Township of Kidder, PA Storm Drainage System Requirements

Where a regulated activity is traversed by or contains a pond, lake, drainage way, channel, storm drainage system, or stream, a drainage easement shall be provided. The minimum easement width shall be 10 feet from each side of the water body, stream, pond, lake or drainage facility, but the Township may require a greater easement when necessary. When required by the Township, bearings and distances shall be provided to define the boundaries of the easements.

Where a regulated activity is traversed by watercourses other than those for which a one-hundred-year floodplain is defined by Kidder Township, there shall be provided drainage easements conforming substantially with the line of such watercourses. The width of any easement shall be adequate to provide for unimpeded flow of storm runoff based on calculations made in conformance with § 148-52 for the one-hundred-year return period runoff and to provide a freeboard allowance of 0.5 foot above the design water surface level. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations which may adversely affect the flow of stormwater within any portion of the easement. Watercourses for which the one-hundred-year floodplain is formally defined are subject to the applicable Kidder Township floodplain regulations.

The developer shall properly grade, seed, and stabilize slopes with erosion control matting, and fence open ditches when a safety hazard can result. Areas within easements shall be kept as lawn or in natural conditions to allow maintenance and entrance.

Storm sewers, culverts, swales, channels, and related facilities shall be designed to accommodate and discharge all runoff from adjacent upstream drainage areas, assuming the upstream area is fully developed.

Flood protection. 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.

§ 148-56 Design of retention and detention facilities.

General requirements.

Where retention and/or detention basins are proposed by the applicant, adequate assurances of maintenance, indemnification, liability insurance, and security shall be provided and approved by the Township.

Retention and detention facilities shall be designed and located so as to not present a hazard to the public health or safety. Their design shall be approved by the Township.

Such facilities shall be designed so that no adverse effects will result from backwater flooding.

General design considerations.

The required volume for stormwater detention or retention shall be calculated to reduce the increased rate of runoff caused by development of the property as established by this part.

The number and location of detention facilities are subject to the approval of the Township.

The detention facilities shall be designed to retard stormwater runoff rates after development to the established peak predevelopment runoff rate.

Specific design considerations.

Detention basins shall meet the following restrictions to minimize the negative visual impact, to prevent hazard to public health and safety and to avoid the need for fencing:

A maximum depth of detained runoff shall be 60 inches for a one-hundred-year storm event; and

Interior side slopes shall not be steeper than a ratio of 10:1, horizontal to vertical; and

A water surface limit no closer than 100 feet to any residential building and no closer than 25 feet to any other type of building.

If the maximum water depth as stipulated in Subsection C(1) above is exceeded, or if the interior slopes are designed steeper than stipulated above, a six-foot high chain link fence is required to fully surround the detention ponds. The fence shall be landscaped from adjacent streets and properties. A fenced detention pond shall have a maximum berm outside side slope of 4:1 and interior slope of 3:1.

An access ramp of 10:1, 10 feet wide, shall be provided to allow maintenance equipment to reach the basin floor of detention basins.

(4)

The minimum slope of the bottom of a detention basin shall be 2%.

(5)

Every stormwater storage area shall be provided with an emergency spillway in accordance with Subsection C(8). The spillway shall either be placed in undisturbed earth or be constructed to withstand shear stresses per Pa. Code Chapter 102.

(6)

Paved surfaces that are to serve as stormwater storage areas shall have minimum grades of 1% and shall be restricted to storage depths of 1/2 foot maximum.

(7)

If a portion of an area within a stormwater storage area is to be paved for parking or recreation purposes, the paved surface shall be placed at the highest elevation within the storage area as possible.

(8)

All stormwater detention facilities shall provide a minimum 1.0 foot freeboard above the maximum pool elevation associated with the two- through twenty-five-year runoff events. The freeboard shall be measured from the maximum pool elevation to the invert of the emergency spillway. The two- through fifty-year storm events shall be controlled by the primary outlet structure. An emergency spillway for each basin shall be designed to pass the one-hundred-year return frequency storm peak basin inflow rate with a minimum 0.5 foot freeboard measured to the top of basin. The freeboard criteria shall be met considering any off-site areas tributary to the basin as developed, as applicable.

(9)

The minimum circular orifice diameter for controlling discharge rates from detention facilities shall be three inches. Designs where a lesser-size orifice would be required to fully meet release rates shall be acceptable, provided that as much of the site runoff as practical is directed to the detention facilities. The minimum three-inch diameter does not apply to the control of the Iv.

(10)

Wet detention ponds designed to have a permanent pool for the Iv shall assume that the permanent pool volume below the primary outlet is full at the beginning of design event routing for the purposes of evaluating peak outflows.

(11)

The following additional conditions shall be complied with for wet bottom stormwater storage areas:

Water surface area shall not exceed 1/10 of the tributary drainage area.

Shoreline protection shall be provided to prevent erosion from wave action.

Minimum normal water depth shall be four feet. If fish are to be used to keep the pond clean, a minimum of 1/4 of the pond area shall be a minimum of 10 feet deep.

(d)

Facilities shall be provided to allow the pond level to be lowered by gravity flow for cleaning purposes and shoreline maintenance.

(e)

Aeration facilities as may be required to prevent pond stagnation shall be provided. Design calculations to substantiate the effectiveness of these aeration facilities shall be submitted with final engineering plans. Agreements for the perpetual operation and maintenance of aeration facilities shall be prepared to the satisfaction of the Township.

(f)

In the event that the water surface of the pond is to be raised for the purpose of storing water for irrigation or in anticipation of the evapotranspiration demands of dry weather, the volume remaining for storage of excess stormwater runoff shall still be sufficient to contain the design year storm runoff.

(12)

Retention and/or detention basins which are designed with earth fill dams shall incorporate the following minimum standards:

The height of berm shall not exceed 10 feet, unless approved by the Township.

The minimum top width of berms up to 10 feet in height shall be eight feet.

A key trench shall be provided under all berms. The key trench shall be at least two feet deep, or extend down to stable subgrade, whichever is deeper. Minimum bottom widths for the cutoff trench and key trench shall be four feet. Maximum side slopes for key trenches shall be one horizontal to one vertical. A compacted impervious core at least eight feet wide at the top, having a maximum side slope of one horizontal to one vertical, shall extend for the full length of the embankment, and the top elevation shall be set at the twenty-five-year design water surface elevation.

(d)

All pipes and culverts through berms shall have properly spaced concrete anti-seep collars.

(e)

The top of berm shall be constructed at least six inches above the design elevations to allow for settlement of the embankment.

§ 148-57 Design of street drainage.

All streets shall be designed to provide for the discharge of surface water from their rights-of-way.

Unless a more conservative design is required by another regulation, or is required because of conditions particular to an individual development, the design storm for fixed pipe systems shall be a fifty-year frequency for all subdivisions, land developments or crossings of any road through culverts. In all instances listed above, total conveyance systems shall be provided to carry the one-hundred-year design storm to the detention basin or drainage facility.

The pavement cross slope on streets shall not be less than 1/4 inch per foot and not more than 1/2 inch per foot. The slope of the shoulder areas shall not be less than 3/4 inch per foot and not more than one inch per foot.

Surface cross drainage at intersections or other roadway sections will not be permitted.

Inlets shall be spaced to limit the gutter flow spread into the travel lanes to 1/2 the lane width during the design storm.

Inlet efficiency and bypass flows, per PennDOT design charts, shall be considered in the design of storm sewer systems.

§ 148-58 Design of collection system.

The stormwater collection system shall be designed using the Rational Method of Design for flow calculation in accordance with American Society of Civil Engineers Manual No. 37 except where noted, unless otherwise approved by the Township. The capacity of the stormwater collection system shall be designed using the standard step method, unless otherwise approved by the Township.

The collection system shall be designed and installed in accordance with the design standards and requirements set forth by this part, the Township, the Township Engineer and as follows:

Subsurface drainage systems shall have accessible manholes spaced at intervals not exceeding 400 feet and shall be located wherever branches are connected or sizes are changed and wherever there is a change in alignment or grade. Inlets or other means of interconnection may be used instead of manholes when approved by the Township, or as required for curbed streets.

On curbed streets, inlets shall be placed at points of abrupt changes in the horizontal or vertical directions of storm sewers, at curb tangents on uphill side of street intersections, at maximum distances as specified in accordance with the required pipe size, and to limit gutter flow as required. The Manning Equation shall be used to calculate the capacities of gutters. Pennsylvania Department of Transportation inlets should be used in accordance with the design procedures outlined in PennDOT Design Manual, Part 2, or other applicable PennDOT Design Procedures. Manholes may be substituted for inlets at locations where inlets are not required to handle surface runoff.

Inlets shall be designed and located to prevent hazards to vehicles, bicycles, and pedestrians.

(4)

Storm sewer lines, within street rights-of-way, shall be located between the center line of the street and the curbline and shall parallel the center line of the street as far as practical. Locating storm sewers under curbs in curves or at street intersections will not be permitted.

(5)

Drainage structures that are to be located within state highway rights-of-way shall be approved by the Pennsylvania Department of Transportation, and a letter from that department indicating such approval shall be submitted to the Township.

(6)

Storm sewers shall have a minimum diameter of 15 inches.

(7)

Storm drains shall be designed to produce a minimum velocity of 3.0 feet per second when flowing full and shall not be designed or installed at less than a 0.5% slope. The maximum permissible velocity shall be 15 feet per second.

(8)

PennDOT approved endwalls or end sections shall be used in lieu of inlets where feasible to minimize clogging of grates with leaves, debris, etc.

(9)

PennDOT approved headwalls shall be used where storm runoff enters the storm sewer horizontally from a natural or man-made channel. The capacity of such storm sewers shall be evaluated using both Manning Equation and inlet/outlet control procedures. The lower flow derived from these two procedures shall be the design capacity of the storm sewer.

(10)

Provisions shall be made to minimize erosion within watercourses and at points of discharge from storm drainage facilities through the use of proper ground cover. Any riprap swale area shall be constructed with mixed stone sizes in accordance with PennDOT criteria for riprap and shall be lined with PennDOT approved geotextile fabric.

(11)

Roof drainage. Stormwater roof drains and pipes shall not discharge water over a sidewalk, driveway or paved area.

(12)

Open swales shall be designed on the basis of Manning Formula as indicated for collection systems with the following considerations:

Roughness coefficient. The roughness coefficient shall be according to Appendix A[1] or if an erosion control matting is used, the roughness coefficient shall be as indicated by the manufacturer.

[1]

Editor's Note: Appendix A is included at the end of this chapter.

Bank slopes. Slopes for swale banks shall not be steeper than one vertical for three horizontal.

Flow velocity. Design velocity in grass or vegetated swales shall not exceed four feet per second, unless use of erosion control matting is proposed, in which case the manufacturer's maximum allowable shear stress or velocity shall be used.

(d)

Right-of-way. A swale right-of-way of sufficient minimum width to include a ten-foot access strip in addition to the width of the swale from bank top shall be shown as an easement for drainage purposes. The Township may, under unusual conditions, require a wider swale right-of-way.

(13)

Discharge structures shall be designed to minimize the impact of development on downstream properties. Flow retarding and dissipating facilities are required to meet this goal.

(14)

Open pipe ends must be fitted with concrete endwalls or wing walls.

(15)

All pipe endwalls or wing walls and all detention basin intake and discharge structures shall be protected from frost related movement and scour activity by the construction of a concrete footer with a minimum depth of 30 inches below ground level.

(16)

Trash racks shall be placed on all stormwater entrance structures.

Materials and construction requirements shall be as specified by the Township, the Township Engineer and as follows:

Pipe materials.

All pipe materials shall be either reinforced cement concrete pipe, Class III, complying with PennDOT Publication 408, Section 601, or smooth-lined high density polyethylene pipe with watertight joints meeting all PennDOT requirements.

Joints for concrete pipe shall be of the "O" ring Type III per current ASTM Specifications C425 or mortared type as approved.

Manholes and inlets shall be equivalent to PennDOT design standards.

Manhole frames and covers must be heavy duty, have a minimum clear opening of 24 inches, and be equal to Neenah Foundry Co. Model P-1030 or Campbell Foundry Co. Pattern 1004 and shall have the words "Storm Sewer" cast thereon in letters two inches high.

(4)

Appropriate safety grates shall be attached to all catch basins, stormwater inlets, pipe openings and other stormwater receiving structures, as needed, to ensure that maximum openings do not exceed 25 square inches. Along streets and pedestrian areas, safety grates shall be used as needed for bicycle safety.

Installation.

All pipe laying shall carefully progress uphill with hubs upgrade and ends fully and closely jointed. Trench widths shall not exceed the outside diameter of the pipe plus 16 inches and depths shall be as required. Trench walls shall be vertical and bottoms shall be horizontal.