A. 
All regulated activities in the municipality shall be subject to the stormwater management requirements of this chapter.
B. 
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.
C. 
The existing locations of concentrated drainage discharge onto adjacent property shall not be altered without written approval of the affected property owner(s).
D. 
Areas of existing diffused drainage discharge onto adjacent property shall be managed such that, at minimum, the peak diffused flow does not increase in the general direction of discharge, except as otherwise provided in this chapter. If diffused flow is proposed to be concentrated and discharged 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.
E. 
Where a site is traversed by watercourses other than those for which a 100-year floodplain is defined by the municipality, 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 § 163-19 for the 100-year return period runoff and to provide a freeboard allowance of 1 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 100-year floodplain is formally defined are subject to the applicable municipal floodplain regulations including a fifty-foot setback.
F. 
Post construction BMPs shall be designed, installed, operated, and maintained to meet the requirements of the Clean Streams Law[1] and implementing regulations, including the established practices in 25 Pa. Code Ordinance 102 and the specifications of this chapter as to prevent accelerated erosion in watercourse channels and at all points of discharge.
[1]
Editor's Note: See 35 P.S. § 691.1 et seq.
G. 
For all regulated earth disturbance activities, erosion and sediment control BMPs shall be designed, implemented, operated, and maintained during the regulated earth disturbance activities (e.g., 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 (E&S Manual), No. 363-2134-008, as amended and updated.
H. 
No earth disturbance activities associated with any regulated activities shall commence until approval by the municipality of a plan which demonstrates compliance with the requirements of this chapter.
I. 
All proposed infiltration facilities located within carbonate geology shall be reviewed by a professional geologist.
No regulated activities shall commence until all necessary permits and approvals by government entities are obtained.
A. 
No regulated earth disturbance activities within the municipality shall commence until approval by the municipality of an Erosion and Sediment Control Plan for construction activities. Written approval by DEP or a delegated County Conservation District shall satisfy this requirement.
B. 
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).
C. 
A DEP NPDES Stormwater Discharges Associated with Construction Activities Permit is required for regulated earth disturbance activities of one acre or greater under Pa. Code Ordinance 102.
D. 
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 municipality before the commencement of an earth disturbance activity.
E. 
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.
A. 
No regulated earth disturbance activities within the municipality shall commence until approval by the municipality of a drainage plan which demonstrates compliance with this chapter. This chapter provides standards to meet NPDES Permit requirements associated with construction activities and MS4 permit requirements.
B. 
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 predevelopment 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 § 163-19I. 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 § 163-16 of this chapter.
C. 
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.
D. 
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.
E. 
Infiltration BMPs shall not be constructed on fill unless the applicant demonstrates that the fill is stable and otherwise meets the infiltration BMP standards of this chapter.
F. 
The applicant shall document the bedrock types(s) present on the site from published sources. Any apparent boundaries between carbonate and noncarbonate bedrock shall be verified through more detailed site evaluations by a qualified geotechnical professional.
G. 
For each proposed regulated activity in the watershed where an applicant intends to use infiltration BMPs, the applicant shall conduct a preliminary site investigation, including gathering data from published sources, a filed inspection of the site, a minimum of one test pit and a minimum of two percolation tests, as outlined in Appendix G.[1] This investigation will determine depth to bedrock, depth to the seasonal high water table, soil permeability and location of special geologic features, if applicable. The site investigation and infiltration testing shall be conducted by or under the direct supervision of a Soil Science Society of America (SSSA) Certified Professional Soil Scientist, or professional member of the PA Association of Professional Soil Scientists (PAPSS), or a licensed professional geologist with professional experience and education in soil science. Additionally, investigations conducted in areas of carbonate geology must also be reviewed by a professional geologist.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
H. 
Sites where applicants intend to use infiltration BMPs must meet the following criteria:
(1) 
Depth to bedrock below the invert of the BMP greater than or equal to two feet.
(2) 
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.
(3) 
Soil permeability (as measured using the standards listed in Appendix C of the Pennsylvania Stormwater Best Practices Manual) greater than or equal to 0.5 inches/hour and less than or equal to 10 inches/hour. Soils with permeability rates greater than 10 inches/hour may require an additional soil buffer and may be considered on a case-by-case basis.
(4) 
Setback distances or buffers as follows:
(a) 
One hundred feet from water supply wells.
(b) 
Fifteen feet downgradient or 100 feet upgradient from building foundations; except for residential development where the required setback is 10 feet downgradient or 40 feet upgradient from building foundations.
(c) 
50 feet from septic system drainfields; except for residential development where the required setback is 25 feet from septic system drain fields.
(d) 
50 feet from a geologic contact with carbonate bedrock unless a preliminary site investigation is done in the carbonate bedrock to show the absence of special geologic features within 50 feet of the proposed infiltration area.
I. 
In entirely carbonate areas, where the applicant intends to use infiltration BMPs, the preliminary site investigation described in § 163-18G shall be conducted. For infiltration areas that appear feasible based on the preliminary site investigation, the applicant shall conduct the Additional Site Investigation and testing as outlined in Appendix G.[2] The soil depth, percolation rate and proposed loading rate, each weighted as described in § 163-19, along with the buffer from special geologic features shall be compared to the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D[3] to determine if the site is recommended for infiltration. In addition to the recommendation from Appendix D, the conditions listed in § 163-15H are required for infiltration in carbonate areas.
[2]
Editor's Note: Said appendix is included as an attachment to this chapter.
[3]
Editor's Note: Said appendix is included as an attachment to this chapter.
J. 
Site areas proposed for infiltration shall be protected from disturbance and compaction except as necessary for construction of infiltration BMPs.
K. 
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 F.[4]
[4]
Editor's Note: Said appendix is included as an attachment to this chapter.
L. 
Stormwater runoff from hot-spot land uses shall be pretreated. Guidance regarding acceptable methods of pretreatment is located in Appendix F.
M. 
The use of infiltration BMPs is prohibited on hot-spot land use areas, such as vehicle fueling stations, public works storage areas, recycling facilities, fleet storage areas, facilities that make or store hazardous materials, etc.
N. 
Stormwater infiltration BMPs shall not be placed in or on a special geologic feature(s). Additionally, stormwater runoff shall not be discharged into existing on-site sinkholes.
O. 
Applicants shall request, in writing, public water suppliers to provide the Zone I Wellhead Protection radius, as calculated by the method outlined in the Pennsylvania Department of Environmental Protection Wellhead Protection regulations, for any public water supply well within 400 feet of the site. In addition to the setback distances specified in § 163-15H, 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.
P. 
The Municipality may, after consultation with DEP, approve alternative methods 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.[5]
[5]
Editor's Note: See 35 P.S. § 691.1 et seq.
Q. 
Infiltration systems may not receive runoff until the entire tributary drainage area to the infiltration system has received final stabilization.
A. 
The entire WQv as calculated in § 163-15B of this chapter shall be captured and treated by either direct recharge (D-RE) or evapotranspiration (ET) BMPs.
B. 
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.
C. 
Existing impervious area that is not proposed to be treated by D-RE BMPs should be excluded from all water balance calculations.
D. 
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.
(1) 
For development sites with greater than 33% proposed impervious cover:
(a) 
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.
(b) 
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.
(c) 
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 C[1] shall be used to assure that the maximum D-RE standard is met.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
(2) 
For development sites with less than 33% proposed impervious cover, all proposed impervious and the entire WQv may be directed to D-RE BMPs.
(3) 
The maximum 30% D-RE standard applies on an overall site basis, rather than in each drainage direction.
A. 
Mapping of stormwater management districts. To implement the provisions of the Forks Township Watershed Stormwater Management Plan, the municipality is hereby divided into stormwater management districts consistent with the Bushkill Creek, Martins/Jacoby Creeks and Delaware Sub-basin I Watershed release Rate Maps presented in the plan update. The boundaries of the stormwater management districts coincide with the subareas delineated on the Act 167 watershed release rate maps which are available for inspection at the Municipal office. A copy of the official map at a reduced scale is included in Appendix A[1] for general reference.
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
B. 
Description of stormwater management districts. The ten-, twenty-five-, and 100-year post-development peak runoff must be controlled to the stated percentage of the predevelopment peak. Release rates associated with the ten-through 100-year events vary from 50% to 100% depending upon location in the watershed.
C. 
Unstudied watersheds. These areas shall be subject to all criteria of this chapter and have a 100% release rate.
A. 
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.
B. 
Any stormwater management controls required by this chapter and subject to release rate criteria shall meet the applicable release rate criteria for each of the ten-, twenty-five- and 100-year return period runoff events consistent with the calculation methodology specified in § 163-19.
C. 
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, bridge, etc.). 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.
D. 
Any capacity analysis conducted in accordance with this chapter shall use the following criteria for determining adequacy for accepting peak flow rates:
(1) 
Natural or man-made channels or swales must be able to convey the increased runoff associated with a two-year return period event within their banks at velocities consistent with protection of the channels from erosion.
(2) 
Natural or man-made channels or swales must be able to convey the increased twenty-five-year return period runoff without creating any hazard to persons or property.
(3) 
Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area must be designed in accordance with DEP Chapter 105 regulations[1] (if applicable) and, at a minimum, pass the increased twenty-five-year return period runoff.
[1]
Editor's Note: See 25 Pa. Code Ch. 105.
E. 
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.
F. 
For a proposed development site located within two or more release rate category subareas, the peak discharge rate from any subarea shall be the predevelopment 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.
G. 
For a proposed development site located partially within a release rate category subarea and partially within conditional/provisional no detention subarea, the size of the predevelopment drainage area on a site may not be changed post-development to create potentially adverse conditions on downstream properties except as part of a "No Harm" or hardship waiver procedure.
H. 
No portion of a site may be regarded between any Forks Township Watershed and any adjacent watershed except as part of a "no harm" or hardship waiver procedure.
I. 
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 § 163-18D and the minimum orifice criteria.
J. 
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 § 163-18D and the detention criteria in § 163-19. In addition to the criteria in § 163-18D, on-site conveyance systems designed to carry runoff to a detention basin must be able to transport the basin's 100-year tributary flow either in-system, in-gutter, or overland.
K. 
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.
L. 
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.
M. 
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 predevelopment are not subject to the release rate provisions of this chapter.
N. 
"No harm" water quantity option. For any proposed development site, the developer has the option of using a less restrictive runoff control if the developer can prove that special circumstances exist for the proposed development site and the "no harm" would be caused by discharging at a higher runoff rate than that specified by the Plan. Special circumstances are defined as any hydrologic or hydraulic aspects of the development itself not specifically considered in the development of the Plan runoff control strategy. Proof of "no harm" would have to be shown from the development site through the remainder of the downstream drainage network to the confluence of the creek with the Delaware River. Proof of "no harm" must be shown using the capacity criteria specified in § 163-18D if downstream capacity analysis is a part of the "no harm" justification.
(1) 
Attempts to prove "no harm" based upon downstream peak flow versus capacity analysis shall be governed by the following provisions:
(a) 
Any available capacity in the downstream conveyance system as documented by a developer may be used by the developer only in proportion to their development site acreage relative to the total upstream undeveloped acreage from the identified capacity (i.e., if their site is 10% of the upstream undeveloped acreage, they may use up to 10% of the documented downstream available capacity).
(b) 
Developer-proposed runoff controls which would generate increased peak flow rates at storm drainage problem areas would, by definition, be precluded from successful attempts to prove "no harm."
(2) 
Any "no harm" justifications shall be submitted by the developer as part of the drainage plan submission per Article IV. Developers submitting "no harm" justifications must still meet all of the water quality requirements in § 163-15.
O. 
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.
P. 
Capacity improvements. In certain instances, primarily within the Conditional/Provisional No Detention areas, local drainage conditions may dictate more stringent levels of runoff control than those upon protection of the entire watershed. In these instances, if the developer could prove that it would be feasible to provide capacity improvements to relieve the capacity deficiency in the local drainage network, then the capacity improvements could be provided by the developer in lieu of additional runoff controls on the development site. Peak flow calculations shall be done assuming that the local watershed is in the existing condition and then assuming that the local watershed is developed per current zoning and using the specified runoff controls. Any capacity improvements would be designed using the larger of the above peak flows and the capacity criteria specified in § 163-18D. All new development in the entire subarea(s) within which the proposed development site is located shall be assumed to implement the developer's proposed drainage control, if any.
Q. 
Capacity improvements shall be provided as necessary to implement any regional detention alternatives or to implement a modified "no harm" option which proposes specific capacity improvements to provide that a less stringent discharge control would not create any harm downstream.
A. 
Stormwater runoff from all development sites shall be calculated using either the Rational Method or the soil cover complex methodology.
B. 
Infiltration BMP loading rate percentages in the Recommendation Chart for Infiltration Stormwater Management BMPs in Carbonate Bedrock in Appendix D[1] shall be calculated as follows:
Area Tributary to infiltration BMP x 100%
Base area of infiltration BMP
The area tributary to the infiltration BMP shall be weighted as follows:
All disturbed areas to be made impervious:
Weight at 100%
All disturbed areas to be made pervious:
Weight at 50%
All undisturbed pervious areas:
Weight at 0%
All existing impervious areas:
Weight at 100%
[1]
Editor's Note: Said appendix is included as an attachment to this chapter.
C. 
The design of any detention basin intended to meet the requirements of this chapter 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.
D. 
BMPs designed to store or infiltrate runoff and discharge to surface runoff or pipe flow shall be routed using the storage indication method.
E. 
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.
F. 
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.
G. 
All aboveground stormwater detention facilities shall provide a minimum 0.5 feet of freeboard above the maximum pool elevation associated with the two- through 100-year runoff events, or an additional 10% of the 100-year storage volume as freeboard volume, whichever is greater. All below-ground stormwater detention and infiltration facilities shall have an additional 10% of the 100-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 aboveground facilities, and from the maximum pool elevation to the lowest overflow elevation for below-ground facilities. The two-through 100-year storm events shall be controlled by the primary outlet structure. An emergency spillway for each aboveground basin shall be designed to pass the 100-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:
(1) 
Bioretention BMPs with a ponded depth less than or equal to 0.5 feet are exempt from the freeboard requirements.
(2) 
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 100-year peak or the 100-year peak with 0.2 feet of freeboard to the top of berm, whichever is greater.
(3) 
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 100-year peak inflow.
If this detention facility is considered to be a dam as per DEP Ordinance 105,[2] the design of the facility must be consistent with the Ordinance 105 regulations and may be required to pass a storm greater than the 100-year event.
[2]
Editor's Note: See 25 Pa. Code Ch. 105.
H. 
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.
I. 
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 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
(inches)
1-year
2.40
2-year
3.00
5-year
3.60
10-year
4.56
25-year
5.52
50-year
6.48
100-year
7.44
A graphical and tabular presentation of the Type II twenty-four-hour distribution is included in Appendix C.[3]
[3]
Editor's Note: Said appendix is included as an attachment to this chapter.
J. 
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 C.
K. 
Runoff curve numbers (CNs) to be used in the soil cover complex method shall be based upon the table presented in Appendix C.
L. 
Runoff coefficients for use in the Rational Method shall be based upon the table presented in Appendix C.
M. 
All time-of-concentration calculations shall use a segmental approach which may include one or all of the flow types below:
(1) 
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.
(2) 
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.
(3) 
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 C.
(4) 
Pipe flow travel times shall be determined from velocities calculated using the Manning Equation assuming full flow and the Manning "n" values from Appendix C.
N. 
If using the Rational Method, all predevelopment calculations for a given discharge direction shall be based on a common time of concentration (Tc) 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.
O. 
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 100-year storm with the full tailwater effect shall be performed to check that the basin has sufficient storage to contain the 100-year tributary flow with a tailwater.
P. 
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 C or other appropriate standard engineering "n" value resources. Pipe capacities shall be determined by methods acceptable to the municipality.
Q. 
The Pennsylvania DEP, Ordinance 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 may differ from the criteria that are used in the permitting of dams under the Dam Safety Program.