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 based on the Town's drainage study.
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:
Where:
|
|
Q
|
=
|
Runoff in cubic feet per second
|
|
C
|
=
|
Runoff coefficient
|
|
I
|
=
|
Rainfall intensity in inches per 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 United States Coast and Geodetic
Survey 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 one
on four 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 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. If a detention
pond is to be used on the site, the following parameters shall be
adhered to:
(a)
The pond shall be designed to accommodate the return interval
storm for the drainage basin size plus a one-foot zero-inch minimum
freeboard.
(b)
The pond outlet should be protected against erosion.
(c)
An overflow mechanism should be designed to allow for the next
larger return interval design storm.
(d)
Ponds designed in fill or using dikes shall consider soil stability
of the facility.
(e)
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)
A United States Coast and Geodetic Survey quadrangle reprint
with the development and drainage basin outlined.
(b)
A tabular form (see Appendix G for typical) 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 feet per second.
(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 conduits. When gradient and tributary runoff requires conduit
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 shall 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. Storm manholes shall be designed to accommodate the
pipes entering and exiting the structures. 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 Recommended Standards for Water Works (1987) and Chapter
281, Water, of the Code of the Town of Macedon.
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 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/Sewer Superintendent.
(3) All water mains shall be a minimum of eight inches, except:
(a)
Where mains are part of a major transmission distribution network,
in which case the Town may require a larger size main.
(b)
Where project demands allow a smaller main while still providing
adequate fire and domestic flows.
(4) 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 maximum intervals of 500 feet in subdivisions and 600 feet
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. Two-inch blowoff units shall be provided 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 shall be provided or where
an easement is 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 350 feet from the center
line of a given road or at the discretion of the Water/Sewer Superintendent.
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 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.