The general intent of this article is to manage
and limit the adverse effects of surface water runoff created by alteration
of the ground cover or natural runoff patterns, to establish storm
drainage requirements and to regulate encroachments and land use in
floodways and flood hazard areas.
[Amended by Ord. No. 7-1992]
The purpose of this article is to protect the
public health, safety and welfare of the citizens of the Township
and the surrounding communities and to accomplish the following purposes:
A. To maintain the adequacy of natural stream channels
and prevent accelerated bank erosion through control of the rate and
velocity of stormwater runoff.
B. To preserve present adequacy of culverts and bridges
by avoiding artificially induced flood peaks.
C. To minimize public expenditures for replacement or
repair of public facilities resulting from induced flood peaks.
D. To prevent damage to life and property from flooding
by controlling excessive rates, velocities and total quantities of
runoff.
E. To maintain or improve the relationship of the site
to the natural or established drainage pattern of the subwatershed(s)
of which it (they) is (are) a part.
F. To minimize public safety hazards at any stormwater
detention facilities constructed as part of a subdivision or pursuant
to a site plan.
[Amended by Ord. No. 7-1992]
A. The stormwater management plan shall be submitted
to the Township Engineer for his review and recommendations. The Township
Engineer shall report to the Planning Board or Zoning Board of Adjustment
as to whether or not the stormwater management plan complies with
the requirements of this article. No development application shall
be considered complete until the Township Engineer submits his report.
The Township Engineer's consideration of the plan shall be guided
by but not limited to the following factors:
(1)
The suitability of the applicant's proposed
surface water management techniques, involving on-tract and/or off-tract
measures, with respect to the total stormwater runoff, velocities
and rates of discharge which the applicant's proposed construction
or land disturbance may generate.
(2)
Existing topographic, present vegetation and
hydrologic soil factors.
(3)
Groundwater recharge and discharge areas, wet
soils, alluvial and poorly drained soils and seasonal high groundwater
table level.
(4)
The design storms as specified in §
170-123, Plan details.
(5)
Natural drainage now and pattern through the
watershed(s) affected by the plan.
(6)
The nature of the watershed of which the proposed
development is a part and the receiving stream channel capacities.
(7)
Land uses in both the immediate vicinity and
surrounding drainage region.
(8)
Any other applicable or relevant environmental
and resource protection ordinances, statutes and regulations.
(9)
Any other factors relevant to the coordinated
and harmonious development of the site, vicinity, Township and region.
(10)
Conformity with any state regulations concerning
the protection of public safety with respect to stormwater detention
facilities adopted pursuant to N.J.S.A. 40:55D-95.1.
B. If the appropriate Board determines the proposed development
will satisfy the standards of this article, the Board shall approve
the stormwater management plan as part of site plan approval or subdivision
approval.
C. If the appropriate Board determines the proposed development
will generate or alter stormwater runoff which will not be managed
in accordance with the standards of this article, the Board shall
disapprove the proposed site plan or subdivision, stating the reason.
D. The appropriate Board may condition its approval of
the stormwater management plan by imposing lawful requirements. These
requirements shall be provided and maintained as conditions to the
establishment, maintenance and continuance of any use or occupancy
of any structure or land.
The stormwater management plan shall include
the following:
A. The lot and block numbers of the site as shown on
the current Tax Map of the Township.
B. The name(s) and addresses of the owner(s) of the site;
size and location of the site on a map of the watersheds.
C. The location, description and quantification of significant
natural and man-made features on and surrounding the site, including
topography, all impervious surfaces, soil and drainage characteristics
with particular attention to the location and description of presently
existing surface water runoff control devices, mechanisms or areas,
watercourses, swamps, floodplains, swales, berms, woods and vegetation,
steep slopes and other features critical to the purposes of this article.
D. The location, description and quantification of proposed
changes to the site, whether of a permanent or temporary nature, with
particular attention to impervious surfaces and interception of currently
dispersed flow which may have an impact upon the capacity of the soil,
vegetative cover and drainageways to absorb, retard, contain or control
stormwater runoff.
E. The proposed measures for stormwater management.
F. The computations, using the rational method (Q=CIA),
showing both the peak rate and peak velocity and total quantity of
stormwater runoff from the site, both before and after the proposed
development. Total quantity of stormwater runoff shall be computed
under the following conditions: a ten-year storm, 2.1 inches of rain
during a sixty-minute period, and a one-hundred-year storm, 3.1 inches
of rain during a sixty-minute period. The rain shall be assumed to
be falling at a uniform rate during the specified period for the computation
of total quantity of runoff and at a varying rate for the computation
of hydrographs.
(1)
The following runoff coefficients shall be used
for the various soil, vegetation and other surface conditions:
|
Runoff Coefficients
|
---|
|
Surface Character
|
Runoff Coefficients
|
---|
|
Ten-Year Storm Frequency
|
|
All paved surfaces
|
0.80 to 0.95
|
|
Roofs
|
0.80 to 0.95
|
|
Lawns, less than 2% slopes
|
0.17 to 0.21
|
|
Lawns, 2% to 7% slopes
|
0.22 to 0.26
|
|
Lawns, over 7% slopes
|
0.29 to 0.41
|
|
Woodlands, less than 2% slopes
|
0.10 to 0.14
|
|
Woodlands, 2% to 7% slopes
|
0.15 to 0.19
|
|
Woodlands, over 7% slopes
|
0.22 to 0.30
|
|
Runoff Coefficients
|
---|
|
Surface Character
|
Runoff Coefficients
|
---|
|
One-Hundred-Year Storm Frequency
|
|
All paved surfaces
|
0.85 to 0.96
|
|
Roofs
|
0.85 to 0.96
|
|
Lawns, less than 2% slopes
|
0.28 to 0.33
|
|
Lawns, 2% to 7% slopes
|
0.34 to 0.37
|
|
Lawns, over 7% slopes
|
0.41 to 0.52
|
|
Woodlands, less than 2% slopes
|
0.20 to 0.24
|
|
Woodlands, 2% to 7% slopes
|
0.26 to 0.31
|
|
Woodlands, over 7% slopes
|
0.34 to 0.42
|
(2)
Where the applicant is of the opinion that required
computations do not adequately reflect the true impact of the proposed
development on stormwater control, computations using any acceptable
engineering approach with data from any documented source may be included
as supplemental information.
G. If, in the opinion of the Township Engineer, a complete
hydrograph is needed to adequately analyze the proposed development,
a hydrograph for the specified ten-year and one-hundred-year storm
shall be included. When required, such hydrographs shall show, in
graphical form, the water flow time sequence for runoff from the site.
Supporting calculation details shall be furnished indicating the assumptions
and formula used, including relevant intermediate results such as
the water flow time profile of the inflow to a retention or detention
basin and the control characteristics and physical design of the discharge
rate metering device (stormwater pipe, weir, etc.).
H. Appropriate plans, profiles and cross sections every
50 feet, of all proposed and existing culverts, bridges, storm sewers,
drainage ditches and streams within the subdivision and within 300
feet upstream and downstream of the subdivision, together with their
sizes, elevations, grades and capacities, as approved by the Township
Engineer.
I. A flood routing of the discharge channel shall be
provided so that the coordination of discharges proposed from the
tract with those from off-tract and the effects of stream bank erosion
can be analyzed.
J. The designation of critical or other areas to be left
undisturbed shall be shown in sufficient detail to be accurately marked
on the plan.
K. The schedule of the implementation of the stormwater
management plan, in connection with the starting and completion dates
of the development.
L. The proposed maintenance schedule for all stormwater
management structures, specifying current maintenance, continued maintenance
and responsibility for the same.
M. All revisions of the plan and such additional data
as the Township Engineer may require.