[Amended 2-16-2021 by Ord. No. 2021-03]
Each applicant shall be required to provide for surface drainage
within his project to ensure that it will not create a burden to the
ultimate users of his tract or create an adverse off-tract effect.
All streets shall be provided with catch basins and pipes where the
same may be necessary for proper surface drainage. The requirement
of this section may not be satisfied by the construction of ditches
or dry wells only. The system shall be adequate to carry off or store
the stormwater and natural drainage water which originates within
the development boundaries and that which originates beyond the development
boundaries and passes through the development calculated on the basis
of maximum potential development as permitted under this chapter.
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 lands without proper
and approved provisions being made for taking care of these conditions,
even if the flooding or overloaded existing drainage systems existed
prior to the applicant taking possession of said property subject
to the approval of the Township or its designated representative.
The time of concentration used in computing stormwater runoff
shall be the time it takes for runoff to travel from the hydraulically
most distant point of the watershed to the point of interest within
a watershed.
See § 444-5 for calculation of stormwater runoff.
The intensity of the stormwater shall be based on the following:
A.
N.J.A.C. 5:21-7.2(c)5.i for residential projects;
B.
As a minimum, a ten-year storm shall be used at low points with overland
relief, or twenty-five-year storm where carried in a pipe;
C.
As a minimum, all box culvert designs shall be based on a twenty-five-year
storm. The Rainfall-Intensity-Duration-Frequency Curve for Southern
Region, Figure 10-C in the State of New Jersey Department of Transportation
Roadway Design Manual, current edition, available here: https://www.state.nj.us/transportation/eng/documents/RDM/.
Time flows curves are also included in the figure for use in design;
D.
Standard headwalls shall be installed on all pipes. Trash rack and/or
bars shall be installed on all pipes equal to or greater than 24 inches
in diameter or as directed by the Township or its designated representative.
A.
Storm sewer pipelines shall be designated by the following method,
and shall be based on the Manning Equation and shall utilize the following
friction factors:
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n = 0.015
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Concrete pipe
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n = 0.024
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Corrugated metal pipe, 1/2 inch
Corrugations, 25% paved
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n = 0.021
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Corrugated metal pipe, 1/2 inch
Corrugations, 50% paved
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n = 0.013
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Corrugated metal pipe, 1/2 inch
Corrugations, 100% paved
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B.
The minimum allowable pipe size is 15 inches. Reinforced concrete
Class III, Wall B, shall be used in pavement areas and wherever there
is vehicular traffic, subject to the approval of the reviewing board
engineer. Where the cover on the pipe will be less than two feet,
reinforced concrete pipe of Class IV, Wall B, shall be used. No pipe
shall have less than one foot of cover. Corrugated metal pipe may
be used under certain conditions subject to the approval of the reviewing
board engineer.
C.
This method is based on the assumption that hydraulic gradient will
match the inside top of the pipe when system is under maximum hydraulic
load.
(1)
For this method, head losses through manholes, inlets, etc.,
shall be ignored.
(2)
The minimum slope of any pipe shall be such that a minimum velocity
of 2.5 fps shall be maintained when the pipe is flowing at 1/4 full.
(3)
When the pipe sizes change, the crowns of the pipes shall be
matched.
(4)
Continuous profiles for each reach of pipe shall be plotted,
along with the location of the hydraulic gradient, and the hydraulic
information shall include the pipe size and type, the "n" factor,
the slope of the hydraulic gradient, slope of the pipe, the design
capacity, and the velocity at the design capacity.
D.
Pipe and hydraulic grade line calculations shall be provided for
all proposed pipe designs.
A.
Stormwater inlets shall be equal to New Jersey State Highway Department
inlet Type B. The maximum collecting capacities of the inlets shall
be considered to be:
(1)
When installed on streets where the grade is 0.75%: five cubic
feet per second;
(2)
When installed on streets where the grade is 2%: 4.8 cubic feet
per second;
(3)
When installed on streets where the grade is 3%: 4.6 cubic feet
per second;
(4)
When installed on streets where the grade is 4%: 4.4 cubic feet
per second;
(5)
When installed on streets where the grade is 5%: 4.2 cubic feet
per second;
(6)
When installed on streets where the grade is 6%: four cubic
feet per second.
B.
Sufficient inlets shall be located and constructed so that the length
of surface runoff will not contribute a runoff to the inlet exceeding
the preceding designated collecting capacities. In no case shall the
distance between inlets be greater than 400 feet.
C.
The gutter grate of all inlets shall be set not more than two inches
below the gutter grade. The surface of the paving adjacent to the
inlets shall be constructed to bend into the lowered gutter grade
at the inlet in such a manner that a sudden drop off or dip at the
inlet will not be created. At such locations where drainage is entirely
dependent on inlets, the collecting capacities of the inlets shall
be designed for 1/2 the preceding considered capacities.
D.
Where surface water is collected from two directions at one street
corner, inlets shall be placed at, or near, the tangent points of
both ends of the radius. The use of one inlet in the radius shall
not be allowed.
E.
Access manholes shall be spaced at 400-foot intervals (maximum) through
rights-of-way and at sewer junctions where there are no catch basins.
Open ditches or channels will not be permitted when the design
capacity requires a fifteen-inch pipe or larger unless approved by
the reviewing board engineer. Where permitted, open channel design
should be based on the following hydraulic consideration:
A.
Manning's equation:
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n = 0.015 - straight, trowel-finished concrete lined
ditch
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n = 0.025 - straight, unlined ditch
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n = 0.033 - 0.15 fair to poor natural streams and
watercourses
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Allowable Velocity
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|---|---|
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Excavation Material
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Velocity
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See Table 11-1 for Allowable Velocity for Various
Soil Textures in the Standards for Soil Erosion and Sediment Control
in New Jersey available here: https://www.nj.gov/agriculture/divisions/anr/
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Concrete-lined ditch
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15 fps
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B.
Ample freeboard not less than one foot zero inches should be provided
on all channels.
C.
The channel should be designed to conform wherever possible to the
adjacent ground conditions. This means that it should not be projecting
above the surrounding ground.
D.
Continuous profiles for each reach of open channel shall be plotted
along with adjacent average ground and the hydraulic information pertinent
to each reach within the system. This information shall include the
type of channel lining, the "n" factor, the width of the channel bottom,
the side slopes, the water depth, the design capacity, and the velocity
at the design capacity.
All culverts shall be limited to a single opening; multiple
pipes will not be permitted subject to the approval of the reviewing
board engineer. The design of culverts shall be such as to minimize
the probability of debris accumulations.
Detention basins will be required in all major developments
and site plans unless it has been demonstrated by the applicant that
a detention basin is not required subject to the approval of the reviewing
board engineer.
A.
Basins shall be designed in accordance with the New Jersey Stormwater
Best Management Practices Manual (BMP Manual) available here: https://www.njstormwater.org/bmp_manual2.htm.
Complete calculations for the basin(s) should be supplied at the time
the preliminary plans are submitted. These calculations should include
maps and runoff calculations prior to development, runoff after development,
and complete calculations for design. All maps and calculations should
be signed and sealed by a state licensed engineer.
C.
The design calculations should be based on time intervals of five
to 10 minutes and indicate inflow, average inflow by time interval,
outflow, average outflow by time interval, incremental change in storage,
and height of water in pond.
D.
Basins, except wet ponds, shall be designed to completely empty after
a rainstorm occurs within the timeframe outlined in the BMP Manual.
Basins shall have provisions for an emergency overflow. In those instances
where existing or proposed permanent ponds will be used as retention
ponds, they must have a minimum depth and provide adequate freeboard
to function as a wet pond as outlined in the BMP Manual.
For both major and minor developments, blocks and lots shall
be graded to secure proper drainage away from all buildings and to
prevent the collection of stormwater in pools and to avoid concentration
of stormwater from each lot to adjacent lots. The minimum/maximum
grading are as follows:
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Specification
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Grading
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|---|---|---|
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Lawn/grass areas
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2.0% minimum
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33% maximum
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Grass swale
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1.5% minimum
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33% maximum
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Sidewalk
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1.0% minimum
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*4.9% maximum
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Driveways
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1.0% minimum
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8.3% maximum
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Driveways (side-entry)
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1.0% minimum
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5.0% maximum
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NOTE *Exceeding 5% slope would be considered a ramp by ADA guidelines,
and the design would need to reflect this.
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Land subject to periodic or occasional flooding shall not be
designed for residential occupancy nor for any other purpose which
may endanger life or property. Such land within a lot shall be considered
for open spaces, yards, or other similar uses in accordance with state
floodplain regulations.
Where a minor or major development is traversed by a watercourse, surface or underground drainage system or stormwater BMP, channel or stream, there shall be provided and dedicated a drainage right-of-way easement meeting any minimum widths and locations shown on any adopted Official Map or Master Plan or as required under Article 29, Easements, of this chapter.
A.
The approving board may require dedication of easements or deed restrictions
along drainage ways, natural watercourses, steep slopes and other
unique botanical, historical, geological and paleontological areas
located therein or adjacent to a proposed development. The easement
or deed restriction shall be indicated on the plan and shall be marked
on the land by concrete monuments at angle points and or property
corners at sufficient locations to enable the dedicated area to be
surveyed. In such cases, the approving Board shall consult with the
Township Planner and Township Engineer in determining the required
shape and size of the easement. The easement or deed restriction shall
be in a form approved by the approving Board's Attorney and shall
include provisions assuring the following:
(1)
Preservation of the channel and floodplain of the watercourse,
including the right to clean, de-snag and all such work necessary
to maintain the shape, slope and water flow of the watercourse.
(2)
Prohibition of any removal of trees and other cleaning and grading
not directly related to the preservation of the channel of a watercourse.
(3)
Grant of a right to the Township to maintain or reconstruct
any drainage facilities necessary for the health and safety of the
public, if applicable.
(4)
Right-of-entry to the Township to install and maintain any drainage
facilities therein, if applicable.
Easements or rights-of-way shall be required in accordance with Article 29 where storm drains are installed outside streets.
