A.
A stormwater management plan shall be part of preliminary
plat (major subdivision) and final plat (minor subdivision) submittals.
The plan shall be prepared in substantial compliance with the latest
issue of the New York Guidelines for Urban Erosion and Sediment Control
developed by the National Resources Conservation Service (NRCS). In
general, the structure and content of the stormwater management plan
shall include:
A.
The off-site impacts of erosion and sedimentation
from a development site should not be any greater during and following
land disturbance activities than under predevelopment conditions.
B.
Water in stream reaches on site and downstream of
construction areas should not have substantial visible contrast relative
to color, taste, odor, turbidity and sediment deposition from the
water in reaches upstream of the construction area.
C.
Sediment laden runoff should not be allowed to enter
any water body in such quantity that would result in deposition on
the bottom of the water body, degrade its natural biological functions,
or be deleterious to the classified usage of the water.
A.
No greater peak flow will be discharged from a project
site than was discharged prior to development for a runoff volume
generated from a two-year twenty-four-hour storm, a ten-year twenty-four-hour
storm, and a one-hundred-year twenty-four-hour storm.
(1)
Runoff volume generated from a two-year, twenty-four-hour
storm should be stored and gradually released for a minimum of 40
hours. This design standard is intended to achieve the stream channel
erosion control objective.
(2)
Runoff volume generated from a ten-year, twenty-four-hour
storm should be attenuated for a minimum of 24 hours. This design
standard is intended to assure the adequacy of existing and proposed
culverts and storm drains.
(3)
Runoff volume generated from a one-hundred-year twenty-four-hour
storm should be attenuated for a minimum of 24 hours. This design
standard is intended to reduce the rate of runoff from the development
to prevent expansion of the one-hundred-year floodplain and to alleviate
flooding of improved properties and roadways.
A.
Stormwater management facilities for capturing and
treating the first flush may include infiltration, retention and extended
detention. Dry detention (ponds) may not be used to treat the first
flush.
B.
Stormwater management facilities for treating the
first flush should be used to capture the first 1/2 inch of runoff
or runoff resulting from a one-year twenty-four-hour storm event,
or whichever is greater, from all land areas for which the perviousness
has been changed over predeveloped conditions due to land clearing,
land grading and construction.
A.
A grading and drainage system plan shall be part of
a preliminary plat (major subdivision), final plat (minor subdivision)
and shall be in conformance with the municipality's stormwater management
plan, where applicable. It shall indicate a proposal for an adequate
system of drainage structures to carry off and store or discharge
the stormwater runoff and material drainage water which originates
within not only the property boundaries but also that which originates
beyond the property boundaries.
B.
The public improvement and utilities plan and profiles
shall show the final drainage plan and street profiles. They shall
be prepared and submitted with the final plat and be reviewed and
approved by the Town Engineer.
C.
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 private
properties or public lands without proper and approved provisions
being made for taking care of these conditions.
A.
Where brooks or ditches are used as outlets, they
shall be designed by the use of Manning's formula as indicated for
collection systems, with the following considerations:
(1)
Side slopes for ditches shall be not more than one
on two.
(2)
Design velocities in earth ditches shall not exceed
three feet per second.
(3)
A ditch or brook right-of-way, of sufficient minimum
width to include a ten-foot access strip in addition to the width
of the ditch or brook from bank top to bank top, shall be offered
for dedication to the Town for drainage purposes. Such right-of-way
shall be shown on drainage plan and on the final plat. A grass-lined
drainage swale shall be used where feasible along lot lines.
A.
Drainage structures which are located on county or
state highways shall be approved by the appropriate highway engineer's
office and a letter or permit from that office indicating such approval
shall be directed to the Planning Board.
B.
Surface drainage flowing along curbs shall be limited
to the equivalent of that flowing from 1.5 impervious acres.
C.
All structures (catch basins, manholes, etc.) shall
be one of the approved designs presented in the Standard Detail Drawings
contained herein.[1] They shall be indicated on the drainage plan by their
identifying numbers.
[1]
Editor's Note: Said Standard Detail Drawings
are included at the end of this chapter.
D.
Precast reinforced concrete manholes, dry wells, drop
inlets, and catch basins shall conform to the requirements of ASTM
Designation C 478 (latest issue). Mastic or mortar shall be used in
all field joints.
A.
Storm drain pipe shall conform to the following material
specifications:
(1)
Concrete pipe shall conform to requirements of ASTM
Designation C 76 (latest issue) for Reinforced Concrete Culvert, Storm
Drain, and Sewer Pipe, Class IV minimum, unless otherwise specified.
(2)
Corrugated steel pipe shall be asphalt coated, 16
gauge minimum, and conforming to the requirements of Section No. 603,
Culverts and Storm Drains, of New York State Department of Transportation
Specifications dated January 2, 1990, with current additions and modifications.
(3)
PVC pipe shall conform to the requirements of ASTM
D 3043 (latest issue) for four-inch diameter through fifteen-inch
diameter Type PSM polyvinyl chloride (PVC) sewer pipe and fittings,
and ASTM F 679 (latest issue) for eighteen-inch diameter and larger
Type PSM polyvinyl chloride (PVC) sewer pipe and fittings. SDR-35
pipe will be used for all work. Push-on joints shall be made with
flexible elastometric seals conforming to ASTM Standard Specification
D 3212 (latest issue).
(4)
HDPE pipe shall be solid polyethylene pipe. All polyethylene
pipe fittings shall conform to the requirements of ASTM D 3350 (latest
issue) and shall be Sure-Lok Pipe as manufactured by Hancor, Inc.,
or equivalent and shall conform to the requirements of AASHTO M 252
and M 294 Type S. All pipe shall be marked with size, type, and schedule.
Both pipe and fittings shall be the product of one manufacturer.
(5)
All underdrains shall be perforated polyethylene pipe
and fittings shall conform to the requirements of ASTM D 3350 (latest
issue) and shall be Sure-Lok Pipe as manufactured by Hancor, Inc.,
or equivalent and shall conform to the requirements of AASHTO M 252
and M 294 Type S. All pipe shall be marked with size, type, and schedule.
Both pipe and fittings shall be the product of one manufacturer.
B.
All pipe shall be laid on undisturbed subgrade with
full firm and even bearing. Backfill and compaction shall be in accordance
with good engineering practice. They shall be indicated on the final
plat with notation as to size, slope and invert elevations. Necessary
easements shall be shown on the drainage plan and the final plat and
shall be not less than 10 feet wide.
C.
Drainage pipe shall be a minimum of 18 inches in diameter.
