A.
For all regulated activities, unless preparation of a drainage plan is specifically exempted in § 220-35:
B.
Drainage plans approved by the Township, in accordance with § 220-38, shall be on-site throughout the duration of the regulated activity.
C.
The Township may, after consultation with DEP, approve measures for
meeting the state water quality requirements other than those in this
chapter, provided that they meet the minimum requirements of, and
do not conflict with, state law including, but not limited to, the
Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
D.
For all regulated earth disturbance activities, erosion, and sediment
control BMPs shall be designed, implemented, operated, and maintained
during the regulated earth disturbance activities (e.g., during construction)
to meet the purposes and requirements of this chapter and to meet
all requirements under Title 25 of the Pennsylvania Code and the Clean
Streams Law. Various BMPs and their design standards are listed in
the Erosion and Sediment Pollution Control Program Manual (E&S
Manual[2]), No. 363-2134-008, as amended and updated.
E.
Impervious areas.
(1)
The measurement of impervious areas shall include all of the impervious
areas in the total proposed development even if development is to
take place in stages;
(2)
For development taking place in stages, the entire development plan
must be used in determining conformance with this chapter; and
(3)
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 § 220-41 and the peak rate controls of § 220-42 do not need to be retrofitted to existing impervious areas that are not being altered by the proposed regulated activity.
F.
Stormwater flows onto adjacent property shall not be created, increased,
or otherwise altered without written notification to the adjacent
property owner(s). Such stormwater flows shall be subject to the requirements
of this chapter. Areas of existing diffused drainage discharge onto
adjacent property shall be managed such that, at minimum, the peak
diffused flow does not increase in the general direction of discharge,
except as otherwise provided in this chapter. If diffused flow is
proposed to be concentrated and discharged onto adjacent property
(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 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 where they are proposed to be concentrated or maintained
as diffused drainage areas.
G.
All regulated activities shall include such measures as necessary
to:
(1)
Protect health, safety, and property; and
(2)
Meet the water quality goals of this chapter by implementing measures
to:
(a)
Minimize disturbance to floodplains, wetlands, and wooded areas;
(b)
Maintain or extend riparian buffers;
(c)
Avoid erosive flow conditions in natural flow pathways;
(d)
Minimize thermal impacts to waters of the commonwealth;
(e)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible; and
(f)
Incorporate methods described in the "Pennsylvania Stormwater
Best Management Practices Manual" (BMP Manual).
H.
The design of all facilities over karst areas shall include an evaluation
of measures to minimize adverse effects.
I.
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.
J.
Normally dry, open top, storage facilities should completely drain
both the volume control and rate control capacities over a period
of time not less than 24 and not more than 72 hours from the end of
the design storm.
K.
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 (NOAA), National Weather Service, Hydrometeorological
Design Studies Center, Silver Spring, Maryland. NOAA's Atlas
14[3] can be accessed at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
L.
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.
N.
Storm drainage system shall be designed to preserve natural watercourses
except as modified by stormwater detention facilities, recharge facilities,
water quality facilities, pipe systems or open channels consistent
with this chapter.
O.
Where a site is traversed by watercourses, swales, ditches, etc., there shall be drainage easements provided 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 post-development storm runoff based on either calculations completed by the developer in conformance with § 220-22 for the 100-year return period runoff, the Bushkill Creek, Fry's Run, Monocacy Creek, and Nancy Run Act 167 100-year return period flows, or Federal Emergency Management Agency (FEMA) 100-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, Fry's Run, Monocacy Creek, and Nancy Run 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 100-year water surface elevations based on HEC-RAS modeling (or other modeling method as approved by the Township). 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 post-development condition. Also, periodic maintenance of the easement to ensure proper runoff conveyance shall be required. Watercourses for which the 100-year floodplain is formally defined by FEMA studies are 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 100-year frequency flood elevation. The 100-year flood elevation to be used to establish the first-floor elevation shall be determined using the greater of the maximum flow rate referenced in FEMA study flows, Act 167 flows, or calculated flows as set forth above.
P.
Any drainage facilities or structures required by this chapter that
are located on state highway rights-of-way shall be subject to approval
by the Pennsylvania Department of Transportation (PENNDOT) and the
Township.
Q.
When it can be shown that, due to topographic conditions, natural
drainage swales on the site cannot adequately provide 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's Equation.
R.
Storm drainage facilities and appurtenances shall be so designed
and provided as to minimize erosion in watercourse channels and at
all points of discharge.
S.
Consideration should be given to the design and use of volume controls
for stormwater management, where geology and soils permit. Areas of
suitable geology for volume controls shall be determined by the Township.
Documentation of the suitability of the soil for volume controls shall
be provided by the applicant. Volume controls shall be acceptable
in areas of suitable geology where the soils are designated as well
drained in the County Soil Survey. Other soils may be acceptable for
use of volume controls based on site-specific soils evaluations provided
by the applicant.
T.
Within areas containing soils identified by the Soil Conservation
Service to be sinkhole prone, detention basins shall be lined with
a material which, after installation, attains a permeability rate
of less than or equal to 1 x 10-7 cm/sec.
U.
Parking lot ponding depth may not exceed two inches in areas of anticipated
pedestrian traffic and six inches in all other areas for a twenty-five-year
frequency storm.
V.
Post-construction BMPs shall be designed, installed, operated, and
maintained to meet the requirements of the Clean Streams Law and implementing
regulations, including the established practices in 25 Pa. Code Chapter
102 and the specifications of this chapter as to prevent accelerated
erosion in watercourse channels and at all points of discharge.
W.
No earth disturbance activities associated with any regulated activities
shall commence until approval by the Township of a plan which demonstrates
compliance with the requirements of this chapter.
X.
Techniques described in Appendix F (Low-Impact Development)[5] of this chapter are encouraged because they reduce the
costs of complying with the requirements of this chapter and the state
water quality requirements.
[5]
Editor's Note: Appendix F is included as an attachment to this chapter.
Y.
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.[6] Infiltration is encouraged for capturing and treating the water quality volume (as calculated in § 220-18), any part of the water quality volume or for otherwise meeting the purposes of this chapter.
[6]
Editor's Note: Appendix D is included as an attachment to this chapter.
Z.
Rates of post-development stormwater runoff (measured in cubic feet
per second) shall not exceed the percentages of the predevelopment
flow rates for any area as mandated by this section. Allowable post-development
percentages shall be as follows:
(1)
For the Bushkill Creek Watershed, as is listed for each individual
stormwater management district as shown on the Watershed Release Rate
Map (Appendix B of this chapter[7]);
[7]
Editor's Note: Appendix B is included as an attachment to this chapter.
(2)
For the Monocacy Creek Watershed, as is listed for each individual
stormwater management district as shown on the Watershed Release Rate
Map (Appendix B of this chapter);
(3)
For the Nancy Run Watershed, as is listed for each individual stormwater
management district as shown on the Watershed Release Rate Map (Appendix
B of this chapter);
(4)
For the Fry's Run Watershed, as is listed for each individual
stormwater management district as shown on the Watershed Release Rate
Map (Appendix B of this chapter); and
(5)
During construction and preparatory earthmoving in all areas of the
Township: 100%.
AA.
Control of runoff from a site shall occur using appropriate means
of detention of the water on the site and/or other approved types
of stormwater management within the requirements of this section.
BB.
Runoff that is detained shall be held and released at a predetermined
controlled rate by appropriately installed devices. The release shall
be in the same manner as the natural or predevelopment means of discharge
from a site (such as point discharge or sheet flow).
CC.
Stormwater runoff shall not be increased or redirected in such a
way that it results in hazards to persons or property or interferes
with the normal movement of vehicles.
DD.
All stormwater management methods are subject to review by the Township
Engineer.
EE.
Stormwater shall be directed away from buildings and on-lot septic
systems.
FF.
All drainage plans shall take into account and provide for existing
flows within the entire watershed.
GG.
The existing points of natural drainage discharge onto adjacent property
shall not be altered nor shall the concentration of water runoff be
increased because of development without the written approval of all
affected landowners.
HH.
No stormwater runoff or natural drainage water shall be so diverted
as to overload existing drainage systems, or create flooding or the
need for additional drainage structures on other private properties
or public lands, without complete approval of provisions being made
by the developer for properly handling such conditions, including
water runoff impoundments, if necessary.
II.
All lots shall be laid out and graded to prevent cross-lot drainage,
to provide positive drainage away from proposed building locations
and any primary or alternate septic system location.
JJ.
An adequate storm sewerage system consisting of inlets and other
underground drainage structures with approved outlets shall be constructed
where the runoff of stormwater and the prevention of erosion cannot
be accomplished satisfactorily by surface drainage facilities, as
determined by the Board of Commissioners based upon the recommendation
of the Township Engineer.
KK.
Outlet locations shall be reviewed by the Township Engineer.
LL.
Sequence of construction. No substantial grading shall occur, and
no building permits shall be issued for any building unless any detention
basin, siltation basin or improved major swale approved to handle
the resulting runoff is in place. Any detention basin shall be seeded
and stabilized and have an installed outlet structure prior to the
construction of any streets or buildings within that drainage basin.
B.
Agricultural activity is exempt from the drainage plan preparation
requirements of this chapter, provided the activities are performed
according to the requirements of 25 Pa. Code Chapter 102.
C.
Forest management and timber operations are exempt from the drainage
plan preparation requirements of this chapter, provided the activities
are performed according to the requirements of 25 Pa. Code Chapter
102.
E.
The Township may deny or revoke any exemption pursuant to this section
at any time for any project that the Township believes may pose a
threat to public health and safety or the environment.
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 and Chapter 105.
C.
Any stormwater management facility that would be located in or adjacent
to surface waters of the commonwealth, including wetlands, subject
to permit by DEP under 25 Pa. Code Chapter 105.
D.
Any stormwater management facility that would be located on a state
highway right-of-way or require access from a state highway shall
be subject to approval by the 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.
A.
No regulated earth disturbance activities within the Township shall
commence until approval by the Township of an erosion and sediment
control plan for construction activities. Written approval by 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
25 Pa. Code § 102.4(b) and must be approved by the Conservation
District per the Memorandum of Understanding between the Township
and the Conservation District (as applicable).
C.
No regulated earth disturbance activities within the Township shall
commence until erosion and sedimentation control facilities are in
place.
E.
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 Township before the commencement
of earth disturbance activity.
F.
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 Township shall
commence until approval by the Township of a drainage plan which demonstrates
compliance with this chapter. This chapter provides standards to meet
NPDES permit requirements associated with construction activities
and MS4 permit requirements.
B.
The water quality volume (WQv) shall be captured and treated. The
WQv shall be calculated two ways.
(1)
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
two-year storm
|
|
P
|
=
|
1.25 inches
|
|
A
|
=
|
Area in acres of proposed regulated activity
|
(2)
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. 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 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.
D.
If an applicant is proposing to use a dry extended detention basin,
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,
Fry's Run, and Monocacy Creek watersheds 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 Subsection O, 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 chapter.
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 geotechnical professional.
H.
For each proposed regulated activity in the watershed where an applicant
intends to use infiltration BMP, the applicant shall conduct a preliminary
site investigation, 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. This investigation may
be done by a certified Sewage Enforcement Officer (SEO) except that
the location(s) of special geologic features shall be verified by
a qualified geotechnical professional. Additionally, the Township
Geotechnical Consultant 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 included as an attachment to this chapter.
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/hour
and less than or equal to 12 inches per hour;
(4)
Setback distances or buffers.
(a)
Setback distances or buffers as follows:
[1]
One hundred feet from water supply wells;
[2]
Fifteen feet downgradient or 100 feet upgradient from building
foundations; except for residential development where the required
setback is 15 feet downgradient or 40 feet upgradient from building
foundations;
[3]
Fifty feet from septic system drainfields; except for residential
development where the required setback is 25 feet from septic system
drainfields;
[4]
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; and
[5]
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.
(b)
A reduction of the setbacks noted above may be permitted based
on the Township Geotechnical Consultant review of the proposal.
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 Subsection U.
(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 Subsection H 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 shall be completed;
(3)
If an applicant proposes infiltration, the Township 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 Subsection O; and
(6)
If REv is infiltrated, it may be subtracted from the WQv required
to be captured and treated.
K.
In entirely carbonate areas, where the applicant intends to use infiltration BMPs, the preliminary site investigation described in Subsection H 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 § 220-6, 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[2] to determine if the site is recommended for infiltration. In addition to the recommendation from Appendix D, the conditions listed in Subsection I are required for infiltration in carbonate areas. Applicants are encouraged to infiltrate the REv, as calculated in Subsection J, 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 Subsection O.
[2]
Editor's Note: Appendix D is included as an attachment to this chapter.
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 chapter to meet the requirements for REv for the whole site through infiltration. If that proves infeasible, infiltration in the carbonate area as described in Subsection K or two other non-infiltration BMPs as described in Subsection O 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 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 unless otherwise approved by Township Geotechnical
Consultant and the Township Engineer.
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 the requirement of this section. Acceptable BMPs are listed
below along with the recommended reference for design.
|
Best Management Practice
|
Design Reference NumberC
|
|---|---|
|
BioretentionA
|
4, 5, 11, 16
|
|
Capture/reuseB
|
4, 14
|
|
Constructed wetlands
|
4, 5, 8, 10, 16
|
|
Dry extended detention ponds
|
4, 5, 8, 12, 18
|
|
Minimum disturbance/minimum maintenance practices
|
1, 9
|
|
Significant reduction of existing impervious cover
|
N/A
|
|
Stormwater filtersA (sand, peat,
compost, etc.)
|
4, 5, 10, 16
|
|
Vegetated buffers/filter strips
|
2, 3, 5, 11, 16, 17
|
|
Vegetated roofs
|
4, 13
|
|
Vegetated swalesA
|
2, 3, 5, 11, 16, 17
|
|
Water quality inletsD
|
4, 7, 15, 16, 19
|
|
Wet detention ponds
|
4, 5, 6, 8
|
|
NOTES:
| |
|
A
|
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 chapter.
|
|
B
|
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.
|
|
C
|
See table below.
|
|
D
|
Water quality inlets include such BMPs as oil/water separators,
sediment traps/catch basin sumps, and trash/debris collectors in catch
basins.
|
|
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 George's 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," Lehigh
Valley Planning Commission, Revised 1997.
|
|
13
|
"Roof Gardens History, Design, and Construction," Osmundson,
Theodore. New York: W.W. Norton and 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 and 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 website (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 Subsection O. Acceptable methods of pretreatment are listed below.
|
Hot Spot Land Use
|
Pretreatment Method(s)
|
|---|---|
|
Vehicle maintenance and repair facilities, including auto parts
stores
|
Water quality 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
| |
|
Vehicle fueling stations
|
Water quality inlets
|
|
Spill prevention and response program
| |
|
Storage areas for public works
|
Water quality 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
|
|
Hot Spot Land Use
|
Pretreatment Method(s)
|
|
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.
|
|
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 requirement would not apply.
| |
|
Pretreatment Method
|
Design ReferenceA
|
|
Constructed wetlands
|
4, 5, 8, 10, 16
|
|
Diversion of stormwater away from potential contamination areas
|
4, 11
|
|
Stormwater collection and reuse (especially for irrigation)
|
4, 14
|
|
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:
| |
|
A
|
These numbers refer to the Design Reference Title chart in Subsection O, above.
|
Q.
The use of infiltration BMPs is prohibited on hot spot land use areas
unless otherwise approved by the Township Geotechnical Consultant
and the Township Engineer.
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 DEP wellhead protection regulations, for any public water supply well within 400 feet of the site. In addition to the setback distances specified in Subsection I, 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 stream bank destabilization,
to satisfy state water quality requirements, by controlling the two-year
post-development runoff to a 30% release rate.
U.
The Township 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.
A.
The entire WQv as calculated in § 220-18B of this chapter shall be captured and treated by either direct recharge/subsurface and/or vegetated/surface BMPs.
B.
As much proposed impervious area as practical shall be directed to
water quality BMPs.
C.
Existing impervious area that is not proposed to be treated by direct
recharge/subsurface BMPs should be excluded from all water balance
calculations.
D.
Vegetated/surface BMPs shall be employed "first" for the site to
capture the equivalent of a minimum of 0.38 inch of runoff for each
square foot of impervious area, unless proven not feasible by the
applicant. For proposed impervious cover directed to multiple BMPs,
the vegetated/surface BMP capture volume chart in Appendix C of this
chapter shall be used to determine overall site compliance. Direct
recharge/subsurface BMPs may be used "first" for portions of the impervious
cover provided the overall vegetated/surface BMP "first" standard
is met.
E.
A maximum of 30% of the total annual rainfall for a site may be directly
recharged to groundwater using direct recharge/subsurface BMPs, for
runoff from impervious areas.
(1)
For development sites with greater than 33% proposed impervious cover:
(a)
If all impervious cover is directed to vegetated/surface BMPs
to capture the entire two-year, twenty-four-hour event, the direct
recharge standard is met;
(b)
Up to 33% of the site as impervious cover may be directed to
direct recharge/subsurface BMPs designed to capture the entire two-year,
twenty-four-hour event, provided the overall vegetated/surface BMP
"first" standard is met. All remaining impervious cover shall be directed
to vegetated/surface BMPs designed to capture the remainder of the
WQv; and
(c)
For vegetated/surface and/or direct recharge/subsurface BMPs
designed for runoff from impervious areas designed to capture less
than the entire two-year, twenty-four-hour event, Appendix C[1] of this chapter shall be used to assure that the maximum
direct recharge standard is met.
[1]
Editor's Note: Appendix C is included as an attachment to this chapter.
(2)
The maximum 30% direct recharge standard applies on an overall site
basis, rather than in each drainage direction.
A.
Mapping of stormwater management districts. To implement the provisions
of the Bushkill Creek, Fry's Run, Monocacy Creek, and Nancy Run
watershed stormwater management plans, the Township is hereby divided
into stormwater management districts consistent with the Bushkill
Creek, Fry's Run, Monocacy Creek, and Nancy Run release rate
maps presented in the plan update. The boundaries of the stormwater
management districts are shown on a Stormwater Management Districts
Map which is available for inspection at the Township Municipal Building
at 4225 Easton Avenue, Bethlehem, PA 18020. A copy of this map at
a reduced scale is included in Appendix A[1] of this chapter for general reference.
[1]
Editor's Note: Appendix A is included as an attachment to this chapter.
B.
Release rate districts in the Monocacy Creek Watershed. There are
six single release rate districts that differ in the extent to which
the post-development runoff must be controlled. The release rate districts
are 50%, 60%, 70%, 80%, 90% and 100%. Within a given district, the
post-development peak rate of storm runoff must be controlled to the
stated percentage of the predevelopment peak rate of runoff for each
of the ten-, twenty-five-, fifty- and 100-year return period storms
to protect downstream watershed areas. There is one dual release rate
district. Within this district, the ten-year return period event needs
to meet a 30% release rate, and the two-year and twenty-five-year
and higher return period events need to meet a 100% release rate.
C.
Conditional no detention districts in the Monocacy Creek Watershed.
These watershed areas peak very early with respect to the total watershed
peak flow and contribute very minimal flow to the watershed peak flow.
For that reason, these watershed areas may discharge post-development
peak runoff without detention for the ten- through 100-year return
periods without adversely affecting the total watershed peak flow.
These areas are designated as "conditional" no detention areas because
in certain instances the "local" runoff conveyance facilities, which
transport runoff from the site to the main channel, may not have adequate
capacity to safely transport the peak flows associated with no detention
for a proposed development. In those instances, a 100% release rate
control would have to be provided or, alternately, the capacity deficiency(ies)
would have to be corrected.
D.
Description of stormwater management districts in the Bushkill Creek,
Nancy Run, and Fry's Run watersheds. Two types of stormwater
management districts may be applicable to the Township, namely conditional/provisional
no detention districts and dual release rate districts as described
below.
(1)
Conditional/provisional no detention districts. Within these districts, the capacity of the "local" runoff conveyance facilities (as defined in Article II of this chapter) 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 in 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 II of this chapter), these watershed areas may discharge post-development peak runoff without detention facilities. If the capacity calculations show that the "local" runoff conveyance facilities lack adequate capacity, the developer shall either use a 100% release rate control or provide increased capacity of downstream elements to convey increased peak flows consistent with § 220-21D of this chapter. 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 § 220-21D of this chapter. By definition, a storm drainage problem area associated with the "local" runoff conveyance facilities indicates that adequate capacity does not exist. Sites in these districts are still required to meet all of the water quality requirements in § 220-18B of this chapter.
(2)
Dual release rate districts. Within these districts for the Bushkill
Creek, Nancy Run, and Fry's Run watersheds, the two-year post-development
peak discharge must be controlled to 30% of the predevelopment two-year
runoff peak. Further, the ten-, twenty-five-, fifty- and 100-year
post-development peak runoff must be controlled to the stated percentage
of the predevelopment peak. Release rates associated with the ten-
through 100-year events vary from 50% to 100% depending upon location
in the watershed. (For the Monocacy Creek and Nancy Run watersheds,
the original single release rate districts become dual release rate
districts due to the channel protection standard requiring developments
to meet a two-year 30% release rate.)
A.
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.
B.
Any stormwater management controls required by this chapter and subject to a dual release rate criteria shall meet the applicable release rate criteria for each of the two-, ten-, twenty-five-, fifty-, and 100-year return period runoff events consistent with the calculation methodology specified in § 220-22.
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
chapter 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; and
(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 100% release rate so long as the total runoff from the
site is controlled to the applicable release rate and no increase
in runoff volume is proposed in the 100% release rate direction(s).
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 100% release rate provided
that the overall site discharge meets the weighted average release
rate and no increase in runoff volume is proposed in the 100% release
rate direction(s).
G.
For a proposed development site located partially within a release
rate category subarea and partially within a conditional/provisional
no detention subarea, the size of the predevelopment drainage area
on a site may not be changed post-development to create potentially
adverse conditions on downstream properties except as part of a no
harm or hardship waiver procedure.
H.
For sites straddling major watershed divides (e.g., Monocacy Creek
and Bushkill Creek), runoff volumes shall be managed to prevent diversion
of runoff unless peak flow rate and volume controls are proposed which
limit post-development peak flow rates to the required release rate
criteria and volume discharges to predevelopment levels between watersheds,
as practicable.
I.
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 and
implemented which limit post-development peak flow rate and volume
discharges to predevelopment levels, or all affected downstream property
owners have granted express permission in the form of recorded easements.
J.
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 1) the applicable release rate flow assuming no closed depression(s) or 2) the existing peak flow actually leaving the site. In cases where 2) 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 D and the minimum orifice criteria.
K.
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 D and the detention criteria in § 220-22. In addition to the criteria of Subsection D of this chapter, on-site conveyance systems designed to carry runoff to a detention basin must be able to transport the basin's 100-year tributary flow either in-system, in-gutter, or overland.
L.
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 areas 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.
M.
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.
N.
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.
O.
"No harm" water quantity option.
(1)
For any proposed development site not located in a conditional/provisional 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 or Lehigh river. Proof of no harm must be shown using the capacity criteria specified in Subsection D if downstream capacity analysis is a part of the no harm justification. 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-, fifty- and
100-year) shall be the values from the calibrated Penn State Runoff
Model (PSRM) Model for the Bushkill Creek, Fry's Run, Monocacy
Creek, and Nancy Run or as calculated by an applicant using an alternate
method acceptable to the municipality. The flow values from the PSRM
Model would be supplied to the developer by the 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 their development site acreage relative to the total upstream undeveloped
acreage from the identified capacity (i.e., if their site is 10% of
the upstream undeveloped acreage, they may use up to 10% of the documented
downstream available capacity); and
(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 Subsection Q.
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 based on
the required release rate at the point of discharge.
Q.
Capacity improvements. In certain instances, primarily within the conditional/provisional 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 D. 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 chapter and the NPDES requirements.
S.
In any stormwater management district, the Township reserves the
right to require a more stringent design release rate 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 and erosion problems, inadequate conveyance
capacity, poorly defined or poorly stabilized downstream conveyance
systems or other factors; or for other good cause shown; and supported
by engineering data of the kind and type commonly accepted by the
civil engineering profession in the evaluation and management of stormwater
runoff.
T.
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 100-year return period storm where the system is designed to convey 100-year storm flows to a detention facility. Bridges and culverts along roadways shall be designed to convey the 100-year return period storm. Flows from off-site upstream areas shall be determined in accordance with the procedure identified in § 220-14O.
U.
Release rates need to be met year-round. Designs involving BMPs that
function differently in winter versus nonwinter conditions (e.g.,
capture/reuse with spray irrigation shut off for the winter) must
still meet release rates during the winter.
A.
Stormwater runoff from all development sites shall be calculated
using either the Rational Method or the soil-cover-complex methodology.
B.
At a minimum, the applicant shall prove to the satisfaction of the Township Engineer that during earthmoving, construction or after development, peak stormwater discharge rates will not exceed the allowable release rate(s) for the stormwater management district(s) in which the site is situated when compared with those that occurred prior to any of these activities (see § 220-14Z of this chapter). The following conditions and storm frequencies (considered individually) shall apply, unless any more restrictive requirements of an applicable official stormwater management plan are adopted by DEP and the county pursuant to state Act 167 of 1978, as amended:
C.
Infiltration BMP loading rate percentages in the Recommendation Chart
for Infiltration Stormwater Management BMPs in Carbonate Bedrock in
Appendix D[1] shall be calculated as follows:
|
(Area Tributary to Infiltration BMP)
| |
|---|---|
|
Base area of infiltration BMP
|
*100%
|
|
The area tributary to the infiltration BMP shall be weighted
as follows:
| |
|
All disturbed areas to be made impervious: weight at 100%.
| |
|
All disturbed areas to be made pervious: weight at 50%.
| |
|
All undisturbed pervious areas: weight at 0%.
| |
|
All existing impervious areas: weight at 100%.
|
[1]
Editor's Note: Appendix D is included as an attachment to this chapter.
D.
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 double ring infiltration
percolation testing as described in the BMP Manual), as follows:
|
Permeability Range*
|
Thickness Factor
|
|---|---|
|
6.0 to 12.0 inches/hour
|
0.8
|
|
2.0 to 6.0 inches/hour
|
1.0
|
|
1.0 to 2.0 inches/hour
|
1.4
|
|
0.75 to 1.0 inch/hour
|
1.2
|
|
0.5 to 0.75 inch/hour
|
1.0
|
|
NOTES:
| |
|
*
|
If the permeability rate (as measured by the double ring infiltration
percolation testing as described in the BMP Manual) falls on a break
between two thickness factors, the smaller thickness factor shall
be used.
|
|
Sites with soil permeability greater than 12.0 in/hr or less
than 0.5 in/hr, as measured by the double ring infiltration percolation
testing as described in the BMP Manual, are not recommended for infiltration.
| |
E.
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 the Universal Rational Hydrograph unless another methodology is approved by the Township. For detention basins with an outlet control structure, the basin routings using the Universal Rational Hydrograph should begin at the elevation of the lowest gravity outlet. For basins proposing zero discharge, the design hydrograph shall be based on a twenty-four-hour storm event (using the twenty-four-hour rainfall depth identified in § 220-22K of this chapter).
F.
BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall be routed using the storage indication method.
G.
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.
H.
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 unless it is documented
that the permanent pond elevation is maintained year round by gravity
or a mechanical pump system for the purpose of elevating peak outflows.
All wet detention ponds shall be subject to review by the Township
Geotechnical Consultant.
I.
All aboveground stormwater detention facilities shall provide a minimum
0.5 foot of freeboard above the maximum pool elevation associated
with the two- through 100-year runoff events, or an additional 10%
of the 100-year storage volume as freeboard volume, whichever is greater.
All below-ground stormwater detention and infiltration facilities
shall have an additional 10% of the 100-year storage volume available
within the storage medium, as well as a minimum of 0.5 foot of freeboard.
The freeboard shall be measured from the maximum pool elevation to
the invert of the emergency spillway for aboveground facilities, and
from the maximum pool elevation to the lowest overflow elevation for
below-ground facilities. The two- through 100-year storm events shall
be controlled by the primary outlet structure. An emergency spillway
for each aboveground basin shall be designed to pass the 100-year
return frequency storm peak basin inflow rate with a minimum 0.5-foot
freeboard measured to the top of basin. The freeboard criteria shall
be met considering any off-site areas tributary to the basin as developed,
as applicable. Exceptions to the freeboard requirements are as follows:
(1)
Bioretention BMPs with a ponded depth less than or equal to 0.5 foot
are exempt from the freeboard requirements;
(2)
Small detention basins, with a ponded depth less than or equal to
1.5 feet or having a depth to the top of the berm less than or equal
to 2.5 feet, may provide 20% additional storage volume measured from
the maximum ponded depth to the invert of the emergency spillway in
lieu of the above requirements. The depth of the emergency spillway
must be sufficient to pass either two times the 100-year peak or the
100-year peak with 0.2-foot of freeboard to the top of berm, whichever
is greater; and
(3)
Small infiltration basins, with a ponded depth less than or equal
to 1.5 feet or having a depth to the top of the berm less than or
equal to 2.5 feet, may provide 20% additional storage volume measured
from the maximum ponded depth to the top of the berm in lieu of the
above requirements. In this case, an emergency spillway is only necessary
if runoff in excess of the detention basin volume would cause harm
to downstream owners. If a spillway is necessary, it must be sufficiently
sized to pass the 100-year peak inflow. 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 DEP Chapter 105 regulations and
may be required to pass a storm greater than the 100-year event.
J.
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 with a three-inch orifice, 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.
K.
Runoff calculations using the soil-cover-complex method shall use
the Natural Resources Conservation Service Type II twenty-four-hour
rainfall distribution. The twenty-four-hour rainfall depths for the
various return periods to be used consistent with this chapter may
be taken from the latest version of the Field Manual for Pennsylvania
Design Rainfall Intensity Charts from NOAA Atlas 14.
|
Return Period
|
24-Hour Rainfall Depth
|
|---|---|
|
2-year
|
3.00 inches
|
|
10-year
|
4.56 inches
|
|
25-year
|
5.52 inches
|
|
50-year
|
6.48 inches
|
|
100-year
|
7.44 inches
|
|
NOTES:
|
|
A graphical and tabular presentation of the Type II twenty-four-hour
distribution is included in Appendix C.[2]
|
[2]
Editor's Note: Appendix C is included as an attachment to this chapter.
L.
Runoff calculations using the Rational Method shall use rainfall
intensities consistent with appropriate times of concentration and
return periods and NOAA Atlas 14, and the Atlas of the United States
Precipitation and Precipitation Frequency Charts, current version.
M.
Runoff Curve Numbers (CNs) to be used in the soil-cover-complex method
shall be based upon the matrix presented in Appendix C.
N.
Runoff coefficients for use in the Rational Method shall be based
upon the table presented in Appendix C.
O.
The stormwater calculations shall include the following:
(1)
Predevelopment and post-development drainage maps showing existing
and proposed grades and including any and all off-site tributary areas;
(2)
Predevelopment and post-development runoff calculations;
(3)
Detention basin design calculations (as applicable);
(4)
Pipe and swale sizing calculations;
(5)
All other information that is needed to construct proposed Stormwater
drainage facilities including, but not limited to, slopes, proposed
elevations, and typical cross sections;
(6)
The stormwater management district(s) in which the site is located
and the applicable release rate(s); and
(7)
Such information as the Township Engineer determines is needed to
determine compliance with this section.
P.
Where crop farming or disturbed earth exists on the site prior to
development, meadow in good condition shall be used as the starting
base for the calculation.
Q.
Where a factor in a calculation is not definitive, the strictest
value shall be used.
R.
Any post-development areas which may be designed to initially be
semipervious (e.g., uncompacted aggregate, porous pavement, etc.)
shall be considered impervious areas unless the developer or landowner
shall guarantee that the semipervious surface shall be maintained
as such to the satisfaction of the Township.
S.
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's Equation. Bankfull flows shall be
used for determining velocities. Manning's "n" values shall be
based on the table presented in Appendix C; and
(4)
Pipe flow travel times shall be determined from velocities calculated
using the Manning's Equation assuming full flow and the Manning's
"n" values from Appendix C.
T.
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 off-site drainage areas. 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.
U.
The Manning's Equation shall be used to calculate the capacity
of watercourses. Manning's "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 Township Engineer.
V.
The DEP, Chapter 105, Rules and Regulations, applies 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 differ from the criteria that are used
in the permitting of dams under the Dam Safety Program.
W.
When conditions exist such that a proposed detention facility may
experience a tailwater effect, the basin shall be analyzed without
any tailwater effect for all storm events for comparison against the
required release rates. An additional routing of the 100-year storm
with the full tailwater effect shall be performed to check that the
basin has sufficient storage to contain the 100-year tributary inflow
and meet freeboard requirements.
X.
Storm sewer piping, roadside swales, and inlet systems shall be designed
for a twenty-four-hour Type II rainfall if using the SCS method. The
openings of culverts and under bridges shall be designed for a 100-year,
twenty-four-hour Type II rainfall. All conveyance swales shall be
designed to handle a 100-year storm, with the flow of such a 100-year
storm contained within the lines of a drainage easement, and with
all structures located at least 25 feet from such an easement.
Y.
Within the 100-year floodplain, any stormwater management structures
and systems shall be designed to handle 100-year storm (based upon
a twenty-four-hour Type II storm if using the soil-cover-complex method).
Z.
The drainage plan shall show that a 100-year, twenty-four-hour storm
can be safely conveyed without jeopardizing any property on or off
the site.
AA.
Storm drainage.
(1)
General requirements. Stormwater management facilities shall
be provided where necessary to adequately control storm runoff in
accordance with all applicable state and local laws and to protect
the general public, and prevent undue damage to public and private
property. To the extent that the provisions of this section conflict
with any stormwater management plan adopted by the Township, the more
stringent criteria shall prevail.
(a)
Any proposed storm drainage plans which affect the drainage
basin of any river or stream shall be approved by the DEP if the drainage
basin so affected has an area of at least 0.5 square mile;
(b)
Storm sewers, culverts, and related installations shall be provided to permit the unimpeded flow of natural watercourses, to ensure the drainage of all low points on the reasonably related to the extent and grade of the area drained. The system shall also be designed in accordance with §§ 220-21T and 220-29:
[1]
Developers shall dedicate easements, pipe collection systems
and structures for storm drainage to the Township.
(c)
No stormwater runoff or natural drainage water shall be so diverted
as to overload existing drainage systems or create flooding or the
need for additional drainage structures on other private or public
lands, without proper and approved provisions being made for taking
care of these conditions:
[1]
The Township Board of Commissioners with the advice of the Township
Engineer shall decide what provisions, including but not limited to
suitable detention basins, shall be made. Where stormwater management
facilities are permitted, adequate assurances of maintenance, indemnification,
liability insurance and security shall be provided by agreement with
the Township, which agreement shall be approved by the Township Solicitor.
(d)
In areas in which street curbs are not required by the Township
Board of Commissioners or Township Engineer, drainage may be accomplished
by natural or artificial swales and culverts. Special structures such
as check dams, drop-outlets, permanent detention basins, or other
energy dissipating structures or riprap may be required to prevent
scour or erosion in locations with large runoff quantities or high
velocities:
(e)
A subsurface collection system with catch basins shall be used
in all areas in which street curbs and gutters are required.
[1]
Underdrain pipe systems shall be required where soil conditions
warrant their installation, as determined by the Township Geotechnical
Consultant.
(f)
Developer shall grade and install all necessary drainage facilities
to ensure the drainage of all low points on subdivided lots or within
the subdivision.
(g)
Designs of storm drainage systems.
[1]
Designs shall be prepared, signed, and sealed by a licensed
professional engineer;
[2]
Complete detailed calculations shall be submitted to the Township
Engineer for approval;
[3]
All designs must be reviewed and approved by the Township Engineer;
and
[4]
Any storm sewers shall be constructed to Township specifications
and shall not interconnect with sanitary sewers.
(2)
Collection system. The collection system shall be designed by
the Rational Method of Design in accordance with American Society
of Civil Engineers Manual No. 37 except as noted using the formula
Q=CiA, as amplified by the following sections:
(a)
"Q" is the required capacity in cubic feet per second for the
collection system at the point of design;
(b)
"C" is the runoff coefficient applicable to the entire drainage area. It shall be based on consideration of soil conditions, average slope of the drainage area, and the ultimate development of the entire drainage area according to comprehensive plans. For various types of ultimate development, the runoff coefficient shall be within the ranges specified in accordance with § 220-22N;
(c)
"i" is the rainfall intensity in inches per hour and shall be determined from a calculated time of concentration and specified storm frequency. Time of concentration shall be computed in accordance with the requirements contained in § 220-22L. Design storm frequencies shall be twenty-five-year for residential and all other developments. Rainfall intensities shall be in accordance with § 220-22L. Any conveyance system designed to transport runoff from a tributary area of greater than 100 acres shall be designed for the 100-year frequency design storm;
(d)
"A" is the drainage area, in acres, tributary to the point of
design, and shall include tributary from outside sources as well as
from within the subdivision itself. All calculations shall be accompanied
by a drainage area map showing all areas tributary to each structure
or discharge point;
(e)
Pipes and conduits shall be designed on the basis of Manning's
formula and the Continuity Equation:
|
v=1.486n*r2/3*
 s |
|
Where:
|
|
"v" is the mean velocity of flow in feet per second
|
|
"n" is the coefficient of roughness (n equals 0.013
for concrete pipe; n equals 0.021 for asphalt coated corrugated metal
pipe, 25% paved)
|
|
"r" is the hydraulic radius in feet
|
|
"s" is the slope of the energy grade line
|
|
"Q" equals VA, where "A" equals cross-sectional
area in square feet Q = V * A
|
(f)
Culverts shall be designed on the basis of inlet or outlet control
as appropriate, except where a more detailed backwater analysis is
deemed warranted by the Township Engineer;
(g)
Manholes shall be spaced at intervals not exceeding 400 feet
and shall be located wherever branches are connected or sizes are
changed and wherever there is a change in alignment or grade;
(h)
For storm sewer lines of at least 36 inches diameter, manholes
may be spaced at intervals greater than 400 feet with the approval
of the Township Engineer;
(i)
Storm sewer lines shall be located between the center line of
the street and the curbline and shall parallel the center line of
the street as far as practical. Sufficient number of structures shall
be provided such that unnecessary crossings of other utility lines
and passage beneath curbs are eliminated; and
(j)
Culvert and/or hydraulic grade analysis, and inlet grate capacity
calculations, shall be provided with storm sewerage system design
calculations.
(3)
Swales. Swales used for outlets shall be designed on the basis
of Manning's formula with the following considerations:
(a)
The roughness coefficient shall be 0.040 for earth swales and
0.015 for paved swales;
(b)
Design velocity in earth swales shall not exceed four feet per
second;
(c)
A swale right-of-way of sufficient minimum width to include
a ten-foot access strip in addition to the width of the swale from
bank top shall be offered for dedication to the Township for drainage
purposes. The Township Engineer may, under unusual conditions, require
a wider swale right-of-way; and
(d)
Side or rear yard swales upstream or downstream of pipe culverts
will be permitted only under the following conditions. If any one
of these conditions cannot be met, the stormwater shall be piped in
an underground system:
[1]
The diameter of the pipe culvert does not exceed 18 inches and
the depth of flow in the swale for a twenty-five-year frequency storm
is less than one foot;
[2]
The side slopes of the swale are not steeper than four horizontal
to one vertical. An easement of sufficient width to encompasses the
design full flow cross section plus one foot of freeboard at the design
cross slope shall be offered for dedication to the Township;
[3]
A note shall be added to the plan to be recorded that the ground
surface elevations in any such drainage easements may not be altered
by the property owner without the express, advance, written permission
of the Township Board of Commissioners; and
[4]
Flared end sections shall be provided on the open pipe ends
in lieu of headwalls. The pipe shall be extended as far as is necessary
to achieve a maximum 4:1 slope on the roadway embankment commencing
at the edge of right-of-way in the case of a curbed roadway or at
the edge of shoulder in the case of a noncurbed roadway.
(4)
Detention basins.
(a)
Permanent detention basins may be required by the Township Engineer
or Board of Commissioners as part of a storm water drainage plan when
the rate of runoff after development will exceed the predevelopment
condition;
(b)
Fencing shall be required around detention basins in the following
cases:
[1]
The maximum depth of water in the basin for a ten-year or a
storm of greater intensity design storm is greater than 30 inches;
[2]
The side slopes of the basin are steeper than four horizontal
to one vertical;
[3]
The time to empty the basin is longer than three hours;
[4]
The detention basin is to be dedicated to Bethlehem Township,
and fencing is requested by the Township; or
[5]
The Board of Commissioners determines that the public safety
would be endangered if the basin is not fenced;
(c)
Fencing and associated warning signs shall be in accordance
with the Township Standard Construction Documents (latest revision);
(d)
Waiving of fencing of a detention basin may be considered by
the Township if the nearest residential zoning district, school, existing
dwelling, or recreation facility is at least 1,500 feet away in walking
distance from the basin;
(e)
Detention basin design shall be based upon the general design requirements provided in this chapter (see § 220-27);
(f)
The rate of outflow from the basin shall be restricted in accordance
with the provisions of this chapter;
(g)
A minimum twelve-foot-wide ramp at a maximum 10% slope shall
be constructed near the basin access fence to permit access to the
bottom of basin for maintenance; and
(5)
Soil erosion and sedimentation control.
(a)
No changes shall be made in the contour of the land, no grading,
excavation, removal, or destruction of the topsoil, trees, or other
vegetative cover of the land shall be commenced until such time that
a plan for minimizing erosion and sedimentation has been reviewed
and approved by the representative for NCCD, Bethlehem Township, and
the Board of Commissioners.
(b)
No subdivision plan shall be approved unless:
[1]
There has been a plan approved by the representative for the
NCCD and the Bethlehem Township Board of Commissioners that provides
in the opinion of the Bethlehem Township Board of Commissioners for
minimizing erosion and sedimentation and acceptable securities are
deposited with the Township in the form of an escrow guarantee which
will ensure installation and completion of the required improvements;
or
[2]
There has been a determination by the representative for the
NCCD and the Bethlehem Township Board of Commissioners that a plan
for minimizing erosion and sedimentation is not necessary;
(c)
Measures used to control erosion and reduce sedimentation shall
comply with the standards and specifications of the NCCD and receive
the approval of the district. Once the subdivision plans have been
finally approved, the district shall ensure compliance with the appropriate
specifications and plans;
(d)
Whenever sedimentation is caused by stripping vegetation, regrading,
or other development, it shall be the responsibility of the person,
corporation, or other entity causing such sedimentation to remove
it from all adjoining surfaces, drainage systems, watercourses, roads,
and rights-of-way, and to repair any damage at this expense within
24 hours of the occurrence;
(e)
Each person, corporation or other entity which makes any surface
changes shall be required to:
[1]
Collect on-site surface runoff and dispose of it to the point
of discharge into the common natural watercourse of the drainage area;
[2]
Handle existing and potential off-site runoff through their
development by designing to adequately handle storm runoff from a
fully developed area upstream; and
[3]
Provide and install at their expense, in accordance with Township
requirement, all drainage and erosion control improvements (temporary
and permanent) as required by the erosion and sediment control plan;
(6)
General design standards.
(a)
Curb inlets shall be located at curb tangents on the uphill
side of street intersections. The Township Engineer shall approve
design and location of curb inlets;
(b)
Drainage structures that are located on state highway rights-of-way
shall be approved by the PENNDOT, and a letter from that office indicating
such approval shall be directed to the Bethlehem Township Board of
Commissioners; and
(c)
The design of the storm sewerage system shall be in accordance
with the Township Standard Construction Documents (latest revision).
(7)
Construction specifications. Township Standard Construction Documents (latest revision) as adopted by the Township will govern. Copies are available at the Township Building upon request and payment of cost of reproduction (see § 220-28).
(8)
The following statements shall be provided on the plans to be
recorded:
"Notwithstanding any provisions of the Township Stormwater Management
Ordinance, including exemption and waiver provisions, any landowner
and any person engaged in the alteration or development of land which
may affect stormwater runoff characteristics shall implement such
measures as are reasonably necessary to prevent injury to health,
safety, or other property. Such measures shall include such actions
as are required to manage the rate, volume, direction, and quality
of resulting stormwater runoff in a manner which otherwise adequately
protects health and property from injury and damage."
"Township review and approval of the drainage plan or the subsequent
observation and approval of stormwater management facilities shall
not constitute land development on behalf of or by the Township or
otherwise cause the Township to be engaged in the alteration or development
of land. By submitting an application under the Township Stormwater
Management Ordinance, the developer hereby agrees to indemnify, defend,
and hold harmless the Township and all its representatives, servants,
employees, officials and consultants of and from any and all claims,
demands, causes of action or suits which arise out of or relate to
the review, approval, construction or observation of the developer's
drainage plan and stormwater management facilities."
Methods of detention or flow delay devices that may be found
to be acceptable by the Township Engineer are:
A.
Wet or dry ponds and detention basins.
B.
Roof storage and increased roof roughness.
C.
Infiltration trenches.
D.
Porous pavements, grassed channels, and vegetated strips.
E.
Cisterns, underground reservoirs or covered ponds.
F.
Increasing the roughness coefficients on the development's surface
area.
G.
Decrease percentage of impervious area.
H.
Groundwater recharge.
I.
Routing flow over lawns in swales within stormwater easements.
J.
Detention storage within the storm sewer.
K.
Another method that may be preapproved by the Township Engineer.
If a roof is to be used for detention, a condition of such use
shall be that the applicant shall submit appropriate calculations
and a signed statement from a registered architect or Pennsylvania-registered
(professional) engineer assuring that the structure will be able to
support the roof loadings. This statement shall be required prior
to issuance of the building permit.
Where porous pavement is used to reduce runoff, the developer
or landowner shall guarantee that the paved surface shall be maintained
to the satisfaction of the Township, and that any resurfacing of the
paved area shall utilize a porous material. Such a guarantee shall
be lettered as a covenant on the recorded plan and shall be signed
and notarized. Porous pavement shall not be utilized in construction
of facilities to be dedicated to the Township. Porous pavement can
only be used when the underlying subgrade soils have proved to be
capable of infiltrating stormwater and provisions have been made to
accommodate the excess runoff.
A.
For the purpose of this section, a retention basin shall be required
to meet the same standards as a detention basin.
B.
Emergency spillways. All detention basins shall be designed with
an emergency spillway:
(1)
These spillways at a minimum shall be able to handle a 100-year post-development
peak discharge of the principal pipe barrel and the emergency spillway;
(2)
Whenever possible, the emergency spillway for detention basins shall
be constructed on undisturbed ground. If the emergency spillway cannot
be constructed on undisturbed ground, it shall be constructed of suitable
material adequately compacted in accordance with specifications preapproved
by the Township Geotechnical Consultant;
(3)
Emergency spillways shall be constructed of reinforced concrete or
stabilized vegetated earth as approved by the Township Geotechnical
Consultant. All emergency spillways shall be constructed so that the
detention basin berm is protected against erosion;
(4)
The emergency spillway shall be designed to pass the 100-year storm
return frequency storm peak basin inflow rate with a minimum 0.5 foot
freeboard measured to the top of detention basin. The emergency spillway
shall convey the 100-year storm at a maximum depth of one foot over
the spillway;
(5)
The downstream slope of the spillway shall as a minimum extended
to the toe of the berm embankment. The edge of the detention basin
grading shall be within the subject property; and
(6)
All detention basin outflow structures shall be designed with trash
racks over the outflows where practicable. Outflow pipes shall be
provided with childproof screening.
C.
Slope of detention basin embankment. The maximum inside slope of
earthen detention basin embankments shall be four horizontal to one
vertical. The maximum outside slope shall be three horizontal to one
vertical. The top or toe of any slope shall be located a minimum of
five feet from any property line. Whenever possible, the side slopes
and detention basin shape shall be amenable to the natural topography.
Straight side slopes are prohibited.
D.
Width and height of berm. The minimum top width of detention basin
berms shall be 10 feet, unless the Township Engineer and/or Geotechnical
Consultant determines that a greater width is needed for maintenance
and/or structural purposes. The berm shall initially be built at least
six inches higher than the design elevation to allow for soil settlement
within the berm.
E.
Slope and lining of basin bottom. In order to ensure proper drainage
of the detention basin, a minimum grade of 2% shall be maintained
for all sheet flow. A minimum grade of 1% shall be maintained for
all channel flow, provided that a synthetic low flow channel of suitable
materials is provided. In areas of carbonate geology, detention basins
shall be provided with an impervious liner of clay, suitable compacted
soil or approved artificial material, with the type of liner approved
by the Township Geotechnical Consultant. Any detention basin that
is proposed to be dedicated to the Township shall be lined with a
synthetic, impervious liner, with the type of liner approved by the
Township Geotechnical Consultant.
F.
Anti-seep collars. Anti-seep collars shall be installed around the
principal pipe barrel within the normal saturation zone of the detention
basin berms in accordance with the requirements of the Conservation
District.
G.
Landscaped screening.
(1)
A detention basin shall be screened from view of existing residences,
a residential zoning district or a public street, unless the basin
would meet both of the following conditions:
(a)
It would have an average slope of less than five to one on the
outside of the detention basin and both the inside and outside would
be planted in grass and intended to be mowed or would be designed
to closely resemble a natural pond; and
(b)
It would not be surrounded by a primarily metal fence.
H.
Multiple detention basins. The use of multiple detention basins should
be investigated over the use of one larger storage facility; however,
the Township Engineer shall be consulted prior to design of multiple
detention basins.
I.
All outflow structures from storage facilities shall be equipped
with a regulatory device that will permit modification to regulate
the amount of outflow. Suitable antivortex and/or velocity retarders
shall be used.
J.
An outflow control structure shall be provided at the outlet of all
detention basins. This structure shall be constructed of metal or
concrete and shall be designed so that the rate of outflow is controlled
by the pipe barrel through the detention basin berm when the depth
of water within the basin exceeds the height of the structure. A trash
rack or similar device shall be provided to prevent debris from entering
the outflow structure. The crest elevation shall be set at a minimum
of 12 inches below the emergency spillway.
K.
Retention basins. Aeration devices may be required, dependent upon
the quality of the influent and retention time.
L.
Recreation. When reasonable, efforts should be made to allow suitable
recreational uses of portions of detention areas. This might include
designing a detention basin so that only a portion would be wet after
a minor storm, and the remainder would be well drained during all
except the most serious storm. These areas may be acceptable, at the
discretion of the Township, as part of any recreation land that may
be required under any Township ordinance.
N.
The design of any detention basin intended to meet the requirements
of this section shall be verified by routing the design storm hydrograph
through the proposed detention basin. Detention basin routing calculations
based on the Rational, Modified Rational or Universal Rational methods
shall not be accepted without the written preapproval of the Township
Engineer. For detention basins designed using the Modified Rational
Method, or other Rational based technique, the detention volume shall,
at minimum, equal the volume derived from the approximate routing
process as contained in SCS Technical Release Number 55 (TR55, most
recent edition).
O.
An outlet structure must be provided to permit draining the detention
or retention basin to a completely dry condition within 24 hours,
unless approved as a wet pond.
A.
Construction and materials of storm drainage and control facilities
(including pipes) and erosion control facilities shall be in accordance
with the approved plans and any accompanying specifications. The construction
details and standards of the following publications or their successor
publications, in their most recent revision, shall be used:
B.
In cases where the above documents conflict with Township specifications,
the Township's specifications shall supersede.
A.
In any stormwater management district, storm sewer piping, and inlet systems shall be designed for a twenty-five-year return period storm, or a 100-year return period storm where the system is designed to convey 100-year storm flows to or from a detention facility. Bridges and culverts along roadways shall be designed to convey the 100-year return period storm. Flows from off-site upstream areas shall be determined in accordance with the procedure identified in § 220-14 of this chapter.
B.
The minimum diameter of any cross-drainage or culvert pipe shall
be 15 inches. Pipe material should conform to the requirements of
the Bethlehem Township Standard Construction Documents.
C.
Storm sewer pipes, culverts, manholes, inlets, endwalls, and end
sections proposed for dedication, or located along streets, shall
conform to the requirements of the Bethlehem Township Standard Construction
Documents and PENNDOT, Bureau of Design, Standards for Roadway Construction,
Publication No. 72, in effect at the time the design is submitted,
as modified by the Bethlehem Township Standard Construction Documents.
D.
The capacities of the pipes, gutters, inlets, culverts, outlet structures,
and swales shall consider all possible hydraulic conditions. The following
are minimum design standards:
(1)
Grass swales and roadside gutters shall consider both the channel
velocity and stability based upon a low degree of retardant ("n" of
0.03), and the channel capacity based upon a high degree of retardant
("n" of 0.05); and
(2)
The velocity to be used in the design of any piped stormwater conveyance
system shall be based on the maximum velocity obtainable. The capacity
shall be based upon 100-year storm conditions. In all cases where
drainage is collected by a headwall or catch basin where inlet or
outlet control may govern, the pipe shall be designed as a culvert,
as outlined in Hydraulic Engineering Design Series No. 5, latest edition
of the U.S. Department of Transportation Federal Highway Administration,
Washington, D.C. The allowable headwater should be determined by the
specific entrance conditions and sound engineering. The capacities
of pipes shall be computed from the Manning's Equation. The design
of culverts shall not create excessive headwater depths.
E.
Open pipe ends shall be fitted with concrete endwalls or prefabricated
end sections.
F.
Drainage pipes shall have a minimum slope of 0.5%. At minimum, the
tops of all pipes shall be at the same elevation when changing pipe
size.
G.
Grass-lined channels shall be designed with a minimum longitudinal
slope of 2% and shall be designed to accommodate design velocities
without erosion.
H.
Pipe sizes with nominal diameters greater than 72 inches shall require
structural design submittals for review and approval.
I.
All culvert structures shall require submission of construction drawings,
to assure compliance to HS-25 loading, and flow design capacity.
J.
All storm sewer pipes and culverts shall be laid to a minimum depth
specified by the pipe manufacturer.
K.
Inlets shall normally be along the curbline at or beyond the curb
radius points. Manholes may be substituted for inlets at locations
where inlets are not required to handle surface runoff.
L.
The capacities of open channels shall be computed from the Manning's
Equation.
M.
Flow velocities from any storm sewer may not result in a deflection
of the receiving channel.
N.
Storm sewers shall be designed with a maximum flow velocity of 15
feet per second.
O.
Energy dissipaters shall be provided at all storm sewer outlets and
shall be designed in accordance with DEP, Office of Water Management,
Erosion and Sediment Pollution Control Program Manual, latest edition.
P.
Manholes or inlets shall be used at all changes in horizontal alignment,
at changes of vertical grade and at all pipe intersections. No run
of pipe shall exceed 400 feet in length without appropriate measures
to allow cleanout. Trash tracks shall be placed on all stormwater
entrance structures.
Q.
Bridges and culverts shall meet PENNDOT constructions standards.
DEP shall be contacted to determine if a dams and waterways permit
is required.
R.
Grating. Appropriate safety grates shall be attached to all catch
basins, stormwater inlets, pipe openings and other stormwater receiving
structures needed, to ensure that maximum openings do not exceed 25
square inches. Along streets and pedestrians' areas, safety grates
shall be used as needed for bicycle safety.
S.
Storm sewer outfall. Storm sewer outfalls shall be designed, with
respect to the elevation of the invert or other features, that when
the receiving watercourse is experiencing a twenty-five-year storm,
the storm sewer will continue to drain the area it is designed to
serve.
T.
Street drainage.
(1)
To minimize sheet flow of stormwater across lots located on the lower
side of streets, and to divert flow away from building areas, the
cross section of the street as constructed shall provide for parallel
ditches or swales or curbing on the lower side which shall discharge
only at drainage easements; and
(2)
Inlet spacing shall be designed such that, in a twenty-five-year
storm, one traffic lane of at least 10 feet in width shall be free
from stormwater.
A.
Where a subdivision or development is traversed by a watercourse,
drainageway, channel, or stream, there shall be provided a drainage
easement conforming substantially with the high-water line of such
watercourse attributable to a flood of a 100-year frequency, in order
to preserve the unimpeded flow of natural drainage and to provide
for future possible widening, deepening, relocating, improving, or
protecting of such drainage facilities.
B.
Structures and other obstructions to flow (except fences that are
made of approved materials and are placed so as to not obstruct flow)
shall be prohibited within the easements. Off-street parking is specifically
prohibited within the easements.
C.
The applicant shall grant the Township the right to enter the easement
to accomplish maintenance work, although the Township assumes no responsibility
for such work. Such grant shall be in the form of a signed and notarized
covenant placed on the record drawing.
D.
It shall be the responsibility of the applicant to obtain all the
easements on, over or through other properties when such easements
are needed to carry out the proposed drainage plan.
E.
Areas where the easements have been or will be granted shall not
be obstructed during or after construction.
A.
All-natural streams, channels, swales, drainage systems, and/or areas
of concentration of surface water shall be maintained in their existing
condition unless alteration is approved by the Township Engineer.
The applicant shall be responsible to obtain all necessary DEP permits
(see Chapter 105 of Title 25 of the state regulations).
B.
Creek alignments. No watercourse shall be realigned, blocked, impeded,
or redirected without the prior written approval of DEP and the Township
Engineer.
C.
Piping of surface water. Natural surface watercourses which have
sustained perennial flows averaging at least five cubic feet per second
shall remain open to sky and shall not be piped or covered.
D.
No activities requiring a permit from DEP, the U.S. Army Corps of
Engineers and/or other governmental agency shall be conducted (e.g.,
in freshwater wetlands) unless the developer has obtained all necessary
permits.
A system for the ownership and maintenance responsibility of
all temporary and permanent stormwater management facilities and erosion
and sedimentation control facilities that is satisfactory to the Board
of Commissioners of the Township shall be established prior to the
final plan approval.
A.
Detention ponds shall be designed and laid out in accordance with
Township requirements so that the area can be dedicated to the Township.
Each developer shall make an offer of dedication to the Township.
All maintenance and upkeep of ponds dedicated to and accepted by the
Township shall be the responsibility of the Township in accordance
with the following provisions:
(1)
That a detention pond maintenance escrow account shall be established
by the Township, and all required contributions from developers for
such maintenance and upkeep of detention ponds shall be maintained
within this escrow account; and
(2)
That the contribution formula from each developer shall be based
on the following formula:
(a)
That the cost of crew (size to be initially determined) cutting
grass once every two weeks at (x hours per cutting) for a period from
May 1 through October 15 of each year;
(b)
That the cost for a spring and fall cleanup of (x) hours for
(x) workers, including any costs for equipment (front loader and trucks);
(c)
That an amount be established for certain major reconstruction
of components such as outlet structures, beams, fencing, etc., during
the first 25 years;
(e)
That the total contribution to the detention pond escrow account
for each proposed development shall be clearly defined prior to final
plan approval for the development and shall be made a part of the
developer's agreement.
B.
Suitable easements shall be provided for all stormwater facilities.
C.
Stormwater management facilities shall be designed to require minimal
maintenance and shall be designed to be accessible for maintenance.
D.
An easement shall be provided to guarantee access for maintenance
purposes if the stormwater management facilities cannot be accessed
from a public road. Such grant of easement shall be in the form of
a signed and notarized covenant placed on the record development plan.
E.
Stormwater management facilities located on private property(ies).
(1)
Stormwater management facilities located on private property shall
be maintained by the owner(s) thereof. The maintenance obligation
shall be acknowledged in the form of a signed and notarized covenant
placed on the record development plan and in the form of a separate
signed and notarized covenants agreement with the Township which shall
be recorded in the Northampton County Recorder of Deeds;
(2)
Should a stormwater management facility not be maintained in proper
working order, the Board of Commissioners may, after due notice to
the responsible party, arrange for the needed maintenance to be accomplished
with all such expenses charged to the responsible party. These expenses
shall be collectible as municipal liens are now collected by law;
and
(3)
The Township Engineer and Code Enforcement staff shall have the right
to enter private property to inspect stormwater management facilities
with reasonable notice to the property owner prior to any such inspection.
