A.
Applicants proposing regulated activities in the Township that do not fall under the exemption criteria shown in § 157-6 shall submit a stormwater management (SWM) site plan consistent with the requirements of this chapter to the municipality for review. The SWM criteria of this chapter shall apply to the total proposed development even if development is to take place in stages. Preparation and implementation of an approved SWM site plan are required. No regulated activities shall commence until the municipality issues written approval of an SWM site plan, which demonstrates compliance with the requirements of this chapter. The applicant shall be responsible for the control of surface runoff entering the development or subdivision originating from an upstream drainage area. The future, fully developed use of undeveloped areas upstream as shown on the approved Township Comprehensive Plan shall be taken into account in the calculation of pipe sizes for storm sewer system designs. Calculations shall be provided that include the off-site runoff entering the development site, as well as calculations indicating the capacity of the receiving storm sewer or watercourse downstream of the proposed development for the one-hundred-year storm.
B.
SWM site plans approved by the Township, in accordance with Article IV, shall be on site throughout the duration of the regulated activity.
C.
The municipality may, after consultation with the Department of Environmental Protection (PADEP), approve measures for meeting the state water quality requirements other than those in this chapter, provided that they meet the minimum requirements of, and do not conflict with, state law, including but not limited to the Clean Streams Law.[1]
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
D.
For all regulated earth-disturbance activities, erosion and sediment (E&S) control best management practices (BMPs) shall be designed, implemented, operated, and maintained during construction to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code and the Clean Streams Law. Various BMPs and their design standards are listed in the Erosion and Sediment Pollution Control Program Manual; No. 363-2134-008 (April 15, 2000), as amended and updated.
E.
For all regulated activities, implementation of the volume controls in § 157-12 of this chapter is required.
F.
Impervious areas.
(1)
The measurement of impervious areas shall include all of the impervious areas in the total proposed development even if development is to take place in stages.
(2)
For development taking place in stages, the entire development plan must be used in determining conformance with this chapter.
(3)
For projects that add impervious area to a parcel, the total impervious area on the parcel is subject to the requirements of this chapter. With exception of residential projects where impervious added since the adoption of this chapter will be subject to the requirements of this chapter.
[Amended 10-17-2022 by Ord. No. 2022-05]
G.
Stormwater flows onto adjacent property shall not be created, increased, decreased, relocated, or otherwise altered without written notification of the adjacent property owner(s) by the developer. Such stormwater flows shall be subject to the requirements of this chapter. Approval of the owners shall be obtained in writing and a copy filed with the Township. Approval of plans by Warwick Township does not authorize or sanction drainage affecting adjoining properties.
H.
All regulated activities shall include such measures as necessary to:
(1)
Protect health, safety, and property;
(2)
Meet the water quality goals of this chapter by implementing measures to:
(a)
Minimize disturbance to floodplains, wetlands, and wooded areas.
(b)
Create, maintain, repair or extend riparian buffers.
(c)
Avoid erosive flow conditions in natural flow pathways.
(d)
Minimize thermal impacts to waters of this commonwealth.
(e)
Disconnect impervious surfaces [i.e., disconnected impervious areas (DIAs)] by directing runoff to pervious areas wherever possible. See Appendix F for detail on DIAs.[2]
[2]
Editor's Note: Appendix F is included at the end of this chapter.
(f)
Provide corrective measures as deemed appropriate by the Board of Supervisors to alleviate any off-site drainage problem affected by the regulated activity. The costs for such measures will be borne entirely by the developer.
(3)
To the maximum extent practicable, incorporate the techniques for low-impact development practices (e.g., protecting existing trees, reducing area of impervious surface, cluster development, and protecting open space) described in the Pennsylvania Stormwater Best Management Practices Manual, Pennsylvania Department of Environmental Protection (PADEP) No. 363-0300-002 (2006). See Appendix E for a summary description.[3]
[3]
Editor's Note: Appendix E is included at the end of this chapter.
I.
Infiltration BMPs should be spread out, made as shallow as practicable, and located to maximize the use of natural on-site infiltration features while still meeting the other requirements of this chapter. Infiltration testing must be completed for all regulated activities that propose infiltration BMPs.
[Amended 10-17-2022 by Ord. No. 2022-05]
J.
The design of all facilities over karst shall include an evaluation of measures to minimize the risk of adverse effects.
K.
Storage facilities should completely drain both the volume control and rate control capacities over a period of time not less than 24 and not more than 72 hours from the end of the design storm.
L.
The design storm volumes to be used in the analysis of peak rates of discharge should be obtained from the Precipitation-Frequency Atlas of the United States, Atlas 14, Volume 2, Version 3.0, United States Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Weather Service, Hydrometeorological Design Studies Center, Silver Spring, Maryland. NOAA's Atlas 14 can be accessed at http://hdsc.nws.noaa.gov/hdsc/pfds/.
M.
For all regulated activities, SWM BMPs shall be designed, implemented, operated, and maintained to meet the purposes and requirements of this chapter and to meet all requirements under Title 25 of the Pennsylvania Code, the Clean Streams Law, and the Stormwater Management Act.[4]
[4]
Editor's Note: See 35 P.S. § 691.1 et seq. and 32 P. S. § 680.1 et seq.
N.
A highway occupancy permit is required from the Pennsylvania Department of Transportation if water is to be carried in any way onto the state highway right-of-way or into the state highway storm drainage system.
Approvals issued and actions taken under this chapter do not relieve the applicant of the responsibility to secure required permits or approvals for activities regulated by any other code, law, regulation or ordinance.
Volume controls will mitigate increased runoff impacts, protect stream channel morphology, maintain groundwater recharge, and contribute to water quality improvements. Stormwater runoff volume control methods are based on the net change in runoff volume for the two-year storm event. Volume controls shall be implemented using the Design Storm Method in Subsection A or the Simplified Method in Subsection B below. For regulated activities equal to or less than one acre, this chapter establishes no preference for either methodology; therefore, the applicant may select either methodology on the basis of economic considerations, the intrinsic limitations of the procedures associated with each methodology, and other factors. All regulated activities greater than one acre must use the Design Storm Method.
A.
Design Storm Method (any regulated activity). This method requires detailed modeling based on site conditions. For modeling assumptions, refer to § 157-14A.
(1)
Post-development total runoff should not be increased from predevelopment total runoff for all storms equal to or less than the two-year, twenty-four-hour-duration precipitation.
(2)
The following applies in order to estimate the increased volume of runoff for the two-year, twenty-four-hour-duration precipitation event: To calculate the runoff volume (cubic feet) for existing site conditions (predevelopment) and for the proposed developed site conditions (post-development), it is recommended to use the Soil Cover Complex Method as shown as follows. The calculated volume shall be either reused, evapotranspired, or infiltrated through structural or nonstructural means. Other means of calculating the runoff volume may be used if approved in advance by the Township Engineer.
| Soil Cover Complex Method | ||||
| Step 1: Runoff (in) = Q = (P - 0.2S)2/(P + 0.8S) | ||||
| Where: | ||||
| P | = | 2-year rainfall (in) | ||
| S | = | (1,000/CN) -10 | ||
| Step 2: Runoff Volume (cubic feet) = Q x Area x 1/12 | ||||
| Where: | ||||
| Q | = | Runoff (in) (from Step 1) | ||
| Area | = | SWM area (square feet), i.e., the square-foot area of the regulated activity | ||
| Step 3: Required Volume = Post-development Runoff Volume – Predevelopment Runoff Volume | ||||
| Once runoff volume is calculated for the site under both existing and proposed developed conditions, the difference between the two site conditions is the increase in runoff volume from predevelopment conditions to post-development conditions for the two-year, twenty-four-hour precipitation event. | ||||
| The calculated volume shall be captured, reused, evapotranspired, or infiltrated through nonstructural or structural means. | ||||
B.
Simplified Method (regulated activities less than or equal to one acre).
(1)
Stormwater facilities shall capture the runoff volume from at least the first two inches of runoff from all new impervious surfaces.
| Volume (cubic feet) = (2-inch runoff/12 inches) * Impervious Surface (square feet) |
(2)
At least the first inch of runoff volume from the new impervious surfaces shall be permanently removed from the runoff flow, i.e., it shall not be released into the surface waters of the commonwealth. The calculated volume shall be either reused, evapotranspired or infiltrated through structural or nonstructural means.
| Volume (cubic feet) = (1-inch runoff/12 inches) * Impervious Surface (square feet) |
(3)
Infiltration facilities should be designed to accommodate the first 0.5 inch of the permanently removed runoff.
(4)
No more than one inch of runoff volume from impervious surfaces shall be released from the site. The release time must be over 24 to 72 hours.
C.
Stormwater control measures. The applicant must demonstrate how the required volume is controlled through stormwater best management practices (BMPs), which shall provide the means necessary to capture, reuse, evaporate, transpire or infiltrate the total runoff volume.
(1)
If natural resources exist on the site, the plan shall indicate the total acreage of protected area where no disturbance is proposed. The acreage of the protected area should be subtracted from the total site area and not included in the stormwater management site area acreage used in determining the volume controls.
| Stormwater Management Site Area = Total Site Area (for both pre- and post-development conditions) – Protected Area | |
|---|---|
| Natural resource areas should be calculated based upon the municipality's own natural resource protection ordinance. If no ordinance exists, see Table B-2 in Appendix B[1] for guidance to assess the total protected area. For additional reference, see Chapter 5, Section 5.4.1, of the Pennsylvania BMP Manual. |
[1]
Editor's Note: Appendix B is included at the end of this chapter.
(2)
Calculate the volume controls provided through nonstructural BMPs. Table B-5 in Appendix B is recommended as guidance.[2]
[2]
Editor's Note: Appendix B is included at the end of this chapter.
(3)
Volume controls provided through nonstructural BMPs should be subtracted from the required volume to determine the necessary structural BMPs.
| Required Volume Control (feet3) | – | Nonstructural Volume Control (feet3) | = | Structural Volume Requirement (feet3) |
(4)
Calculate the volume controls provided through structural BMPs. Table B-6 in Appendix B is recommended as guidance.[3] See the Pennsylvania BMP Manual, Chapter 6, for a description of the BMPs.
[3]
Editor's Note: Appendix B is included at the end of this chapter.
(5)
Infiltration BMPs intended to receive runoff from developed areas shall be selected based on the suitability of soils and site conditions (see Table B-6 in Appendix B for a list of Infiltration BMPs[4]). Infiltration BMPs shall be constructed on soils that have the following characteristics:
(a)
A minimum soil depth of 24 inches between the bottom of the infiltration BMPs and the top of bedrock or seasonally high water table.
(b)
An infiltration rate sufficient to accept the additional stormwater load and dewater completely as determined by field tests. A minimum of 0.2 inch per hour should be utilized, and for acceptable rates a safety factor of 50% should be applied for design purposes (e.g., for soil which measured 0.4 inch per hour, the BMP design should use 0.2 inch per hour to ensure safe infiltration rates after construction).
(c)
All open-air infiltration facilities shall be designed to completely infiltrate runoff volume within three days (72 hours) from the start of the design storm. Subsurface systems shall be designed to infiltrate the stored volume in 48 hours or less with a minimum infiltration rate and percolation rate of greater than 0.2 inch per hour.
[4]
Editor's Note: Appendix B is included at the end of this chapter.
(6)
Soils. A soils evaluation of the project site shall be required to determine the suitability of infiltration facilities. All regulated activities are required to perform a detailed soils evaluation by a qualified design professional which, at a minimum, addresses soil permeability, depth to bedrock, and subgrade stability. The general process for designing the infiltration BMP shall be:
(a)
Analyze hydrologic soil groups as well as natural and man-made features within the site to determine general areas of suitability for infiltration practices. In areas where development on fill material is under consideration, conduct geotechnical investigations of subgrade stability; infiltration may not be ruled out without conducting these tests.
(b)
Provide field tests such as double-ring infiltrometer or hydraulic conductivity tests (at the level of the proposed infiltration surface) to determine the appropriate hydraulic conductivity rate. Percolation tests are not recommended for design purposes. The Township Engineer shall observe all field testing of soils.
(c)
Design the infiltration structure based on field-determined capacity at the level of the proposed infiltration surface and based on the safety factor of 50%.
(d)
If on-lot infiltration structures are proposed, it must be demonstrated to the municipality that the soils are conducive to infiltrate on the lots identified.
(e)
An impermeable liner will be required in detention basins where the possibility of groundwater contamination exists. A detailed hydrogeologic investigation may be required by the municipality.
Peak rate controls for large storms, up to the one-hundred-year event, are essential in order to protect against immediate downstream erosion and flooding. The following peak rate controls have been determined through hydrologic modeling of the Neshaminy Creek Watershed.
A.
Standards for managing runoff from each subarea in the Neshaminy Creek Watershed for the two-, five-, ten-, twenty-five-, fifty-, and one-hundred-year design storms are shown in Table 157-13. Development sites located in each of the management districts must control the proposed development conditions' runoff rates to existing conditions' runoff rates for the design storms in accordance with Table 157-13.
| Table 157-13 | |||
|---|---|---|---|
| Peak Rate Runoff Control Standards by Stormwater Management Districts in the Neshaminy Creek Watershed (includes Little Neshaminy Creek) | |||
| District | Design Storm Post-Development (Proposed Conditions) | Design Storm Predevelopment (Existing Conditions) | |
| A | 2-year | 1-year | |
| 5-year | 5-year | ||
| 10-year | 10-year | ||
| 25-year | 25-year | ||
| 50-year | 50-year | ||
| 100-year | 100-year | ||
| B | 2-year | 1-year | |
| 5-year | 2-year | ||
| 10-year | 5-year | ||
| 25-year | 10-year | ||
| 50-year | 25-year | ||
| 100-year | 50-year | ||
| C | 2-year | 2-year | |
| 5-year | 5-year | ||
| 10-year | 10-year | ||
| 25-year | 25-year | ||
| 50-year | 50-year | ||
| 100-year | 100-year | ||
B.
General. Proposed conditions' rates of runoff from any regulated activity shall not exceed the peak release rates of runoff from existing conditions for the design storms specified on the Stormwater Management District Watershed Map (Appendix D)[1] and in this section of this chapter.
[1]
Editor's Note: Appendix D is included at the end of this chapter; the Management District Maps are on file in the Township offices.
C.
District boundaries. The boundaries of the stormwater management districts are shown on official maps and are available for inspection at the Municipal Office and County Planning Offices. A copy of the map at a reduced scale, and four other maps with zoomed-in extents, are included in Appendix D.[2] 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 SWM site plan.
[2]
Editor's Note: Appendix D is included at the end of this chapter; the Management District Maps are on file in the Township offices.
D.
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 meet the management district criteria for the district in which the discharge is located.
E.
Off-site areas. When calculating the allowable peak runoff rates, developers do not have to account for runoff draining into the subject development site from an off-site area. On-site drainage facilities shall be designed to safely convey off-site flows through the development site.
F.
Site areas. The stormwater management site area is the only area subject to the management district criteria. Nonimpacted areas or nonregulated activities bypassing the stormwater management facilities would not be subject to the management district criteria.
G.
Alternate criteria for redevelopment sites. For redevelopment sites, one of the following minimum design parameters shall be accomplished, whichever is most appropriate for the given site conditions, as determined by the Township:
A.
The following criteria shall be used for runoff calculations:
(1)
For development sites not considered redevelopment, the ground cover used to determine the existing conditions' runoff volume and flow rate shall be as follows:
(a)
Wooded sites shall use a ground cover of "woods in good condition."
(b)
The undeveloped portion of the site, including agriculture, bare earth, and fallow ground, shall be considered as "meadow in good condition," unless the natural ground cover generates a lower curve number (CN) or Rational "C" value (i.e., woods) as listed in Table B-4 or B-7 in Appendix B of this chapter.[1]
[1]
Editor's Note: Appendix B is included at the end of this chapter.
(2)
For development and redevelopment sites, the ground cover used to determine the existing conditions' runoff volume and flow rate for the developed portion of the site shall be based upon actual land cover conditions. If the developed site contains impervious surfaces, 20% of the impervious surface area shall be considered “meadow” in the model for existing conditions.
B.
Stormwater runoff peak discharges from all development sites with a drainage area equal to or greater than 25 acres shall be calculated using a generally accepted calculation technique that is based on the NRCS Soil Cover Complex Method. Table 157-14 summarizes acceptable computation methods. The method selected by the design professional shall be based on the individual limitations and suitability of each method for a particular site. The municipality may allow the use of the Rational Method (Q=CIA) to estimate peak discharges from drainage areas that contain less than 25 acres.
| Q | = | Peak flow rate, in cubic feet per second (cfs) | |
| C | = | Runoff coefficient, dependent on land use/cover | |
| I | = | Design rainfall intensity, in inches per hour | |
| A | = | Drainage area, in acres |
C.
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 according to the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 rain data corresponding to the Doylestown rain gage and the SCS Type II rainfall curve from NOAA. This data may be directly retrieved from the NOAA Atlas 14 website: hdsc.nws.noaa.gov/hdsc/pfds/orb/pa_pfds.html. If a hydrologic computer model such as PSRM or HEC-1/HEC-HMS is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours.
[Amended 10-17-2022 by Ord. No. 2022-05]
| Table 157-14 Acceptable Computation Methodologies for Stormwater Management Plans | ||
|---|---|---|
| Method | Method Developed by | Applicability |
| TR-20 (or commercial computer package based on TR-20) | USDA NRCS | Applicable where use of full hydrology computer model is desirable or necessary |
| TR-55 (or commercial computer package based on TR-55) | USDA NRCS | Applicable for land development plans within limitations described in TR-55 |
| HEC-1/HEC-HMS | U.S. Army Corps of Engineers | Applicable where use of full hydrologic computer model is desirable or necessary |
| PSRM | Penn State University | Applicable where use of a hydrologic computer model is desirable or necessary; simpler than TR-20 or HEC-1 |
| Rational Method (or commercial computer package based on Rational Method) | Emil Kuichling (1889) | For sites less than 200 acres or as approved by the municipality and/or Municipal Engineer |
| Other methods | Varies | Other computation methodologies approved by the municipality and/or Municipal Engineer |
D.
All calculations using the Rational Method shall use rainfall intensities consistent with appropriate times-of-concentration for overland flow and return periods from NOAA Atlas 14, Volume 2, Version 2.1. Times-of-concentration for overland flow shall be calculated using the methodology presented in Chapter 3 of Urban Hydrology for Small Watersheds, NRCS, TR-55 (as amended or replaced from time to time by NRCS). 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 based on Table B-4 in Appendix B.[2]
[2]
Editor's Note: Appendix B is included at the end of this chapter.
F.
Runoff coefficients (C) for both existing and proposed conditions for use in the Rational Method shall be consistent with Table B-7 in Appendix B.
G.
Runoff from proposed sites graded to the subsoil will not have the same runoff conditions as the site under existing conditions because of soil compaction, even after topsoiling or seeding. The proposed condition "CN" or "C" shall increase by 5% to better reflect proposed soil conditions.
H.
The Manning Equation is preferred for one-dimensional, gradually varied, open-channel flow. In other cases, appropriate, applicable methods should be applied; however, early coordination with the municipality is necessary.
I.
Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this chapter using the generally accepted hydraulic analysis technique or method of the municipality.
J.
The design of any stormwater detention facilities intended to meet the performance standards of this chapter shall be verified by routing the design storm hydrograph through these facilities using the Storage-Indication Method. For drainage areas greater than 200 acres in size, the design storm hydrograph shall be computed using a calculation method that produces a full hydrograph. The municipality may approve the use of any generally accepted full-hydrograph approximation technique that shall use a total runoff volume that is consistent with the volume from a method that produces a full hydrograph.
A.
Hot spots.
(1)
The use of infiltration BMPs is prohibited on hot spot land use areas. Examples of hot spots are listed in Appendix G.[1]
[1]
Editor's Note: Appendix G is included at the end of this chapter.
(2)
Stormwater runoff from hot spot land uses shall be pretreated. In no case may the same BMP be employed consecutively to meet this requirement. Guidance regarding acceptable methods of pretreatment is located in Appendix G.
A.
General provisions.
(1)
A storm sewer system and all appurtenances shall be required to be constructed by the applicant in any area from which the surface or subsurface drainage could impair public safety or cause physical damage to adjacent lands or public property. The system(s) shall be designed to collect water at any point where three cubic feet per second is accumulated, at the bottom of all vertical grades and immediately upgrade from all street intersections. The system(s) shall discharge to the nearest practical natural drainage channel or storm system.
(2)
When required, storm drains and appurtenances shall be constructed by the developer to take surface water from the bottom of vertical grades, to lead water away from springs, and to avoid excessive use of cross-cutters at street intersections and elsewhere.
(a)
Open watercourses are encouraged where they exist naturally and where, in the opinion of the Township Engineer, they will not interfere with public convenience or safety but in fact will provide comparable or superior drainage. Where necessary, stream corridor improvements, including rock stabilization and gabions, shall be performed. Naturalized or "bioengineering" methods of stabilization are preferred.
(b)
Design of storm drainage facilities shall be prepared in accordance with accepted engineering practices, subject to approval by the Township Engineer.
(c)
Any necessary corrective measures deemed appropriate by the Board of Supervisors to alleviate any off-site drainage problem affected by the subdivision or land development must be undertaken by the developer. The costs for such measures will be borne entirely by the developer.
(d)
The developer may be required to participate in off-site storm drainage improvements in the watershed within which the proposed development is located. The specific off-site drainage improvements required shall be those specified by the Township Board of Supervisors.
(3)
Storm sewer or drainage easements:
(a)
Easements shall be a minimum of 20 feet in width and shall be provided in undedicated land to accommodate required storm sewer facilities and drainage swales. Such easements shall be offered for dedication to Warwick Township and shall be provided where storm sewers, drainage swales, culverts, or other structures traverse, enter or discharge onto private property. On private property, the owner shall maintain ground cover and landscaping within the easement. The Township shall not maintain and/or repair any improvements within that easement unless stormwater runoff from public roads or public lands crosses through the easement. If stormwater runoff from public roads or public lands crosses through the easement, the Township shall, upon satisfactory installation of improvements as specified in a land development agreement with Warwick Township, maintain and repair only the structural improvements within the easement, if any, such as piping, inlets, stormwater manholes, headwalls/endwalls, and energy-dissipation structures or facilities. Warwick Township will not be responsible for any other repair/maintenance, vermin control, removal of obstructions from drainage swales, removal of accumulated sediment or vegetation from drainage swales, removal of litter or garbage, repair of erosion, and restoration of vegetation/ground cover.
(b)
The record plan and development approved agreement for the approved land development shall define easement ownership, maintenance responsibilities, and access. Specifically, the record plan shall contain a provision permitting access to such easement(s), at any reasonable time, for inspection and/or emergency repair/maintenance, by Warwick Township or its designee, of all facilities deemed critical to public welfare. In the event that the lot owner or homeowners' association fails to honor their maintenance responsibilities set forth herein, in any manner, Warwick Township shall have the right of entry upon and within the area of the easement to undertake any required corrective or maintenance effort. The total cost of such, including administrative, engineering, and legal costs for enforcement, may be imposed upon the responsible party as determined by Warwick Township. Failure to remedy all associated costs described above may be subject of the imposition of a lien by the Township against the owner(s) in question, in the same manner as the Township might otherwise be empowered by law to assess or impose a lien against a property for municipal improvements. The record plan size shall meet the requirements for recording at the office of the Recorder of Deeds of Bucks County.
B.
Design criteria.
(1)
Open channels and swales.
(a)
Open channels should have a triangular or trapezoidal cross section in compliance with accepted engineering practices.
(b)
Existing stream channels should be maintained in their natural state. Only under unusual circumstances will it be permitted to line, straighten, or relocate an existing stream, with approval of the Department of Environmental Protection (DEP) and the Bucks County Conservation District.
(c)
Permissible channel velocities, slopes, and cover shall be in accordance with the Natural Resources Conservation Service Engineering Field Manual, Chapter 7, Grassed Waterways and Outlets.
(d)
Acceptable energy-dissipation devices shall be installed to bring discharge velocities down to limits specified in the DEP Erosion and Sediment Pollution Control Program Manual, latest edition.
(e)
Riprap and/or gabions may be required by the Township Engineer where erosion potential is great.
(f)
Swales and open channels shall be designed to convey the one-hundred-year storm event. Capacity shall be determined by Manning's Equation.
(g)
Curbed sections. The maximum encroachment of runoff on the roadway pavement shall not exceed 1/2 of the traveled lane during a one-hundred-year design storm of five minute's duration. Inlets shall be provided to control the encroachment of water on the traveled lane.
(h)
On-lot drainage swales shall be designed to provide positive conveyance of surface water from the individual lot. Each swale lot shall convey stormwater from the lot to a storm sewer system, street, open space area, or stormwater management easement without crossing or combining with stormwater from more than the adjacent lot.
(i)
Whenever swales are necessary, they shall be centered on a property line and at a location approved by the Township Engineer.
(j)
Vegetated swales proposed to satisfy water quality requirements shall be designed to be consistent with the following:
[1]
The maximum flow velocity in the grass swale for runoff from the water quality design storm (one-year, twenty-four-hour) shall not exceed 1.5 feet per second (fps).
[2]
The average slope of the swale shall not exceed 4%, unless the swale is designed and protected to provide adequate erosion control.
(k)
The maximum velocity of flow, as determined by Manning's Equation, shall not exceed the allowable velocities as shown in the following table for the specific type of material, unless otherwise approved by the Township Engineer and the Bucks County Conservation District or as otherwise updated in the Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conservation publication, Erosion and Sediment Control Program Manual, latest revision.
| Material | Allowable Velocity [feet per second (fps)] | ||
|---|---|---|---|
| Well-established grass on good soil: | |||
| Short, pliant, bladed grass | 4.0 to 5.0 | ||
| Bunch grass, soil exposed | 2.0 to 3.0 | ||
| Stiff-stemmed grass | 3.0 to 4.0 | ||
| Earth without vegetation: | |||
| Fine sand or silt | 1.0 | ||
| Ordinary firm loam | 2.0 to 3.0 | ||
| Stiff clay | 3.0 to 5.0 | ||
| Clay and gravel | 4.0 to 5.0 | ||
| Coarse gravel | 4.0 to 5.0 | ||
| Soft shale | 5.0 to 6.0 | ||
| Shoulders: | |||
| Earth (as defined above) | |||
| Stabilized | 6.0 | ||
| Paved | 10.0 to 15.0 | ||
(2)
Storm sewer design.
(a)
Design flow rate.
[1]
The storm drain collection system shall be designed to carry a one-hundred-year peak flow rate. In addition, the interior street and storm drain system should be designed in such a manner to control runoff in excess of the one-hundred-year peak inflow rate by directing the excess runoff through the use of proper grading techniques and permanent stormwater runoff control structures into drainage channels or detention basins. The peak flow rate shall be determined by the Rational Method formula:
| Q = CIA | ||||
| Where: | ||||
| Q | = | Peak runoff rate, measured in cubic feet per second (cfs) | ||
| C | = | Runoff coefficient | ||
| I | = | Intensity (average rainfall intensity, in inches per hour) | ||
| A | = | Area (drainage area, in acres) | ||
[2]
Appropriate values for the rainfall intensity can be found in the Pennsylvania Department of Transportation Design Manual, Part 2. Appropriate values for the runoff coefficient shall be as presented in Table B-7 in Appendix B.[1]
[1]
Editor's Note: Appendix B is included at the end of this chapter.
[3]
More-specific runoff coefficients, as stated in Pennsylvania Department of Transportation Deign Manual, Part 2, or as stated in the Pennsylvania Department of Environmental Protection publication, Recommended Hydrologic Procedures for Computing Urban Runoff from Small Watersheds in Pennsylvania, may be used upon consultation with the Township Engineer.
(b)
Consideration shall be given to future land use changes in the drainage area in selecting the "C" coefficient. For drainage areas containing several different types of ground cover, a weighted value of "C" shall be used. In no case shall a weighted value of "C" be less than 0.45 for an area to be changed from its natural state.
(c)
In determining the peak flow rate to individual storm sewer inlets (or other collection structures), the time-of-concentration method shall be used for inlet drainage areas in excess of 1.25 acres, unless otherwise specified by the Township Engineer, and a five-minute time of concentration shall be used for all other drainage areas, unless otherwise approved by the Township Engineer.
(d)
In determining the required design flow rate through a storm sewer piping system, a five-minute time of concentration shall be used if the five-minute time of concentration does not result in a maximum expected discharge that exceeds the capacity of a thirty-inch-diameter pipe (or equivalent flow area of 4.9 square feet).
(e)
In determining the required design flow rate through a storm sewer piping system, if a five-minute time of concentration results in a pipe size exceeding a thirty-inch-diameter pipe (or equivalent flow area of 4.9 square feet), the calculated time of concentration shall be used in determining storm duration.
(f)
All pipes shall, at a minimum, provide required carrying capacity as determined by the United States Department of Commerce, Hydraulic Design Series No. 5, Hydraulic Design of Highway Culverts. Where pressure flow is anticipated in storm sewer pipes (non-open-channel flow), the designer shall be required to calculate the elevation of the hydraulic grade line through the storm sewer system.
(g)
All pipe and structures utilized for the storm sewer system shall conform to the design standards of Pennsylvania Department of Transportation (PennDOT) Publications 408 and 72M (Road Construction Standards), as amended. All inlet grates shall be "bicycle safe" structural steel.
(h)
Pipe requirements.
[1]
The minimum diameter of all storm sewer piping shall be 18 inches (or other with an equivalent flow area of 1.76 square feet), including detention basin barrel pipes. Piping shall be laid on a four-inch-minimum bed of PennDOT Type 2A coarse aggregate and shall be designed with a slope not less than 0.50%. All storm drains located within the right-of-way of a street shall be protected by a cover of at least 18 inches. No pipe shall exceed a slope that will permit full-flow velocity in excess of 15 feet per second. Cover over HDPE and corrugated metal pipe (CMP) shall be as per manufacturer's specifications, but not less than 12 inches.
[2]
A. Storm sewer piping shall be reinforced concrete pipe (RCP); however, in areas that are not to be dedicated for public use or not within a public or private right-of-way; smooth-bore, high-density corrugated polyethylene (HDPE) or aluminum corrugated pipe may be permitted as approved by the Township Engineer. All outlet pipes through detention basin and retention basin berms shall be reinforced concrete pipe with watertight O-ring joints (O-ring RCP).
[Amended 10-17-2022 by Ord. No. 2022-05]
[3]
Stormwater runoff shall not be permitted to surcharge from the storm sewer structures for the required design storm. Hydraulic grade line calculations should be submitted to confirm compliance.
[4]
Curved pipe sections shall not be permitted. This includes horizontal deflections exceeding 1°.
(3)
Manholes.
(a)
Storm sewer manholes shall be spaced as necessitated by the proposed piping alignment; however, in no case shall manhole spacing exceed 450 feet. Manholes shall be located at all abrupt changes of grade, at all locations where a transition in pipe sizing is required and at all points of convergence of two or more storm sewer mains, where inlets are not warranted.
(b)
Manhole castings and covers shall conform to the requirements of Pennsylvania Department of Transportation Publications 72M and 408, as amended. Manhole covers shall have the word "STORM" cast in two-inch-high letters on the top of the cover.
(4)
Inlets.
(a)
Storm sewer inlet spacing shall not exceed 250 feet, except between inlets connected by pipe with a diameter of 48 inches or greater, where spacing shall then not exceed 450 feet. Inlets shall be located at all abrupt changes of grade, at all locations where a transition in pipe sizing is required and at all points of convergence of two or more storm sewer mains.
(b)
At street intersections, inlets shall be placed in the tangent and not in the curved portion of the curbing. The gutter adjacent to and immediately upgrade from the inlet shall be so warped as to direct the water into the inlet. Inlets shall be required on the upslope side of all approaches to an intersection when the design flow rate is in excess of 1.0 cfs.
(c)
The crowns of all pipes tying into an inlet or manhole shall be set at equal elevations when pipe inverts are within 12 inches (vertical separation) of each other. A minimum of two inches shall be provided between the inlet pipe invert elevation and the invert elevation of the outlet pipe.
(d)
The capacity of inlets shall be based on a maximum surface flow to the inlet of three cfs. The maximum flow to inlets located in low points of paved areas (vertical curves) shall include the overland flow directed to the inlet, as well as the cumulative bypass surface runoff from the inlets upstream. The bypass runoff from each upstream inlet shall be calculated using inlet efficiently curves found in the Pennsylvania Department of Transportation Design Manual, Part 2, latest revision. An inlet at a low point of a paved area maybe designed to accept a maximum of five cubic feet per second (cfs). Type M inlets shall be designed to accept a maximum of six cfs, unless otherwise approved by the Township Engineer.
(e)
Inlet spacing in paved areas shall be arranged so that a minimum of 95% of the gutter flow tributary to the inlet will be captured. The designer shall be required to verify that bypass surface runoff from the one-hundred-year design storm will enter the storm sewer piping system at some point prior to discharge into a detention basin or other approved outlet point. Inlet capacity shall be based on inlet efficiency curves provided in the Pennsylvania Department of Transportation Design Manual, Part 2.
(f)
All inlets shall be stenciled by the developer to indicate that "No Dumping Allowed — This inlet flows to . . . Creek," or other approved wording by Warwick Township. Specifications for stenciling are to be provided by Warwick Township.
(5)
Headwalls and endwalls.
(a)
An endwall shall be provided at the end of all pipe runs. Headwalls shall be provided at the beginning of all pipe runs. Headwalls/endwalls with a height greater than three feet may be required to have a safety fence or guiderail if determined by the Township Engineer. Rock aprons (riprap) or other approved velocity-dissipation devices shall be placed at all pipe outlets (endwalls) to reduce flow velocity and prevent erosion.
(b)
All headwalls and endwalls shall be stenciled by the developer to indicate that "No Dumping Allowed — This inlet flows to . . . Creek," or other approved wording by Warwick Township. Specifications for stenciling are to be provided by Warwick Township.
(6)
Bridges, culverts, and drainage channels.
(a)
Bridges and culverts shall be designed and constructed to meet current Pennsylvania Department of Transportation construction and loading standards (HS-25 loading standards). They shall be constructed to the full width of the right-of-way or to an adequate dimension to accommodate special grade conditions. Approval of the Pennsylvania Department of Environmental Protection is required for all improvements in and along all waters of the commonwealth. The applicant shall provide verification of Department of Environmental Protection approval for all such proposed bridges and culverts.
(b)
Approval of the Pennsylvania Department of Environmental Protection is required for all improvements in and along waters of the commonwealth. Where applicable, stormwater management facilities or programs shall comply with the requirements of Chapter 102 (Erosion Control), Chapter 105 (Dam Safety and Waterway Management), and Chapter 106 (Floodplain Management) of Pennsylvania Code, Title 25, Rules and Regulations of the Department of Environmental Protection.
(c)
All bridges, culverts and drainage channels shall be designed to convey a flow rate equal to a one-hundred-year, twenty-four-hour storm, as defined by the United States Department of Agriculture, Soil Conversation Services, Technical Release No. 55. All bridges and culverts shall be designed to pass the one-hundred-year design storm without increasing the extent and depth of the one-hundred-year floodplain.
(d)
The capacity of all culverts and drainage channels shall, as a minimum, provide the required carrying capacity. Capacity and stabilization shall be as determined by the United States Department of Transportation, Federal Highway Administration, Hydraulic Design Series No. 5, Hydraulic Charts for the Selection of Highway Culverts; United States Department of Transportation, Federal Highway Administration, Hydraulic Engineering Circular No. 15, Design of Roadside Channels with Flexible Linings, as amended; Federal Highway Administration, Hydraulic Engineering Circular No. 13, Hydraulic Design for Improved Inlets for Culverts; United States Department of Transportation, Design of Roadside Channels with Flexible Linings, as amended; and the United States Department of Transportation, Federal Highway Administration, Visual Urban (HY-22) Drainage Design Programs.
[Amended 10-17-2011 by Ord. No. 2011-10]
(e)
Drainage channels shall be designed to convey the design discharge at a stable, nonerosive velocity. Channel linings that are assumed in the design must be established before the channel is utilized for its stated objective. Diversions or alternate channel linings may be necessary to provide channel conditions in the field to match design assumptions. Where storm sewers discharge into existing drainage channels at an angle greater than 30° from parallel with the downstream channel flow, the far side bank shall be stabilized by the use of riprap or masonry and/or concrete walls. The stabilization shall be designed to prevent erosion and frost heave under and behind the stabilizing media.
(f)
Maximum channel velocities for vegetated and rock-lined channels shall be as set forth in the Pennsylvania Department of Environmental Protection, Bureau of Soil and Water Conversation publication, Erosion and Sediment Control Program Manual, latest revision.
(g)
Any vegetated drainage channel requiring mowing of the vegetation shall have a maximum grade of four horizontal to one vertical (4:1 or 25%) on those areas to be mowed.
(7)
Stormwater detention/retention basins.
(a)
Calculation methodology shall be utilized as noted in this chapter.
(b)
Detention areas shall be designed so that the total rate of runoff from the entire site, after complete development, will not exceed the specified percentage of total predeveloped runoff rate form the entire site. Individual points of concentrated runoff discharge from the site may be designed for up to a 100% release rate so long as the total runoff from the entire site, after development, is controlled to the applicable release rate.
(c)
Discharge piping from detention areas shall be designed to control the rate of runoff for a one-year through one-hundred-year-frequency design storm.
(d)
If permanent ponds (retention basin) are proposed, the developer shall demonstrate that such ponds are designed to protect the public's health and safety.
(e)
Ownership and maintenance of detention or retention basin easements. Prior to the grant of final approval of any subdivision or land development, the owner and developer of the property which is the subject of the subdivision or land development shall execute agreements, in a form satisfactory to the Township, which state that all stormwater management facilities, including detention or retention basins, will be properly maintained. If all or a portion of the facilities are on a property which will be conveyed to an individual, homeowners' association or any other eventual owner, the guaranties must be in such a form that they will carry through to the new owners. Warwick Township will not accept dedication maintenance responsibilities for any detention or retention basin or similar facility located on private grounds, unless otherwise approved by the Board of Supervisors.
[Amended 10-17-2011 by Ord. No. 2011-10]
[1]
When a private entity (homeowners' association) retains ownership of any stormwater management facility, such entity shall be responsible for maintenance of the facility. In such case, approval of the stormwater management facility plans shall be conditioned upon the private entity agreeing to be responsible for all maintenance of the stormwater management facility. This agreement shall be in writing, shall be in recordable form and shall contain a provision permitting access to such facilities deemed critical to the public welfare for inspection at any reasonable time by Warwick Township or its designee.
[2]
When any stormwater management facility is located on an individual lot, and when maintenance thereof is the responsibility of that landowner, a description of the facility or systems and terms of the required maintenance shall be incorporated on a plat of the property. The plat shall be recorded with the Bucks County Recorder of Deeds within 90 days following Township approval. The plat of the property shall also contain a provision permitting access to such facilities deemed critical to public welfare for inspection at any reasonable time by Warwick Township or its designee.
[3]
Upon presentation of proper credentials, duly authorized representatives of Warwick Township may enter at any reasonable time upon any property within the Township to investigate or to ascertain the condition of the subject property.
[4]
The failure of any person, individual lot owner or private entity to properly maintain any stormwater management facility shall be construed to be a violation of this section and is declared to be a public nuisance, subjecting the violator to any and all penalties provided by law. Specifically, in the event that the entity responsible for maintenance fails to honor those responsibilities set forth herein, in any manner, Warwick Township shall have the right of entry upon the area of such facilities to undertake any required corrective or maintenance effort. The total cost of such, including administrative, engineering, and legal costs for enforcement, may be imposed upon the responsible party as determined by Warwick Township. Failure to remedy all associated costs described above may be subject to the imposition of a lien by the Township against the owner(s) in question, in the same manner as the Township might otherwise be empowered by law to assess or impose a lien against a property for municipal improvements.
(f)
When basins are provided, they shall be designed to utilize the natural contours of the land whenever possible. When such design is not practical, the construction of the basin shall utilize slopes as flat as possible to blend the structure into the terrain. Detention basins shall be designed to facilitate regular maintenance, mowing and periodic desilting and reseeding. In residential developments, shallow, broad basins shall be provided for recreational use. The maximum depth of the one-hundred-year water surface in a detention basin shall be five feet.
(g)
Except with the one-year design storm, permanent detention basins shall be designed so that they dewater within approximately 72 hours after termination of the storm, unless the Township Engineer finds that downstream conditions may warrant other design criteria for stormwater release.
[Amended 10-17-2022 by Ord. No. 2022-05]
(h)
Detention basins shall not be located on more than one lot.
(i)
Basins shall not be located within floodplains.
(j)
Landscaping and grading of detention basins. All landscaping and grading of detention basins shall be in accordance with the provisions of this chapter. Naturalized basins are required. Planting and seeding designs shall be prepared by appropriate professionals and approved by the Township.
[1]
The portion of the basin which is dry most of the time shall be landscaped in a combination of the following. Plantings and/or seed mixes shall be as listed in the Army Corps of Engineers Wetlands Manual as FACW or FAC plants, or the Pennsylvania Stormwater Best Management Practices Manual, as amended.
[2]
The portion of the basin which will be wet most of the time shall be landscaped in a combination of the following. Plantings and/or seed mixes shall be as listed in the Army Corps of Engineers Wetlands Manual as FACW or FAC plants, or the Pennsylvania Stormwater Best Management Practices Manual, as amended.
(k)
If a stormwater management basin will serve as a temporary sediment control device, the temporary sediment control measures shall be shown, including perforated riser pipes or standboxes, filter berms, cleanout stakes and other measures as may be required by Pennsylvania Department of Environmental Protection Chapter 102 regulations. Sedimentation basins shall be installed and functional prior to any earthmoving activities within their tributary drainage areas. A perforated riser, sized in accordance with Bucks County Conservation District requirements, shall be provided at each basin outlet structure for sediment control. Risers shall not be removed until such time as the entire area tributary to the basin has been permanently stabilized and until approved by the Bucks County Conservation District and/or the Township Engineer.
(l)
Stormwater management basins shall be in place before the creation of any additional impervious surfaces on the site. Runoff shall not be directed to an infiltration structure until all tributary drainage areas are stabilized.
(m)
Where permanent retention (pond) facilities are proposed, there shall be a safety ledge, three feet wide at the maximum water surface level. If the pond is to be stocked, the Pennsylvania Fish and Game Commission shall approve the stocking plan.
(n)
All basin berms shall have slopes of four horizontal to one vertical (4:1), or less. The top or toe of any slope shall be located a minimum of five feet from any property line.
(o)
Basin embankment. The fill material shall be taken from selected borrow areas. It shall be free of roots, woody vegetation, oversized stones, rocks or other objectionable material. Areas on which fill is to be placed shall be scarified prior to placement of fill. The fill material should contain sufficient moisture so that it can be formed by hand into a ball without crumbling. If water can be squeezed out of the ball, it is too wet for proper compaction. Fill material shall be placed with lifts not exceeding one foot and shall be continuous over the entire length of the fill. Fill material must be compacted to a minimum of 95% of modified proctor density as established by ASTM D-1557. Compaction testing by a certified soils engineer/geologist must be completed as directed by the Township Engineer to verify that adequate compaction has been achieved.
(p)
Emergency overflow facilities/spillway shall be provided with basins in order to convey basin inflow in excess of design flows, out of the basin, or in the event the outlet structure becomes blocked and is unable to convey flow. Emergency spillways discharging over embankments shall be lined. Lining for emergency spillways shall incorporate native colors and materials where possible. The lining shall extend to the toe of the embankment on the outside of the berm and shall extend to an elevation of three feet below the spillway crest on the inside of the berm. Vegetated spillways may be utilized for spillways constructed entirely on undisturbed ground if the designer can demonstrate that flow velocities through the spillway will not cause erosion of the spillway. A dense cover of vegetation shall be rapidly established in such spillways by sodding or seeding with geotextile anchor. Such a vegetated spillway must be stabilized before runoff is directed to the basin. All spillway velocities shall be based upon flows during an assumed clogged primary outlet condition. The minimum capacity of all emergency spillways shall be equivalent to the peak flow rate of the one-hundred-year, post-development design storm with the primary outlet structure blocked.
(q)
For all permanent detention basins, the permanent outlet control structure shall be a Type M inlet, grate and box, or similar structure as approved by the Township Engineer. The inlet grate elevation shall be at least six inches below the emergency spillway elevation.
(r)
The minimum top-of-basin berm width shall be 10 feet. A cutoff trench (keyway) of impervious material shall be provided under all embankments that require fill material. The cutoff trench shall be a minimum of eight feet wide, two feet deep below virgin ground and have side slopes of one horizontal to one vertical.
(s)
The minimum freeboard through the emergency spillway shall be one foot. "Freeboard" is defined as the difference between the design flow elevation through the spillway and the elevation of the top of the settled basin berm.
[Amended 10-17-2022 by Ord. No. 2022-05]
(t)
Anti-seep collars shall be installed around the pipe barrel and shall be centered within the normal saturation zone of the berm. The anti-seep collars shall be cast-in-place and extend a minimum of two feet beyond the outside of the principal pipe barrel. Precast collars may be permitted only when approved by the Township Engineer. A minimum of two collars shall be installed on each outlet pipe.
(u)
Energy-dissipating devices (rock lining/riprap) shall be provided at all basin outlets and shall be sized in accordance with the Pennsylvania Department of Environmental Protection Erosion and Sediment Control Program Manual, latest revision.
(v)
An access easement (minimum 20 feet in width) and stabilized drive to stormwater detention facilities shall be provided for maintenance and operation. Proximity of detention facilities to the public right-of-way shall be encouraged in order to minimize the length of accessways. Multiple accesses shall be encouraged for major facilities. Accessways to basins shall be a minimum of 12 feet in width and be no steeper in slope than 12 feet horizontal to one foot vertical. In addition, depressed curb shall be provided where the accessway enters a street/driveway. The stabilized driveway shall extend from the bottom of the interior basin berm embankment to the point of access to the basin. The access easement shall be owned and maintained by the individual lot owner(s) or a homeowners' association but shall be established to permit access by Warwick Township or its designee for emergency inspection and/or maintenance at any reasonable time.
(w)
The minimum distance between a proposed basin discharge point and a downstream property boundary shall be 50 feet.
(x)
Inlet structures and outlet structures shall be separated to the greatest extent possible in order to maximize the flow path through the basin.
(8)
Underground detention basins and infiltration facilities. Underground detention basins and infiltration facilities shall meet the following minimum design standards:
(a)
A minimum of one foot of freeboard shall be provided between the one-hundred-year water surface elevation and the top of all inlet grates or manhole rims.
(b)
Inlets or storm manhole structures with steps shall be located at each corner of the underground detention basin to provide access for maintenance. If the pipe diameter is less than 24 inches, cleanout ports shall be provided at appropriate locations to permit flushing of the system as necessary.
(c)
The infiltration system shall be set back at least 15 feet from all structures with subgrade elements (i.e., basements) and outside all public rights-of-way.
(d)
Infiltration rates shall not be used in computing the storage volume of the infiltration system.
(e)
Surface inflows shall be designed to prevent direct discharge of sediment. Accordingly, pretreatment shall be provided prior to infiltration.
(f)
Underground detention basins shall be constructed of perforated high-density corrugated polyethylene pipe or approved equal. The required volume shall be provided utilizing only underground pipe capacity.
[Amended 10-17-2022 by Ord. No. 2022-05]
(g)
An emergency overflow weir shall be provided for the outlet structure in order to convey basin inflow in excess of design flows or in the event that the outlet structure becomes blocked and is unable to convey the design flow. The minimum capacity of the emergency overflow weir shall be equivalent to the one-hundred-year peak inflow rate for the post-development design storm. Site improvements and grading downstream of the underground detention basin shall be designed to convey the one-hundred-year peak inflow rate to a natural outfall, storm sewer system or other drainage facility without adversely affecting downstream properties.
(h)
The minimum distance between a proposed basin discharge point and a downstream property boundary shall be 50 feet.
[Added 10-17-2022 by Ord. No. 2022-05]
(i)
Notification of the required infiltration testing shall be sent to the Township and Township Engineer, a minimum of 72 hours prior to the testing being done.
[Added 10-17-2022 by Ord. No. 2022-05]
(9)
Wet basins. Existing ponds or permanent pool basins can be used, provided that they meet the following minimum standards in addition to providing the required release rate and volume control requirements:
(a)
The minimum permanent pool basins can be maintained to allow sufficient depth throughout the year to reduce the growth of unwanted vegetation and mosquitoes.
(b)
The pond must be of sufficient size and depth to allow the appropriate aquatic community needed to maintain healthy pond ecology.
(c)
An outlet structure shall be designed to allow complete drainage of the pond for maintenance.
(d)
The design of a wet basin shall include the determination of the proposed site's ability to support a viable permanent pool. The design should take into account such factors as the required rate and quality of dry-weather inflow, the quality of stormwater inflow, seasonal and longer-term variations in the groundwater table, and effects of suspected pollutant loadings. The Pennsylvania Fish Commission and Natural Resources Conservation Service should be consulted during the design of facilities.
(10)
Riparian buffers proposed to meet the water quality standards shall meet the following minimum requirements:
(a)
The minimum overland flow length through the buffer shall be 25 feet.
(b)
The maximum overland flow length contributing runoff to the boundary of the riparian buffer shall be 150 feet for pervious surfaces and 75 feet for impervious surfaces.
(c)
The average contributing overland slope shall not exceed 5%.
(d)
Runoff shall enter the riparian buffer as sheet flow. A level-spreading device shall be utilized where sheet can no longer be maintained.
(e)
The riparian buffer shall be specifically designated on the final subdivision and/or land development plan and shall be landscaped in accordance with the requirements of and as recommended by the Township Engineer. Plan notes should also indicate the portions of the riparian buffer being used to satisfy the requirements. Generally, the riparian buffer should be increased in effectiveness while maintaining a natural state as much as possible to maximize water quality benefits.
A.
Grading.
(1)
Blocks and lots shall be graded to secure proper drainage away from buildings and to prevent the collection of stormwater in pools, except as approved by the Township Engineer. Grading at buildings shall conform to Township Building Codes, as amended. The minimum allowable slope in lawn areas shall not be less than 2%.
(2)
All drainage provisions shall be of such design as to carry surface water to the nearest practical street, storm drain or natural watercourse.
(3)
The owner shall construct and/or install such drainage structures and/or pipes necessary to prevent erosion damage and to satisfactorily carry off such surface waters.
(4)
No excavation shall be made with a cut face steeper in slope than three horizontal to one vertical, except under one or more of the following conditions, as approved by the Township Engineer:
(a)
The material in which the excavation is made is sufficiently stable to sustain a slope of steeper than three horizontal to one vertical, and a written statement of a civil engineer, licensed by the Commonwealth of Pennsylvania and experienced in erosion control, to that effect is submitted to the Township Engineer and approved by him. The statement shall state that the site has been inspected and that the deviation from the slope specified hereinbefore will not result in injury to persons or damage to property.
(b)
A concrete or stone masonry wall, or modular block wall, constructed in accordance with approved standards is provided to support the face of the excavation.
(c)
Design drawings and supporting calculations, both prepared by an engineer registered to practice in Pennsylvania, shall be submitted to the Township for review prior to construction of retaining walls greater than 42 inches in height measured from the top of the footer or any wall supporting a surcharge.
[Amended 10-17-2022 by Ord. No. 2022-05]
(5)
No fill shall be made which creates any exposed surface steeper in slope than three horizontal to one vertical, except under one or more of the following conditions, as approved by the Township Engineer:
(a)
The fill is located so that settlement, sliding or erosion will not result in property damage or be a hazard to adjoining property, streets, alleys or buildings.
(b)
A written statement from a civil engineer, licensed by the commonwealth and experienced in erosion control, certifying that he has inspected the site and that the proposed deviation from the slope specified above will not endanger any property or result in property damage, is submitted to and approved by the Township Engineer.
(c)
A concrete or stone masonry wall or modular block wall constructed in accordance with approved standards is provided to support the face of the fill.
(d)
Design drawings and supporting calculations, both prepared by an engineer registered to practice in Pennsylvania, shall be submitted to the Township for review prior to construction of retaining walls greater than 42 inches in height measured from the top of the footer or any wall supporting a surcharge.
[Added 10-17-2022 by Ord. No. 2022-05]
(6)
The top or bottom edge of slopes shall be a minimum of five feet from property or right-of-way lines of streets or alleys in order to permit the normal rounding of the edge without encroaching on the abutting property unless a temporary construction easement is obtained from the encroached party.
[Amended 10-17-2022 by Ord. No. 2022-05]
(7)
Grading equipment shall not be allowed to cross any wetlands, watercourses, floodplains, etc., without prior approval by the appropriate Township, state and federal agencies.
(8)
Within all subdivisions and land developments, and all single-family, multifamily residential, commercial or noncommercial buildings, additions or developments, expansion or changes of any impervious areas or surfaces, the owner, agent, builder or builders shall be required to fine grade and seed each individual lot within a subdivision or the lot within the land development. Each lot shall be fine graded to its boundary lines and adjusted accordingly to meet existing grades adjacent to the boundary lines prior to issuance of any use and occupancy permits for any dwelling or building within any subdivision or land development. In the event that the developer cannot complete the required grading and seeding due to mitigating circumstances, the developer shall escrow with Warwick Township the appropriate sums as determined by the Warwick Township Engineer to guarantee the grading or adjustments to any grades in any areas which shall impair stormwater runoff on any adjacent lot in any way.
(9)
“Fine grading” shall be defined as that work which is required to remove all large lumps, particles and debris within the lot area. This shall be accomplished by hand-raking or mechanical equipment mounted with a fine-tooth rake. Dragging with a track-mounted tractor or wheel-mounted tractor will not be considered as fine grading. Fine grading shall also include the installation of a minimum of a four-inch thickness of topsoil.
(10)
Limits of grading and seeding within a wooded lot shall be the same as any other type of lot; and all lots, whether wooded or not, within a subdivision and/or a land development shall be graded and seeded from boundary to boundary unless it is specifically agreed by the subdivider, owner, builder or builders and the purchaser of the lot or lots in writing to the contrary. Evidence of this arrangement must be submitted to the Township Building Inspector for his review prior to the issuance of any use and occupancy permit being issued for the structure on the lot where located, unless waived by Warwick Township. Grading and seeding shall also be a requirement between all areas of sidewalk and curb subject to all the hereinbefore-stated requirements and conditions, except where the same may be waived by Warwick Township.
(11)
Where stormwater drainage swales are installed, if, in the opinion of the Township Engineer, there may be erosion prior to establishment of vegetation, he may require the installation of sod, geotextile matting, or other methods to ensure stabilization.
(12)
Lawn areas shall be considered to be poorly drained if they contain standing water for longer than a twelve-hour period following the cessation of precipitation, which determination may be subject to the consideration of antecedent moisture conditions.
(13)
All fill material utilized shall be clean and free from rock, refuse, debris, stone, concrete, brick, building material scraps, blacktop, organic material or other foreign material.
(14)
All debris, such as but not limited to concrete, blacktop, wood, wood chips, stumps, refuse, building material or other material as determined inappropriate by the Township Engineer, shall be removed from the site and disposed of according to the governing regulations.
(15)
All building foundations, grade slabs and cellar floors located in soils that have a community development limitation degree of moderate to severe seasonal high-water table (as defined in the Bucks County Soil Survey) shall be provided with an underdrain system. This system shall provide for drainage of the enclosed volume above the slab and relief of subsurface water to a depth not less than 18 inches below the slab or foundation bottom. The system will consist of a perforated pipe field of the herringbone or gridiron configuration in coarse gravel-filled trenches that are in direct contact with the slab or foundation subbase. The excavation shall provide a minimum of 0.05 foot/foot slope to the gravel-filled trenches. Foundation drains shall discharge to a storm sewer system or into a natural watercourse as directed by the Township or Township Engineer.
B.
Erosion and sedimentation control.
(1)
No regulated earth-disturbance activities within the Township shall commence until approval of an erosion and sediment control plan by the Township. In addition, the Bucks County Conservation District requires submission of an erosion and sediment control plan for any earth-disturbance activity of 1,000 square feet or more.
(2)
Pursuant to 25 Pa. Code, Chapter 102.5, a DEP NPDES permit for stormwater discharges associated with construction activities is required for any earth-disturbance activity that involves equal to or greater than one acre of earth disturbance prior to commencing the earth-disturbance activity. This includes earth disturbance on any portion or part or during any stage of a larger common plan of development or sale.
(3)
Detailed construction schedules shall be included in all erosion and sedimentation plans and stormwater management plans for sites disturbing in excess of 1,000 square feet of site area.
(4)
Evidence of any necessary permit(s) for regulated activities from the appropriate DEP regional office or County Conservation District must be provided to the municipality. The issuance of an NPDES construction permit or permit coverage under the statewide general permit (PAG-2) satisfies the requirements of Subsection B(1). A copy of the erosion and sediment control plan and any required permit, as required by DEP regulations, shall be available at the project site at all times.
(5)
General performance principles. The following shall be adhered to where applicable during design and construction of approved plans:
(a)
Stripping of vegetation, regrading, or other development shall be done in a way that will minimize erosion.
(b)
Development plans shall preserve salient natural features, keep cut-fill operations to a minimum, and ensure conformity with topography so as to create the least erosion potential and adequately handle the volume and velocity of surface water runoff.
(c)
Whenever feasible, natural vegetation shall be retained, protected, and supplemented.
(d)
Disturbed areas shall be stabilized immediately or, at a minimum, at the end of the day. In addition, any dirt tracked onto roadways outside the subject property shall be cleaned prior to the end of the workday or as directed by the Township Engineer.
(e)
Temporary seeding and/or mulching shall be used to protect exposed critical areas during development.
(f)
The permanent (final) vegetation and mechanical erosion control and drainage shall be installed as soon as practical in the development.
(g)
Sediment in the runoff water shall be trapped until the disturbed area is stabilized by the use of debris basins, sediment basins, silt traps, or similar measures.
(h)
During grading operations, necessary measures for dust control must be exercised.
(i)
Installation and maintenance of all erosion control facilities shall be the responsibility of the applicant until all disturbed areas have been stabilized to the satisfaction of the Township and the Bucks County Conservation District.
(j)
In the event that the developer proceeds to clear and grade prior to recording plans without satisfying conditions of plan approval, the Warwick Township Board of Supervisors may revoke its approval of the preliminary plan.
(k)
Tire-cleaning areas shall be provided at each point of access to the development site.
(l)
No person, corporation or other entity shall block, impede the flow of, alter, construct any structure or deposit any material or thing or commit any act which will affect normal or flood flow in any communal stream or watercourse without having obtained prior approval from the Township or Pennsylvania Department of Environmental Protection (PADEP), whichever is applicable.
(6)
Responsibility.
(a)
Whenever sedimentation is caused by stripping vegetation, regrading or other development, it shall be the responsibility of the applicant and/or person, corporation or other entity causing such sedimentation to remove it from all adjoining surfaces, drainage systems and watercourses and to repair any damage at his expense as quickly as possible.
(b)
Maintenance of all temporary erosion and sedimentation control facilities within any subdivision or land development is the responsibility of the developer until they are accepted by the Township or some other official agency, after which they become the responsibility of the accepting agency.
