Storm drainage systems shall be generally designed
and provided to adequately convey anticipated runoffs occurring from
storms which occur with a frequency of once in 10 years, as indicated
in nomographs prepared by the Monroe County Planning Council.
A. Removal of spring and surface water. The applicant
shall be required by the Planning Board to provide adequate drainage
systems to carry any spring or surface water that may exist either
previous to or as a result of the subdivision. Such drainage facilities
shall be located in the street right-of-way where feasible or in perpetual
unobstructed easements of such widths as designated in this chapter.
B. Drainage structure to accommodate potential development
upstream. A culvert or other drainage facility shall, in each case,
be large enough to accommodate potential runoff from its entire upstream
drainage area, whether inside or outside the subdivision. The Town
Engineer shall approve the design and size of the facility based on
anticipated runoff under ultimate development bases on accepted engineering
criteria and parameters.
C. Responsibility for drainage downstream. The applicant's
engineer shall also study the effect of each subdivision on the existing
downstream drainage facilities outside the area of the subdivision;
this study shall be reviewed by the Town Engineer. Where it is anticipated
that the additional runoff incident to the development of the subdivision
will overload an existing downstream drainage facility, the Planning
Board shall notify the Town Board of such potential condition. In
such case the Planning Board shall not approve the subdivision until
provision has been made for the improvement of said condition.
D. Land subject to flooding. Land subject to flooding
or land deemed by the Planning Board to be uninhabitable shall not
be platted for residential occupancy, nor for such other uses as may
increase danger to health, life or property or aggravate the flood
hazard, but such land within the plat shall be set aside for such
uses as shall not be endangered by periodic or occasional inundation
or improved in a manner satisfactory to the Planning Board to remedy
said hazardous conditions.
E. Flood hazard prevention. The applicant shall be required
to control soil erosion of land surface and drainage channels and
the prevention of inundation and excessive groundwater seepage by
comprehensive site grading and the establishment of adequate elevations
of buildings, building openings and roadways above the observed, anticipated
or computed water levels of storm sewers, streams, channels, floodplains,
retention basins and swales.
F. Runoff computations.
(1) Runoff shall be established from the rational formula
as follows:
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Q = AcI
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Where:
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Q = Runoff (cfs)
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A = Acreage of the drainage basin involved
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c = Coefficient of runoff (minimum for subdivision
development 0.40)
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I = Intensity of rainfall in inches per hour
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(2) Minimum times of concentration can be assumed at 15
minutes.
(3) Nomographs to determine factors for the computation
of the runoff shall be those as developed by the Monroe County Planning
Council.
(4) The applicant's engineer shall submit the following
information regarding the design of storm drainage facilities with
the final map (scale of 1:24,000).
(a)
A USGS section map (scale of 1:24,000) with
the outline of the development and the drainage basin.
(b)
A tabular form (see Appendix B for typical format) showing computed runoffs and design capacities of the
drainage system.
(5) Points of discharge. Storm drainage shall be discharged
to recognized USGS drainage courses. This may require applicants to
obtain downstream easements from adjoining property owners to permit
this drainage across their properties. The applicant shall be required
to construct and maintain temporary silt settling basins at the point
of discharge into the stream. The basin shall be operable until the
completion of the subdivision.
G. Storm drains. Storm drains shall conform to the following
specifications:
(1) Minimum pipe sizes 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) Builders (where necessary) shall provide backwater
valves on all laterals where the storm drain is at such an elevation
to permit gravity drainage from the basements adjacent to the system.
(5) All outfall pipes must be reviewed by the Town Engineer
and Commissioner of Public Works.
H. Storm laterals. Storm laterals, if required, shall
be six inches in diameter. Sump pumps and roof runoff shall not be
permitted to tie into the storm laterals directly unless requested
by the Commissioner of Public Works. Splash pads shall be required
for storm outlets.
I. 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 drains at manholes
except in those areas where the storm drain is 24 inches in diameter
or greater.
J. Storm manholes.
(1) The inside diameter of storm manholes shall be determined
as follows:
Storm Drains
(inches)
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Inside Manhole Diameter
(feet)
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12 to 18
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4
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21 to 30
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5
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36 to 42
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6
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Greater than 42
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Individual structures will be required.
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(2) A schedule of manhole diameters shall be provided
on the final plat.
K. Drainage easements. The minimum width for drainage
easements shall be 20 feet.
(1) Enclosed conduits and appurtenances. An easement not
less than 20 feet in width, sufficient to contain the enclosed conduit
and appurtenances thereof and to provide working space for personnel
and equipment for the service thereof, shall be indicated on the map
of the development and designated as follows: "Drainage Easement to
Town of Irondequoit." Drainage easements, insofar as possible, shall
be placed along or adjacent to lot boundary lines in a parallel or
straight alignment.
(2) Easements for natural watercourses.
(a)
Natural primary watercourses which traverse a development shall be preserved by an easement of sufficient width, including overbanks, which will adequately pass the projected design flow. The gross allowable depth of flow shall not create a flood hazard to existing or proposed development and improvements. The channel and overbank widths, together with a minimum twenty-foot continuous maintenanceway on each side, shall constitute the floodway encroachment limits, as further defined under the EPOD District regulations of Chapter
235, Zoning.
(b)
In natural tertiary and secondary watercourses
which contain insufficient waterway area to convey the flow from the
ultimate development, but which may prove deficient only at infrequent
intervals and location, and where minor improvements could provide
an adequate channel and still preserve, in the main, the natural channel
beauty or fish and wildlife values, the applicant shall make such
minor channel improvements as are required to provide a channel which
would otherwise meet the conditions of this chapter. Additional widths
of scenic areas and areas of natural wetlands which, for economic
reasons or limited suitability, would not warrant improving for urban
development, may be dedicated by the applicant in addition to those
above. Areas offered for dedication to the town as drainage easements,
if considered of special interest to the town by the Planning Board,
may be considered by the Planning Board as dedication for the municipal
purposes of § 278 of the Town Law, as amended or changed,
and its authority thereunder.
(c)
Easements for constructed channels and appurtenances.
Earth channels constructed within the development shall have sufficient
easements dedicated to contain the top width of the channel, plus
a minimum twenty-foot wide continuous maintenanceway, one side for
channels less than 20 feet in width at water surface. A twenty-foot
wide continuous maintenanceway shall be provided on both sides of
a channel with a water surface width greater than 20 feet. The easements
for constructed channels shall be indicated on the map of the development
and designated as follows: "Drainage Easement to Town of Irondequoit."
Water mains shall conform to the specifications
of the Monroe County Water Authority or the Sea Breeze and Vicinity
Water District and local fire districts.
Where land areas are reserved for future connections
to adjacent parcels, all improvements, i.e., sanitary, storm, water,
roads, etc., shall be constructed to the common property line. This
requirement may be waived by the Planning Board.
The materials included herein are intended to
establish the necessary degree of excellence required for installation
within the town. Where other materials may be proposed in substitution
for those herein called for, the applicant or his or her agent shall
submit a written request to the Town Engineer for approval. When new
materials may be made available, their use may be permitted in limited
test sections with the restriction that, should these materials prove
unsatisfactory through the test period, as established by the Town
Engineer, they shall be removed and replaced with those herein called
for at no expense to the town.
Manhole ladders or steps shall be provided in
all sanitary and storm manholes and shall be constructed of one of
the following materials:
A. Noncorrodable, aluminum magnesium alloy ladders, as
made by Fraser and Jones, Solvay, New York, or an approved equal,
with intermediate supports at five-foot intervals.
B. Forged aluminum with a drop-front design and grooved
tread surface.
All materials and methods of installation shall
conform to either the Monroe County Water Authority or the Sea Breeze
and Vicinity Water District specifications for the applicable service
area.