A.
All regulated activities in the Borough of Catasauqua
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 Borough, 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 § 225-18 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.
Postconstruction BMPs shall be designed, installed,
operated and maintained to meet the requirements of the Clean Streams
Law[1] and implementing regulations, including the established
practices in 25 Pa. Code Chapter 102 and the specifications of this
chapter as to prevent accelerated erosion in watercourse channels
and at all points of discharge.
[1]
Editor's Note: See 35 P.S. § 691.1
et seq.
H.
No earth disturbance activities associated with any
regulated activities shall commence until approval by the Borough
of a plan which demonstrates compliance with the requirements of this
chapter.
I.
Techniques described in Appendix F (Low-Impact Development)[2] of this chapter are encouraged because they reduce the
costs of complying with the requirements of this chapter and the state
water quality requirements.
[2]
Editor's Note: Appendix F is included at the end of this chapter.
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.[3]
[3]
Editor's Note: Appendix D is included at the end of this chapter.
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).
A.
No regulated earth disturbance activities within the
Borough shall commence until approval by the Borough 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 Pa. Code § 102.4(b).
C.
A DEP NPDES Stormwater Discharges Associated with
Construction Activities Permit is required for regulated earth disturbance
activities under Pa. Code Chapter 92.
D.
Evidence of any necessary permit(s) for regulated
earth disturbance activities from the appropriate DEP regional office
or County Conservation District must be provided to the Borough 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
Borough shall commence until approval by the Borough 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:
|
WQv = (c)(P)(A)/12
| ||||
|
Where
| ||||
|
WQv
|
=
|
Water quality volume in acre-feet
| ||
|
c
|
=
|
Rational Method postdevelopment 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 postdevelopment for the two-year-return-period
storm. The effect of closed depressions on the site shall be considered
in this calculation. The larger of these two calculated volumes shall
be used as the WQv to be captured and treated, except that in no case
shall the WQv be 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 postdevelopment
drainage direction on a site for sizing BMPs. Site areas having no
impervious cover and no proposed disturbance during development may
be excluded from the WQv calculations and do not require treatment.
D.
If an applicant is proposing to use a 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 Catasauqua
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 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 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.[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.
[1]
Editor's Note: Appendix G is included at the end of 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 is greater
than or equal to two feet.
(2)
Depth to seasonal high-water table below the invert
of the BMP is 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 feet 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[2]) is greater than or equal to 0.5 inch/hour and less than
or equal to 12 inches per hour.
[2]
Editor's Note: Appendix G is included at the end of this chapter.
(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 setback is 15 feet downgradient or 40 feet upgradient
from building foundations.
(c)
Fifty feet from septic system drainfields; except
for residential development where the required setback is 25 feet
from septic system drainfields.
(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 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[3] shall be completed.
[3]
Editor's Note: Appendix G is included at the end of this chapter.
(3)
If an applicant proposes infiltration, the Borough
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.
(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.[4] The soil depth, percolation rate and proposed loading rate, each weighted as described in § 225-18, 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[5] 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.
[4]
Editor's Note: Appendix G is included at the end of this chapter.
[5]
Editor's Note: Appendix D is included at the end of 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 noninfiltration 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 postdevelopment two-year runoff volume leaving the site shall
be 80% or more of the predevelopment runoff volume for the carbonate
portion of the site to prevent infiltration of volumes far in excess
of the predevelopment infiltration volume.
N.
Site areas proposed for infiltration shall be protected
from disturbance and compaction except as necessary for construction
of infiltration BMPs.
O.
If infiltration of the entire WQv is not proposed,
the remainder of the WQv shall be treated by two acceptable BMPs in
series for each discharge location. Sheet flow draining across a pervious
area can be considered as one BMP. Sheet flow across impervious areas
and concentrated flow shall flow through two BMPs. If sheet flow from
an impervious area is to be drained across a pervious area as one
BMP, the length of the pervious area must be equal to or greater than
the length of impervious area. In no case may the same BMP be employed
consecutively to meet 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.
|
|
Number
|
Design Reference Title
| |
|---|---|---|
|
1
|
"Conservation Design For Stormwater Management
— A Design Approach to Reduce Stormwater Impacts From Land Development
and Achieve Multiple Objectives Related to Land Use," Delaware Department
of Natural Resources and Environmental Control, The Environmental
Management Center of the Brandywine Conservancy, September 1997.
| |
|
2
|
"A Current Assessment of Urban Best Management
Practices: Techniques for Reducing Nonpoint Source Pollution in the
Coastal Zone," Schueler, T. R., Kumble, P. and Heraty, M., Metropolitan
Washington Council of Governments, 1992.
| |
|
3
|
"Design of Roadside Channels with Flexible Linings,"
Federal Highway Administration, Chen, Y. H. and Cotton, G. K., Hydraulic
Engineering Circular 15, FHWA-IP-87-7, McLean, Virginia, 1988.
| |
|
4
|
"Draft Stormwater Best Management Practices
Manual," Pennsylvania Department of Environmental Protection, January
2005.
| |
|
5
|
"Evaluation and Management of Highway Runoff
Water Quality," Federal Highway Administration, FHWA-PD-96-032, Washington,
D.C., 1996.
| |
|
6
|
"Evaporation Maps of the United States," U.S.
Weather Bureau (now NOAA/National Weather Service) Technical Paper
37, published by Department of Commerce, Washington D.C., 1959.
| |
|
7
|
"Georgia Stormwater Manual," AMEC Earth and
Environmental, Center for Watershed Protection, Debo and Associates,
Jordan Jones and Goulding, Atlanta Regional Commission, Atlanta, Georgia,
2001.
| |
|
8
|
"Hydraulic Design of Highway Culverts, "Federal
Highway Administration, FHWA HDS 5, Washington, D.C., 1985 (revised
May 2005).
| |
|
9
|
"Low Impact Development Design Strategies, An
Integrated Design Approach," Prince Georges County, Maryland Department
of Environmental Resources, June 1999.
| |
|
10
|
"Maryland Stormwater Design Manual," Maryland
Department of the Environment, Baltimore, Maryland, 2000.
| |
|
11
|
"Pennsylvania Handbook of Best Management Practices
for Developing Areas," Pennsylvania Department of Environmental Protection,
1998.
| |
|
12
|
"Recommended Procedures for Act 167 Drainage
Plan Design," LVPC, revised 1997.
| |
|
13
|
"Roof Gardens History, Design, and Construction,"
Osmundson, Theodore. New York: W.W. Norton & Company, 1999.
| |
|
14
|
"The Texas Manual on Rainwater Harvesting,"
Texas Water Development Board, Austin, Texas, Third Edition, 2005.
| |
|
15
|
"VDOT Manual of Practice for Stormwater Management,"
Virginia Transportation Research Council, Charlottesville, Virginia,
2004.
| |
|
16
|
"Virginia Stormwater Management Handbook," Virginia
Department of Conservation and Recreation, Richmond, Virginia, 1999.
| |
|
17
|
"Water Resources Engineering," Mays, L.W., John
Wiley & Sons, Inc., 2005.
| |
|
18
|
"Urban Hydrology for Small Watersheds," Technical
Report 55, US Department of Agriculture, Natural Resources Conservation
Service, 1986.
| |
|
19
|
US EPA, Region 1 New England 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.
(1)
Acceptable methods of pretreatment are listed below.
|
Hot Spot Land Use
|
Pretreatment Methods
| |
|---|---|---|
|
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
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 Borough 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.
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 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 streambank destabilization, to satisfy state water quality requirements,
by controlling the two-year-postdevelopment runoff to a thirty-percent
release rate.
U.
The Borough 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.[6]
[6]
Editor's Note: See 35 P.S. § 691.1
et seq.
A.
Mapping of stormwater management districts. To implement
the provisions of the Catasauqua Creek Watershed Stormwater Management
Plan, the Borough is hereby divided into stormwater management districts
consistent with the Catasauqua 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 Borough office. A copy of the official map at a reduced scale
is included in Appendix A for general reference.[1]
[1]
Editor's Note: Said Map is included at the end of this chapter.
B.
Description of stormwater management districts. Two
types of stormwater management districts may be applicable to the
Borough, 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 postdevelopment 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 § 225-17P. 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 § 225-17D. 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 § 225-15.
(2)
Dual release rate districts. Within these districts,
the two-year postdevelopment peak discharge must be controlled to
30% of the predevelopment two-year runoff peak. Further, the ten-year,
twenty-five-year, and one-hundred-year postdevelopment peak runoff
must be controlled to the stated percentage of the predevelopment
peak. Release rates associated with the ten-year through one-hundred-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-thirty-percent
release rate.)
A.
Applicants shall provide a comparative preconstruction
and postconstruction 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 § 225-18.
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.
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 Catasauqua
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 Subsection D 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 Subsection D and the detention criteria in § 225-18.
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 Subsection D 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 Catasauqua Creek or as calculated by an applicant using
an alternate method acceptable to the Borough. The flow values from
the PSRM Model would be supplied to the developer by the Borough 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 Subsection P.
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 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.
(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 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 at the end of this chapter.
C.
Soil thickness is to be measured from the bottom of
any proposed infiltration system.
(1)
The effective soil thickness in the Recommendation
Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock
in Appendix D[2] 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[3], 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]
Editor's Note: Appendix D is included at the end of this chapter.
[3]
Editor's Note: Appendix G is included at the end of this chapter.
(2)
Sites with soil permeability greater than 12.0 inches/hour
or less than 0.5 inch/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.
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.
(1)
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.[4]
[4]
Editor's Note: Appendix C is included at the end of this chapter.
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.[5]
[5]
Editor's Note: Appendix C is included at the end of this chapter.
L.
Runoff curve numbers (CN's) to be used in the soil-cover-complex
method shall be based upon the matrix presented in Appendix C.[6]
[6]
Editor's Note: Appendix C is included at the end of this chapter.
M.
Runoff coefficients for use in the Rational Method
shall be based upon the table presented in Appendix C.[7]
[7]
Editor's Note: Appendix C is included at the end of this chapter.
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.[8]
[8]
Editor's Note: Appendix C is included at the end of this chapter.
(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.[9]
[9]
Editor's Note: Appendix C is included at the end of this chapter.
O.
If using the Rational Method, all predevelopment calculations
for a given discharge direction shall be based on a common time of
concentration considering both on-site and any off-site drainage areas.
If using the Rational Method, all postdevelopment calculations for
a given discharge direction shall be based on a common time of concentration
considering both on-site and any off-site drainage areas.
P.
The Manning Equation shall be used to calculate the
capacity of watercourses. Manning 'n' values used in the calculations
shall be consistent with the table presented in Appendix C[10] or other appropriate standard engineering 'n' value resources.
Pipe capacities shall be determined by methods acceptable to the Borough.
[10]
Editor's Note: Appendix C is included at the end of this chapter.
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.
