the published soils data for the site) indicates that the entire site will not be recommended for infiltration based on the ordinance standards, then no further investigation is required.
A. In addition to the recommendation from Appendix D, the following
conditions are required for infiltration in carbonate areas:
(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. (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 greater than or equal to 0.5 inches/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)
Ten feet downgradient or 100 feet upgradient from building foundations.
(c)
Fifty feet from septic system drainfields.
(d)
One hundred feet from the property line unless documentation
is provided to show that all setbacks from wells, foundations and
drainfields on neighboring properties will be met.
B. Applicants 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. If infiltration is not proposed, the WQv shall be treated by two acceptable BMPs, as specified in Subsection
15 in §
17-304.
11. 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 Chapter to control runoff for the whole site through
infiltration. If that proves infeasible, the applicant shall perform
the preliminary site investigation for the carbonate area to determine
the appropriate design strategy. 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.
12. If infiltration BMPs are proposed in carbonate areas, the post-development
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.
13. Site areas proposed for infiltration shall be protected from disturbance
and compaction except as necessary for construction of infiltration
BMPs.
14. If infiltration of the entire WQv is not proposed, the remainder
of the WQv shall be treated by two acceptable BMPs in series for each
discharge location. Sheet flow draining across a pervious area can
be considered as one BMP. Sheet flow across impervious areas and concentrated
flow shall flow through two BMPs. If sheet flow from an impervious
area is to be drained across a pervious area as one BMP, the length
of the pervious area must be equal to or greater than the length of
impervious area. In no case, may the same BMP be employed consecutively
to meet this requirement. Acceptable BMPs are listed below along with
the recommended reference for design.
Best Management Practice
|
Design Reference
|
---|
Bioretention
|
Low-Impact Development Design Strategies, Prince George's
County, Md., June 19992
|
Capture/reuse1
|
Texas Guide to Rainwater Harvesting, 2nd Edition. Texas Water
Development Board, Center for Maximum Potential Building Systems,
19973
|
Constructed wetlands
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment4
|
Minimum disturbance/minimum maintenance practices
|
Conservation Design for Stormwater Management. Delaware Dept.
of Natural Resources and Brandywine Conservancy, September 19975
|
Oil/water separators
|
Georgia Stormwater Management Manual Volume 2 Technical Handbook,
August 20016
|
Sediment traps/catch basin sumps
|
U.S. Environmental Protection Agency's Post-Construction
Stormwater Management in New Development & Redevelopment BMP Fact
Sheet for "Catch Basins/Catch Basin Insert"7
|
Significant reduction of existing impervious cover
|
N/A
|
Stormwater filters (sand, peat, compost, etc.)
|
Design of Stormwater Filtering Systems. Claytor, R. and Schueler,
T., Center for Watershed Protection, December 19968
|
Trash/debris collectors in catch basins
|
Pennsylvania Handbook of BMPs for Developing Areas9 or Latest Pennsylvania Department of Environmental
Protection Manual
|
Vegetated buffers/filter strips
|
Pennsylvania Handbook of BMPs for Developing Areas9 or Latest Pennsylvania DEP Manual
|
Vegetated roofs
|
Roof Gardens: History, Design, and Construction. Osmundson,
T., W.W. Norton & Co., 199810
|
Vegetated swales/filter strips
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment4
|
Water quality inserts for inlets
|
Pennsylvania Handbook of BMPs for Developing Areas9 or Latest Pennsylvania DEP Manual
|
Wet detention ponds
|
Pennsylvania Handbook of BMPs for Developing Areas9 or Latest Pennsylvania DEP Manual
|
NOTES:
|
---|
1
|
If this BMP is used to treat the entire WQv then only
one BMP is required because of this BMPs superior water quality performance.
|
2
|
Available at www.co.pg.md.us/Government/AgencyIndex/DER/PPD/LID/LiDNatl.pdf
as of January 2004.
|
3
|
Available at www.twdb.state.tx.us/publications/reports/RainHarv.pdf
as of January 2004.
|
4
|
Available at www.mde.state.md.us as of January 2004.
|
5
|
Available at www.dnrec.state.de.us/dnrec2000/Divisions/Soil/Stormwater/Apps/Design
ManualRequest.htm as of January 2004.
|
6
|
Available at www.georgiastormwater.com as of January
2004.
|
7
|
Available at http://cfpub.epa.gov/npdes/stormwater/menuofbmps/post_7.cfm
as of January 2004.
|
8
|
Available from the Center for Watershed Protection
(www.cwp.org) as of January 2004.
|
9
|
Available at www.dep.state.pa.us (keyword Stormwater)
as of January 2004.
|
10
|
Available at www.wwnorton.com as of January 2004.
|
15. 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 Subsection
14 above of §
17-304.
A. 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 facilities1
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Fleet storage yards and vehicle cleaning facilities1
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Facilities that store or generate regulated substances1
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Marinas1
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
Certain industrial uses (listed under NPDES)1
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
NOTE:
|
---|
1
|
Regulated under the NPDES stormwater program
|
B. Design references for the pretreatment methods, as necessary, are
listed below. The applicant may demonstrate that due to the site characteristics
the land use is not a hot spot land use.
Pretreatment Method
|
Design Reference
|
---|
Constructed wetlands
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment1
|
Diversion of stormwater away from potential contamination areas
|
Pennsylvania Handbook of BMPs for Developing Areas2 or Latest PA Dept. of Environmental Protection Manual
|
Oil/water separators
|
Georgia Stormwater Management Manual Volume 2 Technical Handbook,
August 20013
|
Sediment traps/catch basin sumps
|
US Environmental Protection Agency's Post-Construction
Stormwater Management in New Development & Redevelopment BMP Fact
Sheet for "Catch Basins/Catch Basin Insert"4
|
Stormwater collection and reuse (especially for irrigation)
|
Texas Guide to Rainwater Harvesting, 2nd Edition, Texas Water
Development Board, Center for Maximum Potential Building Systems,
19975
|
Stormwater filters (sand, peat, compost, etc.)
|
Design of Stormwater Filtering Systems. Claytor, R. and Schueler,
T., Center for Watershed Protection, December 19966
|
Trash/debris collectors in catch basins
|
Pennsylvania Handbook of BMPs for Developing Areas2 or Latest PA Dept. of Environmental Protection Manual
|
Vegetated swales/filter strips
|
2000 Maryland Stormwater Design Manual, Maryland Department
of the Environment1
|
Water quality inserts for inlets
|
Pennsylvania Handbook of BMPs for Developing Areas2 or Latest PA Dept. of Environmental Protection Manual
|
NOTES:
|
---|
1
|
Available at www.mde.state.md.us as of January 2004.
|
2
|
Available at www.dep.state.pa.us (key word Stormwater) as of
January 2004.
|
3
|
Available at www.georgiastormwater.com as of January 2004.
|
4
|
Available at http://cfpub.epa.gov/npdes/stormwater/menuofbmps/post_7.cfm
as of January 2004.
|
5
|
Available at www.twdb.state.tx.us/publications/reports/RainHarv.pdf
as of January 2004.
|
6
|
Available from the Center for Watershed Protection (www.cwp.org)
as of January 2004.
|
16. The use of infiltration BMPs is prohibited on hot spot land use areas.
17. 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.
18. Applicants shall request, in writing, public water suppliers to provide the Zone I wellhead protection radius, as calculated by the method outlined in the Pennsylvania Department of Environmental Protection Wellhead Protection Regulations, for any public water supply well within 400 feet of the site. In addition to the setback distances specified in Subsections
9 and
10 of §
17-304, 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.
19. 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 stream bank destabilization,
to satisfy state water quality requirements.
20. The municipality may, after consultation with 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.
[Ord. 2005-5, 7/14/2005, § 305]
1. Mapping of Stormwater Management Districts. To implement the provisions
of the Little Lehigh Creek and Jordan Creek Watersheds Stormwater
Management Plans, the municipality is hereby divided into stormwater
management districts consistent with the Little Lehigh Creek Release
Rate Map and Jordan Creek Release Rate Map presented in the plan.
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 maps at a reduced scale is included
in Appendix A for general reference.
[Amended by Ord. No. 2020-02, 1/6/2020]
2. Description of Stormwater Management Districts. Two types of stormwater
management districts may be applicable to the municipality, namely
conditional no detention districts and dual release rate districts
as described below.
A. Conditional No Detention Districts. Within these districts, the capacity of the "local" runoff conveyance facilities (as defined in Article 2) must be calculated to determine if adequate capacity exists. For this determination, the developer must calculate peak flows assuming that the site is developed as proposed and that the remainder of the local watershed is in the existing condition. The developer must also calculate peak flows assuming that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified by this Chapter. The larger of the two peak flows calculated will be used in determining if adequate capacity exists. If adequate capacity exists to safely transport runoff from the site to the main channel (as defined in Article 2), these watershed areas may discharge post-development peak runoff without detention facilities. If the capacity calculations show that the "local" runoff conveyance facilities lack adequate capacity, the developer shall either use a one-hundred-percent release rate control or provide increased capacity of downstream elements to convey increased peak flows consistent with Subsection
16 of §
17-306. 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 Subsection
4 of §
17-306. By definition, a storm drainage problem area associated with the "local" runoff conveyance facilities indicates that adequate capacity does not exist.
B. Dual Release Rate Districts. Within this district, the two-year post-development
peak runoff must be controlled to 30% of the predevelopment two-year
runoff peak. Further, the ten-, twenty-five-, and one-hundred-year
post-development peak runoff must be controlled to the stated percentage
of the predevelopment peak. Release rates associated with the five-
through one-hundred-year events vary from 50% to 100%, depending upon
location in the watershed.
[Amended by Ord. No. 2020-02, 1/6/2020]
[Ord. 2005-5, 7/14/2005, § 306]
1. Applicants shall provide a comparative preconstruction and post-construction
stormwater management hydrograph analysis for each direction of discharge
and for the site overall to demonstrate compliance with the provisions
of this Chapter.
2. Any stormwater management controls required by this chapter and subject to a dual release rate criteria shall meet the applicable release rate criteria for each of the two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year return period runoff events consistent with the calculation methodology specified in §
17-307.
[Amended by Ord. No. 2020-02, 1/6/2020]
3. The exact location of the stormwater management district boundaries
as they apply to a given development site shall be determined by mapping
the boundaries using the two-foot topographic contours provided as
part of the 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 upslope to each topographic divide along the path perpendicular
to the contour lines.
4. Any downstream capacity analysis conducted in accordance with this
Chapter shall use the following criteria for determining adequacy
for accepting increased peak flow rates:
A. Natural or man-made channels or swales must be able to convey the
increased runoff associated with a two-year return period event within
their banks at velocities consistent with protection of the channels
from erosion.
B. Natural or man-made channels or swales must be able to convey the
increased twenty-five-year return period runoff without creating any
hazard to persons or property.
C. Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with DEP Chapter 105 regulations (if applicable) and, at minimum,
pass the increased twenty-five-year return period runoff.
5. For a proposed development site located within one release rate category
subarea, the total runoff from the site shall meet the applicable
release rate criteria. For development sites with multiple directions
of runoff discharge, individual drainage directions may be designed
for up to a one-hundred-percent release rate so long as the total
runoff from the site is controlled to the applicable release rate.
6. For a proposed development site located within two or more release
category subareas, the peak discharge rate from any subarea shall
be the predevelopment peak discharge for that subarea multiplied by
the applicable release rate. The calculated peak discharges shall
apply regardless of whether the grading plan changes the drainage
area by subarea. An exception to the above may be granted if discharges
from multiple subareas recombine in proximity to the site. In this
case, peak discharge in any direction may be a one-hundred-percent
release rate, provided that the overall site discharge meets the weighted
average release rate.
7. For a proposed development site located partially within a release
rate category subarea and partially within a 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.
8. No portion of a site may be regraded between the Little Lehigh Creek
Watershed or Jordan Creek Watershed and any adjacent watershed except
as part of a "no harm" or hardship waiver procedure.
[Amended by Ord. No. 2020-02, 1/6/2020]
9. Within a release rate category area, for a proposed development site which has areas which drain to a closed depression(s), the design release from the site will be the lesser of: (a) the applicable release rate flow assuming no closed depression(s); or (b) the existing peak flow actually leaving the site. In cases where (b) would result in an unreasonably small design release, the design discharge of less than or equal to the release rate will be determined by the available downstream conveyance capacity to the main channel calculated using Subsection
4 of §
17-306 and the minimum orifice criteria.
10. Off-site areas which drain through a proposed development site are not subject to release rate criteria when determining allowable peak runoff rates. However, on-site drainage facilities shall be designed to safely convey off-site flows through the development site using the capacity criteria in Subsection
4 of §
17-306 and the detention criteria in §
17-307.
11. For development sites proposed to take place in phases, all detention
ponds shall be designed to meet the applicable release rate(s) applied
to all site areas tributary to the proposed pond discharge direction.
All site tributary areas will be assumed as developed, regardless
of whether all site tributary acres are proposed for development at
that time. An exception shall be sites with multiple detention ponds
in series where only the downstream pond must be designed to the stated
release rate.
12. Where the site area to be impacted by a proposed development activity
differs significantly from the total site area, only the proposed
impact area shall be subject to the release rate criteria. The impact
area includes any proposed cover or grading changes.
13. Development proposals which, through groundwater recharge or other
means, do not increase either the rate or volume of runoff discharged
from the site compared to predevelopment are not subject to the release
rate provisions of this Chapter.
14. "No Harm" Water Quantity Option. For any proposed development site not located in a 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 Lehigh River. Proof of "no harm" must be shown using the capacity criteria specified in Subsection
4 of §
17-306, if downstream capacity analysis is a part of the "no harm" justification.
A. Attempts to prove no harm based upon downstream peak flow versus
capacity analysis shall be governed by the following provisions:
(1)
The peak flow values to be used for downstream areas for the
design return period storms (two-, five-, ten-, twenty-five-, and
one-hundred-year) shall be the values from the calibrated watershed
model for the Little Lehigh and Jordan Creeks or as calculated by
an applicant using an alternate method acceptable to the municipality.
The flow values from the watershed model would be supplied to the
developer by the municipality upon request.
[Amended by Ord. No. 2020-02, 1/6/2020]
(2)
Any available capacity in the downstream conveyance system as
documented by a developer may be used by the developer only in proportion
to his development site acreage relative to the total upstream undeveloped
acreage from the identified capacity (i.e., if his site is 10% of
the upstream undeveloped acreage, he may use up to 10% of the documented
downstream available capacity).
(3)
Developer-proposed runoff controls which would generate increased peak flow rates at storm drainage problem areas would, by definition, be precluded from successful attempts to prove no harm, except in conjunction with proposed capacity improvements for the problem areas consistent with Subsection
16 of §
17-306.
B. Any no harm justifications shall be submitted by the developer as
part of the drainage plan submission per Article 4.
15. Regional Detention Alternatives. For certain areas within the study
area, it may be more cost-effective to provide one control facility
for more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives are the responsibility of
prospective developers. The design of any regional control basins
must incorporate reasonable development of the entire upstream watershed.
The peak outflow of a regional basin would be determined based on
the required release rate at the point of discharge.
16. Capacity Improvements.
A. In certain instances, primarily within the 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 Subsection
4 of §
17-306. All new development in the entire subarea(s) within which the proposed development site is located shall be assumed to implement the developer's proposed discharge control, if any.
B. Capacity improvements may also be provided as necessary to implement
any regional detention alternatives or to implement a modified no
harm option which proposes specific capacity improvements to provide
that a less stringent discharge control would not create any harm
downstream.
[Ord. 2005-5, 7/14/2005, § 307]
1. Stormwater runoff from all development sites shall be calculated
using either the Rational Method or the Soil-Cover-Complex methodology.
2. Infiltration BMP loading rate percentages in the Recommendation Chart
for Infiltration Stormwater Management BMPs in Carbonate Bedrock in
Appendix D shall be calculated as follows:
A. The area tributary to the infiltration BMP shall be weighted as follows:
(1)
All disturbed areas to be made impervious: weight at 100%.
(2)
All disturbed areas to be made pervious: weight at 50%.
(3)
All undisturbed pervious areas: weight at 0%.
(4)
All existing impervious areas: weight at 100%.
3. Soil thickness is to be measured from the bottom of any proposed
infiltration system.
A. 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 follows:
Permeability Range1
(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:
|
---|
1
|
If the permeability rate falls on a break between two thickness
factors, the smaller thickness factor shall be used.
|
B. Sites with soil permeability greater than 12 inches/hour or less
than 0.5 inch/hour are not recommended for infiltration.
4. The design of any detention basin intended to meet the requirements
of this Chapter shall be verified by routing the design storm hydrograph
through the proposed basin using the Storage Indication Method or
other methodology demonstrated to be more appropriate. For basins
designed using the Rational Method technique, the design hydrograph
for routing shall be either the universal rational hydrograph or the
modified rational method trapezoidal hydrograph which maximizes detention
volume. Use of the modified rational hydrograph shall be consistent
with the procedure described in Section "PIPE.RAT" of the Users'
Manual for the Penn State Urban Hydrograph Method (1987).
5. BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall be routed using the Storage Indication Method.
6. 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.
7. 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.
8. All stormwater detention facilities shall provide a minimum 1.0 foot
freeboard above the maximum pool elevation associated with the two-
through twenty-five-year runoff events. A one-half-foot freeboard
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 one-half-foot freeboard measured to the top of
basin. The freeboard criteria shall be met considering any off-site
areas tributary to the basin as developed, as applicable. 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.
9. 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.
10. Runoff calculations using the Soil-Cover-Complex Method shall use
the Natural Resources Conservation Service Type II twenty-four-hour
rainfall distribution. The twenty-four-hour rainfall depths for the
various return periods to be used consistent with this chapter shall
be taken from the latest version of the Precipitation - Frequency
Atlas of the United States, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland. NOAA's Atlas 145 can be accessed
at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
[Amended by Ord. No. 2020-02, 1/6/2020]
A. A graphical and tabular presentation of the Type II twenty-four-hour
distribution is included in Appendix C.
11. Runoff calculations using the Rational Method shall use rainfall
intensities consistent with appropriate times of concentration and
return periods and the Intensity-Duration-Frequency Curves as presented
in Appendix C.
12. Runoff Curve Numbers (CNs) to be used in the Soil-Cover-Complex Method
shall be based upon the matrix presented in Appendix C.
13. Runoff coefficients for use in the Rational Method shall be based
upon the table presented in Appendix C.
14. All time of concentration calculations shall use a segmental approach
which may include one or all of the flow types below:
A. Sheet flow (overland flow) calculations shall use either the NRCS
average velocity chart (Figure 3-1, Technical Release-55, 1975) or
the modified kinematic wave travel time equation (equation 3-3, NRCS
TR-55, June 1986). If using the modified kinematic wave travel time
equation, the sheet flow length shall be limited to 50 feet for designs
using the Rational Method and limited to 150 feet for designs using
the Soil-Cover-Complex Method.
B. Shallow concentrated flow travel times shall be determined from the
watercourse slope, type of surface and the velocity from Figure 3-1
of TR-55, June 1986.
C. Open channel flow travel times shall be determined from velocities
calculated by the Manning Equation. Bankful flows shall be used for
determining velocities. Manning 'n' values shall be based
on the table presented in Appendix C.
D. Pipe flow travel times shall be determined from velocities calculated
using the Manning Equation assuming full flow and the Manning 'n'
values from Appendix C.
15. If using the Rational Method, all predevelopment calculations for
a given discharge direction shall be based on a common time of concentration
considering both on-site and any off-site drainage areas. If using
the Rational Method, all post-development calculations for a given
discharge direction shall be based on a common time of concentration
considering both on-site and any off-site drainage areas.
16. 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.
17. 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 Chapter may not be the same
criteria that are used in the permitting of dams under the Dam Safety
Program.
[Added by Ord. No. 2020-02, 1/6/2020]
The green infrastructure and low-impact development practices
provided in the Pennsylvania Department of Environmental Protection's
Pennsylvania Stormwater Best Management Practices Manual (December
2006), as amended and updated, shall be utilized for all regulated
activities wherever possible. Water volume controls shall be implemented
using the Design Storm Method in Subsection 1 or the Simplified Method
in Subsection 2 below. For regulated activity areas equal to or less
than one acre that do not require hydrologic routing to design the
stormwater facilities, this chapter 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.
1. The Design
Storm Method [CG-1 in the Pennsylvania Department of Environmental
Protection's Pennsylvania Stormwater Best Management Practices Manual
(December 2006), as amended and updated] is applicable to any size
of regulated activity. This method requires detailed modeling based
on site conditions.
A. Do not
increase the post-development total runoff volume for all storms equal
to or less than the two-year, twenty-four-hour duration precipitation.
B. For modeling
purposes:
(1) Existing (predevelopment) nonforested pervious areas must be considered
meadow in good condition.
(2) Twenty percent of existing impervious area, when present, shall be
considered meadow in good condition in the model for existing conditions.
2. The Simplified
Method [CG-2 in the Pennsylvania Department of Environmental Protection's
Pennsylvania Stormwater Best Management Practices Manual (December
2006), as amended and updated] provided below is independent of site
conditions and should be used if the Design Storm Method is not followed.
This method is not applicable to regulated activities greater than
one acre or for projects that require design of stormwater storage
facilities. For new impervious surfaces:
A. Stormwater
facilities shall capture at least the first two inches of runoff from
all new impervious surfaces.
B. At least
the first one inch of runoff from new impervious surfaces shall be
permanently removed from the runoff flow, i.e., it shall not be released
into the surface waters of this commonwealth. Removal options include
reuse, evaporation, transpiration, and infiltration.
C. Wherever
possible, infiltration facilities should be designed to accommodate
infiltration of the entire permanently removed runoff; however, in
all cases at least the first 0.5 inch of the permanently removed runoff
should be infiltrated.
D. This method is exempt from the requirements of §
17-305.
[Added by Ord. No. 2020-02, 1/6/2020]
1. In order
to protect and improve water quality, a riparian buffer easement shall
be created and recorded as part of any subdivision or land development
that encompasses a riparian buffer.
2. Except
as required by Chapter 102, the riparian buffer easement shall be measured to be the
greater of the limit of the 100-year floodplain or a minimum of 35
feet from the top of the streambank (on each side).
3. Minimum
Management Requirements for Riparian Buffers.
A. Existing
native vegetation shall be protected and maintained within the riparian
buffer easement.
B. Whenever
practicable, invasive vegetation shall be actively removed and the
riparian buffer easement shall be planted with native trees, shrubs
and other vegetation to create a diverse native plant community appropriate
to the intended ecological context of the site.
4. The riparian
buffer easement shall be enforceable by the municipality and shall
be recorded in the appropriate County Recorder of Deeds Office, so
that it shall run with the land and shall limit the use of the property
located therein. The easement shall allow for the continued private
ownership and shall count toward the minimum lot area required by
Zoning, unless otherwise specified in the municipal Zoning Ordinance.
5. Any permitted
use within the riparian buffer easement shall be conducted in a manner
that will maintain the extent of the existing 100-year floodplain,
improve or maintain the stream stability, and preserve and protect
the ecological function of the floodplain.
6. The following
conditions shall apply when public and/or private recreation trails
are permitted within riparian buffers:
A. Trails
shall be for nonmotorized use only.
B. Trails
shall be designed to have the least impact on native plant species
and other sensitive environmental features.
7. Septic
drainfields and sewage disposal systems shall not be permitted within
the riparian buffer easement and shall comply with setback requirements
established under 25 Pa. Code Chapter 73.