[Ord. 429, 11/7/2006]
1. 
All regulated activities in Delaware River South Watershed that do not fall under the exemption criteria shown in §23-105 herein shall submit a drainage plan consistent with the Delaware River South Watershed Stormwater Management Plan to the Borough for review. This criteria shall apply to the total proposed development even if development is to take place in stages. Impervious cover 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 exemption criteria.
2. 
Stormwater drainage systems shall be provided in order to permit unimpeded flow along natural watercourses, except as modified by stormwater management facilities or open channels consistent with this Chapter.
3. 
The drainage plan must be designed consistent with the sequencing provisions of §23-304 herein 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 Part 3 of this Chapter.
4. 
The existing points of concentrated drainage that discharge onto adjacent property shall not be altered without permission of the affected property owner(s) and shall be subject to any applicable discharge criteria specified in this Chapter.
5. 
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.
6. 
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.
7. 
Where a development site is traversed by watercourses drainage easements shall be provided conforming to the line of such watercourses. 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.
8. 
When it can be shown that, due to topographic conditions, natural drainageways on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainageways. Work within natural drainageways shall be subject to approval by the Borough and the DEP through the joint permit application process, or, where deemed appropriate by DEP, through the general permit process.
9. 
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 DEP through the joint permit application process, or, where deemed appropriate by DEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the applicant 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 DEP.
10. 
Any stormwater management facilities regulated by this Chapter that would be located on or discharge into State highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
11. 
Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, etc., are required to reduce the size or eliminate the need for detention facilities.
12. 
Roof drains must not be discharged to streets or roadside ditches or connected to sanitary or storm sewers. Overland flow and infiltration/percolation of stormwater shall be promoted where advantageous to do so. Only when it is more advantageous to connect directly to streets or storm sewers, shall it be permitted on a case-by-case basis by the Borough.
13. 
All stormwater runoff shall be pretreated for water quality prior to discharge to surface or groundwater as required by §23-303 of this Chapter.
14. 
All regulated activities within the Borough shall be designed, implemented, operated and maintained to meet the purposes of this Chapter, through these two elements:
A. 
Erosion and sediment control during the earth disturbance activities (e.g., during construction).
B. 
Water quality protection measures after completion of earth disturbance activities (i.e., after construction), including operations and maintenance.
15. 
No regulated earth disturbance activities within the Borough shall commence until the requirements of this Chapter are met.
16. 
Post-construction water quality protection shall be addressed as required by §23-305.
17. 
Operations and maintenance of permanent stormwater BMPs shall be addressed as required by Part 7.
18. 
All best management practices (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 Borough.
19. 
Techniques described in Appendix 23-E, “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.
[Ord. 429, 11/7/2006]
1. 
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:
A. 
All regulated earth disturbance activities subject to permit requirements by DEP under regulations at 25 Pa.Code, Chapter 102.
B. 
Work within natural drainageways subject to permit by DEP under 25 Pa.Code, Chapter 105.
C. 
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 Pa.Code, Chapter 105.
D. 
Any stormwater management facility that would be located on a State highway right-of-way, or require access from a State highway, shall be subject to approval by the Pennsylvania Department of Transportation (PennDOT).
E. 
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 Pa.Code, Chapter 105.
[Ord. 429, 11/7/2006]
1. 
No regulated earth disturbance activities within the Borough shall commence until the Borough approves an erosion and sediment control plan for construction activities.
2. 
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 Pa.Code §102.4(b).
3. 
In addition, under 25 Pa.Code, Chapter 92, a DEP “NPDES Construction Activities” permit is required for regulated earth disturbance activities when there is land disturbance greater than one acre.
4. 
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or County Conservation District must be provided to the Borough. The issuance of an NPDES Construction Permit (or permit coverage under the statewide General Permit (PAG-2) satisfies the requirements of Subsection 1.
5. 
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.
6. 
Additional erosion and sediment control design standards and criteria are recommended to be applied where infiltration BMPs are proposed. They shall include the following:
A. 
Areas proposed for infiltration BMPs shall be protected from sedimentation and compaction during the construction phase to maintain maximum infiltration capacity. Barriers such as orange construction fencing should be used to protect and keep construction traffic in the area where infiltration BMPs are proposed. Inlet or pipes that are installed to these systems should be completely sealed or protected and monitored until the drainage areas are completely stabilized.
B. 
Infiltration BMPs shall not be constructed nor receive runoff until the entire contributory drainage area to the infiltration BMP has achieved final stabilization.
[Ord. 429, 11/7/2006]
1. 
The design of all regulated activities shall include the following steps in sequence to minimize stormwater impacts.
A. 
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.
B. 
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 Borough requirements.
C. 
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.
2. 
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:
A. 
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 [Chapter 22]. Establish stream buffer according to recommended criteria or applicable ordinances.
B. 
Prepare a draft project layout avoiding sensitive areas identified in Subsection 2.A herein 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.
C. 
Identify site specific existing conditions drainage areas, discharge points, recharge areas and hydrologic soil groups A and B.
D. 
Evaluate nonstructural stormwater management alternatives. (See Appendix 23-B, Table 23-B-6).
(1) 
Minimize earth disturbance.
(2) 
Minimize impervious surfaces.
(3) 
Break up large impervious surfaces.
E. 
Satisfy water quality objective (§23-303).
F. 
Satisfy groundwater recharge (infiltration) objective (§23-306) and provide for stormwater treatment prior to infiltration.
G. 
Satisfy streambank erosion protection objective (§23-307).
H. 
Determine what management district the site falls into (Appendix 23-D) and conduct a predevelopment runoff analysis.
I. 
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.
J. 
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 (§23-308 and §23-311).
K. 
Manage any remaining runoff through treatment prior to discharge, as part of detention, bioretention, direct discharge or other structural control.
[Ord. 429, 11/7/2006]
1. 
In addition to the performance standards and design criteria requirements of this Part, the applicant shall comply with the following water quality requirements of this Part.
A. 
No regulated earth disturbance activities within the Borough shall commence until approval by the Borough of a plan which demonstrates compliance with State water quality requirements post-construction is complete.
B. 
The BMPs shall be designed, implemented and maintained to meet State water quality requirements, and any other more stringent requirements as determined by the Borough.
C. 
To control post-construction stormwater impacts from regulated earth disturbance activities, State water quality requirements can be met by BMPs, including site design, which provide for replication of pre-construction stormwater infiltration and runoff conditions, so that post-construction stormwater discharges do not degrade the physical, chemical or biological characteristics of the receiving waters. As described in the DEP Comprehensive Stormwater Management Policy (#392-0300-002, September 28, 2002), this may be achieved by the following:
(1) 
Infiltration. Replication of pre-construction 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.
(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 and downcutting).
D. 
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office must be provided to the Borough.
(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 §23-306 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:
(a) 
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: 305.1
Wqv = [(P)(Rv)(A)]/12
Where:
WQv = Water Quality Volume (acre-feet).
P = Rainfall Amount equal to 90% of events producing this rainfall (in).
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* 100).
(3) 
The P value for the five PennDOT rainfall regions is shown in Figure 23-B-2 in Appendix 23-B and as shown in Appendix Table 23-B-5. Since the Delaware River South is in PennDOT Region 5, the P value to be utilized to meet this requirement is 2.04 inches.
E. 
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 well heads.
(6) 
Erodibility of soils.
(7) 
Land availability and configuration of the topography.
(8) 
Peak discharge and required volume control.
(9) 
Stream bank 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.
F. 
To accomplish the above, the applicant shall submit original and innovative designs to the Borough for review and approval. Such designs may achieve the water quality objectives through a combination of BMPs (best management practices).
[Ord. 429, 11/7/2006]
1. 
Infiltration BMPs shall meet the following minimum requirements:
A. 
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 Subsections 1A(2)(a) or (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.
(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.
(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 Subsection 1A(2)(a) or (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: 306.1
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 23-306-1.
3) 
The recharge volume (Rev) required would therefore be computed as:
Equation: 306.2
Rev = 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 Subsection 1.A.(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 306.1 or the curve in Figure 306.1 should be used to determine the infiltration requirement.
2) 
Where: I = 0.5 inches.
3) 
The recharge volume (Rev) required would therefore be computed as:
a) 
Rev = I * percent impervious area (SF)/12 = (CF).
4) 
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 23-306-1. Infiltration Requirement Based Upon NRCS Curve Number.
023(1).tiff
2. 
The general process for designing the infiltration BMP shall be:
A. 
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 bedrock and subgrade stability.
(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.
(3) 
Design the infiltration structure for the required storm volume based on field determined capacity at the level of the proposed infiltration surface.
(4) 
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 Borough with the drainage plan.
(5) 
If on-lot infiltration structures are proposed by the applicant’s design professional, it must be demonstrated to the Borough that the soils are conducive to infiltration on the lots identified.
3. 
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 25 Pa.Code, Chapter 93, “Antidegradation Regulations.” The Borough 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 Borough.
4. 
The Borough shall require the applicant to provide safeguards against groundwater contamination for uses which may cause groundwater contamination, should there be a mishap or spill.
5. 
Recharge/infiltration facilities shall be used in conjunction with other innovative or traditional BMPs, stormwater control facilities and nonstructural stormwater management alternatives.
[Ord. 429, 11/7/2006]
1. 
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 post-development 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.)
2. 
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-inch 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.
3. 
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.
[Ord. 429, 11/7/2006]
1. 
Delaware River South Watershed has been divided into stormwater management districts as shown on the watershed map in Appendix 23-D. In addition to the requirements specified below, the water quality (§23-305), groundwater recharge (§23-306), and streambank erosion (§23-307) requirements shall be implemented.
2. 
Standards for managing runoff from each subarea in the Delaware River South Watershed are 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
Design Storm Predevelopment
A
2-year
1-year
Yardley Borough
 
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
50-year
 
 
100-year
100-year
 
C
2-year
1-year
Yardley Borough
 
5-year
2-year
Notes:
* 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 post-development 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.
[Ord. 429, 11/7/2006]
1. 
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 (Appendix 23-D) and §23-308.
2. 
District Boundaries. The boundaries of the stormwater management districts are shown on an official stormwater district map that is available for inspections at the Borough office. A copy of the map at a reduced scale is included in Appendix 23-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.
3. 
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 §23-308. 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 100% release rate provided that the overall site discharge meets the weighted average release rate.
4. 
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.
5. 
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.
6. 
“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 Subsection 7 to determine if adequate hydraulic capacity exists. The land applicant shall submit to the Borough this evaluation of the impacts due to increased downstream stormwater flows in the watershed.
A. 
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 streamflow, or any stream channel section, established with the concurrence of the Borough.
B. 
The evaluation shall continue downstream until the increase in flow diminishes due to additional flow from tributaries and/or stream attenuation.
C. 
The peak flow values to be used for downstream areas for the design return period storms (two- , five- , ten- , twenty-five- , fifty- , and 100-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.
D. 
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 §23-310.
E. 
Financial considerations shall not constitute grounds for granting a no harm exemption.
F. 
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.
G. 
Any “no harm” justifications shall be submitted by the applicant as part of the drainage plan submission per Part 4.
7. 
“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:
A. 
Natural or man-made channels or swales must be able to convey the increased runoff associated with a 1.5-year return period event within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the Department of Environmental Protection’s Erosion and Sediment Pollution Control Program manual.
B. 
Natural or man-made channels or swales must be able to convey increased twenty-five-year return period runoff without creating any hazard to persons or property.
C. 
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 25 Pa.Code, Chapter 105, regulations (if applicable) and, at minimum, pass the increased twenty-five-year return period runoff.
8. 
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.
[Ord. 429, 11/7/2006]
1. 
Any stormwater facility located on State highway rights-of-way shall be subject to approval by the Pennsylvania DEP of Transportation (PennDOT).
2. 
Any stormwater management facility (i.e., detention basin) designed to store runoff and requiring a berm or earthen embankment required or regulated by this Chapter shall be designed to provide an emergency spillway to handle flow up to and including the 100-year postdevelopment conditions. The height of embankment must be set as to provide a minimum 1.0 foot of freeboard above the maximum pool elevation computed when the facility functions for the 100-year postdevelopment inflow. Should any stormwater management facility require a dam safety permit under 25 Pa.Code, Chapter 105, “Dam Safety and Waterway Management,” the facility shall be designed in accordance with Chapter 105 and meet the regulations of Chapter 105 concerning dam safety which may be required to pass storms larger than 100-year event.
3. 
Any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls or stream enclosures), and any work involving wetlands as directed in DEP 25 Pa.Code, Chapter 105, regulations (as amended or replaced from time to time by DEP), shall be designed in accordance with 25 Pa.Code, Chapter 105, and will require a permit from DEP. Any other drainage conveyance facility that does not fall under 25 Pa.Code, Chapter 105, regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-year design storm with a minimum 1.0 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 100-year design storm with a minimum 1.0 foot of freeboard measured below the lowest point along the top of the roadway. Any facility that constitutes a dam as defined in DEP 25 Pa.Code, 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.
4. 
Any drainage conveyance facility and/or channel that does not fall under 25 Pa.Code, Chapter 105, regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the ten-year design 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 100-year design storm. Any facility located within a PennDOT right-of-way must meet PennDOT minimum design standards and permit submission requirements.
5. 
Storm sewers must be able to convey postdevelopment runoff from a twenty-five-year design storm without surcharging inlets, where appropriate.
6. 
Adequate erosion protection shall be provided along all open channels, and at all points of discharge.
7. 
The design of all stormwater management facilities shall incorporate sound engineering principles and practices. The Borough shall reserve the right to disapprove any design that would result in the creation, exacerbation, or continuation of an adverse hydrologic or hydraulic condition within the watershed.
[Ord. 429, 11/7/2006]
1. 
Stormwater runoff from all development sites shall be calculated using either the rational method or a soil-cover-complex methodology.
A. 
Any stormwater runoff calculations shall use generally accepted calculation technique that is based on the NRCS soil cover complex method. Table 23-311-1 summarizes acceptable computation methods. It is assumed that all methods will be selected by the applicant based on the individual limitations and suitability of each method for a particular site. The Borough may allow the use of the rational method to estimate peak discharges from drainage areas that contain less than 200 acres. The rational method is recommended for drainage areas under 100 acres.
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 according to the region for which they are located as presented in Table 23-B-1 in Appendix 23-B of this Chapter. If a hydrologic computer model such as HEC-1 or HEC-HMS is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours. The SCS “S” curve shown in Figure 23-B-1, Appendix 23-B, shall be used for the rainfall distribution.
C. 
For the purposes of predevelopment flow rate determination, undeveloped land 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 23-B-2 or 23-B-3 in Appendix 23-B. 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 is Appendix 23-D. The appropriate curve number or rational “C” value from Table 23-B-2 or Table 23-B-3 should then be used.
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 23-B-2 to 23-B-3). 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 obtained from Table 23-B-2 in Appendix 23-B of this Chapter.
F. 
Runoff coefficients (c) for both existing and proposed conditions for use in the rational method shall be obtained from Table 23-B-3 in Appendix 23-B of 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 23-B-4 in Appendix 23-B. Outlet structures for stormwater management facilities shall be designed to meet the performance standards of this Chapter using any generally accepted hydraulic analysis technique or method.
H. 
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 Borough 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.
Table 23-311-1. 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 package based on TR-55)
USDA NRCS
Applicable for land development plans within limitations described in TR-55
HEC-1, HEC-HMS
US 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 Borough and/or Borough Engineer
Other methods
Varies
Other computation methodologies approved by the Borough and/or Borough Engineer
[Ord. 429, 11/7/2006]
1. 
Whenever the vegetation and topography are to be disturbed, such activity must be in conformance with 25 Pa.Code, Chapter 102, Rules and Regulations, Part 1, Commonwealth of Pennsylvania, Department of Environmental Protection, Subpart C, Protection of Natural Resources, Part 2, Water Resources, Chapter 102, “Erosion Control,” and in accordance with the Bucks County Conservation District.
2. 
Additional erosion and sedimentation control design standards and criteria that must be applied where infiltration BMP’s are proposed shall include the following:
A. 
Areas proposed for infiltration BMP’s shall be protected from sedimentation and compaction during the construction phase, so as to maintain their maximum infiltration capacity.
B. 
Infiltration BMP’s shall not be constructed nor receive runoff until the entire contributatory drainage area to the infiltration BMP has received final stabilization.
[Ord. 429, 11/7/2006]
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.