All development projects shall be required to
provide for the adequate conveyance of storm drainage through the
development. The natural drainage patterns are to be followed as much
as possible. Drainage systems shall be sized to accommodate the future
potential runoff based on the probable land use and the ultimate development
of the upland watershed area.
A. Storm sewers and drainage facilities. A drainage area
of up to 1,000 acres shall be designed to transmit the flow of a one-in-ten
year storm. Larger systems and structures on natural watercourse channels
shall have design return intervals as follows:
|
Drainage Area
|
Design Return Interval
|
---|
|
1,000 acres to 4 square miles
|
25-year
|
|
4 square miles to 20 square miles
|
50-year
|
|
20 square miles and above
|
100-year
|
B. Allowance for overflow conditions. Overflow conditions
shall be designed into each system to protect against damage from
major storms and provide an outlet for stormwater, should inlets or
pipes become damaged or plugged.
C. Natural channels and open swales. Natural channels
are generally preferred alignments for major components of a residential
drainage system. However, the utilization of open channels shall be
evaluated as to the ease and cost of maintenance, safety hazards and
aesthetics. The channels may require special invert or side design
to properly convey water while keeping the maintenance cost minimal.
D. Runoff computations.
(1) The design of storm systems shall be generally established
by the Rational Formula (Q = CiA) where:
|
Q
|
=
|
Runoff in cfs
|
|
C
|
=
|
Runoff coefficient
|
|
i
|
=
|
Rainfall intensity in inches/hour
|
|
A
|
=
|
Drainage basin area in acres
|
(2) Rainfall intensity figures shall be taken from the
charts provided in Appendix F for the time of concentration and return
period required for a particular basin.
(3) Times of concentration shall be calculated by the
design engineer, but shall be a maximum of 15 minutes to the first
inlet for a residential subdivision.
(4) Runoff coefficients.
(a)
Runoff coefficients shall also be calculated
by the design engineer to establish a weighted value representative
of the type of development proposed. In general, the following ranges
shall be adhered to:
|
Description of Area or Character of Surface
|
Runoff Coefficient
|
---|
|
Business District
|
0.70 to 0.95
|
|
Residential:
|
|
|
|
Single-family
|
0.40 to 0.50
|
|
|
Apartments
|
0.50 to 0.70
|
|
Industrial
|
0.50 to 0.90
|
|
Unimproved
|
0.10 to 0.30
|
|
Pavement
|
0.70 to 0.95
|
|
Lawns
|
0.10 to 0.35
|
(b)
Factors to be considered in the determination
of the runoff coefficient are: soil type, slope of land, development
density, etc.
(5) Points of discharge shall be recognized USCGS drainage
courses, which may require the developer to acquire downstream easements
for dedication to the town.
(6) Culverts shall be designed to accommodate the design
storm for the drainage area, but shall be checked for the next highest
increment of storm return interval to evaluate the possible complications.
Headwater and/or tailwater calculations will be required to determine
ponding that may occur. In general, the use of multiple culverts is
discouraged because of maintenance problems. Inlets and outlets of
culverts shall be protected from erosion or turbulence problems by
the use of riprap, headwalls, energy dissipaters, etc.
(7) Backyard swales shall be designed with minimum side
slopes of 1:4 and a minimum longitudinal slope of 1.0%. Field inlets
shall be generally provided every 300 linear feet at all low points
and where swales intersect.
(8) Retention or detention ponds.
(a)
Retention or detention ponds may be required
for developments within the town where, in the judgment of the Planning
Board and the town, these facilities may be applied to the existing
conditions or topography which dictate the practicality of this alternative.
(b)
If a detention pond is to be used on the site,
the following parameters shall be adhered to:
[1]
Pond shall be designed to accommodate the return
interval storm for the drainage basin size, plus a one-foot-to-zero-inches
minimum freeboard.
[2]
The pond outlet should be protected against
erosion.
[3]
An overflow mechanism should be designed to
allow for the next larger return interval design storm.
[4]
Ponds designed in fill or using dikes shall
consider soil stability of the facility.
[5]
Runoff calculations for larger facilities may
use alternate methods, such as the unit hydrograph or one of the Soil
Conservation Service methods applicable to the situation and acceptable
to the town.
(9) The design engineer shall submit, as a minimum, the
following information for review of the drainage design:
(a)
USCGS quadrangle reprint with the development
and drainage basin outlined.
(b)
A tabular form (see Appendix G for typical form) showing computed runoffs and design capacities of the
system.
(c)
A map of the development showing the on-site
drainage areas with inlets numbered in conjunction with the tabular
calculation sheet.
E. Storm drains.
(1) Minimum pipe size shall be 12 inches in diameter.
(2) Minimum velocity when flowing full shall be three
fps.
(3) Maximum manhole and catch basin spacing shall be 300
linear feet.
(4) In general, only natural waterways may be continued
in open channels. Street drainage and other parts of a storm sewer
system shall be in closed conduit. When gradient and tributary runoff
requires conduits greater than 36 inches in diameter, then open channel
design may be considered.
F. Storm laterals. Gravity laterals shall be a minimum
of four inches in diameter. Sump pumps with check valves will be permitted
to discharge to storm laterals or, in the absence of storm sewers,
to splash pads directed to side or rear yard drainage swales. Roof
runoff will not be permitted to tie into the storm laterals directly
but discharge to splash pads.
G. Catch basins. Catch basins shall be placed at all
low points and intersections with maximum spacing of 300 feet. Catch
basin leads shall only be connected to the storm sewers at manholes,
except in those areas where the storm sewer is 24 inches in diameter
or greater.
H. Storm manholes.
(1) Storm manholes shall be designed to accommodate the
pipes entering and exiting the structures.
(2) A schedule of manhole diameters shall be provided
on the final plan.
I. Drainage easements. The minimum easement width shall
be 20 feet, but the actual width acceptable to the town will consider
all those factors previously listed.
All work performed and materials furnished for the purpose of supplying the development with potable water shall comply with Chapter
131, Water.
A. Design.
(1) Water supply system shall be designed to provide adequate
domestic usage and fire protection. Where public water supply is not
accessible, an alternate private supply shall be furnished, which
conforms to the New York State Health Department regulations.
(2) All main and service sizing shall be substantiated
by the design engineer using updated flow data provided by the Water
Utilities Department.
(3) All water mains shall be a minimum of eight inches
except:
(a)
Where mains are part of a major transmission
distribution network, the town may require a larger size main.
(b)
Where project demands allow a smaller main while
still providing adequate fire and domestic flows. In no case will
the town accept for dedication a main smaller than four inches in
diameter.
B. Hydrants. Hydrants shall be spaced to comply with
ISO requirements, but at a maximum 500 foot intervals in subdivisions
and 600 foot intervals in open spaces.
C. Valves.
(1) Valves shall be located such that no more than 30
dwelling units and no more than two hydrants need be out of service
for repair of a water main. Valves shall generally be provided at
intersections and shall be no more than 1,200 feet apart along the
water main.
(2) Additional valves may be required at creek and/or
railroad crossings depending on network configuration and permit requirements.
D. Dead-end mains. Provide two-inch blowoff units at
the end of all dead-end mains.
E. Water services. A minimum three-fourths-inch water
service to the right-of-way line of all individual lots or where an
easement is provided shall be provided; the service shall extend to
the easement line. All services under dedicated roads shall be Type
K copper without line couplings.
F. Meter pits (for individual services). Meter pits shall
be installed when the water service length is greater than 250 feet
from the center line of a given road. Remote read meters shall be
placed outside the pit area.
Where required by the Planning Board, sidewalks
shall be concrete, per Appendix T.
Monuments per Appendix L shall be located at:
A. Point of curvature and point of tangent of all horizontal
curves along one side of the right-of-way.
B. Maximum of 1,000 feet along one side of the right-of-way
line.
Where land areas are reserved for future connections
to adjacent parcels, all improvements, i.e., sanitary, storm, water,
roads, will be constructed to the common property line.