A. 
A preliminary grading and drainage system plan shall be submitted with the subdivision preliminary layout. It shall indicate in general terms a proposal for an adequate system of grading and necessary drainage structures to carry off and store or discharge the stormwater runoff and natural drainage water which originate not only within the property boundaries but also that which originates beyond the property boundaries.
B. 
No stormwater runoff or natural drainage water shall be diverted as to overload existing drainage systems or create flooding or the need for additional drainage structures on other private properties or public lands without proper and approved provisions being made for alleviating these conditions.
C. 
Preliminary grading and drainage plan requirements:
(1) 
Sheet size shall be twenty-two by thirty-six (22 x 36) inches minimum.
(2) 
Scale shall be one inch equals 100 feet. If more than one sheet is required, a clearly drawn match line shall be shown on each sheet.
(3) 
The title block shall show the name of subdivision; title: Storm Drainage Plan; date; name of subdivider; and licensed engineer or surveyor.
(4) 
All rights-of-way, easements, street center-line gradients in percent with arrows to establish the direction of flows, and critical street center-line grades shall be shown.
(5) 
The complete drainage system for the entire subdivision shall be shown graphically, with all existing drainage features which are to be incorporated properly identified as existing.
(6) 
Boundaries of stormwater runoff watersheds for each drainage structure and their area in acres shall be shown. Topography shall be shown at a contour interval of not more than five feet. However, expansive drainage areas outside of the subdivision property line may be indicated on a scaled map other than one inch equals 100 feet and at contour intervals of 10 feet when, in the opinion of the Town Engineer, this data clearly identifies the drainage areas.
(7) 
All drainage structures shall be identified by numbers. All appropriate details and dimensions necessary to clearly explain the proposed construction, including type of construction material, size and slope, etc., in accordance with good engineering practice, shall be indicated.
(8) 
If required, location of all test pits and borings and description of soil conditions and the water table elevation is to be shown.
(9) 
Hydraulic computations indicating the adequacy of design shall be presented for all facilities, including computations indicating the ability of the existing or new downstream stormwater facilities to accept the additional anticipated flow.
D. 
Final grading and drainage plan requirement.
(1) 
A final grading and drainage system plan shall be submitted with the subdivision plat and shall include all those features described for the preliminary plan corrected to reflect the final design.
(2) 
A reproducible Mylar and two copies of the as-built storm drainage system drawn on the map scaled one inch equals 100 feet, showing the identification of all structures by number, the location of all structures, pipe size, type of construction material and slopes of pipes with invert and top of cover elevations at structures to the nearest tenth of a foot, all in accordance with good engineering practice, shall be furnished to the Town Clerk before the system will be accepted by the Town.
A. 
Stormwater facilities consisting of side ditches, minor culverts, stormwater sewers and combinations thereof shall be designed to intercept and carry the maximum runoff from the tributary watershed during a ten-year frequency storm. The design for structures for major streams shall be based on an individual analysis utilizing the currently accepted practices of the United States Department of Commerce, Bureau of Public Roads, or the United States Department of Agriculture, Soil Conservation Service.
B. 
For design purposes, a ten-year frequency storm shall be considered to have the following intensity-duration relationship.
(1) 
Maximum five-minute intensity equal to 6.2 inches per hour.
(2) 
Maximum ten-minute intensity equal to 4.6 inches per hour.
(3) 
Maximum fifteen-minute intensity equal to 3.9 inches per hour.
(4) 
Maximum twenty-minute intensity equal to 3.4 inches per hour.
(5) 
Maximum twenty-five-minute intensity equal to 3.0 inches per hour.
(6) 
Maximum thirty-minute intensity equal to 2.7 inches per hour.
(7) 
Maximum sixty-minute intensity equal to 1.7 inches per hour.
C. 
Runoff factors.
(1) 
Except for structures on major streams which may utilize other acceptable methods, runoff computations shall result in flows equal to those computed by the rational method, using a time of concentration and runoff factor in keeping with the local topography and the following:
Runoff Factors Land Slope
Land Use
Flat
(0-5%)
Steep
(Over 5%)
Residential
0.40
0.45
Light commercial
0.70
0.75
Large paved areas
0.80
0.90
Parks, woods, etc.
0.30
0.35
(2) 
Weighted runoff factors shall be considered for composite areas.
D. 
The drainage system shall provide for conveying the runoff to the nearest natural watercourse or storm sewer in a manner approved by the Town's Engineer.
E. 
The Manning formula shall be utilized for the design of stormwater pipes and ditches. The following coefficients of friction ("n") shall be used:
Type
Coefficient
Concrete pipe
n = 0.013
Corrugated steel pipe:
Fully paved
n = 0.013
Paved invert:
Size of Corrugations
(inches)
2 2/3 x 1/2
n = 0.24
3 x 1
n = 0.027
6 x 2
n = 0.032
Earth ditches, seeded
n = 0.030
Paved ditches, concrete, asphalt
n = 0.013
A. 
Longitudinal ditches shall be placed on the high side of all streets and on both sides of streets, where necessary, to intercept water entering the subgrade of the street.
B. 
Unpaved ditch sections shall have sufficient cross-sectional area to maintain maximum runoff velocities below three feet per second to prevent scouring and erosion. Ditches shall be paved or riprapped and check dams shall be installed, where necessary, to maintain safe stream bed velocities. Protection shall be provided to prevent erosion at bends, beneath check dams and at culvert inlets and outlets, where necessary.
C. 
Ditches shall have a minimum grade of 1%, a minimum width at the bottom of the ditch of 12 inches and side slopes not steeper than two horizontal to one vertical.
A. 
Culverts shall be installed to pass water collected in the ditches, or flowing in a natural watercourse, beneath the street. Headwater depths shall be considered in culvert design. Riprap shall be installed upstream and downstream of culverts as required to control erosion. Energy dissipators shall be constructed where necessary.
B. 
Culverts under streets shall extend from toe of slope to toe of slope and shall be set with a minimum of two-foot cover over the top of the pipe unless specifically waived by the Town's Engineer or Town Highway Superintendent.
C. 
Culverts shall also be installed beneath driveways and access roads to carry water flowing in the side ditches. Culverts in side ditches shall be limited to 30 feet in length.
D. 
Culverts shall have a minimum diameter of 15 inches and shall be laid on a minimum of 0.5%. In general, the grade line shall coincide with the existing stream bed or ditch grade.
E. 
Culvert ends.
(1) 
All culverts shall utilize pipe end sections at each end when hydraulically feasible. Poured concrete headwalls shall be used where the use of pipe end sections is not feasible or where headwall construction will provide a more efficient design.
(2) 
Reinforced concrete pipe end sections shall be precast units, and corrugated steel pipe end sections shall be galvanized steel. All end sections shall conform to the standards of the New York State Department of Transportation.
(3) 
On all pipe end sections 24 inches or over, a twelve-inch minimum thick poured concrete cutoff wall shall be constructed a minimum of 24 inches below the end section for the full width of the flared end.
(4) 
Concrete headwalls for culverts shall be constructed of poured concrete extending at least 12 inches above and 24 inches below the pipe. Concrete headwalls shall be at least 12 inches thick and as wide as the top of the ditch, but not less than three pipe diameters wide.
F. 
All culverts crossing a street without curb and gutter where guide rail is not utilized shall be marked at each end by an eighteen-by-eighteen-inch yellow reflectorized hazard marker set at the edge of the shoulder and mounted on a galvanized steel delineator post, all in conformance with the New York State Manual of Uniform Traffic Control Devices.
A. 
No stormwater sewer shall be less than 15 inches in diameter except that catch basin connections may be as small as 12 inches in diameter.
B. 
All storm sewer lines shall be designed and constructed to give mean velocities, when flowing full, of not less than 2.0 feet per second. Velocities over 12 feet per second shall be avoided by the use of manholes. When unavoidable, the pipe shall be anchored to prevent movement, and the standard manhole designs indicated in the Standard Detail Drawings[1] shall be modified to adequately reinforce such structures against the increased forces.
[1]
Editor's Note: The Standard Detail Drawings are included at the end of this chapter.
C. 
Storm sewers shall be laid with a minimum of two feet of cover over the top of the pipe. However, catch basin connections, when constructed of corrugated steel pipe, may have a minimum of one foot of cover at the catch basin.
D. 
Structures.
(1) 
Manholes and catch basins shall be constructed in accordance with the Standard Detail Drawings.[2]
[2]
Editor's Note: The Standard Detail Drawings are included at the end of this chapter.
(2) 
Manholes shall be installed at the end of each line; at all changes in grade, size or alignment; at all intersections; and at intervals not exceeding 350 feet for pipe sizes 21 inches and smaller and 600 feet for pipe sizes 24 inches and larger.
(3) 
Catch basins shall be installed at all intersections and at intervals not exceeding 500 feet.
(4) 
All connections to stormwater sewers from catch basins shall be made at a manhole.
E. 
House drains, which include roof drains and footer drains, shall be connected to storm sewer lines. If there are no storm lines available, the house drains may be discharged to the road side curb, but not through the curb.
A. 
Pipe used in storm sewer systems shall be reinforced concrete pipe or corrugated steel pipe.
B. 
Pipe used for culverts shall be reinforced concrete pipe or corrugated steel pipe.
C. 
Concrete pipe shall conform to ASTM Standard Specification C-76, Class IV, minimum, pipe. Increase in pipe class shall be determined in accordance with the height of fill standards of the New York State Department of Transportation. Joints shall be sealed with flexible, watertight elastomeric gaskets, or approved bituminous or plastic sealers.
D. 
Corrugated steel pipe shall conform to New York State Department of Transportation Specifications, Section 707-02, and the following: All corrugated steel pipe shall be bituminous coated and shall have a bituminous paved invert or be a fully paved pipe. All pipe ends shall have annular corrugations in order to receive annular coupling bands or end sections. Minimum thickness of pipe shall be 16 gauge and shall be increased in gauge in accordance with the height of fill requirements of the New York State Department of Transportation.
A. 
All stormwater drainage systems shall be installed to the line and grade indicated on the approved drawings.
B. 
Pipe bedding and backfill for the type of pipe used shall be in accordance with the Standard Details for the Town of Chenango.[1]
[1]
Editor's Note: The Standard Detail Drawings are included at the end of this chapter.
C. 
Pipe laying shall begin at the downgrade end and progress in the upgrade direction. Pipe with bell and spigot joints shall be laid with bells upgrade. Pipe with tongue and groove shall be laid with the groove upgrade. The pipe shall be laid so that the invert will be smooth and uniform.
All storm sewer lines shall meet the following test in the presence of the Town Inspector: A lamplight shall be clearly visible between manholes. Pipe which is not true in vertical or horizontal alignment or which shows any settlement after laying shall be taken up and relaid at the subdivider's expense.
Pump stations, flap valves, sluice gates and appurtenances to stormwater drainage system shall be designed and constructed to afford maximum public safety, dependability and efficiency in operation and maintenance. Two copies of as-built drawings of these facilities, together with all manuals and descriptive data, shall be furnished to the Town Clerk before the facilities will be accepted by the Town.
Material referred to in Standard Details for Trench Excavation, Pipe Bedding and Backfill[1] shall conform to the following:
A. 
Pea gravel for pipe bedding shall be screened gravel or crushed stone or crushed gravel, and shall consist of clean, hard stone of uniform quality free from coatings and thoroughly washed. It shall be sized to meet gradation No. 1A of the New York State Specifications.
B. 
Angular material for pipe bedding shall be crushed stone or crushed gravel, which shall consist of clean, hard fragments of rock or stone of uniform quality, free from coatings and thoroughly washed. It shall be sized to meet gradation No. 1A of the New York State Specifications.
C. 
The select material shall be excavated material that is free from clods, frozen material, debris and stones in excess of three inches. Such select material shall be hand shoveled from the excavated material with care taken to exclude clods, stones in excess of three inches, frozen material and debris.
D. 
Bank gravel fill shall be a clean, well-graded material. The particles shall be of such a size as will pass through a three-inch square sieve, 30% to 65% by weight shall pass a one-fourth-inch square sieve, and not more than 10% by weight shall pass a No. 200 mesh sieve.
E. 
Screened gravel fill shall be clean, hard and uniformly graded screened gravel, crushed stone or crushed gravel and shall be either size No. 3 or mixed No. 1 and No. 2 of the New York State Department of Transportation Specifications 304-2.02. The size to be used shall be as ordered by the authorized Town Inspector.
[1]
Editor's Note: The Standard Detail Drawings are included at the end of this chapter.