Adequate provisions shall be made to remove surface and subsurface water
from the road. The developer shall furnish and install all bridges, culverts
and catch basins, inlets, manholes, storm sewers, subdrains and other drainage
improvements required to drain properly the water accumulated by the development.
Such drainage facilities shall be located in the road right-of-way, where
feasible, or in perpetual, unobstructed easements of a minimum width of 20
feet. They shall be constructed in accordance with the following design criteria
and shown on the construction details. Stormwater in such a system shall be
delivered as directly as possible to the watercourse which served that watershed
prior to development.
A.
The basis for design of drainage improvements for local drainage areas with small watersheds of 100 acres or less shall be designed, except in an unusual case, for an intensity of two inches per hour likely to occur in a ten-year storm. Where flowing streams are involved and larger watersheds contribute to the drainage structure, these structures shall be designed for an intensity likely to occur in a twenty-five-year storm or as may be determined by the Planning Board, with the advice of the Town Engineer. The necessary size of each drainage facility shall be based upon the above criteria, assuming conditions of maximum watershed development within the proposed subdivision permitted by Chapter 170, Zoning, of the Code of the Town of Somers. The Rational Formula or the Soil Conservation Service (SCS) methodology may be used in engineering calculations for the above criteria.
B.
The Planning Board shall consider the effect of each
subdivision on existing downstream drainage facilities outside the area of
the subdivision. If the downstream facilities cannot handle the expected flows,
the Planning Board shall, with the advice of the Town Engineer, require the
installation of detention basins or downstream improvements as deemed necessary.
A.
Catch basins, inlets or manholes on roads and easement
areas shall be located on all changes in direction of storm drains and at
intervals not to exceed 400 feet on all pipelines between 15 and 24 inches
in diameter unless otherwise approved by the Town Engineer.
B.
Unless otherwise directed by the Planning Board with
the advice of the Town Engineer, curb sections may carry flow for a maximum
distance of 400 feet and must then discharge into a storm drain.
C.
The subdivider shall obtain proper easements to convey
the discharge of stormwater, in excess of current flows, into, upon or through
private property when necessary.
D.
The location and width of all easements shall be indicated
on the subdivision plat. Drainage easements shall be extended from the road
to a natural watercourse or to other drainage facilities.
A.
Catch basins shall be constructed in accordance with
these specifications and/or the construction details as recommended by the
Town Engineer and approved by the Planning Board. Backfill around all catch
basins shall be with Item 3 gravel and tamped in an approved manner. A three-inch
structural masonry brick chimney shall be placed beneath each frame for future
adjustments.
B.
Frames shall be set one inch below finished grade as
measured at a distance 1 1/2 inches in either direction along the gutter
line.
C.
The catch basins shall be precast concrete as manufactured
by the Fort Miller Company, M&M Concrete Precast Corporation or approved
equal. All concrete construction shall conform to the requirements of the
New York State Department of Transportation Specifications Section 555, Structural
Concrete.
D.
Precast concrete catch basins shall be cast with four-thousand-pounds-per-square-inch
concrete at 28 days. The steel shall conform to the requirements of ASTM A615-A497.
Air entrainment shall be a minimum of 5%. The loading shall conform to AASHTO
H-20 with 30% impact and equivalent soil pressure of 130 pounds per cubic
foot.
E.
All catch basins over four feet deep shall be constructed
with aluminum steps as manufactured by Alcoa Aluminum-Type 16207B or approved
equal. Steps shall be set 12 inches on center.
F.
All pipe shall be cut flush with the interior walls of
the catch basins.
G.
All catch basins shall be placed on a six-inch foundation
of three-fourths-inch washed crushed stone.
H.
The catch basin frame and grates shall be cast iron Type
2541 manufactured by Campbell Foundry or approved equal.
I.
The cast iron frames shall be set in a bed of mortar
composed of one part Portland cement and two parts mortar sand.
J.
Catch basins shall have an eighteen-inch sump.
A.
Manholes shall be constructed in accordance with these
specifications and/or the construction details as recommended by the Town
Engineer and approved by the Planning Board. Concrete for the base slab, if
required, shall be formed and shall be one to two to four (1:2:4) concrete
placed in accordance with requirements of the New York State Department of
Transportation Specifications Section 555, Structural Concrete.
B.
Bricks for chimney adjustments shall conform with ASTM
Specification C-12, Grade N.A. Brick and masonry units shall be laid in a
full bed of mortar composed of one part Portland cement and two parts mortar
sand, by a competent mason in a workmanlike manner.
C.
The drainage manholes shall be precast concrete as manufactured
by the Fort Miller Company, Inc., M&M Concrete Precast Corporation or
approved equal. All concrete construction shall conform to the requirements
of the New York State Department of Transportation Specifications Section
555, Structural Concrete.
D.
Precast concrete drain manholes shall be cast with four-thousand-pounds-per-square-inch
concrete at 28 days. The steel shall conform to requirements of ASTM A615-A497.
Air entrainment shall be a minimum of 5%. The loading shall conform to AASHTO
H-20 with 30% impact and equivalent soil pressure of 130 pounds per cubic
foot.
E.
All drain manholes shall be constructed with aluminum
steps as manufactured by Alcoa Aluminum, Type 16207B, or approved equal. The
steps shall be placed 12 inches on center. The steps shall have hooked ends.
F.
All pipe shall be cut flush with the interior walls of
the drain manholes.
G.
All drain manholes shall be placed on a six-inch foundation
of three-fourths-inch washed crushed stone.
H.
The drain manhole frames and covers shall be cast iron
Type 1203 manufactured by Campbell Foundry, for example, or approved equal.
The cover shall be entitled "Drain."
I.
The cast iron frames shall be set in a bed of mortar.
J.
A concrete bench and channel shall be constructed in all drain manholes. All concrete for the bench and channel shall meet the same specifications as per § A174-12A.
K.
A three-inch structural brick chimney shall be placed
beneath each frame for future adjustments.
L.
Frames shall be set one inch below finished grade as
measured at a distance of 1 1/2 inches in all directions from the frame.
A.
Pipes of the required sizes shall be located where necessary
to provide adequate drainage for the roadway as shown on the approved plan.
B.
Culverts at stream crossings shall be single-opening
precast reinforced concrete five-thousand-pounds-per-square-inch at 28 days,
conforming to AASHTO H-20 loading.
D.
All pipe shall meet the approval of the Town Engineer
before construction. The developer shall submit to the Town Engineer a certificate
from the manufacturer setting forth the type and size of pipe to be used.
The manufacturer's certificate shall specify gauge and coatings in addition
to type and size.
E.
Drainage pipes shall have a minimum inside diameter of
15 inches with a minimum cover of 24 inches to finished grade, unless otherwise
specified by the Town Engineer. Culvert grades shall, if possible, lie between
2% and 4% with a minimum of 1%. Inverts shall be 42 inches below finished
grade. A reinforced concrete pipe shall be installed in areas where it is
necessary to install a storm drain at such a slope where erosive velocities
will exist.
F.
Concrete pipe shall be bedded in an earth foundation
which is firm but slightly yielding and carefully shaped to fit the lower
part of the pipe.
G.
Bell and spigot reinforced concrete pipe shall have joints
sealed with flexible water-tight elastomeric gaskets.
H.
Culverts for stream crossings shall be precast reinforced
concrete cast with five-thousand-pounds-per-square-inch concrete at 28 days.
The loading shall conform to AASHTO H-20 requirements.
I.
Pipe specifications:
(1)
Aluminized steel Type 2 - corrugated steel pipe.
(a)
This specification covers aluminum-coated (Armco aluminized
steel Type 2) corrugated steel pipe and pipe-arch for culverts and sewers.
Pipe shall be manufactured in accordance with AASHTO M-274-801.
(b)
Gauge: All steel aluminized pipe to be of the following
gauges unless otherwise stated:
|
Pipe Diameter
(inches)
|
Standard Gauge
|
Decimal Thickness
(inches)
| |
|---|---|---|---|
|
12 to 21
|
16-gauge
|
0.064
| |
|
24
|
16-gauge
|
0.064
| |
|
27 to 36
|
14-gauge
|
0.079
|
(2)
Aluminum pipe.
(a)
The aluminum pipe shall meet the applicable requirements
of current AASHTO specification M-196 or federal specification WW-P-402.
(b)
The pipe shall be formed from sheets conforming to the
requirements of ASTM B 209 Alloy Alclad 3004-H34.
(c)
All aluminum pipe shall be of the following gauges unless
otherwise stated:
|
Pipe Diameter
(inches)
|
Standard Gauge
|
Decimal Thickness
(inches)
| |
|---|---|---|---|
|
6 to 10
|
16-gauge
|
0.060
| |
|
12 to 21
|
14-gauge
|
0.075
| |
|
24
|
12-gauge
|
0.105
| |
|
27 to 36
|
10-gauge
|
0.135
|
The natural, excavated and embankment surface of the roadway adjacent
to both ends of all culverts and drains shall be protected from erosion or
displacement by headwalls of rubble stone masonry or concrete as shown on
the construction details, unless terminated by catch basins or other drainage
structures approved by town authority. If required, in the opinion of the
Town Engineer, wing walls shall be included in the headwall design. The upstream
and downstream areas at all headwalls shall be provided with dumped rip rap
stone of irregular shapes to dissipate the energy of the flowing stormwater.
A.
In areas where there is a bleeding of groundwater, the
developer shall install curtain drains to protect the road. In areas where
the road cut exceeds 30 inches, curtain drains shall be required.
B.
Pipe for use in underdrains shall be perforated, corrugated
metal, HEL-COR or equal approved by the Town Engineer.
C.
Pipe shall be installed as shown on the construction
details.
D.
A synthetic filter material envelope shall be provided
for the underdrain.
A.
Backfill over all of the pipes shall be free from large
stones and shall be compacted in six-inch layers for a depth of one foot over
the pipe by hand and machine tamper so that compaction of 95% is attained.
B.
Under paved areas, especially in roadway crossings, the
above tamping methods shall be carried to the surface of the trench; and backfill
shall be Item 3 gravel as approved by the Town Engineer.
