|
A. All regulated activities in the municipality shall be subject to
the stormwater management requirements of this chapter.
B. Storm drainage systems shall be provided to permit unobstructed flow
in natural watercourses except as modified by stormwater detention
facilities, recharge facilities, water quality facilities, pipe systems
or open channels consistent with this chapter.
C. The existing locations of concentrated drainage discharge onto adjacent
property shall not be altered without written approval of the affected
property owner(s).
D. Areas of existing diffused drainage discharge onto adjacent property
shall be managed such that, at minimum, the peak diffused flow does
not increase in the general direction of discharge, except as otherwise
provided in this chapter. If diffused flow is proposed to be concentrated
and discharged onto adjacent property, the developer must document
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. Areas of existing
diffused drainage discharge shall be subject to any applicable release
rate criteria in the general direction of existing discharge whether
they are proposed to be concentrated or maintained as diffused drainage
areas.
E. Where a site is traversed by watercourses, other than those for which
a one-hundred-year floodplain is defined by the municipality, there
shall be provided drainage easements conforming substantially with
the line of such watercourses. The width of any easement shall be
adequate to provide for unobstructed flow of storm runoff based on
calculations made in conformance with § 205-17 for the one-hundred-year
return period runoff and to provide a freeboard allowance of 0.5 foot
above the design water surface level. The terms of the easement shall
prohibit excavation, the placing of fill or structures, and any alterations
which may adversely affect the flow of stormwater within any portion
of the easement. Also, periodic maintenance of the easement to ensure
proper runoff conveyance shall be required. Watercourses for which
the one-hundred-year floodplain is formally defined are subject to
the applicable municipal floodplain regulations.
F. When it can be shown that, due to topographic conditions, natural
drainage swales on the site cannot adequately provide for drainage,
open channels may be constructed conforming substantially to the line
and grade of such natural drainage swales. Capacities of open channels
shall be calculated using the Manning Equation.
G. 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.
H. No earth disturbance activities associated with any regulated activities
shall commence until approval by the municipality of a plan which
demonstrates compliance with the requirements of this chapter.
I. Techniques described in Appendix F (Low-Impact Development) of this chapter are encouraged because they reduce the
costs of complying with the requirements of this chapter and the state
water quality requirements.
J. 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.
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 Pennsylvania Department of Transportation
(PennDOT).
E. Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area and any facility which
may constitute a dam subject to permit by DEP under 25 Pa. Code Chapter
105.
A. No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of an erosion and
sediment control plan for construction activities. Written approval
by 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).
C. A DEP NPDES Stormwater Discharges Associated with Construction Activities
Permit is required for regulated earth disturbance activities under
25 Pa. Code Chapter 92.
D. Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate DEP regional office or County Conservation
District must be provided to the municipality before the commencement
of an earth disturbance activity.
E. A copy of the erosion and sediment control plan and any permit, as
required by DEP regulations, shall be available at the project site
at all times.
A. No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of a 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, except that in no case
shall be WQv be permitted to exceed 1.25 inches of runoff over the
site area. This standard does not limit the volume of infiltration
an applicant may propose for purposes of water quantity/peak rate
control.
C. The WQv shall be calculated for each 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 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 § 205-14O, except for minor areas on the periphery
of the site that cannot reasonably be drained to an infiltration facility
or other BMP.
F. Infiltration BMPs shall not be constructed on fill unless the applicant
demonstrates that the fill is stable and otherwise meets the infiltration
BMP standards of this 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 BMPs, 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. 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.
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 inches/hour
and less than or equal to 12 inches per hour.
(4) Setback distances or buffers as follows:
(a)
One hundred feet from water supply wells.
(b)
Fifteen feet downgradient or 100 feet upgradient from building
foundations, except for residential development where the required
set back is 15 feet downgradient or 40 feet upgradient from building
foundations.
(c)
Fifty feet from septic system drainfields, except for residential
development where the required setback is 25 feet from septic system
drainfields.
(d)
Fifty feet from a geologic contact with carbonate bedrock unless
a preliminary site investigation is done in the carbonate bedrock
to show the absence of special geologic features within 50 feet of
the proposed infiltration area.
(e)
One hundred feet from the property line unless documentation
is provided to show that all setbacks from existing or potential future
wells, foundations and drainfields on neighboring properties will
be met, except for one- and two-family residential dwellings where
the required setback is 40 feet, unless documentation is provided
to show that all setbacks from existing or potential future wells,
foundations and drainfields on neighboring properties will be met.
J. For entirely noncarbonate sites, the recharge volume (REv) shall
be infiltrated unless the applicant demonstrates that it is infeasible
to infiltrate the REv for reasons of seasonal high water table, permeability
rate, soil depth or setback distances, or except as provided in § 205-14U.
(1) The REv shall be calculated as follows:
|
|
 |
|
|
Where:
|
|
|
|
REv
|
=
|
recharge volume in acre-feet
|
|
|
|
I
|
=
|
impervious area in acres
|
(2) The preliminary site investigation described in § 205-14H
is required and shall continue on different areas of the site until
a potentially suitable infiltration location is found or the entire
site is determined to be infeasible for infiltration. For infiltration
areas that appear to be feasible based on the preliminary site investigation,
the additional site investigation and testing as outlined in Appendix
G shall be completed.
(3) If an applicant proposes infiltration, the municipality may determine
infiltration to be infeasible if there are known existing conditions
or problems that may be worsened by the use of infiltration.
(4) The site must meet the conditions listed in § 205-14I.
(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 § 205-14O.
(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 us infiltration
BMPs, the preliminary site investigation described in § 205-14H
shall be conducted. For infiltration areas that appear feasible based
on the preliminary site investigation, the applicant shall conduct
the additional site investigation and testing as outlined in Appendix
G. The soil depth, percolation rate and proposed loading rate, each
weighted as described in § 205-17, along with the buffer
from special geologic features shall be compared to the Recommendation
Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock
in Appendix D to determine if the site is recommended for infiltration.
In addition to the recommendation from Appendix D, the conditions
listed in § 205-14I are required for infiltration in carbonate
areas. Applicants are encouraged to infiltrate the REv, as calculated
in § 205-14J, but are not required to use infiltration BMPs
on a carbonate site even if the site falls in the recommended range
on the chart in Appendix D. Any amount of volume infiltrated can be
subtracted from the WQv to be treated by noninfiltration BMPs. If
infiltration is not proposed, the full WQv shall be treated by two
acceptable BMPs, as specified in § 205-14O.
L. If a site has both carbonate and noncarbonate areas, the applicant
shall investigate the ability of the noncarbonate portion of the site
to fully meet this 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 § 205-14K or two other
noninfiltration BMPs as described in § 205-14O 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.
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 BMPs 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.
|
|
|
Number
|
Design Reference Title
|
|
|
1
|
"Conservation Design For Stormwater Management — A Design
Approach to Reduce Stormwater Impacts From Land Development and Achieve
Multiple Objectives Related to Land Use," Delaware Department of Natural
Resources and Environmental Control, The Environmental Management
Center of the Brandywine Conservancy, September 1997
|
|
|
2
|
"A Current Assessment of Urban Best Management Practices: Techniques
for Reducing Nonpoint Source Pollution in the Coastal Zone," Schueler,
T.R., Kumble, P. and Heraty, M., Metropolitan Washington Council of
Governments, 1992.
|
|
|
3
|
"Design of Roadside Channels with Flexible Linings," Federal
Highway Administration, Chen, Y. H. and Cotton, G. K., Hydraulic Engineering
Circular 15, FHWA-IP-87-7, McLean Virginia, 1988.
|
|
|
4
|
"Draft Stormwater Best Management Practices Manual," Pennsylvania
Department of Environmental Protection, January 2005.
|
|
|
5
|
"Evaluation and Management of Highway Runoff Water Quality,"
Federal Highway Administration, FHWA-PD-96-032, Washington, D.C.,
1996.
|
|
|
6
|
"Evaporation Maps of the United States," U.S. Weather Bureau
(now NOAA/National Weather Service) Technical Paper 37, Published
by Department of Commerce, Washington D.C., 1959.
|
|
|
7
|
"Georgia Stormwater Manual," AMEC Earth and Environmental, Center
for Watershed Protection, Debo and Associates, Jordan Jones and Goulding,
Atlanta Regional Commission, Atlanta, Georgia, 2001.
|
|
|
8
|
"Hydraulic Design of Highway Culverts," Federal Highway Administration,
FHWA HDS 5, Washington, D.C., 1985 (revised May 2005).
|
|
|
9
|
"Low Impact Development Design Strategies An Integrated Design
Approach, Prince Georges County, Maryland Department of Environmental
Resources, June 1999.
|
|
|
10
|
"Maryland Stormwater Design Manual," Maryland Department of
the Environment, Baltimore, Maryland, 2000.
|
|
|
11
|
"Pennsylvania Handbook of Best Management Practices for Developing
Areas," Pennsylvania Department of Environmental Protection, 1998.
|
|
|
12
|
"Recommended Procedures for Act 167 Drainage Plan Design," LVPC,
Revised 1997.
|
|
|
13
|
"Roof Gardens History, Design, and Construction," Osmundson,
Theodore. New York: W.W. Norton 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 web site (as of August 2005) http://www.epa.gov/NE/assistance/ceitts/stormwater/techs/html.
|
P. Stormwater runoff from hot spot land uses shall be pretreated. In
no case, may the same BMP be employed consecutively to meet this requirement
and the requirement in § 205-14O.
(1) Acceptable methods of pretreatment are listed below.
|
|
Hot Spot Land Use
|
Pretreatment Method(s)
|
|
|
Vehicle maintenance and repair facilities including auto parts
stores
|
Water quality inlets
Use of drip plans 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
Constructed wetlands
Stormwater collection and reuse
|
|
|
Salvage yards and recycling facilities*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
|
Fleet storage yards and vehicle cleaning facilities*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
|
Facilities that store or generate regulated substances*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
|
Marinas*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
|
Certain industrial uses (listed under NPDES)*
|
BMPs that are a part of a stormwater pollution prevention plan
under an NPDES permit
|
|
|
NOTES:
|
|
|
*
|
Regulated under the NPDES stormwater program.
|
(2) Design references for the pretreatment methods, as necessary, are
listed below. If the applicant can demonstrate to the satisfaction
of the municipality that the proposed land use is not a hot spot,
then the pretreatment 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 § 205-14O
above.
|
Q. The use of infiltration BMPs is prohibited on hot spot land use areas.
R. Stormwater infiltration BMPs shall not be placed in or on a special
geologic feature(s). Additionally, stormwater runoff shall not be
discharged into existing on-site sinkholes.
S. Applicants shall request, in writing, public water suppliers to provide
the Zone I Wellhead Protection radius, as calculated by the method
outlined in the Pennsylvania Department of Environmental Protection
Wellhead Protection regulations, for any public water supply well
within 400 feet of the site. In addition to the setback distances
specified in § 205-14I, infiltration is prohibited in the
Zone I radius as defined and substantiated by the public water supplier
in writing. If the applicant does not receive a response from the
public water supplier, the Zone I radius is assumed to be 100 feet.
T. The volume and rate of the net increase in stormwater runoff from
the regulated activities must be managed to prevent the physical degradation
of receiving waters from such effects as scour and streambank destabilization,
to satisfy state water quality requirements, by controlling the two-year
post-development runoff to a thirty-percent release rate.
U. The municipality may, after consultation with DEP, approve alternative
methods for meeting the state water quality requirements other than
those in this section, provided that they meet the minimum requirements
of and do not conflict with state law, including but not limited to
the Clean Streams Law.
A. Mapping of stormwater management districts. To implement the provisions
of the Bushkill Creek Watershed Stormwater Management Plan, the municipality
is hereby divided into stormwater management districts consistent
with the Bushkill Creek Release Rate Map presented in the plan update.
The boundaries of the stormwater management districts are shown on
an official map which is available for inspection at the municipal
office. A copy of the official map at a reduced scale is included
in Appendix A for general reference.
B. Description of stormwater management districts. Two types of stormwater
management districts may be applicable to the municipality, 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) must be calculated to determine if adequate capacity
exists. For this determination, the developer must calculate peak
flows assuming that the site is developed as proposed and that the
remainder of the local watershed is in the existing condition. The
developer must also calculate peak flows assuming that the entire
local watershed is developed per current zoning and that all new development
would use the runoff controls specified by this chapter. The larger
of the two peak flows calculated will be used in determining if adequate
capacity exists. If adequate capacity exists to safely transport runoff
from the site to the main channel (as defined in Article II), these
watershed areas may discharge post-development peak runoff without
detention facilities. If the capacity calculations show that the local
runoff conveyance facilities lack adequate capacity, the developer
shall either use a one-hundred-percent release rate control or provide
increased capacity of downstream elements to convey increased peak
flows consistent with § 205-16P. 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 § 205-16D. 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 § 205-14.
(2) Dual release rate districts. Within these districts, the two-year
post-development peak discharge must be controlled to 30% of the predevelopment
two-year runoff peak. Further, the ten-, twenty-five-, and one-hundred-year
post-development peak runoff must be controlled to the stated percentage
of the predevelopment peak. Release rates associated with the ten-year
through one-hundred-year events vary from 50% to 100% depending upon
location in the watershed.
A. Applicants shall provide a comparative pre- 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-, and one-hundred-year
return period runoff events consistent with the calculation methodology
specified in § 205-17.
C. The exact location of the stormwater management district boundaries
as they apply to a given development site shall be determined by mapping
the boundaries using the two-foot topographic contours provided as
part of the drainage plan. The district boundaries as originally drawn
coincide with topographic divides or, in certain instances, are drawn
from the intersection of the watercourse and a physical feature such
as the confluence with another watercourse or a potential flow obstruction
(e.g., road, culvert, bridge, etc.). The physical feature is the downstream
limit of the subarea and the subarea boundary is drawn from that point
up slope to each topographic divide along the path perpendicular to
the contour lines.
D. Any downstream capacity analysis conducted in accordance with this
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.
(3) Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with DEP Chapter 105 regulations (if applicable) and, at minimum,
pass the increased twenty-five-year return period runoff.
E. For a proposed development site located within one release rate category
subarea, the total runoff from the site shall meet the applicable
release rate criteria. For development sites with multiple directions
of runoff discharge, individual drainage directions may be designed
for up to a one-hundred-percent release rate so long as the total
runoff from the site is controlled to the applicable release rate.
F. For a proposed development site located within two or more release
category subareas, the peak discharge rate from any subarea shall
be the predevelopment peak discharge for that subarea multiplied by
the applicable release rate. The calculated peak discharges shall
apply regardless of whether the grading plan changes the drainage
area by subarea. An exception to the above may be granted if discharges
from multiple subareas recombine in proximity to the site. In this
case, peak discharge in any direction may be a one-hundred-percent
release rate, provided that the overall site discharge meets the weighted
average release rate.
G. For a proposed development site located partially within a release
rate category subarea and partially within a conditional/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. No portion of a site may be regraded between the Bushkill Creek Watershed
and any adjacent watershed except as part of a no harm or hardship
waiver procedure.
I. Within a release rate category area, for a proposed development site
which has areas which drain to a closed depression(s), the design
release from the site will be the lesser of: a) the applicable release
rate flow assuming no closed depression(s); or b) the existing peak
flow actually leaving the site. In cases where b) would result in
an unreasonably small design release, the design discharge of less
than or equal to the release rate will be determined by the available
downstream conveyance capacity to the main channel calculated using
§ 205-16D and the minimum orifice criteria.
J. Off-site areas which drain through a proposed development site are
not subject to release rate criteria when determining allowable peak
runoff rates. However, on-site drainage facilities shall be designed
to safely convey off-site flows through the development site using
the capacity criteria in § 205-16D and the detention criteria
in § 205-17.
K. For development sites proposed to take place in phases, all detention
ponds shall be designed to meet the applicable release rate(s) applied
to all site areas tributary to the proposed pond discharge direction.
All site tributary areas will be assumed as developed, regardless
of whether all site tributary acres are proposed for development at
that time. An exception shall be sites with multiple detention ponds
in series where only the downstream pond must be designed to the stated
release rate.
L. Where the site area to be impacted by a proposed development activity
differs significantly from the total site area, only the proposed
impact area shall be subject to the release rate criteria. The impact
area includes any proposed cover or grading changes.
M. Development proposals which, through groundwater recharge or other
means, do not increase either the rate or volume of runoff discharged
from the site compared to predevelopment are not subject to the release
rate provisions of this chapter.
N. 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 § 205-16D
if downstream capacity analysis is a part of the no harm justification.
(2) Attempts to prove no harm based upon downstream peak flow versus
capacity analysis shall be governed by the following provisions:
(a)
The peak flow values to be used for downstream areas for the
design return period storms (two-, ten-, twenty-five-, and one-hundred-year)
shall be the values from the calibrated PSRM Model for the Bushkill
Creek 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 municipality upon request.
(b)
Any available capacity in the downstream conveyance system as
documented by a developer may be used by the developer only in proportion
to his development site acreage relative to the total upstream undeveloped
acreage from the identified capacity (i.e., if his site is 10% of
the upstream undeveloped acreage, he may use up to 10% of the documented
downstream available capacity).
(c)
Developer-proposed runoff controls which would generate increased
peak flow rates at storm drainage problem areas would, by definition,
be precluded from successful attempts to prove no harm, except in
conjunction with proposed capacity improvements for the problem areas
consistent with § 205-16P.
(3) Any no harm justifications shall be submitted by the developer as
part of the drainage plan submission per Article IV. Developers submitting
no harm justifications must still meet all of the water quality requirements
in § 205-14.
O. 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.
P. Capacity improvements.
(1) 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 § 205-16D. All new development
in the entire subarea(s) within which the proposed development site
is located shall be assumed to implement the developer's proposed
discharge control, if any.
(2) 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.
A. Stormwater runoff from all development sites shall be calculated
using either the Rational Method or the Soil-Cover-Complex Methodology.
B. Infiltration BMPs.
(1) Infiltration BMP loading rate percentages in the Recommendation Chart
for Infiltration Stormwater Management BMPs in Carbonate Bedrock in
Appendix D shall be calculated as follows:
(2) The area tributary to the infiltration BMP shall be weighted as follows:
(a)
All disturbed areas to be made impervious: weight at 100%.
(b)
All disturbed areas to be made pervious: weight at 50%.
(c)
All undisturbed pervious areas: weight at 0%.
(d)
All existing impervious areas: weight at 100%.
C. Soil thickness.
(1) Soil thickness is to be measured from the bottom of any proposed
infiltration system. The effective soil thickness in the Recommendation
Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock
in Appendix D is the measured soil thickness multiplied by the thickness
factor based on soil permeability (as measured by the adapted 25 Pa.
Code § 73.15 percolation test in Appendix G), as follows:
|
|
Permeability Range*
(inches/hour)
|
Thickness Factor
|
|
|
6.0 to 12.0
|
0.8
|
|
|
2.0 to 6.0
|
1.0
|
|
|
1.0 to 2.0
|
1.4
|
|
|
0.75 to 1.0
|
1.2
|
|
|
0.5 to 0.75
|
1.0
|
|
|
NOTES:
|
|
|
*
|
If the permeability rate (as measured by the adapted 25 Pa.
Code § 73.15 percolation test in Appendix G) falls on a
break between two thickness factors, the smaller thickness factor
shall be used.
|
(2) Sites with soil permeability greater than 12.0 inches per hour or
less than 0.5 inch per hour, as measured by the adapted 25 Pa. Code
§ 73.15 percolation test in Appendix G, are not recommended
for infiltration.
D. The design of any detention basin intended to meet the requirements
of this chapter shall be verified by routing the design storm hydrograph
through the proposed basin using the storage indication method or
other methodology demonstrated to be more appropriate. For basins
designed using the Rational Method technique, the design hydrograph
for routing shall be either the universal rational hydrograph or the
modified rational method trapezoidal hydrograph which maximizes detention
volume. Use of the modified rational hydrograph shall be consistent
with the procedure described in Section "PIPE.RAT" of the Users'
Manual for the Penn State Urban Hydrology Model (1987).
E. BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall be routed using the storage indication method.
F. BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall provide storage volume for the full WQv
below the lowest outlet invert.
G. Wet detention ponds designed to have a permanent pool for the WQv
shall assume that the permanent pool volume below the primary outlet
is full at the beginning of design event routing for the purposes
of evaluating peak outflows.
H. All stormwater detention facilities shall provide a minimum 1.0 foot
freeboard above the maximum pool elevation associated with the two-year
through twenty-five-year runoff events. A 0.5 foot freeboard shall
be provided above the maximum pool elevation of the one-hundred-year
runoff event. The freeboard shall be measured from the maximum pool
elevation to the invert of the emergency spillway. The two-year through
one-hundred-year storm events shall be controlled by the primary outlet
structure. An emergency spillway for each basin shall be designed
to pass the one-hundred-year return frequency storm peak basin inflow
rate with a minimum 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. If this detention
facility is considered to be a dam as per DEP Chapter 105, the design
of the facility must be consistent with the Chapter 105 regulations,
and may be required to pass a storm greater than the one-hundred-year
event.
I. The minimum circular orifice diameter for controlling discharge rates
from detention facilities shall be three inches. Designs where a lesser
size orifice would be required to fully meet release rates shall be
acceptable 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.
J. Type II twenty-four-hour rainfall distribution.
(1) Runoff calculations using the Soil-Cover-Complex Method shall use
the Natural Resources Conservation Service Type II twenty-four-hour
rainfall distribution. The twenty-four-hour rainfall depths for the
various return periods to be used consistent with this chapter may
be taken from NOAA Atlas 14, Volume 2, Version 2.1, 2004 or the PennDOT
Intensity — Duration — Frequency Field Manual ("PDT-IDF")
(May 1986) for Region 4. The following values are taken from the PDT-IDF
Field Manual:
|
|
Return Period
|
24-Hour Rainfall Depth
(inches)
|
|
|
1-year
|
2.40
|
|
|
2-year
|
3.00
|
|
|
5-year
|
3.60
|
|
|
10-year
|
4.56
|
|
|
25-year
|
5.52
|
|
|
50-year
|
6.48
|
|
|
100-year
|
7.44
|
(2) A graphical and tabular presentation of the Type II twenty-four-hour
distribution is included in Appendix C.
K. Runoff calculations using the Rational Method shall use rainfall
intensities consistent with appropriate times of concentration and
return periods and NOAA Atlas 14, Volume 2, Version 2.1, 2004 or the
Intensity-Duration-Frequency Curves as presented in Appendix C.
L. Runoff curve numbers (CNs) to be used in the Soil-Cover-Complex Method
shall be based upon the matrix presented in Appendix C.
M. Runoff coefficients for use in the Rational Method shall be based
upon the table presented in Appendix C.
N. All time of concentration calculations shall use a segmental approach
which may include one or all of the flow types below:
(1) Sheet flow (overland flow) calculations shall use either the NRCS
average velocity chart (Figure 3-1, Technical Release-55, 1975) or
the modified kinematic wave travel time equation (equation 3-3, NRCS
TR-55, June 1986). If using the modified kinematic wave travel time
equation, the sheet flow length shall be limited to 50 feet for designs
using the Rational Method and limited to 150 feet for designs using
the Soil-Cover-Complex Method.
(2) Shallow concentrated flow travel times shall be determined from the
watercourse slope, type of surface and the velocity from Figure 3-1
of TR-55, June 1986.
(3) Open channel flow travel times shall be determined from velocities
calculated by the Manning Equation. Bankfull flows shall be used for
determining velocities. Manning 'n' values shall be based
on the table presented in Appendix C.
(4) Pipe flow travel times shall be determined from velocities calculated
using the Manning Equation assuming full flow and the Manning 'n'
values from Appendix C.
O. If using the Rational Method, all predevelopment calculations for
a given discharge direction shall be based on a common time of concentration
considering both on-site and any off-site drainage areas. If using
the Rational Method, all 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.
P. The Manning Equation shall be used to calculate the capacity of watercourses.
Manning 'n' values used in the calculations shall be consistent
with the table presented in Appendix C or other appropriate standard
engineering 'n' value resources. Pipe capacities shall be
determined by methods acceptable to the municipality.
Q. The Pennsylvania DEP, Chapter 105, Rules and Regulations, apply to
the construction, modification, operation or maintenance of both existing
and proposed dams, water obstructions and encroachments throughout
the watershed. Criteria for design and construction of stormwater
management facilities according to this chapter may differ from the
criteria that are used in the permitting of dams under the dam safety
program.
|
