[Ord. 2011-03, 2/3/2011, Art. 3]
1. 
All regulated activities in the Perkiomen Creek Watershed shall be subject to the stormwater management requirements of this Chapter 23B.
[Amended by Ord. No. 2022-05, 10/6/2022]
2. 
Storm drainage systems shall be designed to preserve natural watercourses except as modified by stormwater detention facilities, recharge facilities, water quality facilities, pipe systems, or open channels consistent with this Chapter 23B.
3. 
The existing locations of concentrated drainage discharge onto adjacent property shall not be altered without written approval of the affected property owner(s).
4. 
Areas of existing diffused drainage discharge onto adjacent property shall be managed such that, at minimum, the peak diffused flow rate does not increase in the general direction of discharge, except as otherwise provided in this Chapter 23B. If diffused flow is proposed to be concentrated and discharged directly onto adjacent property, the developer must obtain the written approval of the affected property owner(s). Areas of existing diffused drainage discharge shall be subject to any applicable release rate criteria in the general direction of existing discharge whether they are proposed to be concentrated or maintained as diffused drainage areas.
5. 
Where a site is traversed by watercourses other than those for which a one-hundred-year floodplain is defined by FEMA, there shall be provided drainage easements conforming substantially with the line of such watercourses. The width of any easement shall be adequate to provide for unimpeded flow of storm runoff based on calculations made in conformance with § 23B-308 for the one-hundred-year return period runoff and to provide a freeboard allowance of 1/2 foot above the design water surface level. The terms of the easement shall prohibit excavation, the placing of fill or structures, and any alterations which may adversely affect the flow of stormwater within any portion of the easement. Also, periodic maintenance of the easement to ensure proper runoff conveyance shall be required. Watercourses for which the one-hundred-year floodplain is formally defined by FEMA are subject to the applicable municipal floodplain regulations.
6. 
Post construction BMPs shall be designed, installed, operated, and maintained to meet the requirements of the Clean Streams Law and implementing regulations, including the established practices in 25 Pa.Code Chapter 102 and the specifications of this Chapter 23B as to prevent accelerated erosion in watercourse channels and at all points of discharge.
7. 
No earth disturbance activities associated with any regulated activities shall commence until approval by the Township of a plan which demonstrates compliance with the requirements of this Chapter 23B.
8. 
Techniques described in Appendix 23B-E (Low Impact Development) of this Chapter 23B are encouraged because they reduce the costs of complying with the requirements of this Chapter 23B and the state water quality requirements.
[Ord. 2011-03, 2/3/2011, Art. 3]
1. 
The following environmental permit requirements apply to certain regulated and earth disturbance activities and must be met prior to commencement of regulated and earth disturbance activities, as applicable:
A. 
All regulated and 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 102 and 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. 
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. 2011-03, 2/3/2011, Art. 3]
1. 
No regulated earth disturbance activities within the Township shall commence until approval by the Township of an erosion and sediment control plan for construction activities.
[Amended by Ord. No. 2022-05, 10/6/2022]
2. 
A written erosion and sediment control plan is required by DEP regulations for any earth disturbance activity of 5,000 square feet or more under Pa.Code § 102.4(b).
3. 
A DEP NPDES Stormwater Discharge Associated with Construction Activities Permit is required for regulated earth disturbance activities of one acre or greater under Pa.Code Chapter 102.
4. 
Evidence of any necessary permit(s) for regulated earth disturbance activities from the appropriate DEP regional office or the conservation district must be provided to the Township before the commencement of an earth disturbance activity.
5. 
A copy of the erosion and sediment control plan and any permit, as required by DEP regulations, shall be available at the project site at all times.
[Ord. 2011-03, 2/3/2011, Art. 3]
1. 
No regulated earth disturbance activities within the Township shall commence until approval by the Township of a drainage plan which demonstrates compliance with this Chapter 23B.
2. 
The water quality volume (WQv) shall be captured and treated with evapotranspiration and/or direct recharge BMPs. The WQv shall be calculated as the difference in runoff volume from pre-development to post-development for the twenty-four-hour, two-year return period storm. This may be calculated using either the Soil-Cover-Complex Method or Rational Method using the two-year rainfall depth as noted in § 23B-308, Subsection 8. The effect of closed depressions on the site shall be considered in this calculation. The WQv shall be captured and treated in a manner consistent with the standards outlined in § 23B-305 of this Chapter 23B.
3. 
The WQv shall be calculated for each post-development drainage direction on a site for sizing BMPs. Site areas having no impervious cover and no proposed disturbance during development may be excluded from the WQv calculations and do not require treatment.
4. 
For sites within watersheds with high quality (HQ) or exceptional value (EV) waters as designated by DEP, if an applicant is proposing to use a BMP that ponds water on the land surface and may receive direct sunlight, the discharge from that BMP must be treated by infiltration, a vegetated buffer, filter strip, bioretention, vegetated swale, or other BMP that provides a thermal benefit to protect the designated waters from thermal impacts.
5. 
Sites where applicants intend to use infiltration BMPs must meet the following criteria:
A. 
Depth to bedrock below the invert of the BMP greater than or equal to two feet.
B. 
Depth to seasonal high water table below the invert of the BMP greater than or equal to two feet; except for infiltration of residential roof runoff where the seasonal high water table must be below the invert of the BMP.
C. 
Soil permeability (as measured using the standards listed in Appendix 23B-C of the Pennsylvania Stormwater Best Practices Manual) greater than or equal to 0.1 inches/hour and less than or equal to 10 inches per hour.
D. 
Setback distances or buffers as follows:
(1) 
One hundred feet from public water supply wells or 50 feet from private water supply wells.
(2) 
Ten feet downgradient or 100 feet upgradient from building foundations.
(3) 
Fifty feet from septic system drainfields.
6. 
Site areas proposed for infiltration shall be protected from disturbance and compaction except as necessary for construction of infiltration BMPs.
7. 
If infiltration of the entire WQv is not proposed, the remainder of the WQv shall be treated by acceptable BMPs for each discharge location. Acceptable BMPs are listed in Appendix 23B-F.
8. 
Stormwater runoff from hot spot land uses shall be pre-treated. Guidance regarding acceptable methods of pre-treatment is located in Appendix 23B-F.
9. 
The use of infiltration BMPs is prohibited on hot spot land use areas unless the applicant can demonstrate that existing and proposed site conditions, including any proposed runoff pretreatment, create conditions suitable for runoff infiltration under this Chapter 23B.
10. 
Applicants shall request, in writing, public water suppliers to provide the Zone I Wellhead Protection radius, as calculated by the method outlined in the DEP Wellhead Protection regulations, for any public water supply well within 400 feet of the site. In addition to the setback distances specified in Subsection 5, infiltration is prohibited in the Zone I radius as defined and substantiated by the public water supplier in writing. If the applicant does not receive a response from the public water supplier, the Zone I radius is assumed to be 100 feet.
11. 
The Township may, after consultation with DEP, approve alternative methods for meeting the state water quality requirements other than those in this Chapter 23B, provided that they meet the minimum requirements of, and do not conflict with, state law including but not limited to the Clean Streams Law.
12. 
The use of well injection for discharge of stormwater, including runoff originating from surfaces other than the ground (e.g., roof runoff) is prohibited. The definitions of "well injection" and "well" shall be taken as stated in 40 CFR 144.3.
[Added by Ord. 2017-03, 1/19/2017]
[Ord. 2011-03, 2/3/2011, Art. 3]
1. 
The entire WQv as calculated in § 23B-304, Subsection 2, of this Chapter 23B shall be captured and treated by either direct recharge (D-RE) or evapotranspiration (ET) BMPs.
2. 
Lawn area up to a maximum of 33% of the entire site area may be allowed to bypass water quality BMPs. As much proposed impervious area as practical shall be directed to water quality BMPs.
3. 
Existing impervious area that is not proposed to be treated by D-RE BMPs should be excluded from all water balance calculations.
4. 
A maximum of 30% of the total annual rainfall for a site may be directly recharged to groundwater using direct recharge (D-RE) BMPs, for runoff from impervious areas.
A. 
For development sites with greater than 33% proposed impervious cover:
(1) 
If all impervious cover is directed to ET BMPs to capture the entire two year, twenty-four hour event, the D-RE standard is met.
(2) 
Up to 33% of the site as impervious cover may be directed to D-RE BMPs designed to capture the entire two year, twenty-four-hour event. All remaining impervious cover shall be directed to ET BMPs designed to capture the remainder of the WQv.
(3) 
For ET and/or D-RE BMPs designed for runoff from impervious areas designed to capture less than entire two-year, twenty-four-hour event, Appendix 23B-C shall be used to assure that the maximum D-RE standard is met.
B. 
For development sites with less than 33% proposed impervious cover, all proposed impervious and the entire WQv may be directed to D-RE BMPs.
C. 
The maximum 30% D-RE standard applies on an overall site basis, rather than in each drainage direction.
[Ord. 2011-03, 2/3/2011, Art. 3]
1. 
Mapping of Stormwater Management Districts. To implement the provisions of the Perkiomen Creek Headwaters Watershed Stormwater Management Plan, the Township is hereby divided into stormwater management districts consistent with the Perkiomen Creek Headwaters Watershed Release Rate Map presented in the plan update. The boundaries of the stormwater management districts are shown on an official map which is available for inspection at the municipal office. A copy of the official map at a reduced scale is included in Appendix 23B-A for general reference.
2. 
Description of Stormwater Management Districts. The ten-, twenty-five-, and one-hundred-year post-development peak runoff must be controlled to the stated percentage of the pre-development peak. Release rates associated with the ten- through one-hundred-year events vary from 50% to 100% depending upon location in the watershed. In the event that infiltration is not required in accordance with § 23B-304, the post-development rate of runoff for the two-year return period storm shall not exceed the pre-development rate in accordance with § 22A-708, Subsection 4B(1), of the Lower Macungie Township Subdivision and Land Development Ordinance. [Chapter 22]
[Ord. 2011-03, 2/3/2011, Art. 3]
1. 
Applicants shall provide a comparative pre- and post construction stormwater management hydrograph analysis for each direction of discharge and for the site overall to demonstrate compliance with the provisions of this Chapter 23B.
2. 
Any stormwater management controls required by this Chapter 23B and subject to release rate criteria shall meet the applicable release rate criteria for each of the ten-, twenty-five- and one-hundred-year return period runoff events consistent with the calculation methodology specified in § 23B-308.
3. 
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 provided as part of the drainage plan. The district boundaries as originally drawn coincide with topographic divides or, in certain instances, are drawn from the intersection of the watercourse and a physical feature such as the confluence with another watercourse or a potential flow obstruction (e.g. road, culvert or bridge). The physical feature is the downstream limit of the subarea and the subarea boundary is drawn from that point up slope to each topographic divide along the path perpendicular to the contour lines.
4. 
Any capacity analysis conducted in accordance with this Chapter 23B shall use the following criteria for determining adequacy for accepting peak flow rates:
A. 
Natural or man-made channels or swales must be able to convey the runoff associated with a two-year return period event within their banks at velocities consistent with protection of the channels from erosion.
B. 
Natural or man-made channels or swales, culverts, bridges, storm sewers or any other facilities which must convey flows from the tributary area must be able to convey the twenty-five-year return period runoff.
5. 
For a proposed development site located within one release rate category subarea, the total runoff from the site shall meet the applicable release rate criteria. For development sites with multiple directions of runoff discharge, individual drainage directions may be designed for up to a 100% release rate so long as the total runoff from the site is controlled to the applicable release rate.
6. 
For a proposed development site located within two or more release rate category subareas, the peak discharge rate from any subarea shall be the pre-development peak discharge for that subarea multiplied by the applicable release rate. 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 re-combine 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.
7. 
For sites straddling major watershed divides (i.e., Perkiomen and Saucon or Little Lehigh), runoff volumes shall be managed to prevent diversion of runoff between watersheds, as practicable.
8. 
Within a release rate category area, for a proposed development site which has areas which drain to a closed depression(s), the design release from the site will be the lesser of (A) the applicable release rate flow assuming no closed depression(s) or (B) the existing peak flow actually leaving the site. In cases where (B) would result in an unreasonably small design release, the design discharge of less than or equal to the release rate will be determined by the available downstream conveyance capacity to the main channel calculated using Subsection 4 and the minimum orifice criteria.
9. 
Off-site areas which 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 using the capacity criteria in Subsection 4 and the detention criteria in § 23B-308. In addition to the criteria in Subsection 4, on-site conveyance systems designed to carry runoff to a detention basin must be able to transport the basin's one-hundred-year tributary flow either in-system, in-gutter, or overland.
10. 
For development sites proposed to take place in phases, all detention ponds shall be designed to meet the applicable release rate(s) applied to all site areas tributary to the proposed pond discharge direction. All site tributary areas will be assumed as developed, regardless of whether all site tributary areas are proposed for development at that time. An exception shall be sites with multiple detention ponds in series where only the downstream pond must be designed to the stated release rate.
11. 
Where the site area to be impacted by a proposed development activity differs significantly from the total site area, only the proposed impact area shall be subject to the release rate criteria. The impact area includes any proposed cover or grading changes.
12. 
Development proposals which, through groundwater recharge or other means, do not increase either the rate or volume of runoff discharged from the site compared to pre-development are not subject to the release rate provisions of this Chapter 23B.
13. 
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 developers. 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 based on the required release rate at the point of discharge.
[Ord. 2011-03, 2/3/2011, Art. 3]
1. 
Stormwater runoff from all development sites shall be calculated using either the Rational Method or the Soil-Cover-Complex Methodology.
2. 
The design of any detention basin intended to meet the requirements of this Chapter 23B shall be verified by routing the design storm hydrograph through the proposed basin using the storage indication method or other methodology demonstrated to be more appropriate. For basins designed using the Rational Method technique, the design hydrograph for routing shall be either the Universal Rational Hydrograph or another Rational hydrograph that closely approximates the volume of the Universal Rational hydrograph.
3. 
BMPs designed to store or infiltrate runoff and discharge to surface runoff or pipe flow shall be routed using the storage indication method.
4. 
BMPs designed to store or infiltrate runoff and discharge to surface runoff or pipe flow shall provide storage volume for the full WQv below the lowest outlet invert.
5. 
Wet detention ponds designed to have a permanent pool for the WQv shall assume that the permanent pool volume below the primary outlet is full at the beginning of design event routing for the purposes of evaluating peak outflows.
6. 
All above-ground stormwater detention facilities shall provide a minimum 0.5 feet of freeboard above the maximum pool elevation associated with the two- through one-hundred-year runoff events, or an additional 10% of the one-hundred-year storage volume as freeboard volume, whichever is greater. All below-ground stormwater detention and infiltration facilities shall have an additional 10% of the one-hundred-year storage volume available within the storage medium, as well as a minimum of 0.5 feet of freeboard. The freeboard shall be measured from the maximum pool elevation to the invert of the emergency spillway for above-ground facilities, and from the maximum pool elevation to the lowest overflow elevation for below-ground facilities. The two-through one-hundred-year storm events shall be controlled by the primary outlet structure. An emergency spillway for each above-ground basin shall be designed to pass the one-hundred-year return frequency storm peak basin inflow rate with a minimum 0.5 foot freeboard measured to the top of basin. The freeboard criteria shall be met considering any off-site areas tributary to the basin as developed, as applicable. Exceptions to the freeboard requirements are as follows:
A. 
Bioretention BMPs with a ponded depth less than or equal to 0.5 feet are exempt from the freeboard requirements.
B. 
Small detention basins, with a ponded depth less than or equal to 1.5 feet or having a depth to the top of the berm less than or equal to 2.5 feet, may provide 20% additional storage volume measured from the maximum ponded depth to the invert of the emergency spillway in lieu of the above requirements. The depth of the emergency spillway must be sufficient to pass either two times the one-hundred-year peak or the one-hundred-year peak with 0.2 feet of freeboard to the top of berm, whichever is greater.
C. 
Small infiltration basins, with a ponded depth less than or equal to 1.5 feet or having a depth to the top of the berm less than or equal to 2.5 feet, may provide 20% additional storage volume measured from the maximum ponded depth to the top of the berm in lieu of the above requirements. In this case, an emergency spillway is only necessary if runoff in excess of the basin volume would cause harm to downstream owners. If a spillway is necessary, it must be sufficiently sized to pass the one-hundred-year peak inflow.
If this detention facility is considered to be a dam as per DEP Chapter 105, the design of the facility must be consistent with the Chapter 105 regulations and may be required to pass a storm greater than the one-hundred-year event.
7. 
The minimum circular orifice diameter for controlling discharge rates from detention facilities shall be three inches. Designs where a lesser size orifice would be required to fully meet release rates shall be acceptable with a three-inch orifice provided that as much of the site runoff as practical is directed to the detention facilities. The minimum three-inch diameter does not apply to the control of the WQv.
8. 
Runoff calculations using the Soil-Cover-Complex Method shall use the Natural Resources Conservation Service Type II twenty-four-hour rainfall distribution. The twenty-four-hour rainfall depths for the various return periods to be used consistent with this Chapter 23B may be taken from NOAA Atlas 14, Volume .2 Version 2.1, 2004 or the PennDOT Intensity - Duration - Frequency Field Manual ("PDT-IDF") (May 1986) for Region 4. The following values are taken from the PDT-IDF Field Manual:
Return Period
24-Hour Rainfall Depth
1-year
2.40 inches
2-year
3.00 inches
5-year
3.60 inches
10-year
4.56 inches
25-year
5.52 inches
50-year
6.48 inches
100-year
7.44 inches
A graphical and tabular presentation of the Type II-24 hour distribution is included in Appendix 23B-C.
9. 
Runoff calculations using the Rational Method shall use rainfall intensities consistent with appropriate times of concentration and return periods and NOAA Atlas 14, Volume 2 Version 2.1, 2004 or the Intensity-Duration-Frequency Curves as presented in Appendix 23B-C.
10. 
Runoff curve numbers (CN's) to be used in the Soil-Cover-Complex Method shall be based upon the table presented in Appendix 23B-C.
11. 
Runoff coefficients for use in the Rational Method shall be based upon the table presented in Appendix 23B-C.
12. 
All time of concentration calculations shall use a segmental approach which may include one or all of the flow types below:
A. 
Sheet flow (overland flow) calculations shall use either the NRCS average velocity chart (Figure 3-1, Technical Release-55, 1975) or the modified kinematic wave travel time equation (equation 3-3, NRCS TR-55, June 1986). If using the modified kinematic wave travel time equation, the sheet flow length shall be limited to 50 feet for designs using the Rational Method and limited to 150 feet for designs using the Soil-Cover-Complex Method.
B. 
Shallow concentrated flow travel times shall be determined from the watercourse slope, type of surface and the velocity from Figure 3-1 of TR-55, June 1986.
C. 
Open channel flow travel times shall be determined from velocities calculated by the Manning Equation. Bankfull flows shall be used for determining velocities. Manning 'n' values shall be based on the table presented in Appendix 23B-C.
D. 
Pipe flow travel times shall be determined from velocities calculated using the Manning Equation assuming full flow and the Manning 'n' values from Appendix 23B-C.
13. 
If using the Rational Method, all pre-development calculations for a given discharge direction shall be based on a common time of concentration considering both on-site and any off-site drainage areas. If using the Rational Method, all post-development calculations for a given discharge direction shall be based on a common time of concentration considering both on-site and any off-site drainage areas.
14. 
When conditions exist such that a proposed detention facility may experience a tailwater effect, the basin shall be analyzed without any tailwater effect for all storm events for comparison against the required release rates. An additional routing of the one-hundred-year storm with the full tailwater effect shall be performed to check that the basin has sufficient storage to contain the one-hundred-year tributary flow with a tailwater and the applicable freeboard.
15. 
The Manning Equation shall be used to calculate the capacity of watercourses. Manning 'n' values used in the calculations shall be consistent with the table presented in Appendix 23B-C or other appropriate standard engineering 'n' value resources. Pipe capacities shall be determined by methods acceptable to the Township.
16. 
The Pennsylvania DEP, Chapter 105, Rules and Regulations, apply to the construction, modification, operation, or maintenance of both existing and proposed dams, water obstructions, and encroachments throughout the watershed. Criteria for design and construction of stormwater management facilities according to this Chapter 23B may differ from the criteria that are used in the permitting of dams under the Dam Safety Program.