A.
A hydraulic design report shall be prepared by an
engineer licensed in the State of New York. The report shall contain
design information for all highway or public easement drainage structures,
storm sewers and channels, and shall be approved by the Highway Superintendent
and the Town Engineer. The report should contain the basic design
data required to arrive at each drainage structure size, such as design
year storm, flow rate, grade, velocity, and method used to determine
the waterway size. A consideration should also be given to anticipated
(if any) future development and any urbanization of the area. The
report must address "before" and "after" development drainage conditions
and assess the downstream effects, if any, caused by the development.
The design year storm shall be a twenty-four-hour, twenty-five-year
event for the piping system, and one-hundred-year for all holding,
retention or detention facilities and stream crossings.
B.
The drainage report should preferably be prepared
in accordance with the SCS methodology in TR-55 or TR-20.
C.
There shall be enough information shown on the plans
and profile to properly construct all the required drainage facilities.
The type and size of culverts, and treatments of inlets and outlets,
the gauge of metal pipe or class of concrete pipe or strength/schedule
of plastic pipe, invert elevation of inlets and outlets, ditch and
channel sections, gutters, channel protection and alignment of ditches
are some of the types of information required on the plans and profiles.
A.
All drainage easements shall be a minimum of 40 feet
wide, unless a lesser width is consented to by the Highway Superintendent.
The easement shall grant the Town the right to enter upon said property
for the purposes of installing, maintaining and repairing the ditches,
pipes, swales, and other structures or facilities as placed in such
easement.
B.
It is the policy of the Town that all storm drainage
shall be enclosed in drainage pipe unless waived by the Highway Superintendent.
C.
All easements shall contain provisions providing for
the right to install underground pipes, to discharge stormwater therein,
and to preclude putting any plantings (except grass) and any structure
or fence in the easement.
D.
Where it is proposed that stormwater be drained from
the highway or from other lands of the developer to a point on the
perimeter of the developer's property, easement or releases shall
be provided from the adjoining owners, permitting the discharge of
stormwater drainage onto or across such adjoining lands.
E.
All pipes shall be terminated with end treatment only
at the property line or perennial open watercourse, whichever is greater,
unless said watercourse is prior to the property line. No exceptions
shall be made unless approved in writing by the Highway Superintendent.
A.
Any storm drain or culvert pipe which will be located
underneath the paved portion or curb of a roadway shall be reinforced
concrete or smooth interior corrugated high density polyethylene pipe.
The minimum diameter shall be 18 inches.
B.
Storm drains or culverts in any location other than
under a roadway may be fully aluminum coated Type II corrugated steel,
polymer coated corrugated steel, smooth interior corrugated high density
polyethylene pipe or reinforced concrete pipe. The minimum diameter
shall be 18 inches.
C.
Height of the fill and pipe classes shall be designed
to meet the minimum requirements of H-20 Highway Loading, as designated
by the American Association of State Highway and Transportation Officials.
D.
The minimum cover on all drainage pipes shall be 18
inches.
A.
Whenever a drainpipe begins or ends in an open ditch,
pond or stream, the inlet and outlet end shall be designed to protect
embankments and channels and to preserve the hydraulic efficiency
of the pipe.
C.
When a drainpipe ends in an open ditch, rip-rap shall
be placed in the channel. See Figures IV-2.1, 2.2 and 2.3 to determine
the size and shape of the apron and Figures IV-3.1 and 3.2 to determine
the stone size. The rip-rap shall be sized to be stable under the
velocity of the discharged water.
A.
Underdrains shall be at a minimum grade of 1% toward
an outlet such as a drainage channel or a catch basin or manhole.
B.
Underdrains shall be required in all cut sections
and where the subgrade is lower than the surrounding ground. The underdrain
invert shall be placed at least 36 inches below finished pavement
grade, but not deeper than 48 inches below finished pavement grade.
The locations may be modified to apply to specific conditions.
A.
The Highway Superintendent and the Town Engineer shall
have authority to require the use of larger or heavier materials,
additional materials, reinforcing or other modifications and improvements
in design and construction over those set forth in this section when
they determine that such modifications would provide improved drainage
and are required by site conditions.
B.
Catch basins shall be placed at all points of change
of slope or alignment and at all junction points. Catch basins shall
be located in the lows of sag vertical curves to prevent ponding.
Catch basins shall be placed either near or within a turning circle,
as the Highway Superintendent or the Town Engineer may require, to
assure adequate drainage. At no time shall catch basins be spaced
farther apart than 350 feet on slopes less than 3%, 300 feet on slopes
from 3% to 6%, and 250 feet on slopes over 6% as shown on the profile.
Catch basins shall be connected to a drainage system or to a natural
drainage course.
C.
Manholes may be used in lieu of catch basins only
where it is not planned to permit the entry of surface water. Open
grates shall not be used on manholes.
D.
Pipes in basins and manholes.
(1)
When the diameter of the effluent pipe is greater
than that of an influent pipe, the elevation of the crown of the influent
pipe shall be no lower than the elevation of the crown of the effluent
pipe.
(2)
When the diameter of the effluent pipe is the
same as or smaller than that of an influent pipe, the elevation of
the invert of the influent pipe shall be no lower than the elevation
of the invert of the effluent pipe.
(3)
There shall be a minimum 0.1 foot drop in elevation
between an inlet invert and the outlet invert at each basin or manhole.
A.
Open ditches or swales, in lieu of storm drainpipes,
shall only be permitted:
(1)
When authorized in writing by the Highway Superintendent;
and
(2)
Along back lots and side slopes when the grade
of the land traversed is flat or when it is desirable to drain and
dry up the surrounding area. The design of any such open ditch shall
be approved by the Highway Superintendent and the Town Engineer.
A.
Detention and retention ponds should not be considered
as the normal way to mitigate downstream drainage impact. They should
only be used in cases where all other options have been investigated
and eliminated and where no other recourse is available. In a case
where a detention or retention pond is required, the following shall
be adhered to and written into any drainage easement for the pond.
Under no circumstances shall any of the following be permitted in
the stormwater retention/detention ponds:
(1)
Alteration of topography.
(2)
Placing of fill.
(3)
Channel encroachment.
(4)
Placement of any structures, trees or other
physical object thereon.
(5)
Grading, excavating, or the removal of material.
(6)
Removal or destruction of turf, trees and/or
vegetation.
(7)
Causing siltation or deposition of debris or
other similar material.
(8)
Causing or creating any act that would alter
the drainageway located therein.
(9)
Utilizing any portion thereof for any motorized
vehicle for any purposes, including recreational purposes.
(10)
The erection of any improvements or other developments.
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In addition, the ponds shall have a minimum
one-percent slope in any direction. The banks shall be impervious,
maximum 2 to 1 slope.
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B.
A detention pond shall be designed to limit the post-development
two-, ten- and twenty-five-year storm peak flows to the respective
predevelopment flow.
C.
The pond shall have an overflow spillway, designed
in accordance with the NYSDEC Guidelines for Design of Dams. In all
cases, the minimum design shall be to control a twenty-five-year storm
and to have a spillway capable of passing a one-hundred-year storm.
