Town of Henrietta, NY Design Standards for Storm Drainage

These regulations and standards are to protect the various portions of the urban area from flooding, to provide clean and sanitary channels for runoff, to prevent the encroachment of buildings and improvements on natural drainage channels, to equitably apportion the cost of improvements, to protect natural scenic areas and to provide for the conservation of the natural resources of the area. The regulations, policies and standards herein contained shall apply to the area outlined by the Town of Henrietta, New York, which is hereby made a part of these regulations. All subdivisions of land and all improvements of any character which affect drainage in any portion of the area within the township shall be subject to the provisions of these regulations.

§ A300-2 Classification of drainage channels.

Major drainage channels. "Major drainage channels" are defined as those with a tributary drainage area between four square miles and 20 square miles. Such drainage channels shall be designed for an average recurrence interval of 50 years in the determination of the ultimate channel. The responsibility for major drainage channels shall be the same as stated for secondary drainage channels below.

"Secondary drainage channels" shall be those rivers, streams and other channels which have been so designated by the township. In general, it is the intent of these regulations that channels which serve a drainage area of one square mile to four square miles or more shall be designated as secondary channels. It is intended by these regulations to provide that the maintenance and improvement of secondary drainage channels will be the responsibility of the municipality primarily, since the whole municipality is benefited materially. However, the developer of the land containing the ordinary channel is expected to lay out, design and otherwise plan and carry out his improvements in a manner that will not interfere or increase or restrict the natural flow of water or materially change the condition of runoff. When changes in alignment are required due to the design or layout of a subdivision, or an expansion in cross-sectional area is required due to increased runoff, it shall be the responsibility of the developer to make the changes, and all changes shall be made in accordance with the provisions of these regulations. These channels shall be designed for an average recurrence of 25 years.

"Minor drainage channels" shall include all channels in the area set forth by the Town of Henrietta, New York. It is intended by these regulations that the improvements of channels shall be the responsibility of the developer of the area served by the channel since the primary benefit is to the area served by the minor channel and not to the town as a whole. Where minor channels enter publicly dedicated parks, the channel shall revert to the secondary drainage channels classification in the park area. The design recurrence shall equal 10 years.

§ A300-3 Determination of stream flow and runoff.

The maximum condition of rainfall for a fifty-year interval shall be used for the purposes of determining all runoff for the sizing of drainage channels and structures, unless otherwise specified herein. Values used in formulas for runoff and size of drainage structures shall reflect and shall not be less than the degree of urbanization set forth in the projected land use plan contained in the General Plan. The following formulas and values shall be used for calculating all stream flow and runoff for the policies and regulations established herein:

Runoff from all drainage areas shall be determined by the rational formula (other acceptable methods may be submitted to the Town Board and its Engineer for approval):

	Q =	AIR
In which:

	Q =	Cubic feet per second.
	A =	Area to be drained in acres, determined by field surveys for areas less than 640 acres and by latest government quadrangle maps for larger areas.
	I =	Percent of imperviousness of the area. This may vary between 40% and 95%.
	R =	Rate of rainfall over entire drainage area in inches per hour, based on time of concentration and latest governmental records for the area.

The size of closed storm sewers, open channels, culverts and bridges shall be determined using the Manning formula:

	Q =	a 1486 r 2/3 s 1/2 n
In which:
	Q =	Discharge in cubic feet per second.
	a =	Cross-sectional area of water in conduit in square feet.
	s =	Mean slope of hydraulic gradient, in feet of vertical rise per foot or horizontal distance.
	r =	Hydraulic radius of water in conduit.
	n =	Roughness coefficient, based on the condition and type of material of conduit lining, but not less than 0.013.

§ A300-4 Major drainage channels.

All major drainage channels which are located within or immediately adjacent to an improvement or a subdivision shall be protected and improved by the developer as follows:

All land having an elevation below the fifty-year maximum flood elevation and not protected by levees or dikes shall be dedicated to the town for the purpose of providing drainage and for public park and utility easement use.

The existing channel lying within or immediately adjacent to the subdivision shall be cleaned to provide for the free flow of water, and the channel shall be straightened, widened and improved to the extent required to prevent overflow beyond the limits of the dedicated drainage area.

Site improvements shall provide for the grading of all building sites and streets to an elevation where all lots, building areas and streets will not be subject to overflow and in a manner that will provide for the rapid runoff of all rainfall; however, such improvements shall be carried out in a manner that will preserve and protect large trees and attractive physical features of the area.

Whenever channel improvement is carried out, sodding, backsloping, cribbing, riprapping and other bank protection shall be designed and constructed to control erosion for all the anticipated conditions of flow for the segment of channel involved.

A drainage channel shall not be located in a street easement unless it is placed in an enclosed storm sewer or unless a paved street surface is provided on both sides of a paved channel to give access to abutting properties.

Culverts, bridges and other drainage structures shall be constructed in accordance with the specifications of the town at all locations where drainage channels intersect with continuous streets or alleys. All structures across public streets, alleys and sidewalks shall be designed for a fifty-year flood.

§ A300-5 Secondary drainage channels.

All secondary drainage channels which are located within or immediately adjacent to an improvement or a subdivision shall be protected and improved by the developer as follows:

All land having an elevation below the twenty-five-year maximum flood elevation and not protected by levees or dikes shall be dedicated to the town for the purpose of providing drainage and for public park and utility easement use.

Site improvement shall provide for the grading of all building sites and streets to an elevation where all lots, building areas and streets will not be subject to overflow and in a manner that will provide for the rapid runoff of all rainfall; however, such improvements shall be carried out in a manner that will preserve and protect large trees and attractive physical features of the area.

A drainage channel shall not be located in a street casement unless it is placed in an enclosed storm sewer or unless a paved street surface is provided on both sides of a paved channel to give access to abutting properties.

§ A300-6 Minor drainage channels; surface drainage.

All minor drainage channels which are located within or immediately adjacent to an improvement or a subdivision and all surface drainage conditions shall be protected and improved as follows:

Minor drainage channels which have a primary function of collecting surface water from adjacent properties or intercepting and diverting side hill drainage shall be provided with an improved open channel.

Any drainage not contained in a paved street must be contained in underground piping sized to handle a ten-year-flood capacity, and a paved emergency overflow must also be provided of such a size that the pipe and the overflow together with handle a fifty-year flood.

A drainage channel shall not be located in a street easement unless it is placed in a closed storm sewer or unless a paved street surface is located on both sides of a paved drainage channel to give access to abutting properties.

Site grading shall be carried out in such a manner that surface water from each lot will flow directly to a storm sewer, improved channel or paved street without crossing more than two adjacent lots.

Surface water collected on streets shall be diverted to storm drains at satisfactory intervals to prevent the overflow of stormwater onto any lot during a fifty-year-frequency rain for the area and grades involved; provided, however, that in no case shall the drainage area served by one street exceed 20 acres, regardless of the amount of flow.

Drainage easements of satisfactory width to provide working room for construction and maintenance shall be provided for all storm sewers. In no case shall the total easement be less than 20 feet.

Open channels shall be improved by providing a paved section that will carry the runoff from a rain of twenty-five-year frequency and a sodded section to carry the runoff from a rain of fifty-year frequency. The design of the channel improvements shall be in accordance with the standards set forth on Figure A or Figure B.[1] Whenever an open improved channel is required or authorized for a minor drainage channel under the provisions of these regulations, and the channel crosses residential lots 80% or more of which have a width of not less than 90 feet and an area of not less than 13,500 square feet, and the channel improvement is to be designed as an integral part of the landscaping of the area that will be maintained by the property owners of the area, then the Town Board may modify the requirements of the first part of this subsection to permit a channel improvement design in accordance with Figure C.[2] The developer may elect to provide a paved section to accommodate runoff from a rain of fifty-year frequency, provided that sodding shall be carried out to the extent necessary to protect paved surfaces.

[1]

Editor's Note: Copies of Figures A and B, Improved Drainage Channels, are on file in the office of the Town Clerk.

[2]

Editor's Note: Copies of Figure C, Improved Drainage Channel, are on file in the office of the Town Clerk.

§ A300-7 Requirements relating to improvements.

Bridges and culverts.

(1)

Bridges or culverts shall be provided where watercourses cross continuous streets or alleys.

(2)

Bridge and culverts shall be sized to accommodate a fifty-year-frequency rain, based on the drainage area involved.

(3)

The design of bridges and culverts shall conform to town construction specifications.

Closed storm sewers. Closed storm sewers shall be constructed of precast or prefabricated pipe or built, in place, of closed-box design to conform with town construction specifications to serve the required frequency rain for the drainage area involved.

Open paved storm drainage. Open paved storm drainage channels shall be constructed in accordance with town specifications. Side slopes above the paved section shall be shaped and sodded on a slope of four horizontal to one vertical or flatter. Fences shall not be erected below the shoulder of the sodded section, and in no case shall fences be closer than six feet, measured horizontally, to the edge of the paved section unless the paved section is designed to handle the total fifty-year flood.

§ A300-8 Miscellaneous requirements.

It shall be the policy of the Town Board, under the authority vested in the Town Drainage Ordinance,[1] to require the installation of sedimentation basins and erosion control measures in all new land development projects; details shall be such as are required by the Drainage Ordinance, these regulations and the requirements of the Director of Engineering and Planning or Town Consulting Engineer.

[1]

Editor's Note: See Ch. 84, Drainage, Art. II, Drainage Control.

It shall be the policy of the Town Board, under the authority vested in the Town Drainage Ordinance, to require the installation of permanent and/or temporary stormwater retention basins in new land development where, in the judgment of the Town Board and its Engineer, it is felt necessary in order to provide proper drainage control. Details shall be such as are required by the Drainage Ordinance, these regulations and the requirements of the Director of Engineering and Planning or Town Consulting Engineer. Adequate safety features, such as fencing, shall be provided where required by the town.

The design and construction of new land development shall recognize the need and desirability of a comprehensive drainage plan to assure that no surface water is directed from one property to another in a manner as to create a temporary or permanent nuisance or hazard. To this end the developer shall indicate on his plans how he proposed to provide for this problem, and such plan shall be subject to review and approval by the Director of Engineering and Planning or Town Consulting Engineer, and, further, the town reserves the right to require a guaranty in the form of a letter of credit and/or a performance bond to assure that such plan is properly implemented. The developer shall provide an as-built drainage plan to substantiate that final grading conforms to the approved drainage plan.

Prohibited acts. It shall be the policy of the Town Board, under the authority vested in the Town Drainage Ordinance, to prohibit the following acts:

(1)

Place, deposit or permit to be placed or deposited any debris, fill, sand, stone or other solid materials of any kind or nature or construction of any kind into or across any stream, ditch, culvert, pipe, watercourse or other drainage system.

(2)

Construct and/or place any ditch, pipe, culvert or artificial watercourse of any kind or nature which shall collect and direct the flow of natural surface waters or drainage or increase in intensity or quantity the flow of surface waters or drainage from paved surfaces, structures, roads or improvements directly into any stream, ditch, culvert, pipe or watercourse or other drainage system.

(3)

Fill, obstruct, dam, divert or otherwise change or alter the natural or artificial flow of waters or drainage or the intensity or quantity of flows through any stream, ditch, pipe, culvert, watercourse or other improvement or drainage system.

The developer's engineer shall submit, with his final plans, drainage calculations justifying the size of pipes, channels, impoundment basins and related structures.