The design, material and construction methods shall conform to the applicable sections of the current editions and subsequent revisions of the following documents:
A. 
New York State Stormwater Management Design Manual, January 2015, NYS Department of Environmental Conservation.
B. 
New York State Standards and Specifications for Erosion and Sediment Control, November 2016, NYS Department of Environmental Conservation.
C. 
Design and Construction of Urban Stormwater Management Systems, MOP 77/WEF MOP FD-20, ISBN (PDF): 9780784473665 Water Environment Federation and American Society of Civil Engineers, 1992.
D. 
Stormwater management. Cornell Local Roads Program March 2014 CLRP No. 14-03.
E. 
Upper confidence limits. Extreme Precipitation In New York and New England, Extreme Precipitation Tables, Northeast Regional Climate Center (NRCC).
F. 
Technical Release 55 (TR-55) Urban Hydrology for Small Watersheds, USDA NRCS, June 1986.
G. 
Technical Release No. 20: Computer Program for Project Formulation Hydrology (TR-20).
H. 
NYS DOT Highway Design Manual Chapter 8 Highway Drainage Rev. 87, May 01, 2016.
I. 
Roadway and Roadside Drainage - Cornell Local Roads Program CLRP #98-5, updated February 2003.
J. 
Hydraulic Design of Energy Dissipators for Culverts and Channels-HEC Circular No. 14, Third Edition. US DOT FHWA Pub. No. FHWA-NHI-06-086.
K. 
Hydraulic Design of Highway Culverts Third Edition Hydraulic Design Series Number 5. April 2012 US DOT FHWA Pub. No. FHWA-FHWA-HIF-12-026.
L. 
Maintenance guidance. Stormwater Management Practices, September 7, 2016, NYS Department of Environmental Conservation.
Complete plans and drainage calculations shall be submitted, including drainage basin maps of predevelopment and post development stormwater runoff and hydraulic calculations for all stormwater management practices, pipes and other drainage structures. A SWPPP containing this information should be compiled and submitted.
A. 
Drainage easements or rights-of-way shall be provided for all drainage ways and structures within the development and, when required, downstream of the development.
B. 
Drainage easements widths provided shall be suitable to provide access for future maintenance and improvements and shall be a minimum width of 30 feet and wider where required.
A. 
Methodology.
(1) 
Calculations shall be done for predevelopment and post development runoff for the design recurrences intervals: one-year, ten-year, twenty-five-year and 100-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 for the design and analysis of all downstream structures and drainage facilities.
B. 
Peak runoff.
(1) 
The post development peak rate of stormwater discharge from the project site may not be increased at any point at the project's boundary or beyond as compared to the pre-development peak rate of stormwater discharge for the following design recurrences intervals: one-year, ten-year, twenty-five-year and 100-year, for a SCS 24-Hour Type III rainfall event.
(2) 
The rainfall amounts shall be based upon the Upper Confidence Limits - Extreme Precipitation in New York and New England, Extreme Precipitation Tables, Northeast Regional Climate Center (NRCC) latest documentation.
(3) 
Stormwater management systems and green infrastructure practices shall be used as required to store the additional stormwater runoff from the development and to treat stormwater runoff to obtain the required water quality.
(4) 
An emergency spillway shall be provided for the 100-year storm.
(5) 
An outlet structure shall be provided to minimize sedimentation and plugging and achieve the designed outflow.
(6) 
An increase of no more than 10% in the peak stormwater runoff above pre-development conditions from the project may be allowed if it can be shown by supporting calculations that no downstream property or structures will be impacted. The total potential build-out of the watershed must be considered for a waiver request to be considered.
C. 
Drainage pipe and structures.
(1) 
The recurrence interval to be utilized for determining the peak stormwater runoff for designs shall be as follows:
(a) 
For boulevards and local access roads:
[1] 
Closed storm drainage systems associated with roads, gutter flow (for inlet spacing) and parking areas: ten-year.
[2] 
Ditches and driveway culverts: twenty-five-year.
[3] 
Critical drainage structures as defined by the project and determined by the Town: 100-year minimum or maximum probable flood.
(b) 
For local through roads and collector roads:
[1] 
Closed storm drainage systems associated with roads: twenty-five-year.
[2] 
Gutter flow analysis for inlet spacing: ten-year.
[3] 
Ditches and driveway culverts: fifty-year, with additional 100-year design check in order to determine the potential impact of this large storm and possible designation of the ditch or culvert as a critical structure.
[4] 
Critical drainage structures as defined by the project and determined by the Town: 100-year minimum or maximum probable flood.
(2) 
Storm drainage pipe:
(a) 
The minimum pipe slope shall be 0.5% with a minimum design velocity of two feet per second.
(b) 
The maximum velocity shall not exceed 10 feet per second.
(3) 
Roadside swales may be designed as grassed or lined waterways designed in accordance with the NYS Standards for Erosion and Sediment Control, and shall be sized for a maximum drainage area of five acres, a minimum slope of 0.5% and a maximum slope of 5%. Linings shall be designed to prevent erosion of the ditch soils. Ditch velocities shall not exceed the maximum permissible velocities for waterway lining.
(4) 
The minimum pipe size shall be 15 inches.
(5) 
The maximum length of surface flow on streets and ditches shall be 300 feet and meet the NYS DOT design criteria for allowable gutter flow.
(6) 
Rock outlet protection (riprap outlet erosion protection) on woven geotextile shall be a minimum size 10 feet by 10 feet, and shall be provided at all culvert, pipe inlets to drainage systems and outlets and points of discharge from drainage systems. Rock outlet sizes shall be calculated using the design procedures and sizing provided in the NYS Standards and Specifications for Erosion and Sediment Control. Rock outlet protection may be further required to be further designed in accordance with the "Hydraulic Design of Energy Dissipators for Culverts and Channels-HEC Circular No.14," Third Edition, US DOT FHWA Pub. No. FHWA-NHI-06-086, in order to provide a sized stilling basin.
(7) 
Flared pipe end sections shall be provided.
(8) 
Pipes and structures in traffic areas shall accommodate HS-20 loading.
(9) 
Sedimentation control, sumps, trash racks and other measures shall be provided as required to minimize system maintenance and prevent failure.
(10) 
Storm drainage catch basins at sag points in road vertical alignments shall be provided as follows:
(a) 
One catch basin at the low point station at the gutter line.
(b) 
Two catch basins, one on either site of the low point station at the gutter line.
(c) 
Both sides of a normal crown road section shall be provided as noted above.
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. Underdrains may be eliminated if approved by the Planning Board Engineer and the Town Highway Superintendent in writing.
(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 pipe shall be as follows:
(1) 
Smooth-lined, annular exterior corrugations polyethylene pipe (AASHTO M294) with soil-tight joints (ASTM F447) or watertight joints (ASTM D3212): AASHTO M294 ADS® N-12 or equal.
(2) 
Circular Reinforced Concrete Pipe — RCP, ASTM C-76, C-443, AASHTO—M170.
(3) 
Other pipes as approved by the Planning Board Engineer.
B. 
Subsurface drains shall be as follows:
(1) 
Geotextile filter fabric: Mirafi 160N, Amoco 4547 or Synthetic Industries 451; non-woven geotextile.
(2) 
Stone: NYSDOT Filter Stone 703-02 No. 1 or No. 2 stone per NYS DOT Table 703-4.
(3) 
Corrugated polyethylene pipe: ADS® 401.
(4) 
Corrugated filter sock pipe meeting ASTM F405 standards.
C. 
Underdrains shall be as follows:
(1) 
Perforated PVC SDR 35: ASTM D3034.
D. 
Catch basins and manholes shall be as follows:
(1) 
Precast concrete manhole: ASTM 478. NYS DOT Section 604-2.
(2) 
Mortar: ASTM C270.
(3) 
Hydraulic cement: ASTM C595/C595M-17.
(4) 
Grade adjustment rings:
(a) 
Precast concrete-grade rings shall be used. No brick shall be allowed. NYS DOT Section 604-1.02
(5) 
Drainage manhole covers shall include the words "STORM SEWER" in bold letters cast in on the cover.
E. 
Frame and grates shall be NYSDOT Section 715.
F. 
Stone protection:
(1) 
Shall be NYSDOT Section 620-02, dry riprap, with a minimum medium weight stone greater than 100 pounds.
(2) 
Protection shall be designed and the size provided shall be in accordance with HEC-14 analysis results and the NYS Standards and Specifications for Erosion and Sediment Control.
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 605 and the recommendations of the geotextile manufacturer.