A.
Drainage shall be provided on street frontages in
accordance with the requirements of the village.
B.
Drainage plans shall be submitted in accordance with
the terms and requirements of this Article and shall include complete
forms as provided by the village and, further, shall indicate existing
surrounding drainage systems which may affect the site and shall indicate
that the drainage of the site shall be self-contained and shall not
affect surrounding areas.
C.
Overall site layout shall be designed to minimize
the effect on existing drainageways and channels, whether permanent
or seasonal, and to prevent damage to surrounding properties.
D.
The developer shall be responsible for the solution
to all drainage problems within the site and along all street frontages
bordering the site and off site if caused or contributed to by the
proposed development whether or not they are indicated on the approved
drainage plan.
E.
The Planning Board, with recommendations from the
Village Engineer, may consider alternatives to the drainage requirements
contained herein.
F.
Stormwater collection system.
(1)
The stormwater collection system shall be designed
in accordance with the Rational Method as follows (see Figure 108.1[1]):
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Q
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=
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Air
|
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Q
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=
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Discharge in cubic feet per second.
|
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A
|
=
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Tributary drainage area in acres.
|
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i
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=
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Coefficient of runoff of the drainage area.
Calculations of "i" shall be shown on design sheet.
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R
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=
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Rainfall intensity in inches per hour as determined
by:
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|
R
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=
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120
t + 20
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|
Where:
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t
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=
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Time of concentration in minutes.
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[1]
Editor's Note: Figure 108.1 is located at
the end of this chapter.
(2)
Pipes, conduits or ditches shall be designed by the
use of the Mannings Formula as follows:
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V
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=
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1.486 x R2/3 x S1/2
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|
n
|
|
Where:
| |||
|
V
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=
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Velocity in feet per second
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R
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=
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Hydraulic radius in feet
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n
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=
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Coefficient of roughness where:
| |
|
n
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=
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0.13 for reinforced concrete pipe 24 inches
or smaller in diameter.
| |
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n
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=
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0.15 for reinforced concrete pipe 18 inches
or smaller in diameter.
| |
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n
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=
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To be determined and approved for special conduits
and ditches. (1) Maximum velocity 10.0 feet/second
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S
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=
|
Slope of pipe to be used as hydraulic gradient
of pipe flow except where system will be surcharged when recharge
basin is full. Design gradient in this case may be assumed as lowest
inlet invert to water surface at 80% storage volume where no overflow
is provided. In case of outfall in tidal water, use maximum tide elevation.
| |
(3)
Manholes. The maximum distance apart shall be 350
feet.
(4)
Pipe alignment and locations. Storm sewer pipe shall
be in a straight line between manholes and shall be placed between
the center line of the road and curbline.
(5)
Valley gutters. Valley gutters may be permitted at
T-intersections where they are parallel to the center line of the
through road and shall be installed only after design approval by
the village. In general, the crown of the intersecting road shall
be gradually eliminated starting from a point about 30 feet back from
the flow line of the through street. At other than T-intersections,
valley gutters may be permitted only when warranted by limited traffic
use as approved by the village.
(6)
Gutter flow. Surface drainage in gutters shall be
limited to that flow which shall not exceed five inches in depth at
the curb based on the individual conditions of road grade, runoff
factor, rainfall intensity, tributary area and inlet capacity.
(7)
Catch basins. Not more than two catch basins shall
be interconnected before being connected to a manhole. All drainage
structures under pavement, including overflows, shall have surface
access for cleaning.
(8)
Brooks, ditches and stream beds. Areas such as brooks,
water-bearing ditches and dry stream beds giving evidence of seasonal
runoff use shall be maintained for drainage purposes in their existing
or natural state.
(9)
Drainage structures which are located on state or
county highway rights-of-way shall be approved by the appropriate
highway engineer's office. A letter of approval from that office shall
be filed with the Village Planning Board. Where county highways are
involved, the Planning Board shall obtain the approval from the county
pursuant to § 239-k of the General Municipal Law.
G.
Stormwater recharge basins shall be required as specified
herein and designed in accordance with the village construction standards
in Appendix A[2] and the following:
(1)
Storage capacity. Storage capacity necessary to accommodate
an eight-inch rainfall with coefficient of runoff based on runoff
characteristics shall be provided (see Figure 108.2[3]). However, where a positive overflow acceptable to the
Village Engineer is available, the storage capacity may be designed
for a five-inch rainfall. Where the required volume is less than 4,000
cubic feet, a recharge basin shall not be required. In this case,
precast leaching basins designed to store a two-inch rainfall may
be used.
[3]
Editor's Note: Figure 108.2 is located at
the end of this chapter.
(2)
There shall be a minimum of two feet between the design
depth of any leaching facility and groundwater as determined by test
holes. Test hole locations, soil conditions and water level shall
be shown on all plans.
(3)
Maximum storage depth shall be 14 feet.
[2]
Editor's Note: Appendix A, which contains
the village construction standards, is on file in the office of the
Village Clerk.
