Township of Falls, PA Article III Stormwater Management

§ 187-8 General requirements.

A. All regulated activities in the Township of Falls which do not fall under the exemption criteria shown in § 187-20 shall require submittal of a drainage plan and/or a stormwater management site plan consistent with this chapter to the Township of Falls for review. The following criteria shall apply to the total proposed development even if development is to take place in stages. Impervious surface shall include, but not be limited to, any roof, parking or driveway areas and any new streets and sidewalks. Any areas designed to initially be gravel or crushed stone shall be assumed to be impervious for the purposes of comparison to the waiver criteria listed in § 187-20 of this chapter.

B. A drainage plan shall be provided in order to:

(1) Permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities consistent with this chapter.

(2) Ensure adequate drainage of all low points along the lines of streets, paved and grass areas.

(3) Intercept stormwater runoff along streets at intervals reasonably related to the extent and grade of the area drained and to prevent substantial flow of stormwater across street intersections.

(4) Provide positive drainage away from on-site sewage disposal and structures.

(5) Remove surface water from the bottom of vertical grades, lead water from springs, and avoid the use of cross gutters at street intersections and elsewhere.

(6) Encourage all runoff control measures to infiltrate the stormwater into the ground and aid in the recharge of groundwater.

(7) Prevent erosion damage and to satisfactorily control the rate of release of surface waters.

C. The existing points of concentrated drainage that discharge onto adjacent property shall not be altered without permission of the adjacent property owner(s) and shall be subject to any applicable criteria as specified in this chapter.

D. Areas of existing diffused drainage discharge shall be subject to any applicable discharge criteria in the general direction of existing discharge, whether proposed to be concentrated or maintained as diffused drainage areas, except as otherwise provided by this chapter. If diffused flow is proposed to be concentrated and discharged onto adjacent property, the applicant must document that adequate downstream conveyance facilities exist to safely transport the concentrated discharge, or otherwise prove that no erosion, sedimentation, flooding, or other harm will result from the concentrated discharge.

E. Where a development site is traversed by watercourses, drainage easements shall be provided by the property owner conforming to the line of such watercourses and having a minimum width of 20 feet, measured from top of bank on each side of the watercourse. The terms of the easement shall prohibit excavation, the placing of fill or structures and any alterations that may adversely affect the flow of stormwater within any portion of the easement. Vegetative buffers are encouraged (three to five feet) on both sides of the streambanks, where appropriate. Also, maintenance and removal of material that would impede stream flow within the easement shall be required, except as approved by the Township of Falls.

[Amended 12-18-2018 by Ord. No. 2018-11]

F. When it can be shown that, due to topographic conditions, natural watercourses on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural watercourses. Work within natural watercourses shall be subject to approval by PADEP through the joint permit application process, or, where deemed appropriate by PADEP, through the general permit process.

G. Any stormwater management facilities regulated by this chapter that would be located in or adjacent to waters of the commonwealth or wetlands shall be subject to approval by PADEP through the joint permit application process or, where deemed appropriate by PADEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the applicant/owner and/or his agent to show that the land in question cannot be classified as wetlands. Otherwise, approval to work in the area must be obtained from PADEP and/or the United States Army Corps of Engineers, as applicable and appropriate.

H. Any stormwater management facilities regulated by this chapter that would be located on state highway rights-of-way or that discharge directly to state highway rights-of-way shall also be subject to approval by PennDOT.

[Amended 12-18-2018 by Ord. No. 2018-11]

I. Minimization of impervious surfaces and maximization of infiltration of stormwater runoff are encouraged, where soil conditions permit. This may assist in reducing the size of or eliminating the need for detention basins.

J. Roof drains must not be connected to streets, sanitary or storm sewers or roadside ditches in order to promote overland flow and infiltration/percolation of stormwater. Roof drains shall discharge to infiltration areas or vegetative BMPs to the maximum extent practicable.

K. Downstream hydraulic capacity analysis. Any downstream hydraulic capacity analysis conducted in accordance with this chapter shall use the following criteria for determining adequacy for accepting increased peak flow rates from the 100-year return period storm event:

[Amended 12-18-2018 by Ord. No. 2018-11]

(1) Natural or man-made channels and swales must be able to withstand the increased velocities associated with increased runoff within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the PADEP Erosion and Sediment Pollution Control Program Manual.

(2) Natural or man-made channels or swales must be able to convey the increased runoff without creating any hazard to persons or property.

(3) Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area must be designed in accordance with PADEP Chapter 105 regulations (if applicable) and, at a minimum, pass the increased runoff.

L. For any stormwater management facility located in areas where safety of human life is a concern, perimeter fencing with locked gates a minimum of four feet in height may be required. Likewise, in these areas, steel grates are required on all inlet and outlet structures within stormwater management facilities.

[Amended 12-18-2018 by Ord. No. 2018-11]

M. All regulated activities within the Township shall be designed, implemented, operated, and maintained to meet the purposes of this chapter, through these two elements:

(1) Erosion and sediment control during earth disturbance activities (e.g., during construction); and

(2) Water quality protection measures after completion of earth disturbance activities (i.e., after construction), including operations and maintenance.

N. No regulated earth disturbance activities within the Township shall commence until the requirements of this chapter are met.

O. Postconstruction water quality protection shall be addressed as required by § 187-17.

P. Operations and maintenance of permanent stormwater BMPs shall be addressed as required by Article VII.

Q. All BMPs used to meet the requirements of this chapter shall conform to the state water quality requirements and any more stringent requirements as set forth by the Township.

R. Techniques described in Appendix E[1] (Low Impact Development) of this chapter shall be considered because they reduce the costs of complying with the requirements of this chapter and the state water quality requirements.

[1] Appendix E is included as an attachment to this chapter.

S. The drainage plan must be designed consistent with the sequencing provisions of § 187-11 to ensure maintenance of the natural hydrologic regime and to promote groundwater recharge and protect groundwater and surface water quality and quantity. The drainage plan designer must proceed sequentially in accordance with Article III of this chapter.

T. Whenever a watercourse is located within a development site, it shall remain open in its natural state and location and should not be piped, impeded, or altered (except for road crossings). It is the responsibility of the developer to stabilize existing eroded stream/channel banks.

U. The following permit requirements may apply to certain regulated earth disturbance activities and must be met prior to commencement of regulated earth disturbance activities, as applicable:

(1) All regulated earth disturbance activities subject to permit requirements by DEP under regulations at 25 Pennsylvania Code Chapter 102.

(2) Work within natural drainageways subject to permit by DEP under 25 Pennsylvania Code Chapter 105.

(3) Any stormwater management facility that would be located in or adjacent to surface waters of the commonwealth, including wetlands, subject to permit by DEP under 25 Pennsylvania Code Chapter 105.

(4) Any stormwater management facility that would be located on or discharge directly to a state highway right-of-way or require access from a state highway shall be subject to approval by PennDOT.

[Amended 12-18-2018 by Ord. No. 2018-11]

(5) Culverts, bridges, storm sewers, or any other facilities which must pass or convey flows from the tributary area and any facility which may constitute a dam subject to permit by DEP under 25 Pennsylvania Code Chapter 105.

V. No regulated earth disturbance activities within the Township shall commence until the Township receives an approval from the Bucks County Conservation District of an erosion and sediment control plan for construction activities.

(1) DEP has regulations that require an erosion and sediment control plan for any earth disturbance activity of 5,000 square feet or more, under 25 Pennsylvania Code § 102.4(b).

(2) In addition, under 25 Pennsylvania Code Chapter 92, a DEP NPDES construction activities permit is required for regulated earth disturbance activities.

(3) Evidence of any necessary permit(s) for regulated earth disturbance activities from the DEP southeastern regional office or the Bucks County Conservation District must be provided to the Township

(4) A copy of the erosion and sediment control plan and any required permit, as required by DEP regulations, shall be available on the project site at all times.

§ 187-9 Stormwater management districts.

A. Delaware River South Watershed has been divided into stormwater management districts as shown on the watershed map in Appendix D.[1]

(1) In addition to the requirements specified below, the water quality (§ 187-17), groundwater recharge (§ 187-16), and streambank erosion (§ 187-17B) requirements shall be implemented.

(2) Standards for managing runoff from each subarea in the Delaware River South Watershed is shown below. Development sites located in each of the A, B, or C Districts must control postdevelopment runoff rates to predevelopment runoff rates for the design storms as follows:

District	Design Storm Postdevelopment		Predevelopment Storm
A	2-year 5-year 10-year 25-year 50-year 100-year	Reduced to ----- ----- ----- ----- Reduced to	1-year 5-year 10-year 25-year 50-year 50% of the 100-year
B	2-year 5-year 10-year 25-year 50-year 100-year	Reduced to Reduced to Reduced to Reduced to Reduced to Reduced to	1-year 2-year 5-year 10-year 50-year 50% of the 100-year
C	2-year 5-year 100-year	Reduced to Reduced to Reduced to	1-year 2-year 50% of the 100-year

In District C, development sites which can discharge directly to the Delaware River South main channel or major tributaries or indirectly to the main channel through an existing stormwater drainage system (i.e., storm sewer or tributary) may do so without control of postdevelopment peak rate of runoff greater than the five-year storm. Sites in District C will still have to comply with the groundwater recharge criteria, the water quality criteria, and streambank erosion criteria. If the postdevelopment runoff is intended to be conveyed by an existing stormwater drainage system to the main channel, assurance must be provided that such system has adequate capacity to convey the flows greater than the two-year predevelopment peak flow or will be provided with improvements to furnish the required capacity. When adequate capacity in the downstream system does not exist and will not be provided through improvements, the postdevelopment peak rate of runoff must be controlled to the predevelopment peak rate as required in District A provisions (i.e., ten-year postdevelopment flows to ten-year predevelopment flows) for the specified design storms.

[1] Appendix D is on file in the Township offices.

B. Development on lands adjacent to the Delaware Canal which propose to discharge stormwater into the canal must obtain special right-of-way approval from the Department of Conservation and Natural Resources (DCNR). The DCNR has established a separate policy for granting right-of-way for stormwater drainage into the Delaware Canal, which shall be used in conjunction with this chapter.

§ 187-10 Stormwater management district implementation provisions.

A. General. Postdevelopment peak rates of runoff from any regulated activity shall meet the peak release rates of runoff prior to development for the design storms specified on the Stormwater Management District Watershed Map (Ordinance Appendix D[1]) and § 187-11, of the chapter.

[1] Appendix D is on file in the Township offices.

B. District boundaries. The boundaries of the stormwater management districts are shown on an official stormwater district map that is available for inspection at the municipal office. A copy of the map at a reduced scale is included in the Ordinance Appendix D. The exact location of the stormwater management district boundaries, as they apply to a given development site, shall be determined by mapping the boundaries using the two-foot topographic contours (or most accurate data required) provided as part of the drainage plan.

C. Sites located in more than one district. For a proposed development site located within two or more stormwater management district category subareas, the peak discharge rate from any subarea shall be the predevelopment peak discharge for that subarea as indicated in § 187-11. The calculated peak discharges shall apply regardless of whether the grading plan changes the drainage area by subarea. An exception to the above may be granted if discharges from multiple subareas recombine in proximity to the site. In this case, peak discharge in any direction may be a one-hundred-percent release rate, provided that the overall site discharge meets the weighted average release rate.

D. Off-site areas. Off-site areas that drain through a proposed development site are not subject to release rate criteria when determining allowable peak runoff rates. However, on-site drainage facilities shall be designed to safely convey off-site flows through the development site.

E. Site areas. Where the area of a site being impacted by a proposed development activity differs significantly from the total site area, only the proposed impact area utilizing stormwater management measures shall be subject to the management district criteria. Unimpacted or undisturbed areas that do flow into or are bypassing the stormwater management facilities would not be subject to the management district criteria.

F. Stormwater management easements are required for all areas used for off-site stormwater control.

G. Stormwater management easements shall be provided by the applicant or property owner if necessary for access for inspections and maintenance or the preservation of stormwater runoff conveyance, infiltration, and detention areas and other stormwater controls and BMPs by persons other than the property owner. The purpose of the easement shall be specified in any agreement under § 187-32.

H. "No harm" option. For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less restrictive runoff control (including no detention) if the applicant can prove that "no harm" would be caused by discharging at a higher runoff rate than that specified by the plan. The no harm option is used when an applicant can prove that the postdevelopment hydrographs can match predevelopment hydrographs, or if it can be proved that the postdevelopment conditions will not cause increases in peaks at all points downstream. Proof of "no harm" would have to be shown based upon the following downstream impact evaluation which shall include a "downstream hydraulic capacity analysis" consistent with § 187-10I to determine if adequate hydraulic capacity exists. The land applicant shall submit to the Township this evaluation of the impacts due to increased downstream stormwater flows in the watershed.

(1) The downstream impact evaluation shall include hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications due to the proposed development upon a dam, highway, structure, natural point of restricted stream flow, or any stream channel section, established with the concurrence of the Township.

(2) The evaluation shall continue downstream until the increase in flow diminishes due to additional flow from tributaries and/or stream attenuation.

(3) The peak flow values to be used for downstream areas for the design return period storms (two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year) shall be the values from the calibrated model for the Delaware River South Watershed. These flow values can be obtained from the watershed plan.

(4) Applicant-proposed runoff controls that would generate increased peak flow rates at storm drainage problem areas would, by definition, be precluded from successful attempts to prove no harm, except in conjunction with proposed capacity improvements for the problem areas consistent with § 187-10J.

(5) Financial considerations shall not constitute grounds for granting a no harm exemption.

(6) Capacity improvements may be provided as necessary to implement the no harm option which proposes specific capacity improvements to provide that a less stringent discharge control would not create any harm downstream.

(7) Any no harm justifications shall be submitted by the applicant as part of the overall stormwater management design documents.

[Amended 12-18-2018 by Ord. No. 2018-11]

I. Downstream hydraulic capacity analysis. Any downstream capacity hydraulic analysis conducted in accordance with this chapter shall use the following criteria for determining adequacy for accepting increased peak flow rates:

(1) Natural or man-made channels or swales must be able to convey the increased runoff within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the PADEP Erosion and Sediment Pollution Control Program Manual.

[Amended 12-18-2018 by Ord. No. 2018-11]

(2) Natural or man-made channels or swales must be able to convey increased runoff without creating any hazard to persons or property.

[Amended 12-18-2018 by Ord. No. 2018-11]

(3) Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area must be designed in accordance with the Department of Environmental Protection's Chapter 105 regulations (if applicable) and, at minimum, pass the increased twenty-five-year return period runoff.

J. Regional detention alternatives. For certain areas within the study area, it may be more cost-effective to provide one control facility for more than one development site than to provide an individual control facility for each development site. The initiative and funding for any regional runoff control alternatives are the responsibility of prospective applicants. The design of any regional control basins must incorporate reasonable development of the entire upstream watershed. The peak outflow of a regional basin would be determined on a case-by-case basis using the hydrologic model of the watershed consistent with protection of the downstream watershed areas. "Hydrologic model" refers to the calibrated model as developed for the stormwater management plan. It is a requirement that, even if regional basins are proposed for the water quantity control, that the water quality, streambank erosion and recharge criteria be accomplished on site, or as close to the source of the runoff as possible.

§ 187-11 Stormwater management standards.

The following standards shall be applied to all development within Township of Falls to minimize stormwater runoff, erosion, sediment pollution and flooding:

A. The design of all regulated activities shall include the following steps in sequence to minimize stormwater impacts for nonstructural project design.

(1) The applicant is required to find practicable alternatives to the surface discharge of stormwater, the creation of impervious surfaces and the degradation of waters of the commonwealth, and must maintain as much as possible the natural hydrologic regime of the site.

(2) An alternative is practicable if it is available and capable of being done after taking into consideration cost, existing technology, and logistics in light of overall project purposes and other municipal requirements.

(3) All practicable alternatives to the discharge of stormwater are presumed to have less adverse impact on quantity and quality of waters of the commonwealth unless otherwise demonstrated.

B. The applicant shall demonstrate that they designed the regulated activities in the following sequence to minimize the increases in stormwater runoff and impacts to water quality:

(1) Prepare an existing resource and site analysis map (ERSAM), showing environmentally sensitive areas including, but not limited to, steep slopes, ponds, lakes, streams, wetlands, hydric soils, vernal pools, floodplains, stream buffer zones, hydrologic soil groups A, B, C, and D, any existing recharge areas and any other requirements outlined in the municipal Subdivision and Land Development Ordinance. Establish stream buffer according to recommended criteria or applicable ordinances.

(2) Prepare a draft project layout avoiding sensitive areas identified in § 187-11B(1) and minimizing total site earth disturbance as much as possible. The ratio of disturbed area to the entire site area and measures taken to minimize earth disturbance shall be included in the ERSAM.

(3) Identify site-specific existing conditions drainage areas, discharge points, recharge areas, and hydrologic soil groups A and B.

(4) Evaluate nonstructural stormwater management alternatives (See Appendix A,[1] Table A-5):

(a) Minimize earth disturbance.

(b) Minimize impervious surfaces.

(c) Break up large impervious surfaces.

[1] Appendix A is included as an attachment to this chapter.

(5) Satisfy water quality objective (§ 187-17).

(6) Satisfy groundwater recharge (infiltration) objective (§ 187-16) and provide for stormwater treatment prior to infiltration.

(7) Satisfy streambank erosion protection objective (§ 187-15).

(8) Determine what management district the site falls into (Appendix D[2]) and conduct a predevelopment runoff analysis.

[2] Appendix D is on file in the Township offices

(9) Prepare final project design to maintain predevelopment drainage areas and discharge points, to minimize earth disturbance and impervious surfaces, and to reduce runoff to the maximum extent possible, the use of surface or point discharges.

(10) Conduct a proposed conditions runoff analysis based on the final design and to meet the release rate and, in turn, the overbank flow and extreme event requirements (§ 187-8).

(11) Manage any remaining runoff through treatment prior to discharge, as part of detention, bioretention, direct discharge or other structural control.

C. When the proposed site development is situated in the fully pervious areas (i.e., fallow land cover conditions), the postdevelopment peak rate of runoff from the property shall not exceed 50% of the peak rate of runoff from predevelopment conditions (i.e., prior to development) for the one-hundred-year-return-period storm. However, the applicant/owner may request an increase in outflow peak rate from 50% of the peak rate of runoff from predevelopment conditions by providing adequate hydrologic and hydraulic analyses of the downstream conveyance facilities that would not result in adverse conditions. (Subject to § 187-9.)

[Amended 12-18-2018 by Ord. No. 2018-11]

D. When the proposed site development is situated in an area where a portion of the existing area is impervious, the postdevelopment peak rate of runoff from the property shall also not exceed 50% of the peak rate of runoff from predevelopment conditions for the one-hundred-year-return-period storm.

E. The peak rates of runoff for the predevelopment and postdevelopment conditions shall be calculated for two-, five-, ten-, twenty-five-, fifty- and one-hundred-year-return-period storms, so as to determine the effects of varying intensities of rainfall in the areas influencing the proposed site development.

§ 187-12 Design criteria for stormwater management facilities.

A. Any storm sewer facility located on or directly discharging to a state highway right-of-way shall be subject to approval by PennDOT.

[Amended 12-18-2018 by Ord. No. 2018-11]

B. Side slopes of the earthen basin embankments shall be no steeper than 3 horizontal :1 vertical. Every effort should be made to blend the storage area into the natural topography of its surroundings.

C. The bed of the stormwater storage area shall slope toward the low flow discharge pipe from all directions at a minimum slope of 1%. All concrete low-flow channels shall have a minimum slope of 0.5%, except where the storage area is designed for infiltration or as a stormwater management BMP that requires flat bottom areas.

[Amended 12-18-2018 by Ord. No. 2018-11]

D. All stormwater storage areas must be located outside of the one-hundred-year floodplain as indicated on the Township floodplain mapping. See Ch. 131, Floodplain Management.

[Amended 12-18-2018 by Ord. No. 2018-11]

E. The minimum top width of the detention basin berm shall be 10 feet. A cutoff trench (key-way) of impervious material shall be provided under all embankments that require fill material. The cutoff trench shall be minimum of eight feet wide, two feet deep and have side slopes of 1:1.

F. Prior to grading in the storage area, the topsoil shall be stripped and stockpiled. Upon completion of grading, the topsoil shall be redistributed over the storage area (minimum six inches thick). The area should then be seeded with a mixture approved by the Township Engineer.

G. All fill material to be utilized in embankment areas shall be selected from the more impervious materials available at the site and shall be compacted to a minimum of 95% of the materials' maximum dry density as determined by a standard proctor test. Where necessary, embankment fill materials shall be keyed into virgin soil.

H. Anti-seep collars shall be provided for all discharge pipes. The collars shall be designed in accordance with the PADEP Erosion and Sediment Pollution Control Program Manual.

[Amended 12-18-2018 by Ord. No. 2018-11]

I. All outlet pipes through the basin berm shall be reinforced concrete pipe having O-ring joints.

J. Energy-dissipating devices (riprap, etc.) shall be placed at all basin and pipe outlets. Sizing of riprap shall be based on the one-hundred-year flow rate and the design methods described in the Pennsylvania Department of Environmental Protection Erosion and Sediment Pollution Control Manual.

[Amended 12-18-2018 by Ord. No. 2018-11]

K. A concrete-lined emergency spillway shall be provided for any stormwater management facility (i.e., detention basin) designed to store runoff and requiring a berm or earthen embankment. A reinforced concrete paver block or masonry spillway is also acceptable. The spillway shall be sized to accommodate the peak flow during a one-hundred-year storm assuming a totally blocked or not functioning discharge pipe. In no case shall the spillway be utilized as a primary discharge structure.

The spillway capacity shall be calculated by the formula Q=3.087 x D3/2 x L, where:
Q D L	= = =	Capacity in cubic feet per second Depth of spillway in feet Length of spillway in feet

The minimum depth of spillway shall be two feet.

L. Any stormwater management facility (i.e., detention basin) designed to store runoff and requiring the use of a berm or earthen embankment shall be designed such that the minimum height of the embankment shall have a minimum of one foot of freeboard above the maximum pool elevation, computed when the facility functions for the 100-year-return-period postdevelopment inflow. Also, the designed emergency spillway with one foot of freeboard shall have the capability to discharge the 100-year-return-period postdevelopment inflow. Should any stormwater management facility require a dam safety permit under PADEP Chapter 105 regulations, the facility shall be designed in accordance with PADEP Chapter 105.

[Amended 12-18-2018 by Ord. No. 2018-11]

M. All stormwater detention/retention facilities and erosion and sedimentation control measures shall be in place and functioning prior to the creation of any impervious surface.

N. Underground storage beds will be given consideration in lieu of conventional storage facilities. All underground storage facilities must be designed to manage emergency conditions.

O. Any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls or stream enclosures), and any work involving wetlands as directed in PADEP Chapter 105 regulations (as amended or replaced from time to time by PADEP), shall be designed in accordance with Chapter 105 and will require a permit from PADEP. Any other drainage conveyance facility that does not fall under Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year-return-period storm with a minimum one foot of freeboard measured below the lowest point along the top of the roadway. Roadway crossings located within designated floodplain areas must be able to convey runoff from a one-hundred-year-return-period storm with a minimum one foot of freeboard measured below the lowest point along the top of roadway. Any facility that constitutes a dam as defined in PADEP Chapter 105 regulations may require a permit under dam safety regulations. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.

P. Any drainage conveyance facility and/or channel that does not fall under Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year-return-period storm. Conveyance facilities to or exiting from stormwater management facilities (i.e., detention basins) shall be designed to convey the design flow to or from that structure. Roadway crossings located within designated floodplain areas must be able to convey runoff from a one-hundred-year design storm. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.

Q. Adequate erosion protection shall be provided along all open channels and at all points of discharge.

R. The design of all stormwater management facilities shall incorporate sound engineering principles and practices. The Township of Falls shall reserve the right to disapprove any design that would result in an adverse hydrologic or hydraulic condition(s) within the Township.

§ 187-13 Design criteria for storm and surface drainage.

A. Storm sewers must be able to convey postdevelopment runoff from a one-hundred-year-return-period storm without surcharging inlets. The one-hundred-year flow rate shall be determined by the Rational Method, Q = CIA, where:

Q C I A

= = = =

Peak runoff rate measured in cubic feet per second Runoff coefficient Average rainfall intensity in inches per hour for a time equal to the time of concentration (Figure A-2, Appendix A)[1] Drainage area in acres

[1] Appendix A is included as an attachment to this chapter.

B. Storm pipe.

(1) The minimum allowable pipe size is 15 inches. Where headroom is restricted, equivalent pipe arches may be used in lieu of circular pipe.

(2) All storm pipes shall be reinforced concrete and shall conform to PennDOT specifications. Smooth lined corrugated polyethylene pipe may be approved for certain locations at the discretion of the Township Engineer.

(3) The design of storm pipes shall be based on the Manning Equations utilizing an "n" factor of 0.013, or as appropriate per the pipe material selected.

[Amended 12-18-2018 by Ord. No. 2018-11]

(4) The minimum slope of any pipe shall be such that a minimum velocity of 2.5 fps is attained, however, the slope shall not be less than 0.5%. The maximum velocity in any storm pipe shall not exceed 12 fps.

(5) All pipes shall be designed to provide at least 18 inches of cover over the bell of the pipe. Storm piping shall not be permitted under buildings.

(6) No pipe run shall exceed 300 linear feet without access to the pipe through an inlet or manhole.

C. Inlets.

(1) Unless otherwise permitted by the Township Engineer, all inlets shall be Type C and Type M inlets. Inlet boxes may be constructed of structural brick or concrete, in accordance with current Pennsylvania Department of Transportation specifications.

(2) Inlets shall be located at street intersections to intercept stormwater before it reaches pedestrian crossings and, unless otherwise stipulated, shall be placed on the tangent portion of curblines immediately adjacent to the P.C.'s or P.T.'s of curb returns, at all low points in sag vertical curves and at other locations where excessive volume and velocity of storm runoff is evident.

(3) Where there is a change in pipe size in the inlet or manhole, the crowns of the pipes shall be at the same elevation. When the pipe size does not change, a minimum drop of two inches shall be provided between the inlet pipe invert elevation and the outlet pipe invert elevation.

(4) The minimum freeboard in all inlets and manholes shall be one foot and shall be verified by inlet/outlet control calculations.

(5) Inlet capacities shall be based on a maximum flow of 4.0 cfs.

(6) Manholes or inlets shall be provided at all changes of direction or slope.

D. Curbed sections.

(1) The maximum encroachment of water on the roadway pavement shall not exceed half of a through traffic lane or one inch less than the depth of curb during a ten-year frequency storm of five-minute duration.

(2) Inlets shall be provided to control the encroachment of water on the pavement.

E. Open channel design.

(1) The minimum freeboard for all channels shall be one foot.

(2) The channel should be designed to conform, wherever possible, to the adjacent ground conditions. This means that it should not be projecting excessively above the surrounding ground or placed excessively below the surrounding ground.

(3) Continuous profiles for each reach of open channel shall be plotted, along with the adjacent average ground and the hydraulic information pertinent to each reach within the system. This information shall include the type of channel lining, the “n” factor, the width of the channel bottom, the side slopes, the water depth, the design capacity and the velocity at the design capacity.

(4) Earthen open channel shall have a maximum side slope of 3:1 and shall have adequate slope protection as required by the Township Engineer.

(5) No open watercourses shall be permitted within the right-of-way of any street.

§ 187-14 Calculation methodology.

Stormwater runoff from all development sites shall be calculated using the soil-cover-complex method as defined in Table III-1.

A. All stormwater runoff calculations including on- and off-site areas shall use a generally accepted calculation technique that is based on the NRCS soil-cover-complex method. Table III-1 summarizes acceptable computation methods. The Township Engineer may approve the use of the rational method to estimate peak discharges from drainage areas that contain less than 10 acres on a case-by-case basis.

B. All calculations consistent with this chapter using the soil-cover-complex method shall use the appropriate design rainfall depths for the various return-period storms presented in Table A-1 in Appendix A[1] of this chapter. If a hydrologic computer model such as PSRM, TR-20, HEC-HMS, or HEC-1 is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours. The NRCS Type II Rainfall Distribution shown in Figure A-1, Appendix A of this chapter shall be used for the rainfall distribution.

[1] Appendix A is included as an attachment to this chapter.

C. For the purposes of predevelopment flow rate determination, undeveloped or disturbed earth shall be considered as "meadow" in good condition, unless the natural ground cover generates a lower curve number or rational "C" value (i.e., "forest"), as listed in Table A-2 or Table A-3 in Appendix A of this document, or unless the applicant obtains approval to proceed pursuant to § 187-18. For areas of prior mining disturbance (i.e., strip mining, mine spoil areas, etc.), the designer must first identify in which mining affect area the site is located, using the Management District Map in Appendix D. The appropriate curve number of rational "C" value from Table A-2 or Table A-3 should then be used. Time of concentration calculations shall be submitted as part of the overall stormwater management design report and shall utilize sheet flow "n" values consistent with the soil cover type selected.

[Amended 12-18-2018 by Ord. No. 2018-11]

D. All calculations using the rational method shall use rainfall intensities consistent with appropriate times-of-concentration for overland flow and return periods from the design storm curves from Pennsylvania Department of Transportation Design Rainfall Curves (1986) (Figures A-2 to A-4). Times-of-concentration for overland flow shall be calculated using the appropriate methodology consistent with the rational method. Times-of-concentration for channel and pipe flow shall be computed using Manning's equation.

E. Runoff curve numbers (CN) for both existing and proposed conditions to be used in the soil-cover-complex method shall be obtained from Table A-2 in Appendix A[2] of this chapter. Runoff curve number calculations shall be submitted as part of the overall stormwater management design report.

[Amended 12-18-2018 by Ord. No. 2018-11]

[2] Appendix A is included as an attachment to this chapter.

F. Runoff coefficient (c) for both existing and proposed conditions for use in the rational method shall be obtained from Table A-3 in Appendix A[3] of this chapter

[3] Appendix A is included as an attachment to this chapter.

G. Where uniform flow is anticipated, the Manning equation shall be used for hydraulic computations and to determine the capacity of open channels, pipes and storm sewers. Values for Manning's roughness coefficient (n) shall be consistent with Table A-4 in Appendix A[4] of this chapter Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this chapter using inlet and/or outlet hydraulic controlling conditions by utilizing appropriate hydraulic analysis techniques or methods.

[4] Appendix A is included as an attachment to this chapter.

H. The design of any stormwater detention basin intended to meet the performance standards of this chapter shall be verified by hydrologic routing of the design storm hydrograph through the basin using the storage-indication method. The Township of Falls may approve the use of any generally accepted full hydrograph approximation technique, which shall use a total runoff volume that is consistent with the volume from a method that produces a full hydrograph.

I. The Township of Falls has the authority to require that computed existing peak runoff rates be reconciled with field observations and conditions. If the designer can substantiate through model calibration using actual physical data that more appropriate runoff curve number and time-of-concentration values should be utilized at a particular site, then appropriate variations may be made upon review and recommendations of the Township Engineer. Calibration shall require detailed data, including water surface elevations, rating curves and rainfall distribution data for the particular site in question.

TABLE III-1 Acceptable Computation Methodologies for Stormwater Management Method
Method	Developed by	Applicability
TR-20 or commercial package based on TR-20	USDA - NRCS	When use of full model is desirable or necessary
Tr-55 or commercial package based on TR-55	USDA - NRCS	Applicable for plans within the model's limitations
HEC - 1	U.S. Army Corps of Engineers	When full model is desirable or necessary
PSRM	Penn State University	When full model is desirable or necessary
Rational Method or commercial package based on (1889) Rational Method	Emil Kuiching	For sites less than 10 acres when approved by the Township Engineer
Other methods	Various	As approved by the Township Engineer

§ 187-15 Erosion and sediment control requirements.

A. Whenever the vegetation and topography are to be disturbed, such activity must be in conformance with Chapter 102, Title 25, Rules and Regulations, Part I, Commonwealth of Pennsylvania, Department of Environmental Protection, Subpart C, Protection of Natural Resources, Article II, Water Resources, Chapter 102, Erosion Control, and in accordance with the Bucks Conservation District standards and specifications.

B. Additional erosion and sediment control design standards and criteria are to be applied where infiltration BMPs are proposed.

(1) Areas proposed for infiltration BMPs shall be protected from sedimentation and compaction during the construction phase so as to maintain their maximum infiltration capacity.

(2) Infiltration BMPs shall not be constructed nor receive runoff until the entire contributory drainage area to the infiltration BMP has received final stabilization.

§ 187-16 Groundwater recharge.

A. The ability to retain and maximize the groundwater recharge capacity of the area being developed is encouraged. Design of the stormwater management facilities shall consider groundwater recharge to compensate for the reduction in infiltration that occurs when the ground surface is paved and roofed over. A detailed geologic evaluation of the project site shall be performed to determine the suitability of recharge facilities. The evaluation shall be performed by a registered professional geologist and/or qualified soil scientist and, at a minimum, address soil permeability, depth to limiting zones, susceptibility to sinkhole formation and subgrade stability. Where pervious pavement is permitted to be used, pavement construction specifications shall be noted on the plan. An on-site infiltration testing shall be witnessed by the Township Engineer.

[Amended 12-18-2018 by Ord. No. 2018-11]

B. Infiltration BMPs shall meet the following minimum requirements: Regulated activities will be required to recharge (infiltrate) a portion of the runoff created by the development as part of an overall stormwater management plan designed for the site. The volume of runoff to be recharged shall be determined from §§ 187-16B(2)(a) or 187-16B(2)(b) depending upon demonstrated site conditions.

(1) Infiltration BMPs intended to receive runoff from developed areas shall be selected based on suitability of soils and site conditions and shall be constructed on soils that have the following characteristics:

(a) A minimum depth of 24 inches between the bottom of the BMP and the limiting zone.

(b) An infiltration and/or percolation rate sufficient to accept the additional stormwater load and drain completely as determined by field tests conducted by the applicant's design professional and witnessed by the Township Engineer.

[Amended 12-18-2018 by Ord. No. 2018-11]

(c) The recharge facility shall be capable of completely infiltrating the recharge volume within four days (96 hours).

(d) Pretreatment shall be provided prior to infiltration when required by the Township Engineer.

(e) The requirements for recharge are applied to all disturbed areas, even if they are ultimately to be an undeveloped land use such as grass, since studies have found that compaction of the soils during disturbance reduces their infiltrative capacity.

(2) The recharge volume (Re) shall be computed by first obtaining the infiltration requirement using methods in either §§ 187-16B(2)(a) or l87-16B(2)(b), then multiplying by the total proposed impervious area. The overall required recharge volume for a site is computed by multiplying total impervious area by the infiltration requirement.

(a) NRCS curve number equation. The following criteria shall apply.

[1] The NRCS runoff shall be utilized to calculate infiltration requirements (P) in inches.

[Equation 187-16.1]
For zero runoff: P = I (Infiltration) = (200 / CN) - 2
Where:
	P = I = infiltration requirement (inches)
	CN = SCS(NRCS) curve number of the existing conditions contributing to the recharge facility

[2] This equation can be displayed graphically in, and the infiltration requirement can also be determined from, Figure 187-16-1.

[3] The recharge volume (Re_v) required would, therefore, be computed as:

[Equation 187-16.2]

Re_v = I * impervious area (SF) / 12 = Cubic Feet (CF)

(b) Annual recharge water budget approach.

[1] It has been determined that infiltrating 0.5 inches of runoff from the impervious areas will aid in maintaining the hydrologic regime of the watershed. If the goals of § 187-16B(2)(a) cannot be achieved, then 0.5 inches of rainfall shall be infiltrated from all impervious areas, up to an existing site conditions curve number of 81. Above a curve number of 81, Equation 187-16.1 or the curve in Figure 187-16.1 should be used to determine the infiltration requirement.

Where: I = 0.5 inches

The recharge volume (Re_v) required would, therefore, be computed as:

Re_v = I x percent impervious area (SF) / 12 = (CF)

[2] The recharge values derived from these methods are the minimum volumes the applicant must control through an infiltration/recharge BMP facility. However, if a site has areas of soils where additional volume of infiltration can be achieved, the applicant is encouraged to recharge as much of the stormwater runoff from the site as possible.

Figure 187-16.1. Infiltration requirement based upon NRCS curve number.

C. The general process for designing the infiltration BMP shall be: A detailed soils evaluation of the project site shall be required to determine the suitability of recharge facilities. The evaluation shall be performed by a qualified applicant and, at a minimum, address soil permeability, depth to limiting zones, and subgrade stability.

[Amended 12-18-2018 by Ord. No. 2018-11]

(1) Analyze hydrologic soil groups as well as natural and man-made features within the watershed to determine general areas of suitability for infiltration practices.

(2) Provide field tests, such as double-ring infiltration tests at the level of the proposed infiltration surface to determine the appropriate hydraulic conductivity rate.

(a) Design the infiltration structure for the required storm volume based on field determined capacity at the level of the proposed infiltration surface.

(b) Where the recharge volume requirement cannot be physically accomplished due to the results of the field soils testing, supporting documentation and justification shall be supplied to the Township with the drainage plan.

(c) If on-lot infiltration structures are proposed by the applicant's design professional, it must be demonstrated to the Township that the soils are conducive to infiltration on the lots identified.

D. Extreme caution shall be exercised where infiltration is proposed in geologically susceptible areas such as strip mine or limestone areas. Extreme caution shall also be exercised where salt or chloride would be a pollutant since soils do little to filter this pollutant and it may contaminate the groundwater. Extreme caution shall be exercised where infiltration is proposed in source water protection areas. The qualified design professional shall evaluate the possibility of groundwater contamination from the proposed infiltration/recharge facility and perform a hydrogeologic justification study if necessary. The infiltration requirement in high quality/exceptional value waters shall be subject to the DEP's Title 25: Chapter 93 antidegradation regulations. The Township may require the installation of an impermeable liner in BMP and/or detention basins where the possibility of groundwater contamination exists. A detailed hydrogeologic investigation may be required by the Township.

E. The Township shall require the applicant to provide safeguards against groundwater contamination for uses which may cause groundwater contamination should there be a mishap or spill.

F. Recharge/infiltration facilities shall be used in conjunction with other innovative or traditional BMPs, stormwater control facilities, and nonstructural stormwater management alternatives.

§ 187-17 Water quality requirements.

A. In addition to the performance standards and design criteria requirements of this article, the applicant shall comply with the following water quality requirements of this article.

(1) Adequate storage and treatment facilities will be provided to capture and treat stormwater runoff from developed or disturbed areas. The recharge volume computed under § 187-16 may be a component of the water quality volume if the applicant chooses to manage both components in a single facility. If the recharge volume is less than the water quality volume, the remaining water quality volume may be captured and treated by methods other than recharge/infiltration BMPs. The required water quality volume (WQv) is the storage capacity needed to capture and to treat a portion of stormwater runoff from the developed areas of the site produced from 90% of the average annual rainfall (P).

(2) To achieve this goal, the following criterion is established. The following calculation formula is to be used to determine the water quality storage volume (WQv) in acre-feet of storage for the Delaware River South watershed:

Equation 187-17.1
WQv	=	[(P)(Rv)(A)]/12
WQv	=	Water quality volume (acre-feet)
P	=	Rainfall amount equal to 90% of events producing this rainfall (inches)
A	=	Area of the project contributing to the water quality BMP (acres)
Rv	=	0.05 + 0.009(I) where I is the percent of the area that is impervious surface (impervious area/A x 100)

The P value for the five PennDOT rainfall regions is shown in Figure A-3 in Appendix A within this plan and as shown in Table A-6 in Appendix A.[1] Since the Delaware River South is in PennDOT Region 5, the P value to be utilized to meet this requirement is 2.04 inches.

[1] Appendix A is included as an attachment to this chapter.

B. In addition to the water quality volume, to minimize the impact of stormwater runoff on downstream streambank erosion, the requirement is to design a BMP to detain the postdevelopment two-year, twenty-four-hour design storm to the predevelopment one-year flow using the SCS Type II distribution. Additionally, provisions shall be made (such as adding a small orifice at the bottom of the outlet structure) so that the postdevelopment one-year storm takes a minimum of 24 hours to drain from the facility from a point where the maximum volume of water from the one-year storm is captured. (i.e., the maximum water surface elevation is achieved in the facility.).

(1) Release of water can begin at the start of the storm (i.e., the invert of the water quality orifice is at the invert of the facility). The design of the facility shall consider and minimize the chances of clogging and sedimentation. Orifices smaller than three inches diameter are not recommended. However, if the design engineer can provide proof that the smaller orifices are protected from clogging by use of trash racks, etc., smaller orifices may be permitted.

(2) In "no detention" areas (District C) only, the objective is not to attenuate the larger storms. This can be accomplished by configuration of the outlet structure not to control the larger storms, or by a bypass or channel to divert only the two-year flood into the basin or divert flows in excess of the two-year storm away from the basin.

C. Design of BMPs used for water quality control shall be in accordance with design specifications outlined in the Pennsylvania Handbook of Best Management Practices for Developing Areas or other applicable manuals. The following factors shall be considered when evaluating the suitability of BMPs used to control water quality at a given development site:

(1) Total contributing drainage area.

(2) Permeability and infiltration rate of the site soils.

(3) Slope and depth to bedrock.

(4) Seasonal high water table.

(5) Proximity to building foundations and wellheads.

(6) Erodibility of soils.

(7) Land availability and configuration of the topography.

(8) Peak discharge and required volume control.

(9) Streambank erosion.

(10) Efficiency of the BMPs to mitigate potential water quality problems.

(11) The volume of runoff that will be effectively treated.

(12) The nature of the pollutant being removed.

(13) Maintenance requirements.

(14) Creation/protection of aquatic and wildlife habitat.

(15) Recreational value.

(16) Enhancement of aesthetic and property value.

D. To accomplish the above, the applicant shall submit original and innovative designs to the Township for review and approval. Such designs may achieve the water quality objectives through a combination of BMPs (best management practices).

E. No regulated earth disturbance activities within the Township shall commence until approval by the Township of a plan which demonstrates compliance with postconstruction state water quality requirements.

F. The BMPs shall be designed, implemented, and maintained to meet state water quality requirements and any other more stringent requirements as determined by the Township.

G. To control postconstruction stormwater impacts from regulated earth disturbance activities, state water quality requirements can be met by BMPs, including site design, which provide for replication of preconstruction stormwater infiltration and runoff conditions so that postconstruction stormwater discharges do not degrade the physical, chemical, or biological characteristics of the receiving waters. As described in the DEP Comprehensive Stormwater Management Policy (No. 392-0300-002, September 28, 2002), this may be achieved by the following:

(1) Infiltration: replication of preconstruction stormwater infiltration conditions;

(2) Treatment: use of water quality treatment BMPs to ensure filtering out of the chemical and physical pollutants from the stormwater runoff; and

(3) Streambank and streambed protection: management of volume and rate of postconstruction stormwater discharges to prevent physical degradation of receiving waters (e.g., from scouring).

H. Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office must be provided to the Township.

§ 187-18 Redevelopment activities.

[Amended 12-18-2018 by Ord. No. 2018-11]

Stormwater management designs proceeding pursuant to this section will be considered for sites that have adequate stormwater management facilities in place for the existing improvements, as shown by calculations, and are currently developed to the extent that retrofitting to meet the full requirements of this chapter is not feasible. Pursuant to this section, the entire site must be considered when analyzing pre- and post-development conditions. Other sites will be considered pursuant to this section where the nature of the proposed development and conditions of the site require limited stormwater management improvements as determined by the Township Engineer.

A. To the extent that site characteristics allow, and with the approval of the Township Engineer, proposed redevelopment project designs shall include practices that are designed to result in a net reduction in impervious area by at least 20%, where feasible. Where site constraints prevent impervious area reduction or the implementation of stormwater management practices, practical alternatives may be used to result in an improvement in water quality. The following apply to all redevelopment projects:

(1) All redevelopment projects shall, where possible, reduce existing site impervious area by at least 20%. Where site conditions prevent the reduction of impervious area, stormwater management practices shall be implemented to provide measures that produce an equivalent reduction in impervious area of at least 20%.

(2) The redevelopment activities, with the approval of the Township Engineer, may allow practical alternatives. Such practical alternatives may include, but not be limited to:

(a) Fees paid in accordance with the schedule on file with the Township Secretary;

(b) Off-site BMP implementation for a drainage area comparable to that of the project;

(c) Watershed or stream restoration;

(d) Retrofitting an existing stormwater facility or BMP; or

(e) Other practices approved by the Township Engineer.

(3) The water quality volume (runoff volume generated from a two-year-return-period storm event) to be controlled for redevelopment projects shall reflect a twenty-percent impervious surface area reduction.

B. However, in cases where redevelopment is requested by a developer and the known existence of geologic formations is contributory for transferring stormwater on a vertical and horizontal plane, this would be an acceptable alternative as an underground retention basin where positive water quality controls could be achieved coupled with a more positive stormwater management consideration.

C. Through this direction, the impervious areas may be reduced by the following definition: If the developer submits a request for any reduction in impervious area he will be required to substantiate his position by submitting engineering calculations for the reduction in the twenty-percent minimum of nonpercolating surfaces.