A.
Applicants proposing regulated activities in the municipality that do not fall under the exemption criteria shown in § 301-6 shall submit a drainage plan consistent with this chapter and the respective Act 167 stormwater management plan to the municipality for review. The stormwater management criteria of this chapter shall apply to the total proposed development even if development is to take place in stages.
B.
The applicant is required to find practicable alternatives to the
surface discharge of stormwater, the creation of impervious surfaces,
and the degradation of waters of the commonwealth and must maintain
as much as possible the natural hydrologic regime.
C.
The drainage plan must be designed consistent with the sequencing provisions of § 301-43 to ensure maintenance of the natural hydrologic regime, to promote groundwater recharge, and to protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with Article IV of this chapter.
D.
Stormwater drainage systems shall be designed in order to permit
unimpeded flow along natural watercourses, except as modified by stormwater
management facilities or open channels consistent with this chapter.
E.
Existing points of concentrated drainage that discharge onto adjacent
property shall not be altered in any manner which could cause property
damage without permission of the affected property owner(s) and shall
be subject to any applicable discharge criteria specified in this
chapter.
F.
Areas of existing diffused drainage discharge, whether proposed to
be concentrated or maintained as diffused drainage areas, shall be
subject to any applicable discharge criteria in the general direction
of existing discharge, except as otherwise provided by this chapter.
If diffused drainage discharge is proposed to be concentrated and
discharged onto adjacent property, the applicant must document that
adequate downstream conveyance facilities exist to safely transport
the concentrated discharge or otherwise prove that no erosion, sedimentation,
flooding, or other impacts will result from the concentrated discharge.
G.
Where a development site is traversed by existing streams, drainage easements shall be provided conforming to the line of such streams. The terms of the easement shall conform to the stream buffer requirements contained in § 301-45G of this chapter.
H.
Any stormwater management facilities regulated by this chapter that
would be located in or adjacent to waters of the commonwealth or delineated
wetlands shall be subject to approval by DEP through the joint permit
application or the environmental assessment approval process or, where
deemed appropriate, by the DEP general permit process. When there
is a question as to whether wetlands may be involved, it is the responsibility
of the applicant or his agent to show that the land in question cannot
be classified as wetlands; otherwise, approval to work in the area
must be obtained from DEP.
I.
Any proposed stormwater management facilities regulated by this chapter
that would be located on state highway rights-of-way shall be subject
to approval by PennDOT.
J.
Minimization of impervious surfaces and infiltration of runoff through
seepage beds, infiltration trenches, etc., is encouraged where soil
conditions permit in order to reduce the size or eliminate the need
for detention facilities or other structural BMPs.
K.
All stormwater runoff shall be pretreated for water quality prior
to discharge to surface water or groundwater.
L.
All regulated activities within the municipality shall be designed,
implemented, operated, and maintained to meet the purposes of this
chapter, through these two elements:
M.
No regulated earth disturbance activities within the municipality
shall commence until the requirements of this chapter are met.
O.
Operations and maintenance of permanent stormwater BMPs shall be addressed as required by Article VII.
P.
All BMPs used to meet the requirements of this chapter shall conform
to the state water quality requirements and any more stringent requirements
as set forth by the municipality
Q.
Techniques described in Appendix G (Low-Impact Development) of this
chapter[1] shall be considered because they reduce the costs of complying
with the requirements of this chapter and the state water quality
requirements.
[1]
Editor's Note: Appendixes to this chapter are on file
in the Township offices.
R.
In selecting the appropriate BMPs or combinations thereof, the applicant
shall consider the following:
(1)
Total contributing area.
(2)
Permeability and infiltration rate of the site's soils.
(3)
Slope and depth to bedrock.
(4)
Seasonal high-water table.
(5)
Proximity to building foundations and wells.
(6)
Erodibility of soils.
(7)
Land availability and configuration of the topography.
(8)
Peak discharge and required volume control.
(9)
Stream bank erosion.
(10)
Effectiveness of the BMPs to mitigate potential water quality
problems.
(11)
The volume of runoff that will be effectively treated.
(12)
The nature of the pollutant being removed.
(13)
Maintenance requirements.
(14)
Creation/protection of aquatic and wildlife habitat.
(15)
Recreational value.
The following permit requirements may apply to certain regulated
earth disturbance activities and must be met prior to commencement
of regulated earth disturbance activities, as applicable:
A.
All regulated 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 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 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 the municipality receives an approval from the
Conservation District of an erosion and sediment control plan for
construction activities.
B.
DEP has regulations that require an erosion and sediment control
plan for any earth disturbance activity of 5,000 square feet or more,
under 25 Pa. Code § 102.4(b).
D.
Evidence of any necessary permit(s) for regulated earth disturbance
activities from the appropriate DEP regional office or Montgomery
County Conservation District must be provided to the municipality.
E.
A copy of the erosion and sediment control plan and any required
permit, as required by DEP regulations, shall be available on the
project site at all times.
F.
Additional erosion and sediment control design standards and criteria
are recommended to be applied where infiltration BMPs are proposed.
They shall include the following:
(1)
Areas proposed for infiltration BMPs shall be protected from sedimentation
and compaction during the construction phase to maintain maximum infiltration
capacity. Additional measures, such as placement of orange construction
fencing around proposed infiltration BMPs during construction to minimize
or eliminate traffic overtop of these areas, and temporary sealing
off of pipes and inlet connections to infiltration BMPs to prevent
sediment clogging, should be given consideration.
(2)
Infiltration BMPs shall not be constructed nor receive runoff until
the entire drainage area contributory to the infiltration BMP has
achieved final stabilization.
A.
The design of all regulated activities shall include the following
to minimize stormwater impacts:
(1)
The applicant shall find practicable alternatives to the surface
discharge of stormwater, such as those listed in Appendix C, Table
C-4, the creation of impervious surfaces, and the degradation of waters
of the commonwealth and must maintain as much as possible the natural
hydrologic regime of the site.
(2)
An alternative is practicable if it is available and capable of implementation
after taking into consideration existing technology and logistics
in light of overall project purposes and other municipal requirements.
(3)
All practicable alternatives to the discharge of stormwater are presumed
to have less adverse impact on quantity and quality of waters of the
commonwealth unless otherwise demonstrated.
B.
The applicant shall demonstrate that the regulated activities were
designed in the following sequence. The goal of the sequence is to
minimize the increases in stormwater runoff and impacts to water quality
resulting from the proposed regulated activity:
(1)
Prepare an Existing Resource and Site Analysis Map (ERSAM) showing
environmentally sensitive areas, including, but not limited to, steep
slopes, ponds, lakes, streams, wetlands, hydric soils, vernal pools,
stream buffers, hydrologic soil groups, wooded areas, and potential
infiltration areas. Land development, any existing recharge areas,
and other requirements outlined in the municipal SALDO shall also
be included.[1]
(3)
Prepare a draft project layout avoiding sensitive areas identified in § 301-43B(1).
(4)
Identify site-specific existing conditions drainage areas, discharge
points, recharge areas, and hydrologic soil groups A and B (areas
conducive to infiltration). Infiltration should still be considered
in well-draining soils listed as hydrologic soil group C, but additional
soils testing should be performed to verify on-site conditions and
placement of these BMPs.
(6)
Satisfy the groundwater recharge (infiltration) objective (§ 301-44) and provide for stormwater pretreatment prior to infiltration.
(8)
Provide stream bank erosion protection in accordance with § 301-46 stream bank erosion requirements.
(10)
Prepare final project design to maintain existing conditions
drainage areas and discharge points, to minimize earth disturbance
and impervious surfaces, and, to the maximum extent possible, to ensure
that the remaining site development has no surface or point discharge.
(11)
Conduct a proposed conditions runoff analysis based on the final design that meets the management district requirements (§ 301-47).
(12)
Manage any remaining runoff prior to discharge through detention,
bioretention, direct discharge, or other structural control.
Maximizing the groundwater recharge capacity of the area being developed is required. Design of the infiltration facilities shall consider groundwater recharge to compensate for the reduction in the recharge that occurs when the ground surface is disturbed or impervious surface is created. It is recommended that roof runoff be directed to infiltration BMPs that may be designed to compensate for the runoff from parking areas. These measures are required to be consistent with § 301-3 and to take advantage of utilizing any existing recharge areas. Infiltration may not be feasible on every site due to site-specific limitations such as soil type. If it cannot be physically accomplished, then the design professional shall be responsible to show that this cannot be physically accomplished. Appropriate soils testing and/or geotechnical evaluation should be included as part of any documentation for infiltration BMPs. If it can be physically accomplished, then the volume of runoff to be infiltrated shall be determined from § 301-44A(2).
A.
Infiltration BMPs shall meet the following minimum requirements:
(1)
Infiltration BMPs intended to receive runoff from developed areas
shall be selected based on suitability of soils and site conditions
and shall be constructed on soils that have the following characteristics:
(a)
A minimum depth of 24 inches, between the bottom of the BMP
and the top of the limiting zone (e.g., seasonal high-water table,
groundwater, bedrock, etc.).
(b)
An infiltration rate sufficient to accept the additional stormwater
load and dewater completely as determined by field tests conducted
by the applicant's design professional.
(c)
The infiltration facility shall be capable of completely infiltrating
the recharge (infiltration) volume (Rev) within
three days (72 hours) or less.
(d)
Pretreatment shall be provided prior to infiltration.
(2)
The size of the infiltration facility shall be based upon the Net
Two Year Volume Approach, where the recharge (infiltration) volume
(Rev) to be captured and infiltrated shall
be the volume difference between the pre-development two-year, twenty-four-hour
storm event and post-development two-year, twenty-four-hour storm
event.
(3)
The recharge volume calculated using this section is the minimum
volume the applicant must control through an infiltration BMP facility.
However, if a site has areas of soils where additional volume of recharge
can be achieved, the applicant is encouraged to infiltrate as much
of the stormwater runoff from the site as possible.
B.
Soils testing. If on-lot infiltration is proposed as part of a project,
the applicant's design professional must demonstrate to the satisfaction
of the municipality that the soils are conducive to infiltration at
the proposed location of infiltration facilities. Soils testing shall
be completed as follows:
(1)
Soils testing must be conducted by an individual or company acceptable
to the municipality and, at a minimum, shall address depth to limiting
zone, soil permeability, and subgrade stability. The municipality
must be notified 36 hours prior to soils testing, which may then be
observed by a representative of the municipality.
(2)
Analyze hydrologic soil groups as well as natural and man-made features
within the site to determine general areas of suitability for infiltration
practices. In areas where development on fill material is under consideration,
conduct geotechnical investigations of subgrade stability; infiltration
may not be ruled out without conducting these tests.
(3)
Conduct field testing, including test pits to determine soil horizons
and depth to limiting zone and permeability tests, at the elevation
of the proposed infiltration facility surface, to determine the appropriate
hydraulic conductivity rate. Double ring infiltrometer or hydraulic
conductivity tests should be used to determine soil permeability (percolation
tests are not recommended for design purposes unless permitted by
the municipality Engineer). Site evaluation and soils testing should
be conducted in accordance with Appendix C of the Pennsylvania Stormwater
Best Management Practices Manual.
(4)
The proposed infiltration facilities shall be designed for the required
recharge (Rev) volume based on the field-determined
capacity at the surface elevation of the proposed infiltration facility.
C.
Stormwater hotspots.
(1)
Below is a list of examples of designated hotspots. If a site is
designated as a hotspot, it has important implications for how stormwater
is managed. First and foremost, untreated stormwater runoff from hotspots
shall not be allowed to recharge into groundwater where it may contaminate
water supplies. Therefore, the Rev requirement
shall not be applied to development sites that fit into the hotspot
category (the entire WQv must still be treated).
Second, a greater level of stormwater treatment shall be considered
at hotspot sites to prevent pollutant washoff after construction.
The Environmental Protection Agency's (EPA) NPDES stormwater
program requires some industrial sites to prepare and implement a
stormwater pollution prevention plan.
(2)
Examples of hotspots:
(a)
Vehicle salvage yards and recycling facilities.
(b)
Vehicle fueling stations.
(c)
Vehicle service and maintenance facilities.
(d)
Vehicle and equipment cleaning facilities.
(e)
Fleet storage areas (bus, truck, etc.).
(f)
Industrial sites based on Standard Industrial Codes.
(g)
Marinas (service and maintenance).
(h)
Outdoor liquid container storage.
(i)
Outdoor loading/unloading facilities.
(j)
Public works storage areas.
(k)
Facilities that generate or store hazardous materials.
(l)
Commercial container nursery.
(m)
Other land uses and activities as designated by an appropriate
review authority.
(3)
The following land uses and activities are not normally considered
hotspots:
(4)
While large highways (average daily traffic volume [ADT] greater
than 30,000 are not designated as stormwater hotspots, it is important
to ensure that highway stormwater management plans adequately protect
groundwater.
D.
Caution shall be exercised where infiltration is proposed in SWPAs
as defined by the local municipality or water authority.
E.
Infiltration facilities shall be used in conjunction with other innovative
or traditional BMPs, stormwater control facilities, and nonstructural
stormwater management alternatives.
F.
Caution shall be exercised where salt or chloride (municipal salt
storage) would be a pollutant since soils do little to filter this
pollutant, and it may contaminate the groundwater. The qualified design
professional shall evaluate the possibility of groundwater contamination
from the proposed infiltration facility and perform a hydrogeologic
justification study if necessary. Specific consideration should be
given to the particular type of salt or deicing material to be used
within this watershed in regards to its potential long-term effects
on the soils, especially in areas that contain clay soil.
H.
An impermeable liner will be required in detention basins where the
possibility of groundwater contamination exists. A detailed hydrogeologic
investigation may be required by the municipality.
I.
The municipality shall require the applicant to provide safeguards
against groundwater contamination for land uses that may cause groundwater
contamination should there be a mishap or spill.
J.
Infiltration design criteria.
(1)
All infiltration systems shall have appropriate positive overflow
controls to prevent storage within one foot of the finished surface
or grade.
(2)
All infiltration systems shall have a minimum setback of 15 feet
from principal structures, 10 feet from property lines, 100 feet from
wells, and 50 feet from septic system drain fields. Care should be
taken to prevent any seepage into subgrade structures.
(3)
Surface inflows shall be treated to prevent the direct discharge
of sediment and pollutants into the infiltration system; accumulated
sediment reduces stormwater storage capacity and ultimately clogs
the infiltration mechanism.
(4)
No sand or other particulate matter may be applied to a porous paving
surface for winter ice conditions.
(5)
During site construction, all recharge system components shall be
protected from compaction due to heavy equipment operation or storage
of fill or construction material. Recharge areas shall be protected
from sedimentation. All areas designated for recharge shall not receive
runoff until the contributory drainage area has achieved final stabilization.
(6)
The following procedures and materials shall be required during the
construction of all subsurface facilities:
(a)
Excavation for the infiltration facility shall be performed
with equipment which will not compact the bottom of the seepage bed/trench,
or like facility.
(b)
The bottom of the bed and/or trench shall be scarified prior
to the placement of aggregate.
(c)
Only clean aggregate, free of fines, shall be allowed.
(d)
The top and sides of all seepage beds, trenches, or like facilities
shall be covered with drainage filtration fabric. Fabric shall meet
the specifications of PennDOT Publication 408, Section 735 Construction
Class 1.
(e)
Perforated distribution pipes connected to centralized catch
basins and/or manholes with provision for the collection of debris
shall be provided in all facilities. The perforated pipes shall distribute
stormwater throughout the entire seepage bed/trench, or like facility.
(7)
All infiltration facilities which service more than one lot and are
considered a common facility shall have an easement provided to the
municipality for future access if necessary.
(8)
No more than 50% of the required infiltration volume may be provided
in detention basin bottoms. The remaining 50% of infiltration volumes
shall be provided at or near the proposed impervious coverage.
The applicant shall comply with the following water quality
requirements of this article:
A.
No regulated earth disturbance activities within the municipality
shall commence until approval by the municipality of a plan that demonstrates
compliance with post-construction state water quality requirements.
B.
The BMPs shall be designed, implemented, and maintained to meet state
water quality requirements and any other more stringent requirements
as determined by the municipality.
C.
To control post-construction stormwater impacts from regulated earth
disturbance activities, state water quality requirements can be met
by BMPs, including site design, which provide for replication of pre-construction
stormwater infiltration and runoff conditions so that post-construction
stormwater discharges do not degrade the physical, chemical, or biological
characteristics of the receiving waters. As described in the DEP Comprehensive
Stormwater Management Policy (No. 392-0300-002, September 28, 2002),
this may be achieved by the following:
(1)
Infiltration: replication of pre-construction stormwater infiltration
conditions;
(2)
Treatment: use of water quality treatment BMPs to ensure filtering
out of the chemical and physical pollutants from the stormwater runoff;
and
(3)
Stream bank and streambed protection: management of volume and rate
of post-construction stormwater discharges to prevent physical degradation
of receiving waters (e.g., from scouring).
D.
Developed areas shall provide adequate storage and treatment facilities necessary to capture and treat stormwater runoff. If site conditions allow for infiltration, the water quality volume and the recharge volume are the same volume and may be managed in a single facility. If infiltration cannot be physically accomplished, the water quality volume should be calculated using the Net Two Year Volume Approach described in § 301-44A(2). In this case, the water quality volume may be captured and treated by methods other than infiltration BMPs. This volume requirement can be accomplished by the permanent volume of a wet basin or the detained volume from other BMPs. Where appropriate, wet basins shall be utilized for water quality control and shall follow the guidelines of the BMP manuals referenced in Appendix D.[1] The water quality volume shall take a minimum of 24 hours
to be discharged from a BMP facility. Release of the water quality
volume can begin at the start of the storm (i.e., the invert of the
water quality orifice is at the invert of the facility). The design
of the facility shall provide for protection from clogging and unwanted
sedimentation.
[1]
Editor's Note: Appendixes to this chapter are on file
in the Township offices.
E.
For areas within defined special protection subwatersheds that include
EV and HQ waters, the temperature and quality of water and streams
shall be maintained through the use of temperature-sensitive BMPs
and stormwater conveyance systems.
F.
To accomplish the above, the applicant shall submit original and
innovative designs to the Municipal Engineer for review and approval.
Such designs may achieve the water quality objectives through a combination
of different BMPs.
G.
If a perennial or intermittent stream passes through the site, the
applicant shall create a stream buffer extending a minimum of 50 feet
to either side of the top-of-bank of the channel. The buffer area
shall be maintained with and encouraged to use appropriate native
vegetation (refer to Appendix B of the Pennsylvania Stormwater Best
Management Practices Manual, latest version, for plant lists). If
the applicable rear or side yard setback is less than 50 feet or a
stream traverses the site, the buffer width may be reduced to 25%
of the setback and/or to a minimum of 10 feet. If an existing buffer
is legally prescribed (i.e., deed, covenant, easement, etc.) and it
exceeds the requirements of this chapter, the existing buffer shall
be maintained. This does not include lakes or wetlands.
H.
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office must be provided to the municipality. The issuance of an NPDES construction permit (or permit coverage under the statewide general permit [PAG-2]) satisfies the requirements of § 301-45A.
A.
In addition to the control of water quality volume (in order to minimize
the impact of stormwater runoff on downstream stream bank erosion),
the primary requirement is to design a BMP to detain the proposed
conditions two-year, twenty-four-hour design storm to the existing
conditions one-year flow using the SCS Type II distribution. Additionally,
provisions shall be made (such as adding a small orifice at the bottom
of the outlet structure) so that the proposed conditions one-year
storm takes a minimum of 24 hours to drain from the facility from
a point where the maximum volume of water from the one-year storm
is captured (i.e., the maximum water surface elevation is achieved
in the facility). Release of water can begin at the start of the storm
(i.e., the invert of the water quality orifice is at the invert of
the facility).
B.
The minimum orifice size in the outlet structure to the BMP shall
be three inches in diameter where possible, and a trash rack shall
be installed to prevent clogging. On sites with small drainage areas
contributing to this BMP that do not provide enough runoff volume
to allow a twenty-four-hour attenuation with the three-inch orifice,
the calculations shall be submitted showing this condition. Orifice
sizes less than three inches can be utilized, with approval by the
municipality Engineer, provided that the design will prevent clogging
of the intake.
A.
Upper Pottsgrove Township is hereby divided into Stormwater Management
Districts based on watershed boundaries. The Swamp Creek Watershed
shall be District I and shall be in accordance with the Swamp Creek
Watershed Act 167 Stormwater Management Plan prepared by Montgomery
County and approved by PADEP. The remainder of the Township shall
be considered District II. The boundaries of the stormwater management
districts are shown on the map included in Appendix B.[1]
[1]
Editor's Note: Appendixes to this chapter are on file
in the Township offices.
B.
Peak runoff control shall be designed to reduce the post-development
peak flow as follows:
(1)
In District I (Swamp Creek Watershed): to 50% of the pre-development
peak flow for the two-year, five-year, ten-year, twenty-five-year,
fifty-year, and one-hundred-year storm events.
C.
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.
D.
Off-site areas. Off-site areas that 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.
E.
Site areas. Where the site area to be impacted by a proposed development
activity differs from the total site area, only the proposed impact
area utilizing stormwater management measures shall be subject to
the peak rate control standards noted above. In other words, unimpacted
areas bypassing the stormwater management facilities would not be
subject to the peak rate control standards.
F.
Alternate criteria for redevelopment sites. For redevelopment sites,
one of the following minimum design parameters shall be accomplished,
whichever is most appropriate for the given site conditions as determined
by Upper Pottsgrove Township:
A.
Stormwater runoff from all development sites with a drainage area
of greater than five acres shall be calculated using a generally accepted
calculation technique that is based on the NRCS Soil Cover Complex
Method. Table 301-48-1 summarizes acceptable computation methods,
and the method selected by the design professional shall be based
on the individual limitations and suitability of each method for a
particular site. Note that successors to the methods listed in Table
301-48-1 are also acceptable, such as WinTR55 for TR-55 and WinTR20
for TR-20. The municipality may allow the use of the Rational Method
to estimate peak discharges from drainage areas that contain less
than five acres.
|
Table 301-48-1
| |||
|---|---|---|---|
|
Acceptable Computation Methodologies for Stormwater Management
Plans
| |||
|
Method
|
Developed by
|
Applicability
| |
|
TR-20 (or commercial computer package based on TR-20)
|
USDA NRCS
|
Applicable where use of a full hydrologic computer model is
desirable or necessary
| |
|
TR-55 (or commercial computer package based on TR-55)
|
USDA NRCS
|
Applicable for land development plans within limitations described
in TR-55
| |
|
HEC-1/HEC-HMS
|
U.S. Army Corps of Engineers
|
Applicable where use of a full hydrologic computer model is
desirable or necessary
| |
|
PSRM
|
Penn State University
|
Applicable where use of a hydrologic model is desirable or necessary;
simpler than TR-20 or HEC-1
| |
|
Rational Method (or commercial computer package based on Rational
Method)
|
Emil Kuichling (1889)
|
For sites less than five acres or as approved by the municipality
and/or Municipal Engineer
| |
|
Other methods
|
Varies
|
Other computation methodologies approved by the municipality
and/or Municipal Engineer
| |
B.
All calculations consistent with this chapter using the Soil Cover
Complex Method shall use the appropriate design rainfall depths for
the various return period storms according to the region in which
they are located as presented in Table C-1 in Appendix C of this chapter.[1] If a hydrologic computer model such as PSRM or HEC-1/HEC-HMS
is used for stormwater runoff calculations, then the duration of rainfall
shall be 24 hours.
[1]
Editor's Note: Appendixes to this chapter are on file
in the Township offices.
C.
The following criteria shall be used for runoff calculations:
(1)
For development sites not considered redevelopment, the ground cover
used in determining the existing conditions flow rates shall be as
follows:
(a)
Wooded sites shall use a ground cover of "woods in good condition."
A site shall be considered to be a wooded site where a biological
community dominated by trees and other woody plants exists that covers
an area of 10,000 square feet or more and contains at least 100 trees
with at least 50% of those trees having a dbh of two inches or greater.
(Duerksen, Christopher J., with Suzanne Richman, Tree Conservation
Ordinances, Planning Advisory Service Report Number 446, American
Planning Association, Chicago, Illinois, and Scenic America, Washington,
D.C., August 1993.)
(b)
The undeveloped portion of the site, including agriculture,
bare earth, and fallow ground, shall be considered as "meadow in good
condition," unless the natural ground cover generates a lower curve
(CN) number or Rational "c" value (i.e., woods) as listed in Tables
C-2 or C-3 in Appendix C of this chapter.[2]
[2]
Editor's Note: Appendixes to this chapter are on file
in the Township offices.
(c)
Off-site land use conditions used to determine storm flows for
designing storm facilities shall be based on existing land uses assuming
winter or poor land cover conditions.
(2)
For development considered redevelopment sites, the ground cover
used in determining the existing conditions flow rates for the developed
portion of the site shall be based upon actual land cover conditions.
D.
All calculations using the Rational Method shall use rainfall intensities
consistent with appropriate times of concentration for overland flow
and return periods presented in the appropriate curves from the PennDOT
Storm-Duration-Frequency Chart. (Region 4 is included as Figure E-3-A.
The user should refer to the Atlas 14, Volume 2, Storm-Duration-Frequency
Chart.) Times of concentration for overland flow shall be calculated
using the methodology presented in Chapter 3 of Urban Hydrology for
Small Watersheds, NRCS, TR-55 (as amended or replaced from time to
time by NRCS). Times of concentration for channel and pipe flow shall
be computed using Manning's Equation.
F.
Runoff coefficients (c) for both existing and proposed conditions
for use in the Rational Method shall be obtained from Table C-3 in
Appendix C of this chapter.
G.
Where uniform flow is anticipated, the Manning Equation shall be
used for hydraulic computations and to determine the capacity of open
channels, pipes, and storm sewers. Values for Manning's roughness
coefficient (n) shall be in accordance with Table C-5 in Appendix
C.
H.
Outlet structures for stormwater management facilities shall be designed
to meet the performance standards of this chapter using any generally
accepted hydraulic analysis technique or method.
I.
The design of any stormwater detention facilities intended to meet
the performance standards of this chapter shall be verified by routing
the design storm hydrograph through these facilities using the Storage-Indication
Method. The design storm hydrograph shall be computed using a calculation
method that produces a full hydrograph. The municipality may approve
the use of any generally accepted full hydrograph approximation technique
that shall use a total runoff volume that is consistent with the volume
from a method that produces a full hydrograph.
A.
Any BMP intended to hold standing water for four days or longer shall
be designed to incorporate biologic controls consistent with the West
Nile Guidance found in Appendix E, PADEP document 363-0300-001, "Design
Criteria - Wetlands Replacement Monitoring" (as amended) (or contact
the Pennsylvania State Cooperative Wetland Center or the Penn State
Cooperative Extension Office for design information).
B.
Any stormwater basin required or regulated by this chapter designed
to store runoff and requiring a berm or earthen embankment shall be
designed to provide an emergency spillway to safely convey flow up
to and including the one-hundred-year proposed conditions. The height
of embankment shall provide a minimum one foot of freeboard above
the maximum pool elevation computed when the facility functions for
the one-hundred-year proposed conditions inflow. Should any BMP require
a dam safety permit under Pa. Chapter 105 regulations,[1] the facility shall be designed in accordance with and
meet the regulations of Pa. Chapter 105 concerning dam safety. Pa.
Chapter 105 may require the safe conveyance of storms larger than
the one-hundred-year event.
[1]
Editor's Note: See 25 Pa. Code Chapter 105.
C.
Any drainage conveyance facility and/or channel not governed by Pa.
Chapter 105 regulations shall be designed to convey, without damage
to the drainage facility or roadway, runoff from the twenty-five-year
storm event. Larger storm events fifty-year and one-hundred-year storms)
shall also be safely conveyed in the direction of natural flow without
creating additional damage to any drainage facilities, nearby structures,
or roadways. Conveyance facilities to or exiting from stormwater management
facilities (i.e., detention basins) shall be designed to convey the
design flow to or from the facility.
D.
Roadway crossings or structures located within designated floodplain
areas shall be able to convey runoff from a one-hundred-year design
storm consistent with Federal Emergency Management Agency National
Flood Insurance Program, Floodplain Management Requirements.
E.
Any facility located within a PennDOT right-of-way shall comply with
PennDOT minimum design standards and permit submission and approval
requirements.
F.
Adequate erosion protection and energy dissipation shall be provided
along all open channels and at all points of discharge. Design methods
shall be consistent with the Federal Highway Administration Hydraulic
Engineering Circular No. 11 (Publication No. FHWA-IP-89-016, as amended)
and the PADEP Erosion and Sediment Pollution Control Program Manual
(Publication No. 363-2134-008, as amended), or other design guidance
acceptable to the Municipal Engineer.
G.
The design of all stormwater management facilities shall incorporate
sound engineering principles and practices. The municipality reserves
the right to disapprove any design that would result in construction
in or continuation of a stormwater problem area.
The following provisions shall be followed and incorporated
into the stormwater management design and construction process:
A.
Stormwater management facilities, including but not limited to recharge
facilities, detention facilities, storm sewers, culverts, bridges
and related drainage installations shall be designed and constructed
to meet the following purposes:
(1)
To permit unimpeded flow of natural watercourses;
(2)
To insure adequate drainage of all low points.
(3)
To intercept stormwater runoff along streets at intervals reasonably
related to the extent and grade of the area drained to prevent flow
of stormwater across intersections;
(4)
To insure adequate and unimpeded flow of stormwater over or under
driveways;
(5)
To prevent excessive flow on or across streets, sidewalks, drives,
parking areas, and any other paved surface or accessway; and
(6)
To lead stormwater away from springs.
B.
All natural streams, channels, swales, drainage systems, and/or areas
of concentration of surface water shall be maintained in their existing
condition except as necessary for those uses that may be permitted
by the Township Zoning Ordinance[1] and as approved by the Township.
C.
Man-made structures shall be kept to a minimum.
D.
Bridges, culverts, or riprap to be placed in or over a stream shall
be chosen and constructed to maintain the natural characteristics
of the stream and shall meet the approval of the municipality and
must obtain necessary approvals from PADEP.
E.
The municipality may require that a landowner or developer provide
reasonable corrective measures to alleviate any existing off-site
drainage problem that may be affected by the proposed land development
or any other regulated activity.
F.
No person shall deposit or place any debris or any other material
whatsoever, or cause such to be thrown or placed, in any channel or
stormwater facility in such a manner as to obstruct free flow.
G.
No stormwater facility shall create health, safety or sanitation
problems.
H.
No stormwater facility shall impact the ability of on-lot sewage
disposal systems to treat waste or adequately infiltrate treated wastewater
effluent.
I.
Various BMPs, both structural and nonstructural, other than those
listed in the following sections, can be utilized in the stormwater
design. Any BMP not addressed in this chapter shall be designed in
accordance with the design parameters found in the PADEP BMP manual,
latest edition. Any design parameters found in the Pennsylvania BMP
Manual for the below BMPs shall apply unless otherwise specified herein.
J.
Reference to publications and source documents shall be deemed to
include any amendments and revisions thereof.
A.
General requirements for all types of basins.
(1)
Basins shall meet the following minimum setbacks measured from the
top and/or toe of slope (whichever is closer):
(a)
From a special geologic feature as defined herein: 50 feet;
(b)
From any property line*: 50 feet;
(c)
From any right-of-way*: 50 feet;
(d)
From any structure*: 50 feet;
(e)
From a wetland: 50 feet; and
(f)
From the top of bank of existing streams: 50 feet.
|
NOTE:
|
|---|
|
* Lesser setbacks can be approved by the Municipal Engineer
on a case-by-case basis.
|
(2)
The use of multiple basin facilities that are smaller and less intrusive
on the site is encouraged.
(3)
Privately owned basin facilities and BMPs shall be located entirely
on one parcel unless otherwise permitted by the municipality.
(4)
Maintenance of a basin facility shall be the responsibility of only one lot owner or, if the facility is located in a common area, the responsibility of the applicable homeowners' association. See Article VII.
(5)
When PADEP requires basin facilities to have a state permit, the
developer shall submit all information to PADEP and obtain all necessary
approvals and permits.
B.
Design requirements for all types of basins.
(1)
For basins that combine rate and volume controls, the infiltration
"discharge" should not be taken into consideration when routing the
peak discharge amounts, nor shall the infiltration volume be used
in the routing.
(2)
It shall be the developer's responsibility to verify if the
site is underlain by karst. Whenever basins will be located in an
area underlain by karst:
(a)
A geological evaluation of the proposed location shall be conducted
to determine susceptibility to sinkhole formations.
(b)
The design of all facilities over limestone formations shall
include measures to prevent groundwater contamination and, where necessary,
sinkhole formation.
(c)
The installation of an impermeable liner may be required.
(d)
A detailed hydrogeologic investigation may be required.
(e)
Uses where a mishap or spill may cause groundwater contamination
will require the developer to provide safeguards against contamination.
(3)
Inlet and outlet structures shall be located at maximum distances
from one another. For aboveground basins, a rock filter berm, rock-filled
gabions, or other baffle may be required between inlet and outlet
areas when the distance is deemed insufficient for water quality purposes.
(4)
A reinforced concrete outlet structure box shall be used to regulate
water flow through all basins and shall incorporate the following
components and criteria:
(a)
A multiple stage outlet release design is encouraged.
(b)
The minimum circular orifice diameter for controlling discharge
rates from basin facilities shall be three inches. Designs where a
lesser size orifice would be required to fully meet release rates,
a three-inch orifice shall be acceptable, provided that as much of
the site runoff as practical is directed to the basin facilities.
(c)
The outlet structure top elevation shall be such that no flow
enters the structure for the twenty-five-year-frequency storm event.
(d)
The base of the outlet structure shall extend a minimum of one
foot below the bottom of the basin for aboveground basins.
(e)
Outlet structure connections shall be watertight.
(f)
A concrete wash (flow channel) across the bottom of the structure
shall be provided.
(g)
Basins with a water depth less than or equal to 1.5 feet may
be exempted from the outlet structure requirements as determined by
the municipality.
(5)
A trash rack shall be provided for all aboveground orifices.
(6)
The outlet pipe shall be reinforced concrete pipe with rubber gaskets/O-ring
joints.
(8)
When the outfall point of a proposed basin facility is located at
a point subject to tailwater conditions, a tailwater elevation at
the outfall point will need to be assumed when performing the basin
facility routing calculations. The tailwater elevation assumed shall
be based on the same frequency of the storm being routed.
(9)
Any pipe or other component that discharges into an aboveground basin
shall discharge at the bottom of the basin and shall be provided with
an appropriate energy dissipater.
(10)
Any pipe or other component that discharges out of a basin shall
be provided with an appropriate energy dissipater.
(11)
Where appropriate, adequate drainage channels shall be provided
and maintained for discharge(s) from the basin. If the basin will
not discharge to a suitable natural drainage channel, the developer
may be required to provide facilities to safely and efficiently convey
the discharge to a suitable drainage channel. Securing necessary drainage
easements for this purpose shall be the sole responsibility of the
developer.
C.
Basins that are designed with berms/earthen embankments shall incorporate
the following minimum standards:
(1)
The height of the berm shall not exceed 15 feet, unless all appropriate
permits are issued by the PADEP.
(2)
The minimum top width of berms shall be 10 feet.
(3)
Side slopes of basins shall:
(a)
Whenever possible, the side slopes and basin shape shall be
as shallow as possible and blend/conform to the natural topography.
(c)
Depending upon the location and the intended use of the detention
facilities during nonrain event times, a flatter side slope, for one
or both slopes, may be required.
(d)
When a basin is to be maintained by a residential lot owner,
the side slope shall be four units horizontally to one unit vertically.
(4)
A key trench shall be provided:
(a)
Extending at least two feet deep in undisturbed soil or to stable
subgrade, whichever is deeper;
(b)
Constructed of compacted relatively impervious material (Unified
Soil Classification CL or ML);
(c)
Having a minimum bottom width of four feet; and
(d)
Having maximum side slopes of one horizontal to one vertical.
(6)
All pipes and culverts through berms shall have properly spaced antiseep
collars incorporating the following requirements:
(7)
Basin bottom grades shall be a minimum of 2% unless designed in combination
with an infiltration facility or other BMP where bottom grade is not
indicated or with the approval of the Municipal Engineer.
(8)
(9)
An emergency spillway shall be provided incorporating the following
requirements:
(a)
The emergency spillway shall be placed in undisturbed earth
whenever possible.
(b)
Emergency spillways shall be designed to safely convey the one-hundred-year
post-development basin inflow with a minimum of six inches of freeboard
above the water surface elevation to the top of berm, assuming blocked
outlet structure conditions. The total minimum depth of emergency
spillways shall be one foot.
(c)
Emergency spillways shall be constructed such that the basin
berm is protected against erosion. When necessary, erosion protection
shall extend along the upstream and downstream berm slopes.
(d)
Basins with a water depth less than or equal to 1.5 feet are
exempt from emergency spillway and freeboard requirements unless otherwise
deemed necessary by the Municipal Engineer.
(10)
When deemed necessary by the Township, stormwater basin facilities
shall be enclosed with a fence of a type acceptable to the Township.
D.
Under ground basins shall incorporate the following minimum standards:
(1)
Flow through the outlet structure shall be attenuated with a concrete
weir wall with appropriately sized orifices. Other designs will be
considered with approval of the municipality.
(2)
Underground facilities that propose pipe storage as a means of detention
shall be constructed of reinforced concrete pipe (RCP) or high-density
polyethylene pipe (HDPE pipe). No ferrous metal pipe shall be allowed.
E.
Wet basins shall incorporate the following minimum standards:
(1)
Water surface area shall not exceed 1/10 of the tributary drainage
area.
(2)
Bank protection shall be provided to prevent erosion.
(3)
Minimum normal water depth shall be four feet.
(4)
Facilities shall be provided to allow the pond level to be lowered
by gravity flow for cleaning purposes and bank and other maintenance.
(5)
Aeration facilities shall be required as necessary to prevent pond stagnation. Manufacturer's information to substantiate the effectiveness of such aeration facilities shall be submitted with the site plans. Agreements for the perpetual operation and maintenance of aeration facilities shall be prepared and provided for review. See Article VII.
(6)
In the event that the water surface of the pond is to be raised for
the purposes of storing water for irrigation or in anticipation of
the evapotranspiration demands of dry weather, the volume remaining
for storage of excess stormwater runoff shall be sufficient to contain
the fifty-year design storm runoff.
F.
The following items shall be submitted for basin review:
(1)
Design computations for the sizing of the outlet structure;
(2)
Stage-storage curve;
(3)
Routed hydrographs for each storm;
(4)
Storage requirement calculations;
(5)
Plan(s) showing the berm/embankment and outlet structure in plan
and cross-section views as well as details, including but not limited
to:
(a)
Inlet pipe and energy dissipater;
(b)
Top-of-berm elevations;
(c)
Width of the top of the berm;
(d)
Outlet pipe and energy dissipater;
(e)
Side slopes;
(f)
Emergency spillway elevation;
(g)
Elevations of all features of the outlet structure;
(h)
Clay core;
(i)
Key trench;
(j)
Dimensions and spacing of antiseep collars;
(k)
Trash rack; and
(l)
Anti vortex device (if included in the design).
A.
General.
(1)
Storm sewers and associated structures shall be required to be constructed
to:
(a)
Intercept runoff at such intervals as necessary along streets
to provide safe vehicular movement;
(b)
Eliminate standing water at the bottom of all grades regardless
of location;
(c)
Eliminate the use of cross gutters at street intersections and
elsewhere, including in parking lots; and
(d)
Discharge collected water (from any and all locations, including
but not limited to streets, parking lots and lawn area) to an infiltration
facility, detention basin or other acceptable BMP, that discharges
to the nearest practical natural channel.
(2)
Manholes, inlets, headwalls and other stormwater structures must
conform to the standards established by PennDOT and be per details
shown in PennDOT Standards for Roadway Construction or as approved
by the Municipal Engineer. When such structures are to be dedicated
to the municipality, they must be supplied by a PennDOT Bulletin 15
approved supplier. These requirements shall be noted on the plan.
(3)
When stormwater collection and conveyance systems are to be dedicated
to the municipality, all materials, workmanship, and installation
shall conform to PennDOT specifications contained in Chapter 408,
current edition.
(4)
Whenever practical, storm sewers and associated structures that drain
the street system shall be located within the right-of-way of the
street.
(5)
Easements shall be provided for all conveyance and collection systems that are not located within street rights-of-way and shall be a minimum of 20 feet in width. Easements shall meet the applicable requirements in § 301-85.
(6)
No stormwater conveyance facility shall be constructed within 50
feet of a special geologic feature (as defined herein), unless it
is constructed of reinforced concrete pipe utilizing rubber gasket/O-ring
joints; such pipe shall be a minimum of 25 feet from a special geologic
feature.
(7)
Collection and conveyance systems shall be installed to prevent concentrated
flow from crossing or following sidewalks. Pipe and inlet size and
materials used for this purpose shall be acceptable to the Municipal
Engineer.
(8)
Collection and conveyance systems shall be provided where runoff
is concentrated in rear, side or front yards as necessary to prevent
erosion.
(9)
Collection and conveyance systems shall be provided in order to adequately
drain parking lots.
B.
Sizing criteria.
(1)
Collection and conveyance systems in public streets shall be adequate
for the anticipated runoff when the area draining to the system is
fully developed as permitted by zoning.
(2)
Collection and conveyance systems regardless of location shall be
designed to carry the twenty-five-year peak flow rate determined using
the Rational Formula and good engineering practice.
(3)
The system shall be evaluated for both gravity (Manning's Equation)
and pressure (inlet/outlet control, hydraulic grade line) as appropriate.
(4)
Provisions must be made to transport the runoff from a one-hundred-year-frequency
storm to an appropriate stormwater management facility in a manner
that does not damage property or flood streets.
C.
Stormwater pipes.
(1)
The minimum inside diameter of all pipe to be installed shall be
not less than 15 inches. When cover is 25 feet or greater, the minimum
inside diameter shall be 24 inches.
(2)
All pipes shall be reinforced concrete Class III or better meeting
PennDOT's one-hundred-year life criteria unless otherwise permitted
by the Township Public Works Director.
(3)
Joints shall be provided with rubber gaskets/O-rings.
(4)
The minimum pipe slope shall be 1/2%.
(5)
The minimum cover of stormwater pipe shall be 24 inches. This minimum
cover shall be provided and maintained during construction in order
to protect pipe from damage.
(6)
Where cover is restricted, equivalent elliptical concrete pipe or
concrete arch pipe may be used in lieu of circular pipe.
(7)
When located within a street cartway, pipe shall be bedded on six
inches of PennDOT 2A stone and backfilled with 2A stone placed and
compacted in six-inch lifts.
(8)
All pipe shall be laid in a straight line. A manhole or inlet shall
be provided at all horizontal deflections.
(9)
Storm pipe shall not be permitted under buildings or structures.
(10)
Underdrains and/or pavement base drains shall be:
(11)
A water quality/pretreatment structure (or structures as necessary
based on design flow) shall be:
(a)
Provided at or near the terminus of all conveyance systems;
(b)
Capable of capturing floatables, sediment, gravel, leaves and
liquid contaminates (oil, antifreeze, etc.) prior to leaving the right-of-way
and/or entering a channel or stormwater BMP whether an infiltration
BMP or detention basin, etc.; and
(c)
Located such that they are easily accessible from the street,
along a vehicular path to facilitate maintenance.
(12)
Prior to dedication of public streets and release of the maintenance
bond:
(a)
A video inspection of all collection and conveyance systems
located within the street right-of-way shall be required using methods
acceptable to the Municipal Engineer.
(b)
A record of the video inspection shall be provided in an electronic
format acceptable to the Municipal Engineer.
(c)
Depending on the results of the video inspection, all pipes
and inlets shall be cleaned and/or restored, repaired or replaced,
etc., per original design specifications.
D.
Inlets.
(1)
Inlets shall be spaced to limit the gutter spread to no more than
1/2 of the width of the travel lane during the design storm (twenty-five-year).
(2)
The capacity of all C-, M-, or S-type inlets shall be determined
using the commonwealth of Pennsylvania, Department of Transportation,
Design Manual, Part 2, "Highway Design."
(3)
The maximum allowable headwater depth shall be one foot below the
top of the inlet grate.
(4)
If double inlets are proposed, they shall be separated by a minimum
of 20 feet.
(5)
Inlet capacity calculations shall be provided in the stormwater management
report, including the design twenty-five-year peak flow rate to each
inlet.
(6)
In nonsump areas, inlets shall be placed such that flow to any single
inlet shall not exceed four cubic feet per second (cfs) for standard
(two inches by four inches) inlets and five cfs for Type 1 standard
(two inches by six inches) inlets, whether located in streets, parking
lots or lawn areas.
(7)
In sump areas, other than within a street, the maximum depth of water
above the inlet top elevation shall be six inches. The inlet top elevation
in landscaped areas shall be sumped a minimum of 12 inches.
(8)
Regardless of capacity calculations, inlets shall be located to intercept
runoff prior to handicapped ramps, prior to every street or driveway
(not including those serving single-family dwellings) intersection
radius, and at sag points of vertical curves and any other low points
whether in streets or in parking lots.
(9)
Inlets shall be placed prior to the radius of an intersection not
on the curved portion unless unavoidable in order to be located at
a low point.
(10)
No inlet smaller than standard PennDOT inlet types C, M and
S shall be used within streets.
(11)
Inlets with a depth greater than four feet must be provided
with antislip ladder rungs.
(12)
A minimum drop of 0.20 foot shall be provided across inlets
between the invert elevations of the incoming and outgoing pipes of
the same diameter. For pipes of different diameters, the elevation
of the crowns of the pipes shall be equal.
(13)
Inlets shall contain the statement "No Dumping Drains to Creek"
either cast or inserted into the tops to discourage the placement
of anything other than stormwater into the inlet.
(14)
Inlets in paved areas shall be equipped with bicycle-safe grates.
All inlets shall be designed and located to prevent hazards to vehicles,
bicycles and pedestrians.
(15)
Inlet grates shall be depressed one inch in paved areas with
inlet tops flush with the curb.
(16)
To promote smooth flow and self-cleaning, the bottoms of inlets
shall be provided with concrete washes (flow channels).
(17)
All pipe entering an inlet shall be cut flush with the inside
of the inlet box.
(18)
Weep holes shall be provided in inlets per PennDOT RC Standards.
(19)
Only a single pre-cast concrete grade adjustment ring, a maximum
of six inches in height, shall be allowed.
(20)
The annular space where pipes enter inlet boxes shall be sealed
with nonshrinking grout.
(21)
All backfill around inlets shall be compacted PennDOT 2A stone.
E.
Manholes.
(1)
Manholes shall not be spaced more than 400 feet apart for pipes of
less than or equal to twenty-four-inch diameter and 500 feet apart
for pipes of greater than twenty-four-inch diameter.
(2)
A manhole shall be placed on a continuous storm sewer at all changes
in alignment, grade or pipe size and at all points of convergence
of two or more influent storm sewer lines.
(3)
Inlets may be substituted for manholes where they serve a useful
purpose.
(4)
Manhole covers shall have the word "STORM" cast on the top of the
cover.
(5)
A minimum drop of 0.2 foot shall be provided across manholes between
the invert elevations of the incoming and outgoing pipes of the same
diameter. For pipes of different diameters, the elevation of the crowns
of the pipes shall be equal.
(6)
The maximum allowable headwater depth shall be one foot below the
top of the inlet grate or manhole cover.
(7)
To promote smooth flow and self-cleaning, the bottoms of manholes
shall be provided with concrete washes (flow channels).
(8)
All pipe entering a manhole shall be cut flush with the inside of
the manhole.
(9)
The annular space where pipes enter manholes shall be sealed with
non shrinking grout.
(10)
Manholes with a depth greater than four feet must be provided
with anti slip ladder rungs.
F.
End treatments (headwalls, endwalls, flared end sections, and similar
structures).
(1)
At-grade pipe outlets shall be provided with one of these structures.
(2)
All end treatments shall be concrete, regardless of pipe material.
(3)
Safety grates may be required at the municipality's discretion.
(4)
Acceptable energy dissipation devices shall be installed per PADEP's
Erosion and Sedimentation Pollution Control Program Manual at every
end treatment.
(5)
Any part of an end treatment shall not be located closer than 10
feet from the edge of a sidewalk, curb or cartway edge.
G.
Man-made open channels/swales.
(1)
Properly designed, graded, and lined channels may be permitted in
lieu of storm sewers where it can be demonstrated that the channel
will be stable under permanent conditions.
(2)
The channel shall not be less than 2% in grade nor more than 10%.
(3)
Underdrains may be required as determined by the Municipal Engineer.
(4)
Channels shall be located on lot lines as necessary to minimize stormwater
from draining across lot lines.
(5)
Channels shall have a maximum side slope grade of three horizontal
to one vertical (3:1).
(6)
Channels shall be provided with a minimum six-inch freeboard, measured
from the top of the design storm (twenty-five-year) flow to the top
of bank of the channel.
(7)
Channels leading away from emergency spillways, and other channels
in areas where damage to property would result, shall be designed
to convey the runoff from a one-hundred-year storm.
A.
Cul-de-sac street turnarounds shall be graded to direct all stormwater
to the curb in order to minimize icing from sheet flows in freezing
temperatures.
B.
A minimum grade of 2% shall be provided along the curb gutter line
of the turnaround portion of a cul-de-sac street.
C.
All grading (cut and fill) shall be set back from property lines
a sufficient distance to prevent any adverse effects on adjacent properties
but in no case less than 10 feet.
D.
Grading shall not be done in such a way so as to divert water onto
the property of another landowner.
E.
Sites shall be graded to secure proper drainage away from buildings
(minimum 2%) and to allow for the proper collection and conveyance
of stormwater.
F.
Grading operations shall be kept to a minimum to ensure conformity
with the natural topography, to minimize erosion hazard, and to adequately
handle the surface runoff.
G.
Except as specified elsewhere in this article, cut and fill slopes
shall not be steeper than 4:1, unless otherwise permitted by the Municipal
Engineer.
H.
During grading operations, necessary measures for dust control shall
be exercised.
A.
When subdivision, land developments or other earth disturbances are
submitted to the municipality for approval in phases, plans and calculations
shall be submitted for the design of the entire tract, not for a single
phase.
B.
If construction is contemplated for less than the entire project,
the proposed design of the stormwater from the constructed phase(s)
shall be provided. The design shall prevent damage to adjacent properties
and future phases. Any temporary construction required for the phased
design shall be included with the submittal.
C.
In the event that temporary measures cannot insure protection to
adjacent properties or future phases, the permanent BMPs and permanent
collection and conveyance system, as necessary, shall be included
as part of the construction for the currently proposed phase.
