[Ord. No. 872, 11/7/2022]
1.
All regulated activities in the municipality shall be subject to
the stormwater management requirements of this Part.
2.
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 Part.
3.
Stormwater management plans approved by the municipality, in accordance
with § 148, shall be on site throughout the duration of
the regulated activity.
4.
The municipality may, after consultation with DEP, approve measures
for meeting the state water quality requirements other than those
in this Part, 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.
5.
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 Part 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), No. 363-2134-008, as amended and updated.
6.
Storm drainage systems 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 Part.
7.
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 Part. If diffused flow is proposed to be concentrated
and discharged onto adjacent property, the developer must obtain the
written approval of the affected property owner(s). 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.
8.
Where a site is traversed by watercourses other than those for which
a 100-year floodplain is defined by the municipality, there shall
be provided drainage easements conforming substantially with the line
of such watercourses. The width of any easement shall be adequate
to provide for unimpeded flow of storm runoff based on calculations
made in conformance with § 128 for the 100-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 100-year floodplain is formally defined are subject to the applicable
municipal floodplain regulations.
9.
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 Part as to prevent accelerated
erosion in watercourse channels and at all points of discharge.
11.
Infiltration for stormwater management is encouraged where soils
and geology permit, consistent with the provisions of this Part and,
where appropriate, the Recommendation Chart for Infiltration Stormwater
Management BMPs in Carbonate Bedrock in Appendix D.[3]
[3]
Editor's Note: Said appendix is on file in Borough offices.
12.
All regulated activities shall include such measures as necessary
to:
A.
Protect health, safety, and property.
B.
Meet the water quality goals of this Part by implementing measures
to:
(1)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(2)
Maintain or extend riparian buffers.
(3)
Avoid erosive flow conditions in natural flow pathways.
(4)
Minimize thermal impacts to waters of this Commonwealth.
(5)
Disconnect impervious surfaces by directing runoff to pervious
areas, wherever possible.
C.
Incorporate methods described in the Pennsylvania Stormwater Best
Management Practices Manual (BMP Manual).
13.
The design of all facilities over karst shall include an evaluation
of measures to minimize adverse effects.
14.
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 Part.
15.
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.
16.
The design storm volumes to be used in the analysis of peak rates
of discharge should be obtained from the latest version of the Precipitation-Frequency
Atlas of the United States, National Oceanic and Atmospheric Administration
(NOAA), National Weather Service, Hydrometeorological Design Studies
Center, Silver Spring, Maryland. NOAA's Atlas 14 can be accessed
at: http://hdsc.nws.noaa.gov/hdsc/pfds/.
17.
18.
Various BMPs and their design standards are listed in the BMP Manual.
[Ord. No. 872, 11/7/2022]
1.
Other regulations contain independent permit requirements that apply
to certain regulated and earth disturbance activities eligible for
authorization by the Municipality in accordance with the permitting
requirements in this Part. Permit requirements pursuant to those other
regulations must be met prior to commencement, and during the conduct,
of such 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, including wetlands, subject to permit by DEP under
25 Pa. Code Chapter 105.
D.
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.
E.
Projects that involve use of PennDOT right-of-way, or that involve
new discharges onto or toward PennDOT right-of-way, are subject to
the requirements, including the permitting requirements, of Title
67, Chapter 441 of the Pennsylvania Code.
[Ord. No. 872, 11/7/2022]
1.
No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of an erosion and
sediment control plan for construction activities. Written approval
by DEP or a delegated County Conservation District shall satisfy this
requirement.
2.
A written erosion and sediment control plan is required by DEP regulations
for any earth disturbance activity under Pa. Code § 102.4(b).
3.
A DEP NPDES stormwater discharges associated with construction activities
permit is required for regulated earth disturbance activities of one
acre or greater under Pa. Code Chapter 92.
4.
Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate DEP regional office or County Conservation
District must be provided to the municipality before the commencement
of an earth disturbance activity.
5.
A copy of the erosion and sediment control plan and any permit, as
required by DEP regulations, shall be available at the project site
at all times.
[Ord. No. 872, 11/7/2022]
1.
The green infrastructure and low-impact development practices provided in the BMP Manual shall be utilized for all regulated activities wherever possible. Water volume controls shall be implemented using the Design Storm Method in Subsection 1A.
A.
The Design Storm Method (CG-1 in the BMP Manual) is applicable to
any size of regulated activity. This method requires detailed modeling
based on site conditions.
B.
The water volume controls 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 water volume controls calculations and do not
require treatment.
C.
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.
D.
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: Said appendix is on file in Borough offices.
E.
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 two feet; except for infiltration of residential
roof runoff where the seasonal high water table must be below the
invert of the BMP.
(3)
Soil permeability (as measured using the standards listed in
Appendix C of the Pennsylvania Stormwater Best Practices Manual) greater
than or equal to 0.1 inches/hour and less than or equal to 10 inches
per hour.
(5)
Fifty feet from septic system drainfields.
(6)
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.
F.
In entirely carbonate areas, where the applicant intends to use infiltration
BMPs, the preliminary site investigation described in Appendix G[2] 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, along with the buffer from special geologic features shall be
compared to the Recommendation Chart for Infiltration Stormwater Management
BMPs in Carbonate Bedrock in Appendix D[3] to determine if the site is recommended for infiltration. In addition to the recommendation from Appendix D, the conditions listed in § 124, Subsection 1F are required for infiltration in carbonate areas.
G.
Site areas proposed for infiltration shall be protected from disturbance
and compaction except as necessary for construction of infiltration
BMPs.
I.
Stormwater runoff from hot spot land uses shall be pre-treated. Suggested
methods of pre-treatment are listed in Appendix H.
J.
The use of infiltration BMPs is prohibited on hot spot land use areas
unless the applicant can demonstrate that existing and proposed site
conditions, including any proposed runoff pre-treatment, create conditions
suitable for runoff infiltration under this Part.
K.
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.
L.
Stormwater drainage wells may only be used for runoff from roof areas.
M.
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 § 124, Subsection 1F, 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.
N.
The municipality may, after consultation with DEP, approve alternative
methods for meeting the state water volume control requirements other
than those in this Part, provided that they meet the minimum requirements
of, and do not conflict with, state law, including but not limited
to the Clean Streams Law.[5]
[5]
Editor's Note: See 35 P.S. § 691.1 et seq.
[Ord. No. 872, 11/7/2022]
1.
The entire water volume control as calculated in § 124,
Subsection 1A of this Part shall be captured and treated by either
direct recharge/subsurface and/or vegetated/surface BMPs.
2.
As much proposed impervious area as practical shall be directed to
water volume control BMPs.
3.
Existing impervious area that is not proposed to be treated by direct
recharge/subsurface BMPs should be excluded from all water balance
calculations.
4.
Vegetated/surface BMPs shall be employed "first" for the site to
capture the equivalent of a minimum of 0.38 inches 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[1] 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.
[1]
Editor's Note: Said appendix is on file in Borough offices.
5.
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.
A.
For development sites with greater than 33% proposed impervious cover:
(1)
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.
(2)
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
water volume control.
(3)
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 shall
be used to assure that the maximum direct recharge standard is met.
B.
The maximum 30% direct recharge standard applies on an overall site
basis, rather than in each drainage direction.
[Ord. No. 872, 11/7/2022]
1.
Mapping of Stormwater Management Districts. To implement the provisions
of the Catasauqua Creek Watershed and Lehigh River Subbasin 4 Stormwater
Management Plan, the Borough is hereby divided into stormwater management
districts consistent with the Catasauqua Creek Release Rate Map presented
in this Part. 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 appendix is on file in Borough offices.
2.
Description of Stormwater Management Districts. Three types of stormwater
management districts may be applicable to the Borough, namely Conditional
No Detention I Districts, Conditional No Detention II Districts and
Dual Release Rate Districts, as described below:
A.
Conditional No Detention I Districts. Within these districts, the
capacity of the "local seven" runoff conveyance facilities (as defined
in Subpart 1A 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 Part. 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 Subpart 1A), 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 § 127, Subsection 15. 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 § 127, Subsection 4 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 volume requirements § 124.
B.
Conditional No Detention II Districts. Within these districts, the capacity of the local runoff conveyance facilities must be calculated in the same manner as the Conditional No Detention I Districts. In this case, however, adequate capacity must be demonstrated from the site to the Lehigh River. After determining if adequate capacity exists, the developer shall use either no detention, 100% release rate or provide capacity improvements as detailed in Subsection 2A, Conditional No Detention I Districts.
C.
Dual Release Rate Districts. Within this district, the two-year post-development
runoff must be controlled to 30% of the redevelopment two-year runoff
peak. Further, the ten-year, twenty-five year, and 100-year post-development
runoff must be controlled to 100% of the predevelopment peak.
[Ord. No. 872, 11/7/2022]
1.
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 Part.
2.
Any stormwater management controls required by this Part and subject
to a dual release rate criteria shall meet the applicable release
rate criteria for each of the two-, ten-, twenty-five- and 100-year
return period runoff events consistent with the calculation methodology
specified in § 128.
3.
The exact location of the Stormwater Management District boundaries
as they apply to a given development site shall be determined by mapping
the boundaries using the two-foot topographic contours provided as
part of the drainage plan. The District boundaries as originally drawn
coincide with topographic divides or, in certain instances, are drawn
from the intersection of the watercourse and a physical feature, such
as the confluence with another watercourse or a potential flow obstruction
(e.g., road, culvert, bridge, etc.). The physical feature is the downstream
limit of the subarea, and the subarea boundary is drawn from that
point upslope to each topographic divide along the path perpendicular
to the contour lines.
4.
Any downstream capacity analysis conducted in accordance with this
Part shall use the following criteria for determining adequacy for
accepting increased peak flow rates:
A.
Natural or man-made channels or swales must be able to convey the
increased runoff associated with a two-year return period event within
their banks at velocities consistent with protection of the channels
from erosion. Acceptable velocities shall be based upon criteria included
in the DEP Erosion and Sediment Pollution Control Program Manual (April
1990). Permissible velocities from the DEP Manual for selected channels
are presented in Appendix C.[1]
[1]
Editor's Note: Said appendix is on file in Borough offices.
B.
Natural or man-made channels or swales must be able to convey the
increased twenty-five-year return period runoff without creating any
hazard to persons or property.
C.
Culverts, bridges, storm sewers or any other facilities which must
pass or convey flows from the tributary area must be designed in accordance
with DEP Chapter 105 regulations (if applicable) and, at minimum,
pass the increased twenty-five-year return period runoff.
5.
For a proposed development site located within one release rate category
subarea, the total runoff from the site shall meet the applicable
release rate criteria for development sites with multiple directions
of runoff discharge; individual drainage directions may be designed
for up to a 100% release rate so long as the total runoff from the
site is controlled to the applicable release rate.
6.
For a proposed development site located within two or more release
category subareas, the peak discharge rate from any subarea shall
be the predevelopment peak discharge for that subarea multiplied by
the applicable release rate. The calculated peak discharges shall
apply regardless of whether the grading plan changes the drainage
area by subarea. An exception to the above may be granted if discharges
from multiple subareas recombine in proximity to the site. In this
case, peak discharge in any direction may be a 100% release rate,
provided that the overall site discharge meets the weighted average
release rate.
7.
For a proposed development site located partially within a release
rate category subarea and partially within a conditional/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. No portion of a site may be re-graded
between areas within the Catasauqua Creek Watershed Study Area and
any adjacent watershed except as part of a no-harm or hardship waiver
procedure.
8.
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 § 127, Subsection 4 and the minimum orifice criteria.
9.
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 § 127, Subsection 4 and the detention criteria in § 128. In addition to the criteria in § 127, Subsection 4 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.
10.
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.
11.
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.
12.
Development proposals which, through groundwater recharge or other
means, do not increase the rate or volume of runoff discharged from
the site are not subject to the release rate provisions of this Part.
13.
No-Harm Water Quantity Option. 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 this Part. Special circumstances are defined as any hydrologic or hydraulic aspects of the development itself not specifically considered in the development of the plan runoff control strategy. Proof of "no harm" would have to be shown from the development site through the remainder of the downstream drainage network to the confluence of the creek with the Lehigh River. Proof of no harm must be shown using the capacity criteria specified in § 127, Subsection 4 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- and 100-year) shall
be the values from the calibrated PSRM Model for the Catasauqua Creek
Watershed 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.
D.
Any downstream capacity improvements proposed by the developer as part of a "no harm" justification would be designed using the capacity criteria specified in § 127, Subsection 4 Peak flow contributions to the proposed improvements shall be calculated as the larger of: (1) assuming the local watershed is in the existing condition, or 2) assuming that the local watershed is developed per current zoning and using the specified runoff controls.
14.
Regional Detention Alternatives. For certain areas within the study
area, it may be more cost effective to provide one control facility
for more than one development site than to provide an individual control
facility for each development site. The initiative and funding for
any regional runoff control alternatives are the responsibility of
prospective developers. The design of any regional control basins
must incorporate reasonable development of the entire upstream watershed.
The peak outflow of a regional basin would be determined on a case-by
case-basis using the hydrologic model of the watershed consistent
with protection of the down- stream watershed areas. "Hydrologic model"
refers to the calibrated version of the Penn State Runoff Model as
developed for the stormwater management plan.
15.
Capacity Improvements. In certain instances, primarily within the conditional no detention areas, local drainage conditions may dictate more stringent levels of runoff control than those based upon protection of the entire watershed. In these instances, if the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then the capacity improvements could be provided by the developer in lieu of runoff controls on the development site. Peak flow calculations are to 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 peak flows and the capacity criteria specified in § 127, Subsection 4. 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.
16.
Release rates need to be met year round. Designs involving BMPs that
function differently in winter versus non-winter conditions (e.g.,
capture/reuse with spray irrigation shut off for the winter) must
still meet release rates during the winter.
[Ord. No. 872, 11/7/2022]
1.
Stormwater runoff from all development sites shall be calculated
using either the Rational Method or the Soil-Cover-Complex methodology.
2.
Infiltration BMP loading rate percentages in the Recommendation Chart
for Infiltration Stormwater Management BMPs in Carbonate Bedrock in
Appendix D[1] shall be calculated as follows:
|
Area Tributary to infiltration BMP
|
*100%
|
|
Base Area of infiltration BMP
|
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%.
[1]
Editor's Note: Said appendix is on file in Borough offices.
3.
The design of any detention basin intended to meet the requirements
of this Part 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 another
Rational hydrograph that closely approximates the volume of the Universal
Rational Hydrograph.
4.
BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall be routed using the storage indication method.
5.
BMPs designed to store or infiltrate runoff and discharge to surface
runoff or pipe flow shall provide storage volume for the full water
volume control below the lowest outlet invert.
6.
Wet detention ponds designed to have a permanent pool for the water
volume control 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.
7.
All aboveground stormwater detention facilities shall provide a minimum
0.5 feet 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 feet 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:
A.
Bioretention BMPs with a ponded depth less than or equal to 0.5 feet
are exempt from the freeboard requirements.
B.
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 feet of freeboard to the top of berm, whichever
is greater.
C.
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 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 Chapter 105 regulations and may be required to pass a storm greater
than the 100-year event.
8.
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
water volume control.
9.
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 Part may be
taken from NOAA Atlas 14, Precipitation Frequency Atlas of the United
States, current volume, or the Pennsylvania Department of Transportation
Drainage Manual, 2015 Edition for Region 4. The following values are
taken from the Drainage Manual:
|
Return Period
|
24-Hour Rainfall Depth
|
|---|---|
|
1-year
|
2.64 inches
|
|
2-year
|
3.16 inches
|
|
5-year
|
3.91 inches
|
|
10-year
|
4.57 inches
|
|
25-year
|
5.60 inches
|
|
50-year
|
6.53 inches
|
|
100-year
|
7.63 inches
|
A graphical and tabular presentation of the Type II
twenty-four-hour distribution is included in Appendix C.[2]
[2]
Editor's Note: Said appendix is on file in Borough offices.
10.
Runoff calculations using the Rational Method shall use rainfall
intensities consistent with appropriate times of concentration and
return periods and NOAA Atlas 14, Precipitation Frequency Atlas of
the United States Precipitation and Intensity Charts, current volume,
as presented in Appendix C.
11.
Runoff curve numbers (CN's) to be used in the Soil-Cover-Complex
method shall be based upon the table presented in Appendix C.
12.
Runoff coefficients for use in the Rational Method shall be based
upon the table presented in Appendix C.
13.
All time of concentration calculations shall use a segmental approach
which may include one or all of the flow types below:
A.
Sheet flow (overland flow) calculations shall use either the NRCS
average velocity chart (Figure 3-1, Technical Release-55, 1975) or
the modified kinematic wave travel time equation (equation 3-3, NRCS
TR-55, June 1986). If using the modified kinematic wave travel time
equation, the sheet flow length shall be limited to 50 feet for designs
using the Rational Method and limited to 150 feet for designs using
the Soil-Cover-Complex method.
B.
Shallow concentrated flow travel times shall be determined from the
watercourse slope, type of surface and the velocity from Figure 3-1
of TR-55, June 1986.
C.
Open channel flow travel times shall be determined from velocities
calculated by the Manning Equation. Bankfull flows shall be used for
determining velocities. Manning 'n' values shall be based
on the table presented in Appendix C.
D.
Pipe flow travel times shall be determined from velocities calculated
using the Manning Equation assuming full flow and the Manning 'n'
values from Appendix C.
14.
If using the Rational Method, all pre-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. 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.
15.
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 flow
and meet freeboard requirements.
16.
The Manning Equation shall be used to calculate the capacity of watercourses.
Manning 'n' values used in the calculations shall be consistent
with the table presented in Appendix C[3] or other appropriate standard engineering 'n'
value resources. Pipe capacities shall be determined by methods acceptable
to the municipality.
[3]
Editor's Note: Said appendix is on file in Borough offices.
17.
The Pennsylvania DEP, Chapter 105, Rules and Regulations, apply to
the construction, modification, operation or maintenance of both existing
and proposed dams, water obstructions and encroachments throughout
the watershed. Criteria for design and construction of stormwater
management facilities according to this Part may differ from the criteria
that are used in the permitting of dams under the Dam Safety Program.
[Ord. No. 872, 11/7/2022]
1.
In order to protect and improve water quality, a riparian buffer
easement shall be created and recorded as part of any subdivision
or land development that encompasses a riparian buffer.
2.
Except as required by Chapter 102, the riparian buffer easement shall
be measured to be the greater of the limit of the 100-year floodplain
or a minimum of 35 feet from the top of the streambank (on each side).
3.
Minimum Management Requirements for riparian buffers.
A.
Existing native vegetation shall be protected and maintained within
the riparian buffer easement
B.
Whenever practicable invasive vegetation shall be actively removed
and the riparian buffer easement shall be planted with native trees,
shrubs and other vegetation to create a diverse native plant community
appropriate to the intended ecological context of the site.
4.
The riparian buffer easement shall be enforceable by the municipality
and shall be recorded in the Northampton County Recorder of Deeds
Office, so that it shall run with the land and shall limit the use
of the property located therein. The easement shall allow for the
continued private ownership and shall count toward the minimum lot
area as required by Zoning, unless otherwise specified in the Borough
Zoning Ordinance.
5.
Any permitted use within the riparian buffer easement shall be conducted
in a manner that will maintain the extent of the existing 100-year
floodplain, improve or maintain the stream stability, and preserve
and protect the ecological function of the floodplain.
7.
Septic drainfields and sewage disposal systems shall not be permitted
within the riparian buffer easement and shall comply with setback
requirements established under 25 Pa. Code Chapter 73.
