[HISTORY: Adopted by the Town Board of the
Town of Henrietta 12-15-1971. Amendments noted where applicable.]
These regulations and standards are to protect
the various portions of the urban area from flooding, to provide clean
and sanitary channels for runoff, to prevent the encroachment of buildings
and improvements on natural drainage channels, to equitably apportion
the cost of improvements, to protect natural scenic areas and to provide
for the conservation of the natural resources of the area. The regulations,
policies and standards herein contained shall apply to the area outlined
by the Town of Henrietta, New York, which is hereby made a part of
these regulations. All subdivisions of land and all improvements of
any character which affect drainage in any portion of the area within
the township shall be subject to the provisions of these regulations.
A.
Major drainage channels. "Major drainage channels"
are defined as those with a tributary drainage area between four square
miles and 20 square miles. Such drainage channels shall be designed
for an average recurrence interval of 50 years in the determination
of the ultimate channel. The responsibility for major drainage channels
shall be the same as stated for secondary drainage channels below.
B.
"Secondary drainage channels" shall be those rivers,
streams and other channels which have been so designated by the township.
In general, it is the intent of these regulations that channels which
serve a drainage area of one square mile to four square miles or more
shall be designated as secondary channels. It is intended by these
regulations to provide that the maintenance and improvement of secondary
drainage channels will be the responsibility of the municipality primarily,
since the whole municipality is benefited materially. However, the
developer of the land containing the ordinary channel is expected
to lay out, design and otherwise plan and carry out his improvements
in a manner that will not interfere or increase or restrict the natural
flow of water or materially change the condition of runoff. When changes
in alignment are required due to the design or layout of a subdivision,
or an expansion in cross-sectional area is required due to increased
runoff, it shall be the responsibility of the developer to make the
changes, and all changes shall be made in accordance with the provisions
of these regulations. These channels shall be designed for an average
recurrence of 25 years.
C.
"Minor drainage channels" shall include all channels
in the area set forth by the Town of Henrietta, New York. It is intended
by these regulations that the improvements of channels shall be the
responsibility of the developer of the area served by the channel
since the primary benefit is to the area served by the minor channel
and not to the town as a whole. Where minor channels enter publicly
dedicated parks, the channel shall revert to the secondary drainage
channels classification in the park area. The design recurrence shall
equal 10 years.
The maximum condition of rainfall for a fifty-year
interval shall be used for the purposes of determining all runoff
for the sizing of drainage channels and structures, unless otherwise
specified herein. Values used in formulas for runoff and size of drainage
structures shall reflect and shall not be less than the degree of
urbanization set forth in the projected land use plan contained in
the General Plan. The following formulas and values shall be used
for calculating all stream flow and runoff for the policies and regulations
established herein:
A.
Runoff from all drainage areas shall be determined
by the rational formula (other acceptable methods may be submitted
to the Town Board and its Engineer for approval):
Q =
|
AIR
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In which:
| |||
Q =
|
Cubic feet per second.
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A =
|
Area to be drained in acres, determined by field
surveys for areas less than 640 acres and by latest government quadrangle
maps for larger areas.
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I =
|
Percent of imperviousness of the area. This
may vary between 40% and 95%.
| ||
R =
|
Rate of rainfall over entire drainage area in
inches per hour, based on time of concentration and latest governmental
records for the area.
|
B.
The size of closed storm sewers, open channels, culverts
and bridges shall be determined using the Manning formula:
Q =
|
a 1486 r 2/3 s 1/2
n
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In which:
| |||
Q =
|
Discharge in cubic feet per second.
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a =
|
Cross-sectional area of water in conduit in
square feet.
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s =
|
Mean slope of hydraulic gradient, in feet of
vertical rise per foot or horizontal distance.
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r =
|
Hydraulic radius of water in conduit.
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n =
|
Roughness coefficient, based on the condition
and type of material of conduit lining, but not less than 0.013.
|
All major drainage channels which are located
within or immediately adjacent to an improvement or a subdivision
shall be protected and improved by the developer as follows:
A.
All land having an elevation below the fifty-year
maximum flood elevation and not protected by levees or dikes shall
be dedicated to the town for the purpose of providing drainage and
for public park and utility easement use.
B.
The existing channel lying within or immediately adjacent
to the subdivision shall be cleaned to provide for the free flow of
water, and the channel shall be straightened, widened and improved
to the extent required to prevent overflow beyond the limits of the
dedicated drainage area.
C.
Site improvements shall provide for the grading of
all building sites and streets to an elevation where all lots, building
areas and streets will not be subject to overflow and in a manner
that will provide for the rapid runoff of all rainfall; however, such
improvements shall be carried out in a manner that will preserve and
protect large trees and attractive physical features of the area.
D.
Whenever channel improvement is carried out, sodding,
backsloping, cribbing, riprapping and other bank protection shall
be designed and constructed to control erosion for all the anticipated
conditions of flow for the segment of channel involved.
E.
A drainage channel shall not be located in a street
easement unless it is placed in an enclosed storm sewer or unless
a paved street surface is provided on both sides of a paved channel
to give access to abutting properties.
F.
Culverts, bridges and other drainage structures shall
be constructed in accordance with the specifications of the town at
all locations where drainage channels intersect with continuous streets
or alleys. All structures across public streets, alleys and sidewalks
shall be designed for a fifty-year flood.
All secondary drainage channels which are located
within or immediately adjacent to an improvement or a subdivision
shall be protected and improved by the developer as follows:
A.
All land having an elevation below the twenty-five-year
maximum flood elevation and not protected by levees or dikes shall
be dedicated to the town for the purpose of providing drainage and
for public park and utility easement use.
B.
The existing channel lying within or immediately adjacent
to the subdivision shall be cleaned to provide for the free flow of
water, and the channel shall be straightened, widened and improved
to the extent required to prevent overflow beyond the limits of the
dedicated drainage area.
C.
Site improvement shall provide for the grading of
all building sites and streets to an elevation where all lots, building
areas and streets will not be subject to overflow and in a manner
that will provide for the rapid runoff of all rainfall; however, such
improvements shall be carried out in a manner that will preserve and
protect large trees and attractive physical features of the area.
D.
Whenever channel improvement is carried out, sodding,
backsloping, cribbing, riprapping and other bank protection shall
be designed and constructed to control erosion for all the anticipated
conditions of flow for the segment of channel involved.
E.
A drainage channel shall not be located in a street
casement unless it is placed in an enclosed storm sewer or unless
a paved street surface is provided on both sides of a paved channel
to give access to abutting properties.
F.
Culverts, bridges and other drainage structures shall
be constructed in accordance with the specifications of the town at
all locations where drainage channels intersect with continuous streets
or alleys. All structures across public streets, alleys and sidewalks
shall be designed for a twenty-five-year flood.
All minor drainage channels which are located
within or immediately adjacent to an improvement or a subdivision
and all surface drainage conditions shall be protected and improved
as follows:
A.
Minor drainage channels which have a primary function
of collecting surface water from adjacent properties or intercepting
and diverting side hill drainage shall be provided with an improved
open channel.
B.
Any drainage not contained in a paved street must
be contained in underground piping sized to handle a ten-year-flood
capacity, and a paved emergency overflow must also be provided of
such a size that the pipe and the overflow together with handle a
fifty-year flood.
C.
A drainage channel shall not be located in a street
easement unless it is placed in a closed storm sewer or unless a paved
street surface is located on both sides of a paved drainage channel
to give access to abutting properties.
D.
Site grading shall be carried out in such a manner
that surface water from each lot will flow directly to a storm sewer,
improved channel or paved street without crossing more than two adjacent
lots.
E.
Surface water collected on streets shall be diverted
to storm drains at satisfactory intervals to prevent the overflow
of stormwater onto any lot during a fifty-year-frequency rain for
the area and grades involved; provided, however, that in no case shall
the drainage area served by one street exceed 20 acres, regardless
of the amount of flow.
F.
Drainage easements of satisfactory width to provide
working room for construction and maintenance shall be provided for
all storm sewers. In no case shall the total easement be less than
20 feet.
G.
Open channels shall be improved by providing a paved
section that will carry the runoff from a rain of twenty-five-year
frequency and a sodded section to carry the runoff from a rain of
fifty-year frequency. The design of the channel improvements shall
be in accordance with the standards set forth on Figure A or Figure
B.[1] Whenever an open improved channel is required or authorized
for a minor drainage channel under the provisions of these regulations,
and the channel crosses residential lots 80% or more of which have
a width of not less than 90 feet and an area of not less than 13,500
square feet, and the channel improvement is to be designed as an integral
part of the landscaping of the area that will be maintained by the
property owners of the area, then the Town Board may modify the requirements
of the first part of this subsection to permit a channel improvement
design in accordance with Figure C.[2] The developer may elect to provide a paved section to
accommodate runoff from a rain of fifty-year frequency, provided that
sodding shall be carried out to the extent necessary to protect paved
surfaces.
A.
Bridges and culverts.
(1)
Bridges or culverts shall be provided where watercourses
cross continuous streets or alleys.
(2)
Bridge and culverts shall be sized to accommodate
a fifty-year-frequency rain, based on the drainage area involved.
(3)
The design of bridges and culverts shall conform to
town construction specifications.
B.
Closed storm sewers. Closed storm sewers shall be
constructed of precast or prefabricated pipe or built, in place, of
closed-box design to conform with town construction specifications
to serve the required frequency rain for the drainage area involved.
C.
Open paved storm drainage. Open paved storm drainage
channels shall be constructed in accordance with town specifications.
Side slopes above the paved section shall be shaped and sodded on
a slope of four horizontal to one vertical or flatter. Fences shall
not be erected below the shoulder of the sodded section, and in no
case shall fences be closer than six feet, measured horizontally,
to the edge of the paved section unless the paved section is designed
to handle the total fifty-year flood.
A.
It shall be the policy of the Town Board, under the
authority vested in the Town Drainage Ordinance,[1] to require the installation of sedimentation basins and
erosion control measures in all new land development projects; details
shall be such as are required by the Drainage Ordinance, these regulations
and the requirements of the Director of Engineering and Planning or
Town Consulting Engineer.
B.
It shall be the policy of the Town Board, under the
authority vested in the Town Drainage Ordinance, to require the installation
of permanent and/or temporary stormwater retention basins in new land
development where, in the judgment of the Town Board and its Engineer,
it is felt necessary in order to provide proper drainage control.
Details shall be such as are required by the Drainage Ordinance, these
regulations and the requirements of the Director of Engineering and
Planning or Town Consulting Engineer. Adequate safety features, such
as fencing, shall be provided where required by the town.
C.
The design and construction of new land development
shall recognize the need and desirability of a comprehensive drainage
plan to assure that no surface water is directed from one property
to another in a manner as to create a temporary or permanent nuisance
or hazard. To this end the developer shall indicate on his plans how
he proposed to provide for this problem, and such plan shall be subject
to review and approval by the Director of Engineering and Planning
or Town Consulting Engineer, and, further, the town reserves the right
to require a guaranty in the form of a letter of credit and/or a performance
bond to assure that such plan is properly implemented. The developer
shall provide an as-built drainage plan to substantiate that final
grading conforms to the approved drainage plan.
D.
Prohibited acts. It shall be the policy of the Town
Board, under the authority vested in the Town Drainage Ordinance,
to prohibit the following acts:
(1)
Place, deposit or permit to be placed or deposited
any debris, fill, sand, stone or other solid materials of any kind
or nature or construction of any kind into or across any stream, ditch,
culvert, pipe, watercourse or other drainage system.
(2)
Construct and/or place any ditch, pipe, culvert or
artificial watercourse of any kind or nature which shall collect and
direct the flow of natural surface waters or drainage or increase
in intensity or quantity the flow of surface waters or drainage from
paved surfaces, structures, roads or improvements directly into any
stream, ditch, culvert, pipe or watercourse or other drainage system.
(3)
Fill, obstruct, dam, divert or otherwise change or
alter the natural or artificial flow of waters or drainage or the
intensity or quantity of flows through any stream, ditch, pipe, culvert,
watercourse or other improvement or drainage system.
E.
The developer's engineer shall submit, with his final
plans, drainage calculations justifying the size of pipes, channels,
impoundment basins and related structures.