Town of Schodack, NY Article XI Drainage

§ 188-46 Applicable standards.

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.

§ 188-47 Submittals.

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.

§ 188-48 Drainage easements.

A. Drainage easements or rights-of-way shall be provided for all drainageways and structures within the development and, when required, downstream of the development.

B. Drainage easements shall be a minimum width of 30 feet and wider where required.

§ 188-49 Design standards.

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.

(1) The design storm shall be:

(a) Twenty-five-year for general site work, local roads and collector roads.

(b) One-hundred-year for critical structures which may impact downstream property.

(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.

§ 188-50 Materials.

A. Drainage pipe shall be as follows:

(1) Smooth-lined corrugated polyethylene pipe: AASHTO M294-ADS® N-12 or equal.

(2) Bituminous-coated corrugated steel pipe and coupling bands: NYSDOT Section 707-02.

(3) Corrugated aluminum alloy pipe and bands: AASHTO M196.

B. Subsurface drains shall be as follows:

(1) Fabric: Trevira Spunbound Type 1114 or equal.

(2) Stone: NYSDOT Filter Stone 703-02 No. 1 and No. 2 stone.

(3) Corrugated polyethylene pipe: ADS® 401 or 601 or equal.

C. Underdrains shall be as follows:

(1) Perforated PVC SDR 35: ASTM D3034.

(2) Perforated corrugated metal pipe with bituminous coating: NYSDOT Section 707-07.

D. Catch basins and manholes shall be as follows:

(1) Precast concrete manhole: ASTM 478.

(2) Mortar: ASTM C270.

E. Frame and grates shall be NYSDOT Section 715.

F. Stone protection shall be NYSDOT Section 620-02, dry riprap, medium-weight stone greater than 100 pounds.

§ 188-51 Construction methods.

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.