Village of The Branch, NY Article IX Drainage System

§ 238-25 Grading and drainage system plan.

A. A preliminary grading and drainage system plan shall be a part of the preliminary layout. It shall indicate in general terms a proposal for an adequate system of drainage structures to carry off and store or discharge the stormwater runoff and natural drainage water which originates not only within the property boundaries but also that which originates beyond the property boundaries.

B. The public improvement and utilities plan and profiles shall show the final drainage plan and street profiles. They shall be prepared and submitted with the final plat after the approval of the preliminary layout and drainage plan (see § 238-11).

C. No stormwater runoff or natural drainage water shall be so 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 taking care of these conditions.

§ 238-26 Design standards.

A. Collection system. The collection system shall be designed in accordance with the rational method of design, using the formula: Q=A i R.

(1) "Q" is the required capacity in cubic feet per second for the collection system at the point of design.

(2) "A" is the tributary drainage area in acres and shall include tributary areas from outside sources as well as from within the subdivision itself.

(3) "i" is the coefficient of runoff applicable to the drainage area and shall be based on consideration of soil conditions, average slope of the drainage area and degree of ultimate development of the area, but in no case shall be less than the following coefficients:

Undeveloped land	0.10
2-acre lot, residential development	0.15
1-acre lot, residential development	0.17
1/2-acre lot, residential development	0.20
10,000-square-foot lot, residential development	0.32
Business areas	0.90

(4) "R" is the rainfall intensity in inches per hour and shall be determined by the following formula:

R =

120 t+ 20

Where:
	t	=	the time of concentration in minutes at the point of design

(5) Pipes or conduits shall be designed using Manning's formula for velocity:

V =

1,486 n

x R 2/3 x S 1/2

Where:
	R	=	is the hydraulic radius of the conduit flowing full.
	n	=	is the coefficient of friction (n=0.015 for pipes 18 inches or smaller in diameter, n = 0.013 for pipes over 18 inches in diameter or for concrete culverts).
	S	=	is the slope of the pipe in feet per foot. "S" shall generally be considered as being the same as the slope of the invert of the pipe; however, such slope shall be checked against the available hydraulic gradient wherever the system discharges into a stormwater recharge basin, pond or other body of water.

(6) Wherever possible, design velocities in pipes shall be three feet per second or over. Where steep grades are encountered, velocities over 15 feet per second shall be avoided by the use of drop manholes in the line.

(7) Manholes shall be provided in drain lines not more than 350 feet apart and wherever branches are connected or sizes are changed and wherever there is a change in alignment or grade.

(8) Alignment of pipes shall be in a straight line between manholes.

(9) Drain lines shall be placed between the center line of the road and the curbline and shall, as far as practical, parallel the center line of the road.

(10) Not more than two catch basins shall be interconnected before being connected to a manhole.

B. Stormwater recharge basins. Stormwater recharge basins shall be provided wherever there is no available outlet for stormwater or where the available outlets are inadequate, provided that test pits indicate that the earth materials encountered have desirable seepage qualities.

(1) Recharge basins shall provide storage capacity for five inches' rainfall on the tributary area where suitable means for overflow are provided.

(2) Recharge basins without suitable means for overflow shall provide storage capacity for an eight-inch rainfall on the tributary area.

(3) The coefficient of runoff for recharge basin design shall be based on the soil characteristics and average slope of the drainage area, but in no case shall the coefficient be less than 0.30.

C. Brooks or ditches. Where brooks or ditches are used as outlets, they shall be designed by the use of Manning's formula as indicated for collection systems in Subsection A(5), with the following considerations:

(1) The friction factor shall be:

(a) 0.025 for earth ditches; and

(b) 0.013 for paved ditches.

(2) Slopes for ditch banks shall not be steeper than one on two.

(3) Design velocities in earth ditches shall not exceed three feet per second.

(4) A ditch or brook right-of-way, of sufficient minimum width to include a ten-foot access strip in addition to the width of the ditch or brook from bank top to bank top, shall be offered for dedication to the Village for drainage purposes. Such right-of-way shall be shown on the drainage plan and on the final plan.

D. General design standards.

(1) Valley gutters will be permitted at T-intersections where they are parallel to the center line of the through road, and shall be constructed to the specifications and design to be furnished by the Village Engineer. This is to be accomplished by gradually taking out the crown of the intersecting street starting from a point about 30 feet back from the flow line of the through street. At other than T-intersections, valley gutters will be permitted only when warranted by limited traffic use and never across heavily trafficked roads.

(2) Surface drainage in gutters shall be limited to the equivalent of that flowing from 1.5 impervious acres; however, where the tributary impervious area exceeds the runoff from 1.0 impervious acres, a double-inlet catch basin shall be used.

(3) Drainage structures which are located on county or state highway rights-of-way shall be approved by the appropriate highway engineer's office, and a letter from that office indicating such approval shall be directed to the Planning Board.

§ 238-27 Specifications for drainage system structures. [1]

The following shall be the minimum required standards:

A. Catch basins. All catch basins shall be one of the approved designs presented in Drawings 2 and 3. They shall be indicated on the drainage plan by their identifying number. Standard inlet and manhole cover and frame designs are presented in Drawings 4 through 7.

B. Seepage basins. In unusual conditions where small areas are not adaptable to other prescribed means of drainage, seepage basins may be used if approved by the Planning Board.

(1) The construction of seepage basins shall be similar to that of catch basins, except that the sidewalls shall be constructed entirely of eight-inch seepage blocks.

(2) If additional storage volume is needed, additional basins or cells may be constructed next to the first with a common wall of eight-inch seepage block. The additional basins or cells may not need inlets but they shall each have a manhole.

(3) Such seepage basins shall be connected by slotted pipe surrounded by a minimum of six inches of gravel to an overflow basin or area. The overflow from such basin or area shall not overload any other drainage system.

C. Culverts.

(1) All culverts shall be constructed of reinforced concrete pipe or shall be reinforced concrete box culverts and shall have reinforced concrete headwalls similar to that shown on Drawing 17, unless another detail is approved for a specific installation.

(2) A chain link fence four feet high, similar in quality to that for recharge basins, shall be provided along the right-of-way line at the headwall on each end of the culvert and extending at least four feet beyond the top of the ditch or brook bank on each side of the headwall.

D. Manholes. All manholes shall be one of the approved designs presented in Drawings 9 through 16. They shall be indicated on the final drainage plan by their identifying number. Standard manhole cover and frame designs are presented in Drawings 4 through 6. All manholes located in the street paving shall be located on the center line unless this specification is waived.

E. Storm-drain pipe. All storm-drain pipes shall be reinforced concrete pipe laid on undisturbed subgrade with full, firm and even bearing. Backfill and compaction shall be in accordance with good engineering practice. They shall be indicated on the final drainage plan with notation as to size, slope and invert elevations. Necessary easements shall be shown on the drainage plan and the final plat and shall be not less than 10 feet wide.

(1) Pipe 18 inches or less in diameter shall be of the bell-and-spigot type.

(2) Pipe over 18 inches in diameter shall be of the internal-bell type or slip-joint type.

F. Stormwater recharge basins. Stormwater recharge basins shall be constructed in accordance with the requirements of this regulation and the detail drawing of the basin as approved with the final drainage plan by the Planning Board.

(1) Test hole. At least one test hole shall be dug on the site of each proposed recharge basin before preparation of the final drainage plan.

(a) The test hole shall be dug to a depth at least five feet below the proposed bottom elevation of the basin or groundwater level, if it is encountered at a lesser depth.

(b) A representative of the Village Engineer shall be notified when the test hole is open and shall inspect it.

(c) Upon approval of the side for a recharge basin by such representative, the final drainage plan shall be prepared.

(2) Detailed drawing. A detailed plan of the stormwater recharge basin shall be submitted for approval as a part of the public improvement and utilities plan and profiles and shall be prepared in accordance with the following requirements:

(a) The plan shall show to scale the property line and planting screen, fence and gate location, top and bottom of slope, outline of maximum design water level, access ramp, location of inlet pipes and headwalls and sluices, elevations on bottom of basin of the maximum design water level and control elevations on curb and top of slope.

(b) Where the planting screen is placed outside of the fence, a berm width of 10 feet shall be provided between the fence and the top of slope. Where the planting strip is located inside the fence, a fifteen-foot berm width shall be provided between the top of slope and the fence. The berm width shall be increased at corners to provide sufficient area for a service truck to negotiate the turn. The top of the slope shall be not less than one foot higher than the curb.

(c) The maximum slope for the sides of the recharge basin shall be one on two and shall be so indicated on the plan.

(d) Dikes shall be avoided, but where they are necessary they shall be constructed in accordance with specifications furnished by the Village Engineer.

(e) Rights-of-way providing access to recharge basins shall have a minimum width of 20 feet.

(f) The access ramp shall be so designed that it starts at the elevation and location of the top of the basin side and provides easy access to the higher of the two levels of the basin bottom. It shall be 12 feet wide with a stabilized surface and have a gradient not to exceed 5%.

(g) Headwalls shall be shown in their proper locations and shall be constructed in accordance with Drawing 17. Inlets into the recharge basin shall lead into the lower area of the basin bottom.

(h) The perimeter, or berm, of the recharge basin shall be so graded that no water will drain across it into the basin except in sluices properly designed for that purpose. Wherever possible, the perimeter area shall be so graded that the adjacent land will slope away from the recharge basin. The proposed grading shall not adversely affect adjacent property.

(i) The recharge basin bottom shall be designed with two elevations, one a minimum of two feet higher than the other. The lower elevation shall not be more than 10 feet below the overflow elevation. The lower elevation shall be at least two feet above the potential high groundwater level.

(j) The recharge basin design shall include an overflow so that the stored water shall not exceed a depth of 10 feet. Such overflow shall flow directly onto a street surface or by means of an adequate pipe system flow to some other point of disposal.

(k) The following information shall be noted on the stormwater recharge basin detail drawing:

[1] Total area for which the recharge basin has been designed.

[2] Coefficient of runoff used.

[3] Required capacity in cubic feet.

[4] Capacity provided in cubic feet.

[5] Total excavation in cubic yards.

(3) Fence and gate. A fence and gate shall be constructed in accordance with the requirements of this regulation and the following specifications:

(a) A concrete curb six inches wide (minimum) by 24 inches deep shall be constructed under the entire length of the fence and gate, and unless otherwise approved, the top of the curb shall be flush with the established grade. The curb shall be centered under the fence and shall be made of one part cement to five parts' mineral aggregate free from silt or clay, using not more than 7 1/2 gallons of water per bag of cement. Wood forms shall be used along the top of the curb to provide straight, parallel sides six inches apart at least 3 1/2 inches deep.

(b) Posts.

[1] Line posts shall be two-inch-outside-diameter pipe, 2.72 pounds per foot, hot galvanized or equivalent H-section, set not more than 10 feet o.c. Corner posts shall be two-and-one-half-inch-outside-diameter pipe, 3.65 pounds per foot, hot galvanized. Gateposts shall be four-inch-outside-diameter pipe, 9.11 pounds per foot, hot galvanized.

[2] All posts shall be nine feet long and shall extend three feet below the top of the concrete curb, which shall be thickened and deepened at the posts to provide three inches of concrete cover on the posts. Corner posts and gateposts shall be properly braced with one-and-five-eighths-inch-outside-diameter pipe, 2.27 pounds per foot, hot galvanized with rod and turnbuckle attachment.

[3] A one-and-five-eighths-inch-outside-diameter toprail, weighing not less than 2.27 pounds per lineal foot, shall be installed along the entire length of the fence. The fence fabric shall be tied to the toprail every two feet with No. 9 gauge aluminum or galvanized tie wires.

(c) Fabric.

[1] Fabric shall be two-inch-mesh No. 9 steel wire, hot-dipped galvanized, six feet high with barbed edges top and bottom, attached to the posts so that the bottom of the wire is not more than one inch above the curb. The wire shall be fastened to each post by means of six "hook and hook" type clips.

[2] The fabric shall be anchored to the curb by means of five-sixteenths-inch galvanized steel rods 12 inches long anchored in the curb and clinched to the fabric. These tie rods shall be spaced two feet apart.

(d) Barbed wire. All posts shall be fitted with barbed wire arms at the top to support three strands of four-point hot-dipped galvanized or bethanized barbed wire, the top wire being one foot above the top of the fabric. Arms shall make an angle of 45° with the post and shall extend inward toward the basin. Barbed wire shall be tightly stretched and shall be securely tied to the arms.

(e) Gates. Gate openings shall be 16 feet with double gates having a one-hundred-eighty-degree swing. Gate frames shall be made of two-inch-outside-diameter pipe or two-inch-square tubing weighing not less than 2.72 pounds per foot, hot galvanized, with malleable iron corner castings or welded at all corners and properly braced against sagging. Hinges shall be of malleable iron securely fastened to gate and post. All gates shall be double gates equipped with a drop-bar locking device. The bottom of the gates shall be not more than two inches above the curb. Gates shall be fitted with three strands of barbed wire to the same height as that on the fence. The center block shall be of a design which can be easily cleaned. A pipe center block shall not be used.

(4) Planting screen. A planting screen shall be established on the perimeter of the stormwater recharge basin. The screen area shall be five feet wide except as set forth in Subsection F(4)(c) below, and shall conform to the following:

(a) When the adjacent property is a part of the lot pattern of the same subdivision, the planting shall be placed on the outside of the fence on the adjacent plot. Such planting shall become a part of that plot and shall be maintained by its owner. In this location the fence shall be set one foot inside the property line on the stormwater recharge basin site.

(b) When the adjacent property is not owned by the subdivider, the planting screen shall be placed inside the fence, which shall be set one foot inside the property line on the stormwater recharge basin site.

(c) When the stormwater recharge basin abuts a street, the fence shall be set 40 feet inside the property line on the recharge basin site, and the area between the property line and fence shall be landscaped with plant materials native to this area as directed by the Planning Board upon approval of the final plat.

(d) The berm area between the property line and the top of slope shall be covered with six inches of topsoil and satisfactorily grass-seeded.

(e) The planting screen shall be planted in accordance with the requirements set forth in Subsection F(4) of the construction specifications for public improvements, except as described in Subsection F(4)(c) above.

(5) Safety requirements. During the period after the excavation has been started and before the fence and gate have been completely installed, the contractor shall provide at all times such guard or guards as shall be necessary to keep unauthorized persons off the construction site, provided that if the fence and gate have been completely installed, no guard or guards will be required during the time when the gate is closed and securely locked. It is hereby declared the policy of the Planning Board that recharge basins, once started, shall be completed in as short a time as possible consistent with good practice, and, further, that the public safety shall be safeguarded until such time as the recharge basins are completed.

(6) Upon final approval and acceptance of the stormwater recharge basin by the Village Engineer, the developer's key to the lock shall be turned over to the Superintendent of Highways.

G. The Village Engineer and the Village Superintendent of Highways, upon a joint determination by them, may accept equal or better specifications in lieu of any of the specifications set forth herein in Subsections A through F, when in their judgment such alternates accrue to the public benefit.

[1] Editor's Note: All drawings referred to in this section are on file in the office of the Village Engineer.