[Amended 12-11-2007 by L.L. No. 3-2007; 12-11-2012]
A.
Applicability. The purpose of this article is to establish the criteria to be used in the design of as well as to specify the standards and materials to be employed in construction of, the storm drainage system for projects in the Town that are not subject to regulation under Article XIV of Chapter 245, Zoning, of the Town Code or the New York State Department of Environmental Conservation State Pollutant Discharge Elimination System (SPDES) General Permit for Construction Activities, Permit No. GP-0-10-001, or as amended or revised.
B.
Compliance with stormwater management regulations. For all land development activities subject to the requirements of Article XIV of Chapter 245, Zoning, of the Town Code, and the New York State Department of Environmental Conservation State Pollutant Discharge Elimination System (SPDES) General Permit for Construction Activities, Permit No. GP-0-10-001, or as amended or revised, the design criteria, applicable design storm frequency, construction specifications, standards, and materials to be employed in the construction of the storm drainage system, stormwater management facilities, and any other portion of the project shall be determined in accordance with and shall comply with the New York Standards and Specifications for Erosion and Sediment Control Manual; the New York State Stormwater Management Design Manual; and any stormwater pollution prevention plan approved by the Town in accordance with Article XIV of Chapter 245, Zoning, of the Town Code.
The storm drain system for the Town of Niagara
consists of all facilities constructed to convey surface runoff only
to free drainage outlets on or adjacent to the project site. These
facilities include swales, pipes, culverts, ditches, open channels
and any related permanent structures used in conjunction with the
operation of these facilities.
A.
All workmanship will be done in strict accordance
with the approved plans. Any work done in a substandard manner will
not be acceptable to the Town and will be removed at no expense to
the Town by the developer immediately upon notice by the Town Inspector.
B.
All worker facilities and construction methods shall
be in strict compliance with the latest OSHA and New York State Labor
Department standards.
C.
All materials used in construction of any facilities
to be dedicated to the Town shall be in strict conformance with the
New York Department of Transportation Standard Specifications for
Construction and Materials (latest edition), as well as all national
and state standards, as their jurisdictions apply.
The design criteria used for determination of
the surface runoff shall be in accordance with the procedures outlined
in Chapter IV, "Storm Sewer Design Criteria", Storm Drainage Design
Manual by Erie and Niagara Counties Regional Planning Board, July
1972 (reprinted July, 1977).
A.
A ten-year design storm will be used to design all
storm drain systems in the Town of Niagara. The peak rate of surface
runoff will be calculated using the Rational Method where Q = CiA.
The runoff coefficient should be selected using the properties of
the watershed in conjunction with the United States Department of
Agriculture Soil Conservation System (SCS) hydro logic soil groups
and their properties.
B.
Removal of spring and surface water. The developer
may be required by the Planning Board to carry away by pipe or open
ditch any spring or surface water that may exist either previous to
or as a result of the development. Such drainage facilities shall
be located in the street right-of-way where feasible, or in perpetual
unobstructed easements of appropriate width.
C.
Drainage structure to accommodate potential development.
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 project area. The Town Engineer
shall approve the design and size of the facility based on anticipated
runoff from ten-year storm under conditions of total potential development
permitted by the Zoning Law[1] in the watershed.
D.
Responsibility for drainage downstream. The developer's
engineer shall also study the effect of each element of the project
on the existing downstream drainage facilities outside the area of
the project. This study shall be approved by the Town Engineer. Where
it is anticipated that the additional runoff incidental 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 project until provision has been made for the
improvement of said condition.
E.
Retention/detention requirements.
(1)
Where a proposed development has been determined to
potentially impact downstream drainage facilities, the use of a retention/detention
system within the development may be required. The necessity of managing
stormwater runoff generated from new development and associated impacts
downstream must be addressed on a case-by-case basis.
(2)
Generally, the use of a retention/detention system
is warranted when any of the following may occur:
(3)
Initial screening process.
(a)
Prior to the design of proposed storm conveyance
facilities for a new site development, a thorough review of the existing
drainage system(s) contemplated for use adjacent to the proposed development
is required.
(b)
After initial evaluation of the existing sewer
facilities, and discussion with the developer, the Town Engineer will
set the criteria for the evaluation, managing and conveying of stormwater
runoff from the proposed development to the existing drainage facilities.
(c)
Criteria for evaluating stormwater runoff from
a proposed development shall be based upon either the Rational Method
or the SCS Hydrograph Method, as found in the Storm Drainage Design
Manual published by the Erie-Niagara Regional Planning Board.
(d)
The method of runoff evaluation may vary, depending
upon the magnitude and extent of the proposed development and the
adequacy of the existing drainage systems contemplated for use.
(e)
Should retention/detention not be required,
the stormwater runoff system shall be designed to convey runoff generated
from a ten-year design storm as determined by the Rational Method.
(4)
Design procedure for retention/detention. Should retention/detention
facilities be required, the following procedures shall be utilized
in determining the magnitude and extent of detention facilities necessary
to manage and convey storm water runoff generated within a proposed
development, through use of the Hydrograph Method (SCS Procedure).
(a)
The predevelopment (i.e., existing) stormwater
runoff shall be determined by utilizing the outline described in the
Storm Drainage Design Manual prepared by the Erie and Niagara Counties
Regional Planning Board. Using a ten-year design storm, the runoff
for the predeveloped (existing) conditions of the site considered
for development must be determined. This procedure will identify the
maximum allowable discharge rate from the site under most conditions,
unless otherwise directed by the Town Engineer, and forms the basis
for an outfall design hydrograph.
(b)
As a second step, the proposed development shall
be evaluated and runoff to be generated shall be determined by the
same method, except the twenty-five-year curve and a six-hour storm
duration is to be utilized. This procedure will define the inflow
hydrograph to be used in determining the volume and extent of retention/detention
necessary for the proposed development.
(c)
Finally, through a comparison of the inflow
hydrograph (representing stormwater runoff generated on site) to the
outflow hydrograph (representing the amount of water allowed to be
conveyed from the site), the volume of water which must be stored
or retained on site is to be determined. The procedure, leading to
determining the volume of water which must be stored on site, does
not address the means by which the maximum rate of discharge of stormwater
runoff leaves the site. Consideration of conveyance of runoff from
the site must be addressed separately.
(d)
Prior to addressing the means by which the discharge
of stormwater runoff leaves the site, the geometric configuration
of how the volume of stormwater runoff retained on site must be addressed.
It is recommended that one or a combination of the following means
for retaining stormwater runoff on site be considered:
(e)
Regardless of the type of on site storage ultimately
determined, the design of the outfall structure conveying the stored
runoff on site to the downstream drainage system must ultimately be
approved by the Town and in no case shall the maximum rate of discharge
exceed that as directed by the Town.
(f)
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
endanger health, life or property or aggravate the flood hazard. Instead,
such land within the plat shall be set aside for such uses as shall
not be endangered by periodic or occasional inundation or shall be
improved in a manner satisfactory to the Planning Board to remedy
any such risk of periodic or occasional inundation.
(g)
Sizing and capacity.
[1]
All enclosed storm drains should be designed
to flow full at the design storm frequency.
[2]
Storm drainage systems shall be designed to
provide adequate capacity for full upstream development when existing
or proposed drainage systems are intercepted or altered. The use of
the Town zoning and planning maps for reference is recommended.
[3]
The minimum size of any storm drain within public
right-of-way or easement shall be a twelve-inch diameter pipe. Twelve-inch
diameter pipe may be utilized only after review and approval of the
Town Engineers and Highway Superintendent.
[4]
In all new development or construction, a closed,
covered, piped, drainage system shall be constructed in the Town right-of-way.
The system shall be constructed of materials and in a manner called
for under Town local laws and ordinances and be of a size consistent
with the Town Master Drainage study, as amended, and these specifications.
[5]
Where infilling with new construction within
an existing development where open drainage courses exist, the construction
of an open drainage system, consistent with the Town Master Drainage
study, shall be permitted.
(h)
Recommended velocity. The minimum velocity of
2.5 feet per second will be used to prevent sedimentation. The maximum
velocity allowed is 10 feet per second. No velocity which will cause
damage by scour or erosion in the particular circumstances is permitted.
(i)
Roughness coefficients (N-Values). Roughness
coefficients for pipes and channels used in the Manning formula shall
be in the ranges as recommended by the American Society of Civil Engineers.
(j)
Manhole and inlet spacing.
[1]
Manholes must be located at all changes in pipe
grade and direction. Where connections are made to the system manholes,
catch basins and inlets may also be required.
[2]
Inlets shall be located to protect areas from
ponding or ice buildups. These include low points in sidewalks, driveways
and parking areas, swales and roadside ditches. Inlets shall be so
constructed to prevent harm to persons or property.
[3]
At least one catch basin will be located upstream
of any free culvert outlet whenever a series of inlets and or catch
basins is used in a drainage system. The above does not pertain to
roadway or driveway cross culverts.
A.
The developer shall employ competent engineering services
to provide all construction layout for work done within public right-of
way or easement according to the approved plans.
B.
Line and grade for storm drain construction shall
be referenced to the project horizontal and vertical control system.
Cut sheets shall be provided prior to the start of construction for
a particular phase of the work to the Town. The layout stakes for
line and grade shall be maintained for the duration of the construction
and made available for checking purposes to the Town Engineer at all
times.
C.
The permissible tolerance for storm drain pipe in
place will be plus or minus 0.02 feet vertically and plus or minus
0.20 feet horizontally.
The construction of all new storm drain pipes,
culverts, drainage structures, open channels and ditches shall conform
to the standards of these specifications.
All excavation and related work consisting of but not limited to clearing and grubbing, temporary sheeting, dewatering, excavation for pipe and structures, excavation of rock, bedding backfill, concrete, disposal of materials, protection of existing facilities and maintenance and protection of traffic shall comply with the standards and specifications as outlined in Article III, Construction Methods and Materials, and all grading, construction and erosion control standards as outlined in Article VI, Roads, Pavement and Grading Standards of these specifications.
The Town permits the use of the following storm
drain pipe in a public right-of-way or easement:
A.
Reinforced concrete pipe (R.C.P.).
(1)
All reinforced concrete pipe shall conform to ASTM
C76, Wall Designation B as manufactured by a reputable supplier. All
R.C.P. shall have rubber, O-ring joints meeting the requirements of
ASTM C 443.
(2)
All pipe will be clearly marked so as to indicate
the name of the manufacturer, date of manufacture, diameter, class
and wall designation.
B.
Corrugated metal pipe (C.M.P) and pipe arches (C.M.P.A).
(1)
Corrugated metal pipe, pipe arches and metal end sections
shall be plain galvanized. All bolts and nuts shall be hot dip zinc
coated and conform to the requirements of ASTM A 153. The use of heleial
pipe is recommended. All C.M.P or C.M.P.A shall be of a sixteen-gauge
minimum.
(2)
Perforated corrugated metal underdrain pipe shall
conform to the requirements as stated above.
(3)
The use of PVC or steel for underdrain pipe within
public right-of-way or easement is not permitted.
(4)
The use of ends sections (concrete or metal) is recommended
for all culverts or outlets.
C.
High density smooth interior corrugated polyethylene
pipe (HDPE).
(1)
Smooth interior corrugated polyethylene pipe shall
conform to NYSDOT Specifications Item 18603.97xx.
(2)
Acceptance of this pipe will be based on the manufacturer's
name appearing on the NYSDOT Material Bureau's Approved list and the
manufacturer's certification of compliance with NYSDOT requirements.
(3)
Metal end sections are required where HDPE pipe is
specified. HDPE end sections are not permitted. Joints shall be made
with split couplings and provide for a tight joint. The use of HDPE
pipe shall be based solely upon the discretion and direction of the
Town Engineer and/or Town Highway Superintendent.
A.
Manholes.
(1)
Size. All manholes shall be a minimum four feet in
diameter. Larger diameters will be permitted where required by the
configuration of pipes at the structure. Sumps in manholes are not
permitted.
(2)
Materials.
(a)
Manhole walls shall be constructed of reinforced
precast concrete in conformance with ASTM 478 or eight-inch solid
concrete block, in conformance with ASTM C 139, laid in full beds
of mortar. When concrete block is used, the exterior wall of the manhole
will be covered with a three-fourths-inch thick parging of mortar.
See standard detail.[1]
[1]
Editor's Note: Standard detail drawings are
on file in the Town offices.
(c)
Where precast manhole riser sections are used,
O-ring rubberjoints conforming to ASTM C 443 with mastic compound
shall be used. Waterproof grout shall be used to seal the joint from
the exterior. Joints between layers of concrete block shall be 1/2
inch thick.
(d)
Common brick may be used for adjustment of manhole
casting only. Brick shall be solid clay or concrete and conform to
ASTM C 32, laid in full beds of mortar. Brick shall be thoroughly
wetted before installation.
(e)
Concrete grade rights in conformance with ASTM
C 478 may be used in lieu of common brick. Grade rights shall be smooth
and free from cracks, wetted before installation and laid in a full
bed of mortar. The exterior of the grade rings shall be covered with
a three-fourths-inch thick parging of mortar.
(f)
Manhole steps are required for a structure over
three feet in depth. Steps shall be mortared in place with a concrete
grout after the structure is completed. Steps shall extend out a minimum
of four inches from walls and shall be placed on twelve-inch centers.
(g)
Manhole covers and frames, inlet and catch basin
frames and grates shall be Class 30 gray cast iron, conforming to
the requirements of ASTM A 48. Castings shall be clean, smooth, true
to pattern and of sufficient strength to support anticipated traffic
loading. Manhole covers will be inscribed as shown on the standard
detail.[3]
[3]
Editor's Note: Standard detail drawings are
on file in the Town offices.
(h)
After adjustment to final grade and set level,
castings will be set in a full bed of mortar consisting of one part
portland cement to four parts sand by volume. Castings will be well
covered and anchored with mortar to resist traffic. All interior surfaces
will be tooled smooth with any excess mortar removed.
B.
Special structures.
(1)
When standard manholes, catch basins or inlet structures
cannot be adapted to a particular alignment or grade situation, the
use of special structures for drainage will be permitted.
(2)
Standards for materials to be used in any special
structure shall comply with all articles of these specifications.
The developer, as part of the complete engineering plans for the project,
must submit detailed construction drawings and shop drawings for all
fabrication and installation to be used for construction of the special
structure. The Town will not approve any portion of the drainage plans
until all shop drawings have been submitted, reviewed and approved
by the Town. The developer shall submit samples at his or her expense
when requested by the Town for testing.
(3)
The approval of the shop drawings by the Town does
not release the developer from the responsibility for any omissions
or methods by which the structure is constructed in relation to the
approved plans.
A.
Open channels for drainage will be allowed only when
an existing bona fide watercourse or existing drainage channel is
intercepted or relocated as part of a proposed project.
B.
All open channel construction not located within public
right-of-way shall be located within a permanent drainage easement,
granted to the Town of Niagara, prior to final approval of the drainage
plan by the Town.
The design criteria for the configuration and
construction of open channels shall be in accordance with Chapter
V of Open Channel Design Criteria, Storm Drainage Design Manual, Erie
and Niagara Counties Regional Planning Board, July 1972 (reprinted
June 1977).
A.
Capacity. The minimum capacity of the channel should
confine the peak flow based on a ten-year storm.
B.
Maximum velocities. The maximum velocity permitted
in open channels shall not exceed five feet per second.
C.
Minimum velocity. The minimum velocity shall be at
least two feet per second as to prevent deposit of any sediment in
the channel.
D.
Depth of flow. The channel shall be designed to permit
a peak flow which will have a maximum depth of flow which is at least
two feet below the lowest top of the bank along any portion of the
proposed new channel.
F.
Slope construction.
(1)
All sideslopes and bottom of any newly constructed
open channel shall be seeded or sodded and vigorous growth shall be
established before the entire new open channel construction is approved
by the Town.
(2)
Riprap of the sideslopes will be required where changes
in alignment in the centerline of the new channel is less than a one-hundred-foot
radius of curvature. Riprap shall be sized and constructed as follows:
(a)
Minimum six-inch diameter stone shall be used.
(b)
All stone riprap less than 12 inches in diameter
shall be grouted in place.
(c)
All new rip-rap shall be permanently anchored
at both the channel invert and to the sideslope near the top of the
riprap section.
(d)
Riprap shall extend to within two feet of the
top of the bank of the channel.
A.
The developer shall be responsible for control of erosion over the entire project site for the duration of the proposed new construction. See § 135-89, Erosion control.
B.
At the request of the Town of Niagara, the developer
shall construct and maintain erosion control measures, approved by
the Town, at the downstream end of the proposed new construction to
prevent damage to downstream properties when new construction directly
affects existing watercourses or drainage ditches.
Whether covered or uncovered, channels for drainage
purposes will be located on permanent easements to the Town of Niagara
on a channel or course of not less than 20 feet wide.
