[Adopted 10-27-1993 by Ord. No. 93-30 as
Ch. 108, Art. III, of the 1993 Code]
The general intent of this article is to manage
the increased rate and velocity of surface water runoff created by
alteration and modifications of ground cover and natural runoff patterns
and maintain water quality of Manalapan Township's surface and groundwater
resources.
This article is deemed essential and necessary
to protect the public health, safety and welfare of the citizens of
Manalapan Township and the surrounding communities by accomplishing
the following purposes:
A.
To maintain the hydraulic adequacy of natural stream
channels and prevent accelerated bank erosion by controlling the rate
and velocity of runoff discharge to these watercourses so as to avoid
increasing frequency of the bank full stage.
B.
To preserve present adequacy of culverts and bridges
by suppressing artificially induced flood peaks.
C.
To reduce public expenditures for replacement or repair
of public facilities resulting from artificially induced flood peaks.
D.
To prevent damages to life and property from flooding
resulting from excessive rate and velocities of runoff.
E.
To preserve present water quality of Manalapan Township
watercourses and groundwater resources.
A.
Stormwater management improvement review and approval shall be required concurrently with preliminary site plan approval or preliminary major subdivision site improvement and utility plan approval as required by Chapter 95, Development Regulations, of the Code of the Township of Manalapan.
B.
The Board may waive the need for stormwater management
improvements after finding that there is no appreciable increase anticipated
in rate, velocity or duration of runoff based on plans submitted.
C.
The Board may waive the specific requirements of this
article where such waiver would be in the best interest of the Township
of Manalapan or surrounding municipalities.
D.
Runoff control details. In order to duplicate as nearly
as possible natural drainage and water quality conditions, regulation
and control of stormwater runoff and erosion for any land area to
be developed shall be through on-site stormwater detention or retention
and/or ground absorption systems which include but are not limited
to the following:
(1)
Detention and retention areas which may be depressions
in parking areas, excavated basins, basins created through use of
curbs, stabilized earth berms, dams or dikes, or any other form of
grading which serves to temporarily impound and store water.
(2)
Innovative surface water runoff control and recharge
devices may be proposed, such as rooftop storage, dry wells, cisterns,
roof drain infiltration trenches, and other subsurface recharge or
storage facilities, provided that they are accompanied by detailed
engineering plans and performance capabilities.
A.
Runoff to remain in watershed. Runoff within a site
shall ultimately leave the site in the same watershed in which it
originated and shall be released in such a manner so as to not overload
exiting drainage systems, create flooding creating need for additional
drainage facilities on other public or private lands, or increase
predevelopment erosion of adjacent lands.
B.
Rate of runoff. The peak rate of runoff from a site
during and after development shall not exceed the predevelopment peak
rate of runoff. Development upstream of known areas of problem flooding
of properties shall be required to further reduce the peak rate of
runoff below the predevelopment rate.
C.
Minimize volume increase. The increase in volume of
runoff from a site, during and after development, from the predevelopment
total of volume of runoff shall be minimized. Runoff control measures
shall be used to retard or reduce runoff and increase recharge. Natural
and artificial recharge areas and systems should be employed whenever
practical to minimize the volume of surface water runoff. These include,
but are not limited to, infiltration pits, dry wells, infiltration
trenches, and the extensive use of sheet flow through vegetated areas.
The use of runoff control/recharge devices should be considered in
all known areas of aquifer or groundwater recharge as determined by
United States Geological Survey studies and USDA HYDRO soil groups
A and B as shown on Monmouth County soil survey mapping. The use of
such measures will not eliminate or reduce, even partially, the need
for other requirements of this article.
D.
Runoff peak rate of discharge calculation. The peak
rate of runoff for areas of up to 50 acres shall be calculated by
the Rational Method of Derivatives. The equation for the Rational
Method is as follows:
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Qp= CIA
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Where
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Qp = the peak runoff rate in cubic feet per
second (CFS)
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C = the runoff coefficient
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I = the average rainfall intensity in inches
per hour (IN/HR), occurring at the time of concentration tc (MIN)
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tc= the time of concentration in minutes (MIN)
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A = the size of the drainage area in acres (AC)
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(1)
Typical runoff coefficients ("C" values) are provided
in the Technical Manual for Stream Encroachment, prepared by the New
Jersey Department of Environmental Protection (NJDEP), page 51, Table
3.1-2(B-1). Runoff coefficient "C" used in the rational formula shall
be weighted if there is more than one kind of land use within the
drainage basin under consideration.
(2)
The time of concentration (tc) is defined as the time required for water to reach the point in
question from the most hydraulically distant point in the basin. Time
of concentration (tc) shall be estimated from
the "Nomograph for the Determination of Time of Concentration," prepared
by the State of New Jersey Highway Authority. The analysis shall also
consider the procedure outlined in Sections 3.12(c) for Technical
Release (TR) Number 55, Urban Hydrology for Small Watersheds, United
States Department of Agriculture, Soil Conservation Series, as supplemented
and amended (SCS method).
(3)
Rainfall intensity as a function of duration and storm
recurrence frequency shall be based upon geographically appropriate
data as depicted in the plates in Technical Paper Number 25, Rainfall
Intensity Duration-Frequency Curves, United States Department of Commerce,
Weather Bureau, as supplemented and amended. Intensity curves may
be based on local rainfall frequency data, i.e. Sandy Hook or Old
Bridge curves, where available. In all instances, a minimum time of
concentration of five minutes should be used.
(4)
The peak rate of runoff for areas greater than 50
acres shall be calculated by the hydrograph analysis method as outlined
in TR Number 55 (SCS method), as supplemented and amended.
E.
Runoff volume calculation.
(1)
Runoff volume shall be calculated by the hydrograph
analysis method as outlined in TR Number 55 (SCS method). This method
shall be used for watersheds with drainage areas of less than five
square miles. For drainage areas of less than five acres, the Rational
Method triangular hydrograph approximation with the peak rate occurring
at the time of concentration and the end of the hydrograph at three
times the time of concentration may be used as an alternative.
(2)
Runoff volume for drainage areas of greater than five
square miles shall be calculated by Special Report Number 38, Magnitude
and Frequency of Floods in New Jersey with Effects of Urbanization,
State of New Jersey, Department of Environmental Protection, Division
of Water Resources (Stankowski Method).
B.
Detention and all other stormwater management facilities
shall conform to the standards under the New Jersey Stormwater Management
Act, N.J.S.A. 7:8 et seq.
C.
Where detention or retention facilities are deemed
necessary, they shall accommodate site runoff generated from two-year,
ten-year and one-hundred-year storms considered individually, unless
the detention or retention basin is classified as a dam, in which
case the facility must also comply with the Dam Safety Standards,
N.J.A.C. 7:20. These design storms shall be defined as either a twenty-four-hour
Type III storm using the rainfall distribution recommended by the
United States Soil Conservation Service (such as United States Soil
Conservation Service, Urban Hydrology for Small Watersheds, Technical
Release Number 55) or as the estimated maximum rainfall for the estimated
time of concentration of runoff at the site when using a design method
such as the Rational Method.
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Runoff greater than that occurring from the
five-hundred-year, twenty-four-hour storm will be passed over an emergency
spillway. Detention will be provided such that after development the
peak rate of flow from the site will not exceed that by similar storms
prior to development. For purposes of computing runoff, lands in the
site shall be assumed, prior to development, to be in good condition
(if the lands are woods,) or with conservation treatment (if the land
is cultivated), regardless of conditions existing at the time of computation.
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D.
In calculating the site runoff to be accommodated
by a detention facility, the method to be used is a tabular hydrograph
method as presented in TR Number 55 (SCS method) as supplemented and
amended.
E.
Detention facilities shall be located as far horizontally
from surface water and as far vertically from groundwater as is practicable.
F.
Detention facilities shall not intercept the post-development
groundwater table, where practicable.
G.
Only 1/2 of the area devoted to detention or retention
facilities shall be considered nonimpervious surfaces in calculating
the maximum percentages as set forth in other sections of this article.
The area devoted shall be the area encompassed by the depth of water
to the emergency spillway plus one foot.
A.
In addition to addressing water quantity generated
by development, a stormwater management system shall also enhance
the water quality of stormwater runoff.
B.
In order to enhance water quality of stormwater runoff,
stormwater management shall provide for the control of a water quality
design storm. The water quality design storm shall be defined as the
one-year frequency SCS Type III twenty-four-hour storm, a 1.25-inch
two-hour rainfall or as defined by the New Jersey Department of Environmental
Protection.
C.
The water quality design storm shall be controlled
by best management practices. These include but are not limited to
the following:
(1)
In dry detention basins, provisions shall be made
to ensure that the runoff from the water quality design storm is retained
such that not more than 90% will be evacuated prior to 36 hours for
all nonresidential projects or 18 hours for all residential projects.
The retention time shall be considered a brim-drawdown time, and therefore
shall begin at the time of peak storage. The retention time shall
be reduced in any case which would require an outlet size diameter
of three inches or less. Therefore, three-inch-diameter orifices shall
be the minimum allowed.
(2)
In permanent ponds or wet basins, the water quality
requirements of this section shall be satisfied where the volume of
permanent water is at least three times the volume of runoff produced
by the water quality design storm.
A.
Principal outlets quantity control.
(1)
To minimize the chance of clogging and to facilitate
cleaning, outlet pipes shall be at least six inches in diameter. All
outlet piping is to be watertight, reinforced concrete pipe. In addition,
aluminum, stainless steel or epoxy coated steel trash racks and/or
antivortex devices may be required where deemed necessary by the Township.
(2)
Eight-inch-thick anti-seep collars are to be installed
along outlet pipes. Such collars shall be constructed of reinforced
concrete with minimum Number 5 bars, each way, and three inches of
cover. A minimum of two anti-seep collars shall be provided on the
outlet pipes.
(3)
Where applicable, a concrete cradle shall be provided
for outlet pipes.
(4)
All principal outlet structures shall be concrete
block, precast reinforced concrete, or cast-in-place reinforced concrete.
All construction joints are to be watertight. All construction shall
be in conformance with New Jersey Department of Transportation standard
specifications.
(5)
Suitable channel lining shall be placed downstream
of principal outlets as necessary to prevent scour and erosion. Such
lining shall conform to the criteria contained in Standards for Soil
Erosion and Sediment Control in New Jersey published by the New Jersey
State Soil Conservation Committee.
B.
Principal outlets quality control.
(1)
Based upon the requirement limiting the size of the
outlet to a minimum of six inches in diameter, water quality control
shall be maintained by providing an amount of storage equal to the
total amount of runoff which will be produced by the one-year frequency
SCS Type III twenty-four-hour storm, or a 1.25-inch, two-hour rainfall
or as defined by the New Jersey Department of Environmental Protection
at the bottom of the proposed detention basin along with a minimum
three-inch-diameter outlet.
(2)
The invert(s) of the principal outlet(s) used to control
the larger storms for flood control purposes would then be located
at the resultant water surface elevation required to produce this
storage volume. Therefore, the principal outlets would be utilized
for storms in excess of the 1.25-inch, two-hour event which, in turn,
would be completely controlled by the lower, three-inch outlet. If
the above requirements would result in a pipe smaller than three inches
in diameter, the period of retention shall be waived so that three
inches will be the minimum pipe size used. It should be remembered
that, in all cases, the basin should be considered initially empty
(i.e., the storage provided for the quality requirements and the discharge
capacity of its outlet should be utilized during the routing of the
larger flood control storms).
A.
Emergency spillways shall be suitably lined and shall
comply with criteria contained in Standards for Soil Erosion and Sediment
Control.
B.
Maximum velocities in emergency spillways shall be
checked based on the velocity of the peak flow in the spillway resulting
from the routed five-hundred-year storm emergency spillway hydrograph.
Where maximum velocities exceed those contained in Standards for Soil
Erosion and Sediment Control in New Jersey, suitable lining of the
emergency spillway and its downstream slope shall be provided.
A.
The minimum top widths of all dams and embankments
are listed below. These values have been adopted from the Standards
for Soil Erosion and Sediment Control in New Jersey published by the
New Jersey State Soil Conservation Committee.
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Minimum Top Widths
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Height
(feet)
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Top Width
(feet)
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0 to 15
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10
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15 to 20
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12
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20 to 25
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14
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B.
The design top elevation of all dams and embankments,
after all settlement has taken place, shall be equal to or greater
than the maximum water surface elevation in the basin resulting from
the routed five-hundred-year storm Freeboard Hydrograph. Therefore,
the design height of the dam or embankment, defined as the vertical
distance from the top down to the bottom of the deepest cut, shall
be increased by the amount needed to ensure the design top elevation
will be maintained following all settlement. This increase shall not
be less than 5%. Where necessary, the Engineer shall require consolidation
tests of the undisturbed foundation soil to more accurately determine
the necessary.
C.
Maximum side slopes for all dams and embankments are
three horizontal to one vertical. One section of the embankment shall
have a flatter slope which will allow access to the bottom of the
basin by maintenance vehicles.
D.
All earth fill shall be free from brush, roots, and
other organic material subject to decomposition.
E.
Cutoff trenches are to be excavated along the dam
or embankment center line to impervious subsoil or bedrock.
F.
Safety ledges shall be constructed on the side slopes
of all detention and retention basins having a permanent pool or water.
The edges shall be four to six feet in width and located approximately
2 1/2 to three feet below and one to 1 1/2 feet above the
permanent water surface.
G.
The fill material in all earth dams and embankments
shall be compacted to at least 95% of the maximum density obtained
from compaction tests performed by the appropriate method in ASTM
D698.
H.
All dry detention basins shall be provided with a
concrete low flow channel with a perforated pipe underdrain in a stone
trench wrapped in a nonwoven geotextile fabric. The underdraining
shall be connected to the basin outlet structure.
I.
The top of bank for facilities constructed in cut
and the toe of slope for facilities constructed in fill shall be located
no closer than 15 feet to an existing or proposed property line.
J.
Detention basins shall be sodded, attractively buffered
and landscaped, and designed so as to minimize propagation of insects,
particularly mosquitoes. All landscaping and buffering shall be approved
by the Township. No trees or shrubs shall be permitted on slopes or
banks for facilities constructed in fill. All detention and retention
basins with permanent dry weather pools of water shall have a water
depth to minimize propagation of mosquitoes and provided with mechanical
aeration for water quality.
There will be no detention basins in the floodplain
except for those on-stream and shall comply with all applicable regulations
under the Flood Hazard Control Act, N.J.S.A. 58:16A-50 et seq., and
the New Jersey Stormwater Management Act, N.J.S.A. 7:8 et seq.
Detention basins located in freshwater wetlands
may be allowed only in accordance with the Freshwater Wetlands Protection
Act, N.J.S.A. 13:9B-1 et seq., and any rules adopted pursuant thereto.
A.
Responsibility for operation and maintenance of stormwater
management facilities, including periodic removal and disposal of
accumulated particulate material and debris, shall remain with owner
or owners of the property with permanent arrangements that it shall
pass to any successive owner, unless assumed by a government agency.
If portions of the land are to be sold, legally binding arrangements
shall be made to pass the basic responsibility to successors in title.
These arrangements shall designate for each project the property owner,
governmental agency, or other legally established entity to be permanently
responsible for maintenance, hereinafter in this section referred
to as the responsible person.
B.
The applicant shall enter into an agreement with the
Township (or county) to ensure the continued operation and maintenance
of the facility. This agreement shall be in a form satisfactory to
the Township Attorney, and may include, but may not necessarily be
limited to, personal guarantees, deed restrictions, covenants, and
bonds. In cases where property is subdivided and sold separately,
a homeowner's association or similar permanent entity should be established
as the responsible entity, absent an agreement by a governmental agency
to assume responsibility.
(1)
An applicant seeking approval for construction of
a stormwater management facility shall provide the funds necessary
to permanently maintain the facility. The amount necessary to permanently
maintain the facility shall be calculated by the Planning Board Engineer
based upon current estimates for maintenance with an annual increase
of 4%. The Planning Board Engineer shall also assume that the investment
will yield a return equal to the ninety-day certificate of deposit
interest rate paid by the First Fidelity Bank or its successor on
the date the calculation is made.
(2)
The form of security for the maintenance of the facility
shall be approved by the municipal attorney and finance officer.
C.
In the event that the stormwater management facility
becomes a danger to public safety or public health, or if it is in
need of maintenance, the municipality shall so notify in writing the
responsible person. From that notice, the responsible person shall
have 14 days to effect such maintenance and repair of the facility
in a manner that is approved by the Township Engineer or his designee.
If the responsible person fails or refuses to perform such maintenance
and repair, the municipality may proceed to do so and shall bill the
cost thereof to the responsible person.
A.
All projects containing stream encroachments within
the flood hazard area and one-hundred-year floodplain, at locations
having a drainage area of over 50 acres and all "Projects of Special
Concern," as defined in N.J.A.C. 7:13-5, are subject to the approval
of NJDEP, Division of Coastal Resources.
B.
All projects containing a drainage area over 50 acres
must establish the one-hundred-year floodplain zone in accordance
with N.J.A.C. 7:13-1.8.
[Amended 5-13-2003 by Ord. No. 2003-04]
A.
Where required by the approving authority of the Township
of Manalapan, stormwater management facilities shall be dedicated
to the Township of Manalapan as a drainage utility easement, a right-of-way,
a separate lot or parcel, or a combination thereof. For stormwater
basins to be dedicated in the form of an easement, the easement line
shall be located in a manner to contain an area of a minimum of 15
feet from the top of bank of facilities in cut and toe of slope of
facilities constructed in fill. For stormwater management basins to
be dedicated to the Township on separately platted lots, the lots
conveyed shall conform to this chapter or as approved by the approving
authority. Inlet and outlet piping and maintenance access shall be
contained within easements that are at a minimum in accordance with
the residential site improvement standards as established by the State
of New Jersey. Upon dedication to the Township, no relocation, construction
or reconstruction shall take place within the area of the easement,
nor shall any structures be located within such area, nor shall any
action be taken which may alter or impair the effectiveness of present
or future drainage facilities or cause soil erosion without prior
approval by the approving authority or Township Committee.
B.
The approving authority shall condition the approval
of any subdivision on the dedication of the stormwater facilities
to the Township, where applicable. The developer's agreement shall
provide for the dedication of the facilities by a deed approved by
the Township Attorney, free of all liens and encumbrances. The developer
shall provide a title report for the area being dedicated.
C.
The Township Engineer, upon completion of the stormwater
facilities to his satisfaction, shall notify the Township Committee
that the facilities are constructed in accordance with the Township
regulation and suitable for dedication to the Township in the manner
prescribed by the Approval Authority. Upon acceptance and approval
of the Township Engineer's recommendation by the Township Committee,
the Township Engineer shall require the developer to provide the appropriate
deed and title information. The Township Engineer shall review and
approve the deed descriptions for accuracy and, upon approval of same,
forward this information to the Township Attorney for the preparation
of the ordinance necessary to implement the dedication process.
D.
The dedication of the stormwater facilities and the
assumption of maintenance responsibilities and liability thereof shall
occur only after the effective date of a resolution duly adopted by
the Township Committee.
