The provisions contained in this article, together with the
Town drainage report, maps and charts appended thereto, which are
hereby incorporated in this article, are for the purpose of achieving
and maintaining an adequate, efficient and balanced drainage and flood
prevention system coordinated with existing and projected land uses
and in compliance with minimum protection levels to be integrated
with all public works planning, open land uses, conservation objectives,
watershed management and any community-inspired proposals designed
to promote the public welfare, but not prejudicial to or inconsistent
with the primary purpose of adequate drainage and flood hazard prevention
requirements.
A.
Applicability. The requirements set forth in this article shall apply only to development within the Town of Lewiston that is not already subject to review under Article II of this chapter.
B.
Conflict. Where any of the conditions imposed by any provision of
this article are either more restrictive or less restrictive than
comparable conditions imposed by the provisions of any other applicable
law, ordinance, resolution, rule or regulation of any kind, the regulations
which are more restrictive and impose higher standards or requirements
shall govern.
A.
Developments shall be protected from flood hazard and inundation
by stormwater, springs and other surface waters. The design and construction
of drainage systems shall be such that watercourses traversing the
development and natural water emanating from within the development
will be carried through and off the development without injury to
improvements, building sites or buildings existing or to be installed
within or adjacent to the tract. Drainage water entering the development
shall be received and discharged at locations and as nearly as possible
in the manner that existed prior to construction of the drainage facilities
within the development. The design of drainage facilities within the
development shall be such that they will conform to the ultimate drainage
requirements of the land uses within the development watershed. The
discharged flow at the downstream area of the development shall be
conducted in drainage facilities such that the flow effects shall
be restored as near to predevelopment conditions as possible prior
to leaving the development area or reasonably distant therefrom.
C.
Drainage easements and rights-of-way and additional areas as dedicated
under these provisions need not necessarily be fenced but shall be
identified by monuments, acceptable to the Town Engineer, set at an
angle point and at such other location which allow intervisibility.
In special cases, such as extra-deep ditches or storage ponds, the
Town may require safety precautions.
A.
Hydrologic.
(1)
The drainage channels for watercourses identified in the Town drainage
report and drainage map (Exhibit 1[1]) shall be provided to accommodate not less than the minimum
flows indicated in the drainage report appendix. These values shall
be independently verified by their users using hydrologic technology
recommended herein, and the hydrologic analysis thereof shall become
a part of the supporting data of the proposed drainage plans. The
minimum flow requirements for the ultimate channel of the watercourses
shall be determined in accordance with an average recurrence interval
of 10 years, in the determination of the ultimate channel. Rainfall
intensities are shown graphically and tabulated for the Town of Lewiston
in Exhibits 3 and 4.[2] Subdivision designers may assume i = 15 minutes to achieve
saturation or minimum rainfall duration.
[1]
Editor's Note: Exhibit 1, Official Drainage Map, is on file
and available for public inspection in the office of the Town Clerk.
[2]
Editor's Note: Exhibit 3, Rainfall Intensity, Duration, Frequency-Buffalo,
N.Y., and Exhibit 4, Rainfall Intensity and Duration, are on file
and available for public inspection in the office of the Town Clerk.
(2)
The capacity of the channel that will occupy the ultimate drainage
easement or right-of-way within the development shall be based on
the ultimate runoff coefficients computed in the drainage report and
shown on Exhibit 2.[3] As the anticipated ultimate land use changes from time
to time, the runoff coefficients may be revised.
[3]
Editor's Note: Exhibit 2, Ultimate Runoff Coefficients, is
on file and available for public inspection in the office of the Town
Clerk.
(3)
Design flows.
(a)
Design flows for minor and secondary drainage systems may be
determined by the developers engineer by use of the rational method
or an accepted modification thereof. Minor and secondary drainage
systems are considered to have a tributary area (A) less than four
square miles.
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Q = C i A
|
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Where:
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Q
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=
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project design flow in cubic feet per second
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C
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=
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design coefficient of runoff (see Exhibit 2[4])
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i
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=
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intensity of rainfall in inches per hour (see Exhibits 3 and
4[5])
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A
|
=
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tributary drainage area in acres. Must include entire upstream
drainage area, not just area to be developed.
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[4]
Editor's Note: Exhibit 2, Ultimate Runoff Coefficients, is
on file and available for public inspection in the office of the Town
Clerk.
[5]
Editor's Note: Exhibit 3, Rainfall Intensity, Duration, Frequency-Buffalo,
N.Y., and Exhibit 4, Rainfall Intensity and Duration, are on file
and available for public inspection in the office of the Town Clerk.
(b)
Rainfall intensity and duration frequency charts are included
in the Lewiston drainage report and attached exhibits. Working copies
may be obtained from the Town Clerk.
B.
Hydraulic.
(1)
The hydraulic design of development drainage systems shall be in
accordance with modem standard procedures, endorsed by the American
Society of Civil Engineers.
(2)
Hydraulic design shall conform to the latest professional manuals
dealing with the many facets which constitute a comprehensive drainage
system. Reference to manual sources herein are for only the principal
features of drainage systems having a tributary area (A) greater than
four square miles. These do not imply any limitations in the use of
such references, but rather should be supplemental with all essential
detailed references to assure sound design.
(3)
Manning formula.
(a)
For the design of minor and secondary drainage systems, the
basic formula and minimum standard for enclosed pipe design and open
channel flow shall be the Manning formula. This formula, relating
flow rate to carrier geometry, is as follows:
|
V = 1.486 n-1
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R2/3
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S1/2
| |
|---|---|---|---|
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Q = 1.486 n-1
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AR2/3
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S1/2
|
|
Where:
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Q
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=
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peak rate of runoff in cubic feet per second
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A
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=
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cross-sectional area of the flow in square feet
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V
|
=
|
velocity in feet per second
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R
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=
|
hydraulic radius in feet (area divided by wetted perimeter)
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S
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=
|
slope of the carrier in feet per foot
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n
|
=
|
roughness coefficient of
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0.013 for concrete pipe
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0.024 for corrugated metal pipe
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0.016 to 0.040 for open channels depending on proposed channel
living
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(b)
The velocity in all enclosed carriers of the drainage system
should be 2.5 feet per second with an absolute minimum of 2.0 feet
per second. Channel sections are to be designed trapezoidal with side
slopes of two horizontal to one vertical and have a minimum bottom
depth of four feet (see Exhibit 5[6]).
[6]
Editor's Note: Exhibit 5, Open Channel Flow, is on file and
available for public inspection in the office of the Town Clerk.
(4)
Roadway culverts between ditches shall be designed using the criteria
and nomographs presented in the Bureau of Public Roads Hydraulic Engineering
Circular No. 5 and the Erie-Niagara Regional Planning Board's Storm
Drainage Design Manual. Minimum size driveway culvert shall be 20
lineal feet of fifteen-inch pipe with end sections or headwalls.
(5)
Drainage downstream. The subdivider'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 during a ten-year storm,
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
or until an acceptable storage basin design has been submitted by
the developer. Storage basins (retention or detention basins) must
aesthetically blend into the overall development in order to be considered
and approved by the Town.
(6)
A development grading plan, similar to the F.H.A. grading plan, indicating
a contour interval suitable for the map scale, shall be provided to
the Town showing detailed comprehensive and efficient surface drainage
for all lots within and immediately adjacent to the development. The
grading map shall give finish grade elevations on all lot corners
as well as at the building. Lots with B- or C-type grading shall have
to be provided with a minimum four-inch drain tile along the rear
lots and a receiver at every second lot line.
C.
Structural. Catch basins, manholes, inlet structures and other appurtenances
placed within the development shall conform to standards approved
by the Town Board. The structural design of all drainage appurtenances
shall be subject to the approval of the Town Engineer and shall conform
to standard specifications adopted by the Town Board as the same may
from time to time be amended.
(1)
Channels. The minimum center-line radius of constructed curved channels
shall be at least three times the bottom width of the channel for
subcritical flow. The minimum bottom width of constructed channels
shall be four feet. The creation of an excessive number of curves
in open channels shall be avoided by reason of the increase in friction
loss and the potential erosion due to spiral flow. Outer bank protection,
especially at the downstream end of the curve and to a lesser degree
on the inner bank at the beginning of the curve, may be required by
the Town Engineer. Earth channels constructed within the development
shall have side slopes of one on two or flatter and shall be landscaped
prior to acceptance by the Town of Lewiston.
(2)
Enclosed conduits. Except for adequate natural watercourses, all
storm drainage within the development which is capable of being transmitted
in a pipe 36 inches in diameter or smaller shall be carried in an
enclosed conduit. This size may be varied, either increased or decreased
according to topographic conditions or an economic analysis of the
cost of conduit against an equivalent open channel including the right-of-way
land value, provided that the ultimate selection is in the public
interest. The minimum conduit size shall be 15 inches in diameter.
Manholes shall be provided at all changes in grade and direction.
Spacing of manholes and minimum cover of conduit shall conform to
standard practice endorsed by the American Society of Civil Engineers,
and manhole spacing shall be no greater than 400 feet apart for pipe
36 inches in diameter and smaller. Inverted siphons shall not be permitted
except for temporary structures.
(3)
Storage basins shall be provided by detention and retention basins
acting with open channel systems and should be calculated on the basis
of the one-hundred-year recurrence rainfall. The detention volume
required is that necessary to retain the runoff of a one-hundred-year
rainfall, for any and all durations, from the fully developed tributary
area, less that volume discharged during the same duration.
A.
Easement for 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 servicing thereof, shall be indicated on the
map of the development and designated as follows: "Drainage Easement
to Town of Lewiston." Drainage easements for enclosed conduits shall,
insofar as possible, be placed along or adjacent to lot boundary lines
in a parallel and straight alignment.
B.
Right-of-way for natural watercourses.
(1)
Natural major watercourses which traverse a development shall be
preserved by a right-of-way of sufficient width, including overbanks,
which will adequately pass the project design flow (see Exhibit 5[1]). The gross allowable depth of flow shall not create a
flood hazard to existing or proposed developments and improvements.
The channel and overbank widths, together with a minimum fifty-foot
total maintenanceway, shall constitute the floodway encroachment limits
as shown on Exhibit 5.[2] Wherever such natural watercourses are endowed with significant
natural beauty and have adequate capacity, or have been determined
to have value for fish and wildlife, the developer may dedicate widths
in addition to those required above on the map of the development
in lieu of fees for parks and recreation.
(2)
In natural minor 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 locations,
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 developer may make such minor channel improvements
as are required to provide a channel which would otherwise meet the
conditions of these regulations. However, the developer shall dedicate
the full width required to contain the ultimate channel together with
a minimum fifty-foot-wide-total maintenanceway (see Exhibit 5[3]). The outside of the continuous maintenanceway shall constitute
encroachment limits. 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 developer in addition to those above. Areas offered for dedication
to the Town as drainage rights-of-way, if considered of special interest
to the Town by the Planning Board, may be considered by the Planning
Board as dedication for municipal purposes in lieu of fees for parks
and recreation.
[3]
Editor's Note: Exhibit 5, Open Channel Flow, is on file and
available for public inspection in the office of the Town Clerk.
C.
Right-of-way for constructed channels and appurtenances. Earth channels
constructed within the development shall have minimum fifty-foot right-of-way
dedicated. The ultimate channel shall meet the flow requirements for
the development of the tributary drainage area. The allowable depth
of flow to pass the project design flow shall not create a flood hazard
to existing and proposed developments and improvements. A minimum
of one foot freeboard above the design hydraulic gradient shall be
provided to contain the effects of flow transmission factors. The
outside of the continuous maintenanceway shall constitute encroachment
limits. The right-of-way for constructed channels shall be indicated
on the map of the development and designated as follows: "Drainage
Right-of-Way to Town of Lewiston."
Before final Planning Board approval of a development plan,
the developer shall submit drainage plans with a report containing
sufficient data for the Town Engineer to check the feasibility of
the drainage system as proposed by the developer. The following data
shall be included:
B.
Hydraulic:
(1)
The plan and profile of all drainage systems shall be provided.
(2)
Sizes and types of drainage improvements, including special structures,
typical sections, easements, width, right-of-way and fencing.
(3)
When required, supporting calculations for upstream and downstream
channel capacities as they affect water surface levels and backwater
within the development. Such calculations shall be supported by such
additional survey information as may be required to determine profile
and cross-section of the upstream and downstream channel reaches of
the development under consideration.
(4)
A development grading plan prepared to suitable contour intervals
with grading details to indicate proposed street grades and elevations,
building site elevations and surface elevations at critical points
throughout the development (similar to the F.H.A. type grading plan).
A.
The final construction plans for drainage disposal within the development
shall conform to the provisions of these regulations, subsequent amendments
thereto, and any particular conditions as required by the Town Engineer
in approving the proposed plans and supporting data thereof. The construction
plans for the drainage requirements shall be approved by the Town
Engineer prior to the construction of any drainage facilities within
the development.
B.
The plans shall bear the certification of a professional engineer
as evidence of the professional responsibility for the drainage planning
within the development.
C.
All drainage construction shall be subject to inspection by the Town
Building Inspector or the Town Engineer. Any field changes which affect
the intent of these provisions shall have the prior approval of the
Town Engineer.
In order to ensure the proper performance of the work to be completed under plans as approved under § 143-16 above, the Town may require a cash deposit or a performance bond issued by an acceptable bonding or surety company.
The approval of plans for proposed drainage systems and flood
hazard prevention requirements shall not constitute a representation,
guaranty or warranty of any kind or nature by the Town of Lewiston
or by an officer or employee thereof of the safety, operation, adequacy
or intent of the proposed facilities, and shall create no liability
upon or cause for action against such public body, officer or employee
for any damage that may result from construction pursuant thereto.
The provisions of §§ 143-10 through 143-18 hereof are intended to apply primarily to runoff of natural waters in subdivisions and other developments of land use occurring after the enactment of this article and are not intended to repeal or amend the provisions of Local Law No. 8-1966, being Chapter 340 of the Code of the Town of Lewiston, except to the extent that the provisions of this article are inconsistent therewith, in which case the provisions hereof shall govern.
Before issuing any building permit within the Town of Lewiston,
the Building Inspector shall review the application to determine whether
the site is located within any flood hazard area or is reasonably
safe from flooding. If he shall find that the site is subject to flood
hazard, he shall require that the construction be designed and anchored
as to prevent flotation, collapse or lateral movement, that the construction
materials used and the method of construction are resistant to flood
damage, and that adequate drainage is provided to reduce exposure
to flood hazards.
A.
A violation of any of the provisions of this article is hereby declared
to be an offense against such article.
B.
For every violation of any provision of this article, the person
violating the same shall be subject to a fine of not more than $100
or imprisonment for not exceeding 30 days, or both.
C.
Violation of any provision of this article shall constitute grounds
for revocation of the building permit or for refusal of issuance of
a certificate of occupancy.
D.
The Town of Lewiston shall have such other and additional remedies
as are provided by law to enforce the provisions of this article and
to restrain, correct or abate any violations thereof.
