A.
Rates of postdevelopment stormwater runoff (measured in cubic fees
per second) shall not exceed the percentages of the predevelopment
flow rates for any area as mandated by this Part 1. Allowable postdevelopment
percentages shall be as follows:[1]
[Amended 6-21-1993 by Ord. No. 6-93]
(1)
For the Bushkill Creek Watershed, as is listed for each individual
stormwater management district as shown on the Watershed Release Rate
Map (Appendix B).[2]
[Amended 6-21-1993 by Ord. No. 6-93]
[2]
Editor's Note: Appendix B, Stormwater Management Districts Release Rate Map, is included at the end of this chapter.
(2)
For the Monocacy Creek Watershed, as is listed for each individual
stormwater management district as shown on the Watershed Release Rate
Map (Appendix B).
(3)
For the Nancy Run Watershed, as is listed for each individual stormwater
management district as shown on the Watershed Release Rate Map (Appendix
B).
(4)
For any area within the general stormwater district: 100%.
(5)
During construction and preparatory earthmoving in all areas of the
Township: 100%.
(6)
For the Fry's Run Watershed, as is listed for each individual stormwater
management district as shown on the Watershed Release Rate Map (Appendix
B).
[Amended 5-1-2000 by Ord. No. 2-00]
B.
Control of runoff from a site shall occur using appropriate means
of detention of the water on the site and/or other approved types
of stormwater management within the requirements of this Part 1.
C.
Runoff that is detained shall be held and released at a predetermined
controlled rate by appropriately installed devices. The release shall
be in the same manner as the natural or predevelopment means of discharge
from a site (such as point discharge or sheet flow).
[Amended 6-21-1993 by Ord. No. 6-93]
D.
Stormwater runoff shall not be increased or redirected in such a
way that it results in hazards to persons or property or interferes
with the normal movement of vehicles.
E.
All stormwater management methods are subject to approval by the
Township Engineer.
F.
Stormwater shall be directed away from buildings and on-lot septic
systems.
G.
All drainage plans shall take into account and provide for existing
flows within the entire watershed.
H.
The existing points of natural drainage discharge onto adjacent property
shall not be altered nor shall the concentration of water runoff be
increased because of development without the written approval of all
affected landowners.
I.
No stormwater runoff or natural drainage water shall be so diverted
as to overload existing drainage systems, or create flooding or the
need for additional drainage structures on other private properties
or public lands, without complete approval of provisions being made
by the developer for properly handling such conditions, including
water runoff impoundments, if necessary.
J.
All lots shall be laid out and graded to prevent cross lot drainage,
to provide positive drainage away from proposed building locations
and any primary or alternate septic system location.
K.
An adequate storm sewer system consisting of inlets and other underground
drainage structures with approved outlets shall be constructed where
the runoff of stormwater and the prevention of erosion cannot be accomplished
satisfactorily by surface drainage facilities, as determined by the
Board of Commissioners based upon the recommendation of the Township
Engineer.
L.
Outlet locations shall be approved by the Township Engineer.
M.
Sequence of construction. No substantial grading shall occur and
no building permits shall be issued for any building unless any detention
basin, siltation basin or improved major swale approved to handle
the resulting runoff is in place. Any detention basin shall be seeded
and stabilized and have an installed outlet structure prior to the
construction of any streets or buildings within that drainage basin.
A.
Stormwater calculations shall be submitted in a clear and legible
manner for any lot or tract that would result in more than 5,000 square
feet of total impervious cover.
B.
These calculations shall follow a method preapproved by and acceptable
to the Township Engineer. The following methods are recommended:
(1)
Rational Method. See description in Appendix A.[1]
[1]
Editor's Note: Appendix A, Stormwater Runoff Calculations, is included at the end of this chapter.
(2)
Soil-Cover-Complex Method. See U.S. Soil Conservation Service Technical
Release No. 55, "Urban Hydrology for Small Watersheds."
C.
Methodologies shall not be combined.
D.
Rainfall data shall be from the charts in the Appendix.[2]
[2]
Editor's Note: Appendix A, Stormwater Runoff Calculations, is included at the end of this chapter.
E.
The stormwater calculations shall include the following:
(1)
Pre- and postdevelopment drainage maps showing existing and proposed
grades and including any and all off-site tributary areas.
(2)
Pre- and postdevelopment runoff calculations.
(3)
Detention basin design calculations (as applicable).
(4)
Pipe and swale sizing calculations.
(5)
All other information that is needed to construct proposed stormwater
drainage facilities including, but not limited to, slopes, proposed
elevations and typical cross sections.
(6)
The stormwater management district(s) in which the site is located
and the applicable release rate(s).
(7)
Such information as the Township Engineer determines is needed to
determine compliance with this Part 1.
F.
Where crop farming or disturbed earth exists on the site prior to
development, meadow in good condition shall be used as the starting
base for the calculation.
G.
Where a factor in a calculation is not definitive, the strictest
value shall be used.
H.
Any postdevelopment areas which may be designed to initially be semipervious
(e.g., uncompacted aggregate, porous pavement, etc.) shall be considered
impervious areas unless the developer or landowner shall guarantee
that the semipervious surface shall be maintained as such to the satisfaction
of the Township.
[Amended 6-21-1993 by Ord. No. 6-93]
A.
At a minimum, the applicant shall prove to the satisfaction of the Township Engineer that during earthmoving, construction or after development, peak stormwater discharge rates will not exceed the allowable release rate(s) for the stormwater management district(s) in which the site is situated when compared with those that occurred prior to any of these activities (see § 218-17A).
(1)
The following conditions and storm frequencies (considered individually)
shall apply, unless any more restrictive requirements of an applicable
official stormwater management plan are adopted by DEP and the county
pursuant to State Act 167 of 1978, as amended:[1]
[Amended 5-1-2000 by Ord. No. 2-00]
(a)
Two-year storm.
(b)
Five-year storm.
(c)
Ten-year storm.
(d)
Twenty-five-year storm.
(e)
Fifty-year storm.
(f)
One-hundred-year storm.
[1]
Editor's Note: See 32 P.S. § 680.1 et seq.
(2)
The SCS calculation method with twenty-four-hour Type II storm shall
be used in the calculations required by this subsection.
B.
Storm sewer piping, roadside swales and inlet systems shall be designed
for a twenty-five-year storm. A twenty-four-hour Type II rainfall
shall be used if using the SCS method. The openings of culverts and
under bridges shall be designed for a fifty-year, twenty-four-hour
Type II rainfall (except within the one-hundred-year floodplain).
All conveyance swales shall be designed to handle a one-hundred-year
storm, with the flow of such a one-hundred-year storm contained within
the lines of a drainage easement, and with all structures located
at least 25 feet from such an easement.
C.
Within the one-hundred-year floodplain, any stormwater management
structures and systems shall be designed to handle a one-hundred-year
storm (based upon a twenty-four-hour Type II storm if using the Soil-Cover-Complex
Method).
D.
The drainage plan shall show that a one-hundred-year, twenty-four-hour
storm can be safely conveyed without jeopardizing any property on
or off the site.
A.
All plans showing the proposed stormwater control system (including any storm sewer construction) shall be accompanied by a complete design signed, stamped and certified by a Pennsylvania registered (professional) engineer and shall be submitted along with any required preliminary or final plan under Chapter 230, Subdivision and Land Development, of the Code of the Township of Bethlehem.
B.
When subdivisions or land developments are submitted to the Township
for approval in sections, a complete general stormwater control system
(including any storm sewer construction) design for the proposed subdivision
or land development shall be submitted at the preliminary plan level.
The proposed design shall take into account the entire tract and the
watershed.
C.
All stormwater controls shall be designed to function adequately
after the completion of each phase of a subdivision or land development.
This may require the use of temporary structures, which shall be shown
on submitted plans.
D.
The construction of stormwater controls in areas of future phases
of a development shall be required prior to construction of earlier
phases if the Township Engineer determines that is necessary to make
sure that the system will work after the completion of each phase.
This shall, for example, include the extension of the main outfall
line.
E.
A set of approved design plans shall be maintained on file at the
site during construction, as record drawings.
F.
Drainage structures that are located on state highway rights-of-way
shall be found to be acceptable to PennDOT and PennDOT approval shall
be a condition of any final approval of the Township.
G.
Submission requirements.
(2)
In addition to the above-referenced requirements, when any activity that would result in the addition of greater than 10,000 square feet of impervious cover is specifically regulated by Article IV of this Part 1, drainage plans shall be submitted to the Lehigh Valley Planning Commission for review. Such drainage plans shall also contain the following:
[Amended 5-1-2000 by Ord. No. 2-00]
(b)
Map(s) of the project area showing:
[1]
The location of the project relative to highways, municipalities
or other identifiable landmarks.
[2]
Existing contours at intervals of two feet. In areas of steep
slopes (greater than 15%) five-foot contour intervals may be used.
[3]
Streams, lakes, ponds or other bodies of water within the project
area.
[4]
Other physical features including existing drainage swales and
areas of natural vegetation to be preserved.
[5]
Locations of proposed underground utilities, sewers and water
lines.
[6]
An overlay showing soil types and boundaries.
[7]
Proposed changes to land surface and vegetative cover.
[8]
Proposed structures, roads, paved areas and buildings.
[9]
Final contours at intervals of two feet. In areas of steep slopes
(greater than 15 feet) five-foot contour intervals may be used.
[10]
Stormwater management district boundaries applicable
to the site.
(c)
Stormwater management controls.
[1]
All stormwater management controls shall be shown on a map and
described, including:
[a]
Groundwater recharge methods such as seepage pits,
beds or trenches (When these structures are used, the locations of
septic tank infiltration areas and wells shall be shown.); and,
[b]
Other control devices or methods such as rooftop
storage, semipervious paving materials, grass swales, parking lot
ponding, vegetated strips, detention or retention ponds, storm sewers,
etc.
[2]
All calculations, assumptions and criteria used in the control
device or method shall be shown.
[Amended 6-21-1993 by Ord. No. 6-93; 5-1-2000 by Ord. No. 2-00]
For areas of a development that are located within a watershed
for which a stormwater management plan has been approved by Pennsylvania
DEP and adopted by the county (pursuant to the State Stormwater Management
Act), the release rates contained therein shall supersede any conflicting
release rates of this Part 1.
A.
Stormwater management facilities may be planned and constructed in
coordination by two or more developments, provided that the installation
of improvements complies with all other portions of this Part 1.
B.
The Township may require developers to contribute their fair share
of the costs of a comprehensive regional or subregional stormwater
system in place of requiring an on-site detention basin.
Methods of detention or flow delay devices that may be found
to be acceptable by the Township Engineer are:
A.
Wet or dry ponds and detention basins.
B.
Roof storage and increased roof roughness.
C.
Parking lot detention.
D.
Infiltration trenches.
E.
Porous pavements, grassed channels and vegetated strips.
F.
Cisterns, underground reservoirs or covered ponds.
G.
Increasing the roughness coefficients on the development's surface
area.
H.
Decrease percentage of impervious area.
I.
Groundwater recharge.
J.
Routing flow over lawns in swales within stormwater easements.
K.
Detention storage within the storm sewer.
L.
Another method that may be preapproved by the Township Engineer.
If a roof is to be used for detention, a condition of such use
shall be that the applicant shall submit appropriate calculations
and a signed statement from a registered architect or Pennsylvania-registered
(professional) engineer assuring that the structure will be able to
support the roof loadings. This statement shall be required prior
to issuance of the building permit.
A maximum of 30% of a paved parking lot may be found acceptable
as a stormwater detention but not a retention facility. Ponding shall
be arranged so that pedestrians may cross the parking lot relatively
dryly. There shall be a maximum designed depth of six inches, and
the pavement shall be designed to withstand the effects of ponded
water. The area used for the storage shall be the least used portion
of the parking lot.
Where porous pavement is used to reduce runoff, the developer
or landowner shall guarantee that the paved surface shall be maintained
to the satisfaction of the Township, and that any resurfacing of the
paved area shall utilize a porous material. Such a grantee shall be
lettered as a covenant on the recorded plan and shall be signed and
notarized. Porous pavement shall not be utilized in construction of
facilities to be dedicated to the Township.
In general, all runoff control measures shall be designed to
encourage groundwater recharge, if suitable subsurface conditions
are present. However, in any such recharge, proper precautions shall
be taken to prevent pollution of the groundwater, prevent the formation
of sinkholes and to promote safety.
A.
For the purpose of this section, a retention basin shall be required
to meet the same standards as a detention basin.
B.
Emergency spillways. All detention basins shall be designed with
an emergency spillway.
(1)
These spillways at a minimum shall be able to handle a one-hundred-year
postdevelopment peak discharge of the principal pipe barrel and the
emergency spillway.
(2)
Whenever possible, the emergency spillway for detention basins shall
be constructed on undisturbed ground. If the emergency spillway cannot
be constructed on undisturbed ground, it shall be constructed of suitable
material adequately compacted in accordance with specifications preapproved
by the Township Engineer.
(3)
Emergency spillways shall be constructed of reinforced concrete,
vegetated earth or concrete rubble. All emergency spillways shall
be constructed so that the detention basin berm is protected against
erosion.
(4)
The emergency spillway shall be a minimum of two feet below the berm
elevation. The emergency spillway shall convey a one-hundred-year
storm at a maximum depth of one foot over the spillway.
(5)
The downstream slope of the spillway shall as a minimum extended
to the toe of the berm embankment. The edge of the basin grading shall
be within the subject property.
(6)
All detention basin outflow structures shall be designed with trash
racks over the outflows where practicable.
C.
Slope of detention basin embankment. The maximum inside slope of
earthen detention basin embankments shall be four horizontal to one
vertical. The maximum outside slope shall be three to one. The top
or toe of any slope shall be located a minimum of five feet from any
property line. Whenever possible the side slopes and basin shape shall
be amenable to the natural topography. Straight side slopes are prohibited.
D.
Width and height of berm. The minimum top width of detention basin
berms shall be 10 feet, unless the Township Engineer determines that
a greater width is needed for maintenance and/or structural purposes.
The berm shall be built at least six inches higher than the design
elevation to allow for soil settlement within the berm.
[Amended 6-21-1993 by Ord. No. 6-93]
E.
Slope and lining of basin bottom. In order to insure proper drainage
of the detention basin, a minimum grade of 2% shall be maintained
for all sheet flow. A minimum grade of 1% shall be maintained for
all channel flow, provided that a synthetic low flow channel of suitable
materials is provided. In areas of carbonate geology, detention basins
shall be provided with an impervious liner of clay, suitable compacted
soil or approved artificial material, with the type of liner approved
by the Township Engineer. Any basin that is proposed to be dedicated
to the Township shall be lined with a synthetic, impervious liner,
with the type of liner approved by the Township Engineer.
[Amended 5-1-2000 by Ord. No. 2-00]
F.
Antiseep collars. Antiseep collars shall be installed around the
principal pipe barrel within the normal saturation zone of the detention
basin berms. Antiseep collars shall not be required on basins designed
to have a depth of water of less than three feet. The antiseep collars
and their connections to the pipe barrel shall be watertight. The
antiseep collars shall extend a minimum of two feet beyond the outside
of the principal pipe barrel. The maximum spacing between collars
shall be 10 times the minimum projection of the collar measured perpendicular
to the pipe.
G.
Fencing.
(1)
A detention basin shall be required to be surrounded with minimum
four-foot-high galvanized vinyl clad chain link metal fencing or an
alternative type of fence acceptable to the Township if any of the
following conditions are present:
H.
Landscaped screening.
(1)
A detention basin shall be screened from view of existing residences,
a residential zoning district or a public street, unless the basin
would meet both of the following conditions.
I.
Multiple basins. The use of multiple detention basins should be investigated
over the use of one larger storage facility; however, the Township
Engineer shall be consulted prior to design of multiple basins.
J.
All outflow structures from storage facilities shall be equipped
with a regulatory device that will permit modification to regulate
the amount of out flow. Suitable antivortex and/or velocity retarders
shall be used.
K.
An outflow control structure shall be provided at the outlet of all
detention basins. This structure shall be constructed of metal or
concrete and shall be designed so that the rate of outflow is controlled
by the pipe barrel through the basin berm when the depth of water
within the basin exceeds the height of the structure. A trash rack
or similar device shall be provided to prevent debris from entering
the outflow structure. The crest elevation shall be set at a minimum
of 12 inches below the emergency spillway.
L.
Retention basins. Aeration devices may be required, dependent upon
the quality of the influent and retention time.
M.
Recreation. When reasonable, efforts should be made to allow suitable
recreational uses of portions of detention areas. This might include
designing a detention basin so that only a portion would be wet after
a minor storm, and the remainder would be well drained during all
except the most serious storm. These areas may be acceptable, at the
discretion of the Township, as part of any recreation land that may
be required under any Township ordinance.
O.
The design of any detention basin intended to meet the requirements
of this Part 1 shall be verified by routing the design storm hydrograph
through the proposed basin. Basin routing calculations based upon
the rational, modified rational or universal rational methods shall
not be accepted, without the written preapproval of the Township Engineer.
For basins designed using the Modified Rational Method, or other rational
based technique, the detention volume shall, at minimum, equal the
volume derived from the approximate routing process as contained in
SCS Technical Release Number 55 (TR55, most recent addition).
Construction and materials of storm drainage and control facilities
(including pipes) and erosion control facilities shall be in accordance
with the approved plans and any accompanying specifications. The construction
details and standards of the following publications or their successor
publications, in their most recent revision shall be used:
A.
The construction of new storm sewers or the connection into acceptable
existing storm sewers shall be required or allowed by the Board of
Commissioners if the Township Engineer deems this to be the most feasible
and reasonable option.
B.
Any storm sewers shall be constructed to Township specifications
and shall not interconnect with sanitary sewers.
A.
The minimum diameter of any cross-drainage or culvert pipe shall
be 15 inches. Corrugated polymeric coated metal pipe shall be used
unless an alternative is accepted by the Township Engineer and except
that reinforced concrete pipe shall be used under all streets and
in connection with a detention basin outlet structure.
B.
Open pipe ends shall be fitted with concrete end walls or prefabricated
end sections.
C.
Drainage pipes shall have a minimum slope of 0.5% and drainage swales
and gutters 1%. As minimum, the tops of all pipes shall be at the
same elevation when changing pipe size.
D.
Manholes or inlets shall be used at all changes in horizontal alignment,
at changes of vertical grade and at all pipe intersections. No run
of pipe shall exceed 400 feet in length without appropriate measures
to allow cleanout. Trash tracks shall be placed on all stormwater
entrance structures.
E.
Bridges and culverts shall meet PennDOT constructions standards.
Pennsylvania DEP shall be contacted to determine if a dams and waterways
permit is required.
[Amended 5-1-2000 by Ord. No. 2-00]
F.
Grating. Appropriate safety grates shall be attached to all catch
basins, stormwater inlets, pipe openings and other stormwater receiving
structures needed, to ensure that maximum openings do not exceed 25
square inches. Along streets and pedestrians areas, safety grates
shall be used as needed for bicycle safety.
G.
Storm sewer outfall. Storm sewer outfalls shall be designed, with
respect to the elevation of the invert or other features, that when
the receiving watercourse is experiencing a twenty-five-year storm,
the storm sewer will continue to drain the area it is designed to
serve.
H.
Street drainage.
(1)
To minimize sheet flow of stormwater across lots located on the lower
side of streets, and to divert flow away from building areas, the
cross section of the street as constructed shall provide for parallel
ditches or swales or curbing on the lower side which shall discharge
only at drainage easements.
(2)
Inlet spacing shall be designed such that in a twenty-five-year storm,
one traffic lane of at least 10 feet in width shall be free from stormwater.
A.
Where a subdivision or development is traversed by a watercourse,
drainageway, channel or stream there shall be provided a drainage
easement conforming substantially with the high water line of such
watercourse attributable to a flood of a one-hundred-year frequency,
in order to preserve the unimpeded flow of natural drainage and to
provide for future possible widening, deepening, relocating, improving
or protecting of such drainage facilities.
B.
Structures and other obstructions to flow (except fences that are
made of approved materials and are placed so as to not obstruct flow)
shall be prohibited within stormwater easements. Off-street parking
is specifically prohibited within stormwater easements.
C.
The applicant shall grant the Township the right to enter the easement
to accomplish maintenance work, although the Township assumes no responsibility
for such work. Such grant shall be in the form of a signed and notarized
covenant placed on the record drawing.
D.
It shall be the responsibility of the applicant to obtain all stormwater
easements on, over or through other properties when such easements
are needed to carry out the proposed drainage plan.
E.
Areas where stormwater easements have been or will be granted shall
not be obstructed during or after construction.
A.
All natural streams, channels, swales, drainage systems and/or areas
of concentration of surface water shall be maintained in their existing
condition unless alteration is approved by the Township Engineer.
The applicant shall be responsible to obtain all necessary DEP permits
(see Chapter 105 of Title 25 of the State Regulations).
[Amended 5-1-2000 by Ord. No. 2-00]
B.
Creek alignments. No watercourse shall be realigned, blocked, impeded
or redirected without the prior written approval of Pennsylvania DEP
and the Township Engineer.
[Amended 5-1-2000 by Ord. No. 2-00]
C.
Piping of surface water. Natural surface watercourses which have
sustained perennial flows averaging at least five cubic feet per second
shall remain open to sky and shall not be piped or covered.
D.
No activities requiring a permit from Pennsylvania DEP, the U.S.
Army Corps of Engineers or other governmental agency shall be conducted
(e.g., in freshwater wetlands) unless the developer has obtained all
necessary permits.
[Amended 5-1-2000 by Ord. No. 2-00]
A system for the ownership and maintenance responsibility of
all temporary and permanent stormwater facilities and erosion and
sedimentation control facilities that is satisfactory to the Board
of Commissioners shall be established prior to the final plan approval.
A.
Detention ponds shall be so designed and laid out in accordance with
Township requirements so that the area can be dedicated to the Township.
Each developer shall make an offer of dedication to the Township.
All maintenance and upkeep of ponds dedicated to and accepted by the
Township shall be the responsibility of the Township in accordance
with the following provisions:
(1)
That a detention pond maintenance escrow account shall be established
by the Township, and all required contributions from developers for
such maintenance and upkeep of detention ponds shall be maintained
within this escrow account.
(2)
That the contribution formula from each developer shall be based
on the following formula:
(a)
That the cost of crew (size to be initially determined) cutting
grass once every two weeks at (x hours per cutting) for a period from
May 1 through October 15 of each year.
(b)
That the cost for a spring and fall cleanup of (x) hours for
(x) workers, including any costs for equipment (front loader and trucks).
(c)
That an amount be established for certain major reconstruction
of components such as: outlet structures, beams, fencing, etc., during
the first 25 years.
(3)
That
the total contribution to the detention pond escrow account for each
proposed development shall be clearly defined prior to final plan
approval, and shall be made a part of the developer's agreement.
B.
Suitable easements shall be provided for all stormwater facilities.
C.
Stormwater facilities shall be designed to require minimal maintenance
and shall be designed to be accessible for maintenance.
D.
An easement shall be provided to guarantee access for maintenance
purposes if the facilities cannot be accessed from a public road.
Such grant of easement shall be in the form of a signed and notarized
covenant placed on the record plan.
E.
Facilities located on private property(ies).
(1)
Facilities located on private property shall be maintained by the
owner(s) thereof. The maintenance obligation shall be acknowledged
in the form of a signed and notarized covenant placed on the record
plan and in the form of a separate signed and notarized covenants
agreement with the Township which shall be recorded in the Northampton
County Courthouse.
(2)
Should a facility not be maintained in proper working order, the
Board of Commissioners may, after due notice to the responsible party,
arrange for the needed maintenance to be accomplished with all such
expenses charged to the responsible party. These expenses shall be
collectible as municipal claims are now collected by law.
(3)
The Township Engineer and Code Enforcement staff shall have the right
to enter private property to inspect storm drainage facilities. Reasonable
effort should be made to contact the property owner prior to any such
inspection.
