The design, material and construction methods
shall conform to the applicable sections of the current editions and
subsequent revisions of the following documents. These documents may
be reviewed in the office of the Town Planning Board.
A.
Design and Construction of Sanitary and Storm Sewers,
Manual of Practice No. 9, Water Pollution Control Federation.
B.
Technical Release No. 55 (TR-55), Soil Conservation
Service (SCS).
C.
United States Army Corps of Engineers.
D.
New York State Guidelines for Urban Erosion and Sediment
Control (NYSGUESC), Soil and Water Conservation Society.
Complete plans and drainage calculations shall
be submitted, including drainage basin maps of predevelopment and
postdevelopment stormwater runoff and hydraulic calculations for all
detention basins, pipes and other drainage structures.
A.
Methodology.
(1)
Calculations shall be done for predevelopment and
postdevelopment runoff for the ten-, twenty-five-, and one-hundred-year
storm events.
(2)
SCS TR-55 or TR-20 shall be used for all calculations,
except that the rational method may be used for sites of less than
two acres.
(3)
Calculations shall consider the total upstream drainage
area as potentially developed and all downstream structures and drainage
facilities.
B.
Peak runoff.
(1)
The postdevelopment peak runoff from the site may
not be increased from the predevelopment amount during a twenty-five-year
storm event.
(2)
Detention basins or other storage facilities shall
be used as required to store the additional runoff from the development.
(3)
An emergency spillway shall be provided for the one-hundred-year
storm.
(4)
An outlet structure shall be provided to minimize
sedimentation and plugging and achieve the designed outflow.
(5)
The requirement for storage facilities can be waived
in special circumstances if it can be shown that no downstream property
or structures will be impacted. The total potential build-out of the
watershed must be considered for a waiver to be granted.
C.
Drainage pipe and structures.
(2)
The minimum pipe slope shall be 0.5%.
(3)
Ditch slopes greater than 5% and where velocity exceeds
five feet per second shall be protected with stone lining.
(4)
The minimum pipe size shall be 15 inches.
(5)
The maximum length of surface flow on streets and
ditches shall be 400 feet.
(6)
Stone apron on filter fabric, minimum size 10 feet
by 10 feet, shall be provided at all pipe inlets and outlets and points
of discharge. Size and details shall be in accordance with NYSGUESC.
(7)
Flared pipe end sections shall be provided.
(8)
Pipes and structures in traffic areas shall accommodate
HS-20 loading.
(9)
Sedimentation control, sumps, trashracks and other
measures shall be provided as required to minimize system maintenance
and prevent failure.
D.
Subsurface drainage.
(1)
In areas of high groundwater or springs, measures
shall be taken to control subsurface water so as not to impact building
basements and foundations, on-site wastewater systems or other structures
or facilities.
(2)
Transverse and longitudinal subsurface drains and
underdrains shall be provided within the street right-of-way to fully
drain the road base.
(3)
Stormwater facilities/capacity shall be provided to
accommodate roof and foundation drains. Drains shall be connected
into storm manholes, catch basins or junction boxes.
(4)
Backflow prevention devices or check valves shall
be provided.
E.
Surface drainage.
(1)
Proper grading and drainage facilities shall be provided
to accommodate site drainage, including runoff from upstream areas,
in a controlled manner without adverse impact to or flooding of on-site
or downstream buildings, roads, wastewater systems or other facilities.
(2)
Additional temporary drainage measures shall be provided
as required to accomplish soil erosion and sedimentation control during
construction operations.
A.
Drainage structures and facilities shall be staked
out prior to construction.
B.
Pipe and ditches shall be installed to the designed
line and grade.
C.
Pipe catch basins and manholes shall be installed
in accordance with NYSDOT Section 604-3.
D.
Underdrains with filter stone and geotextile fabric
shall be installed in accordance with NYSDOT Section 6.05 and the
recommendations of the geotextile manufacturer.