Borough of Jim Thorpe, PA Article III Stormwater Management

§ 377-9 General requirements.

A. All regulated activities in the Borough of Jim Thorpe which do not fall under the exemption criteria shown in § 377-5 of this chapter shall submit a stormwater management site plan consistent with the Jim Thorpe Borough Watershed Stormwater Management Plan to the Borough for review. This criteria will 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 purposes of comparison to the waiver criteria.

B. Storm drainage systems shall be provided to permit unimpeded flow in natural watercourses except as modified by stormwater detention facilities or open channels consistent with this chapter.

C. The existing points 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 a 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 document that there are adequate downstream conveyance facilities to safely transport the concentrated discharge or otherwise prove that no harm will result from the concentrated discharge. 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, 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 § 377-13 for the 100-year return period runoff and to provide a freeboard allowance of 0.5 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 floodplain regulations.

F. Any drainage facilities or structures required by this chapter that are located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation.

G. When it can be shown that due to topographic conditions natural drainage swales on the site cannot adequately provide for drainage, open channels may be constructed conforming substantially to the line and grade of such natural drainage swales. Capacities of open channels shall be calculated using the Manning equation.

H. Storm drainage facilities and appurtenances shall be so designed and provided as to minimize erosion in watercourse channels and at all points of discharge.

I. Consideration should be given to the design and use of volume controls for stormwater management, where geology and soils permit. Areas of suitable geology for volume controls shall be determined by the municipality. Documentation of the suitability of the soil for volume controls shall be provided by the applicant. Volume controls shall be acceptable in the areas of suitable geology where the soils are designated as well-drained in the County Soil Survey. Other soils may be acceptable for use of volume controls based on site-specific soils evaluations provided by the applicant.

J. 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 PA DEP through the joint permit application process or, where deemed appropriate by PA DEP, the general permit process. When there is a question whether wetlands may be involved, it is the responsibility of the developer 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 PA DEP and any other agencies with jurisdiction.

K. Minimization of impervious surfaces and infiltration of runoff through seepage beds, infiltration trenches, etc., are encouraged, where soil conditions permit, to reduce the size or eliminate the need for detention facilities.

L. Roof drains must not be connected to streets, sanitary or storm sewers, or roadside ditches to promote overland flow and infiltration/percolation of stormwater where advantageous to do so. When it is more advantageous to connect directly to streets or storm sewers, then it shall be permitted on a case-by-case basis by the Borough.

M. The design of all facilities over karst shall include an evaluation of measures to minimize adverse effects.

N. Infiltration BMPs should be spread out, made as shallow as practical, and located to maximize use of natural on-site infiltration features while still meeting the other requirements of this chapter.

O. Normally dry, open top, storage facilities should completely drain both the volume control and rate control capacities over a period of time not less than 24 and not more than 72 hours from the end of the design storm.

§ 377-10 Stormwater management districts.

A. Mapping of stormwater runoff peak rate districts. In order to implement the provisions of the Jim Thorpe Borough Watershed Stormwater Management Plan, the Borough of Jim Thorpe is hereby divided into stormwater runoff peak rate districts consistent with the plan. The boundaries of the districts are indicated on the runoff peak rate district map that is available for inspection at the Borough building. A large-scale boundary map is included in the appendix for reference.

B. The exact location of the stormwater runoff peak rate district boundary as it applies to a given development site shall be determined by mapping the boundaries using the two-foot or five-foot topographic contours provided as part of the stormwater management plan developed for the site in accordance with Chapter 390, Subdivision and Land Development. 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 to the topographic divide consistent with topography of the watershed. The physical feature is the downstream limit of the subarea and the subarea boundary is drawn from that point upslope to each topographic divide along the perpendicular to the contour lines. The locations determined on the stormwater management plan shall be reviewed and verified by a municipal representative.

C. Watersheds.

(1) Slaughterhouse Creek Watershed, description of stormwater management districts. Four types of stormwater management districts may be applicable to the municipality, namely, 75% Release Rate District, 90% Release Rate District, 100% Release Rate District, and Conditional No Detention District.

(a) Subarea SR-1, 75% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 75% of the predevelopment peak.

(b) Subarea SR-2, 90% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 90% of the predevelopment peak.

(c) Subarea SR-3, 100% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(d) Subarea SR-4, Conditional No Detention District. Within this district, the capacity of the local runoff conveyance facilities (as defined in Article II) must be calculated to determine if adequate capacity exists. For this determination, the developer must calculate peak flows assuming that the site is developed as proposed and that the remainder of the local watershed is in the existing condition. The developer must also calculate peak flows assuming that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified by this chapter. The larger of the two peak flows calculated will be used in determining if adequate capacity exists. If adequate capacity exists to safely transport runoff from the site to the main channel, these watershed areas may discharge postdevelopment peak runoff without detention facilities. If the capacity calculations show that the local runoff conveyance facilities lack adequate capacity, the developer shall either use a 100% release rate control or provide increased capacity of downstream elements to convey increased peak flows consistent with § 377-13N. Any capacity improvements must be designed to convey runoff from development of all areas tributary to the improvement consistent with the capacity criteria specified in § 377-11C. By definition, a storm drainage problem area associated with the local runoff conveyance facilities indicates that adequate capacity does not exist.

(2) Mauch Chunk Creek Watershed, description of stormwater management districts. Four types of stormwater management districts may be applicable to the municipality, namely 100% Release Rate District, 95% Release Rate District, 90% Release Rate District, and 85% Release Rate District.

(a) Subarea MC-7, 100% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(b) Subareas MC-8 and MC-11, 95% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 95% of the predevelopment peak.

(c) Subarea MC-9, 90% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 90% of the predevelopment peak.

(d) Subarea MC-10, 85% Release Rate District. Within this district, two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 85% of the predevelopment peak.

(3) Mahoning Creek Watershed, description of stormwater management districts. Seven types of stormwater management districts may be applicable to the municipality; namely 65/85/100% Release Rate District, 75/100% Release Rate District, 95/100% Release Rate District, 100% Release Rate District, 85/95/100% Release Rate District, 100/75/100% Release Rate District, and 95/90/100% Release Rate District.

(a) Subarea M-56, 65/85/100% Release Rate District. Within this district, the two-year postdevelopment runoff must be controlled to 65% of the predevelopment peak, ten-year postdevelopment runoff must be controlled to 85% of the predevelopment peak, and twenty-five- and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(b) Subarea M-59 and 75, 95/100% Release Rate District. Within this district, the two-, ten-year postdevelopment runoff must be controlled to 95% of the predevelopment peak, and the twenty-five-, and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(c) Subarea M-74, 100% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(d) Subarea M-76, 85/95/100% Release Rate District. Within this district, the two-year postdevelopment runoff must be controlled to 85% of the predevelopment peak, the ten-year postdevelopment runoff must be controlled to 95% of the predevelopment peak, and twenty-five- and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(e) Subarea M-77, 100/75/100% Release Rate District. Within this district, the two-year postdevelopment runoff must be controlled to 100% of the predevelopment peak, ten-year postdevelopment runoff must be controlled to 75% of the predevelopment peak, and twenty-five- and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(f) Subarea M-78, 95/90/100% Release Rate District. Within this district, the two-year postdevelopment runoff must be controlled to 95% of the predevelopment peak, the ten-year postdevelopment runoff must be controlled to 90% of the predevelopment peak, and the twenty-five- and 100-year postdevelopment runoff must be controlled to 100% of the predevelopment peak.

(4) Silk Mill Run Watershed, description of stormwater management districts. Five types of stormwater management districts may be applicable to the municipality, namely 95% Release Rate District, 90% Release Rate District, 85% Release Rate District, 80% Release Rate District, and 75% Release Rate District.

(a) Subarea SMR-1, 95% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 95% of the predevelopment peak.

(b) Subarea SMR-2, 90% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 90% of the predevelopment peak.

(c) Subarea SMR-3, 85% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 85% of the predevelopment peak.

(d) Subarea SMR-4, 80% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 80% of the predevelopment peak.

(e) Subarea SMR-5, 75% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 75% of the predevelopment peak.

(5) Robertson Run Watershed, description of stormwater management districts. Four types of stormwater management districts may be applicable to the municipality, namely 90% Release Rate District, 85% Release Rate District, 80% Release Rate District, and 75% Release Rate District.

(a) Subarea RR-1, 90% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 90% of the predevelopment peak.

(b) Subarea RR-2, 85% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 85% of the predevelopment peak.

(c) Subarea RR-3, 80% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 80% of the predevelopment peak.

(d) Subarea RR-4, 75% Release Rate District. Within this district, the two-, ten-, twenty-five-, and 100-year postdevelopment runoff must be controlled to 75% of the predevelopment peak.

(6) General Districts, description of the general stormwater management districts. The G1 and G2 stormwater management districts are conditional no detention districts.

(a) Subarea G-1, Conditional No Detention District. Within this district, the watershed area tends to peak very early with respect to the total watershed peak flow and contribute very minimal flow to the watershed peak flow. For that reason, areas within this district that discharge directly into the Lehigh River may discharge postdevelopment peak runoff without detention for the ten- through 100-year return periods without adversely affecting the total watershed peak flow. This area is designated as conditional no detention areas because in certain instances the local runoff conveyance facilities, which transport runoff from the site to the main channel, may not have adequate capacity to safely transport the peak flows associated with no detention for a proposed development. In those instances, a 100% release rate control would have to be provided or, alternately, the capacity deficiency(ies) would have to be corrected.

(b) Subarea G-2, Conditional No Detention District. Areas within this district discharge into an adjacent municipality (including any watercourse along said municipal boundary) and shall maintain a 100% release rate control, unless the entire conveyance system from the discharge point to the Lehigh River is reviewed and accepted by the adjacent municipality.

§ 377-11 Stormwater management district implementation provisions (performance standards).

A. General. Postdevelopment rates of runoff from any regulated activity shall not exceed the specified hydrologic district peak release rates of runoff for the design storms specified on the Stormwater Runoff Peak Rate Districts Map and § 377-10. Calculations must be provided to ensure that postdevelopment runoff peak rates from storms including the two-, ten-, twenty-five-, and 100-year frequency storms do not exceed predevelopment peak rates, or the hydrologic district peak release rate for that district, for similar frequency storms.

B. Groundwater recharge.

(1) Developed areas shall maintain groundwater recharge consistent with predevelopment conditions, dependent on hydrologic soil groups and impervious cover. A minimum of one inch of runoff shall be infiltrated unless the developer can prove the inability of the site to achieve this specific volume based on existing site conditions. The maximum available recharge shall be calculated based on utilizing the most capable recharge areas of the site. This volume of runoff is termed the "recharge volume" and is calculated in accordance with § 377-13P.

(2) Design of the stormwater management facilities shall provide for groundwater recharge to compensate for the reduction in the percolation that occurs when the ground surface runoff characteristics have been altered. A detailed geologic evaluation of the project site shall be performed to determine the suitability of recharge facilities. The evaluation shall be performed by a qualified geologist and/or soil scientist and shall, at a minimum, address soil permeability, depth to bedrock, susceptibility to sinkhole formation, and subgrade stability. Where pervious pavement is permitted for parking lots, recreational facilities, nondedicated streets, or other areas, pavement construction specifications shall be noted on the plan.

(3) Whenever a stormwater facility will be located in an area underlain by limestone, a geological evaluation of the proposed location shall be conducted to determine susceptibility to sinkhole formations. The design of all facilities over limestone formations shall include measures to prevent groundwater contamination and, where necessary, sinkhole formation. Soils used for the construction of basins shall have low erodibility factors ("K" factors). The Borough may require the installation of an impermeable liner in detention basins. If the developer can prove through analysis that the site is in an area underlain by limestone, and such geologic conditions may result in sinkhole formations, then the site is exempt from recharge requirements. However, the site shall still be required to meet all other hydrologic and water quality management standards as found in this chapter.

(4) It shall be the developer's responsibility to verify if the site is underlain by limestone. The following note shall be attached to all stormwater management site plans and signed and sealed by the developer's engineer/surveyor/landscape architect/architect: "I, __________, certify that the proposed detention basin (circle one) is/is not underlain by limestone."

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

(1) Natural or man-made channels or swales must be able to convey the increased runoff associated with a two-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 DEP Erosion and Sediment Pollution Control Program Manual (April 1990) or its updates. Permissible velocities from the DEP manual for selected channels are presented in the appendix of this chapter.

(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 (where applicable) and, at a minimum, pass the increased twenty-five-year return period runoff.

D. 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 within 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.

E. Sites located in more than one district. For a proposed development site located within two or more release 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 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.

F. For a proposed development site located partially within a release rate category subarea and partially within a conditional no detention subarea, in no event shall a significant portion of the site area subject to the release rate control be drained to the discharge point(s) located in the no detention subarea.

G. Proposed development site has significant areas which drain to closed depression(s).

(1) Within a release rate category subarea, for a proposed development site which has significant areas which drain to a closed depression(s), the design release from the site will be the lesser of:

(a) The total development site runoff times the applicable release rate; or

(b) The existing peak flow actually leaving the site.

(2) In cases where Subsection G(1)(b) would result in a zero design release, the design discharge of less than or equal to the release rate calculated in Subsection G(1)(a) will be determined by the municipal engineer using the available downstream conveyance capacity to the main channel and the minimum orifice criteria.

H. Water quality. Developed areas will provide adequate storage and treatment facilities necessary to capture and treat the water quality volume (WQv) consistent with Articles III and IV of this chapter. The water quality volume is calculated in accordance with § 377-130. The recharge volume may be a component of the water quality volume. 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.

I. District boundaries. 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 the appendix of this chapter.[1] 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 topographic contours at an appropriate level of detail, but in no case less than two-foot intervals. The Borough may determine that a more frequent contour interval is necessary to adequately delineate the district boundary. This information will be provided as part of the stormwater management site plan.

[1] Editor's Note: Said map is on file in the Borough offices.

J. 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.

K. Site areas. 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.

L. Stormwater conveyance corridor protection (riparian corridor preservation and vegetation).

(1) Runoff from developed areas of the site, including but not limited to areas of impervious surface, shall be managed through a series of riparian corridor vegetation facilities whenever possible. This will be accomplished in a manner satisfactory to the Borough utilizing the "Pennsylvania Handbook of Best Management Practices for Developing Areas," 1998, Riparian Forested Buffer, and the priority goal of the riparian vegetation will be the reduction of thermal impacts on stormwater runoff associated with impervious areas, with a secondary goal being the protection of capacity of existing stormwater conveyance channels. These goals will be achieved through the use of design criteria in § 377-12J of this chapter, and shall be in addition to any other municipal ordinance provisions.

(2) Within a particular district, the Borough may require the submission of a downstream hydraulic capacity analysis to verify stormwater management routing, timing, combined peak effects, etc., associated with unanticipated impervious cover and development, such as may result from changes in zoning or conditional uses which exceed projected growth for a particular watershed. Such analysis shall be conducted in accordance with this chapter and is subject to the review and approval of the municipal engineer.

M. 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 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.

§ 377-12 Design criteria for stormwater management facilities.

A. Any stormwater facility located on state highway rights-of-way shall be subject to approval by the Pennsylvania Department of Transportation.

B. 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 PA DEP Chapter 105, 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.

C. Any facilities that constitute water obstructions (e.g., culverts, bridges, outfalls, or stream enclosures), and any work involving wetlands as directed by PA DEP Chapter 105 regulations (as amended or replaced from time to time by PA DEP), shall be designed in accordance with Chapter 105 and will require a permit from PA DEP. Any other drainage conveyance facility that doesn't fall under Chapter 105 regulations must be able to convey, without damage to the drainage structures or roadway, runoff from the twenty-five-year design storm with a minimum of 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 roadway. Any facility that constitutes a dam as defined in PA DEP Chapter 105 regulations may require a permit under dam safety regulations. Any facility located within a PA DOT right-of-way must meet PA DOT minimum design standards and permit submission requirements.

D. Any drainage conveyance facility and/or channel that doesn't fall under Chapter 105 regulations must be able to convey, without damage to the drainage structure or roadway, runoff from the twenty-five-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 PA DOT right-of-way must meet PA DOT minimum design standards and permit submission requirements.

E. Storm sewers must be able to convey postdevelopment runoff from a twenty-five-year design storm without surcharging inlets, where appropriate.

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

G. Design of all stormwater management facilities shall incorporate sound engineering principles and practices. Guidelines established by the Pennsylvania Handbook of Best Management Practices for Developing Areas shall be utilized in determining stormwater management facility design. The Borough shall reserve the right to disapprove any design that would result in the occupancy or continuation of an adverse hydrologic or hydraulic condition within the watershed.

(1) In selecting the appropriate BMPs or combinations thereof, the land developer shall take into account the following:

(a) Total contributing area.

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

(c) Slope and depth to bedrock.

(d) Seasonal high water table.

(e) Proximity to building foundations and wellheads.

(f) Erodibility of soils.

(g) Land availability and configuration of the topography.

(2) The following additional factors should be considered when evaluating the suitability of BMPs used to control water quality at a given development site:

(a) Peak discharge and required volume control.

(b) Streambank erosion.

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

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

(e) The nature of the pollutant being removed.

(f) Maintenance requirements.

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

(h) Recreational value.

(i) Enhancement of aesthetic and property value.

H. Pipe or artificial swale discharge shall be set back 75 feet from a receiving waterway, and the pipe discharge shall be immediately diffused or spread out to reduce and eliminate high-velocity discharges to the impacted ground surface. The conveyance mechanism shall minimize disturbance and minimize velocity of discharge.

I. All infiltration devices and groundwater recharge facilities shall be designed to completely drain all water in three days (72 hours) subsequent to any storm event.

J. Riparian corridor preservation. The area up to 50 feet from top of streambank on either side of a stream shall be planted in accordance with Zone I and Zone II buffer planting requirements as depicted in "Pennsylvania Handbook of Best Management Practices for Developing Areas," 1998, Riparian Forested Buffer. Zone I will comprise, at a minimum, the first 15 feet from top of bank, with Zone II comprising the remaining 35 feet. This replanting may be waived by the Borough along streambank areas which receive overland or shallow flow from upstream, disturbed, meadow or other existing pervious surfaces.

K. All developments which create impervious surface shall provide capacity for and treatment of the water quality volume and recharge volume, unless exempt from applicability under § 377-4.

L. Special requirements for areas falling within defined exceptional value and high-quality sub-watersheds:

(1) The temperature and quality of water and streams that have been declared as exceptional value or high quality is to be maintained as defined in Chapter 93, Water Quality Standards, Title 25 of Pennsylvania Department of Environmental Protection Rules and Regulations. Temperature-sensitive BMPs and stormwater conveyance systems are to be used and designed with storage pool areas and supply outflow channels and should be shaded with trees. This will require the modification of berms for permanent ponds and the relaxation of restrictions on planting vegetation within the facilities, provided that capacity for volume and rate controls is maintained. At a minimum, the southern half of pond shorelines shall be planted with shade or canopy trees within 10 feet of the pond shoreline. In conjunction with this requirement, the maximum slope allowed on the berm area to be planted is 10 to 1. This will lessen the destabilization of berm soils due to root growth.

(2) A long-term maintenance schedule and management plan for the thermal control BMP is to be established and recorded for all development sites.

M. Development proposals which, through groundwater recharge or other means, do not increase the rate or volume of runoff discharged from the site are not subject to the release rate provisions of this chapter.

N. In any stormwater management district, the municipal engineer may specify a more stringent design release for a development site or other amendments to a drainage plan to address problems in the local runoff conveyance system downstream of the site. Such problems include existing flooding problems, inadequate conveyance capacity, poorly defined or poorly stabilized downstream conveyance systems, or other factors.

O. "No harm" option. For any proposed development site not located in a conditional no-detention district, the developer has the option of using a less-restrictive runoff control (including no detention) if the developer can prove that no harm would be caused by discharging at a higher runoff rate than that specified by the plan. 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 Lehigh River, as applicable. Proof of no harm must be shown using the capacity criteria specified in § 377-11C 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) The peak flow values to be used for downstream areas for the design return period storms (two-, ten-, twenty-five-, and 100-year) shall be the values from the calibrated Penn State Runoff Models for the watershed and its unnamed creeks. For the Conditional No Detention II areas, the PSU-IV peak flow values will be used.

(b) Any available capacity in the downstream conveyance system as documented by a developer may be used by the developer only in proportion to the development site acreage relative to the total upstream undeveloped acreage from the identified capacity (i.e., if the developer's site is 10% of the upstream undeveloped acreage, he may use up to 10% of the documented downstream available capacity).

(c) 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, except in conjunction with proposed capacity improvements for the problem areas consistent with § 377-13N.

(2) Any no harm justifications shall be submitted by the developer as part of the drainage plan submission per Article IV.

P. Capacity improvements.

(1) In certain instances, primarily within the conditional no-detention areas, local drainage conditions may dictate more stringent levels of runoff control than those based 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 runoff controls on the development site. Peak flow calculations are to 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 § 377-11C. 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 discharge control, if any.

(2) Capacity improvements may also 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.

Q. Compatibility with NPDES requirements. Any proposed regulated activity for which a permanent stormwater quality control detention basin is required under the NPDES regulations shall use the more stringent runoff control criteria between this chapter and the NPDES requirements.

§ 377-13 Calculation methodology.

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 involving drainage areas greater than 200 acres, including on- and off-site areas, shall use generally accepted calculation technique that is based on the NRCS soil cover complex method. Table 1 summarizes acceptable computation methods. It is assumed that all methods will be selected by the design professional based on the individual limitations and suitability of each method for a particular site. The Borough may approve the use of the Rational Method to estimate peak discharges from drainage areas that contain less than 200 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 presented in the appendix of this chapter.[1] If a hydrologic computer model such as PSRM or HEC-1 is used for stormwater runoff calculations, then the duration of rainfall shall be 24 hours. The NRCS "S" curve shown in the appendix of this chapter shall be used for the rainfall distribution.

[1] Editor's Note: Said calculations are included as an attachment to this chapter.

C. For the purposes of predevelopment flow rate determination, undeveloped land shall be considered as meadow, good condition, unless the natural ground cover generates a lower curve number or Rational "C" value (i.e., forest).

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 PA Department of Transportation Design Rainfall Curves (1986) (figure in appendix).[2] 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.

Table 1 Acceptable Computation Methodologies for Stormwater Management Plans
Method	Method Developed by	Applicability
TR-20 or commercial package based on TR-20	USDA-NRCS	When use of full model is desirable or necessary
TR-55 or commercial package based on TR-55	USDA-NRCS	Applicable for plans within the model's limitations
HEC-1	U.S. Army Corps of Engineers	When full model is desirable or necessary
PSRM	Penn State University	When full model is desirable or necessary
Rational Method or commercial package based on Rational Method	Emil Kuiching (1889)	For sites less than 200 acres
Other methods	Various	As approved by the municipal engineer

[2] Editor's Note: Said figure is on file in the Borough offices.

E. Runoff curve numbers (CN) for both existing and proposed conditions to be used in the soil cover complex method shall be obtained from the table in the appendix of this chapter.[3]

[3] Editor's Note: Said tables are included as an attachment to this chapter.

F. Runoff coefficient (c) for both existing and proposed conditions for use in the Rational Method shall be obtained from the table in the appendix of this chapter.[4]

[4] Editor's Note: Said table is included as an attachment to this chapter.

G. Where uniform flow is anticipated, the Manning equation shall be used for hydraulic computations, and to determine the capacity of open channels, pipes, and storm sewers. Values for Manning's roughness coefficient (n) shall be consistent with the tables in the appendix of this chapter.[5] 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.

[5] Editor's Note: Said tables are included as an attachment to this chapter.

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. For drainage areas greater than 20 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.

I. All stormwater detention facilities shall provide a minimum 1.0 foot freeboard, measured to the invert of the emergency spillway, above the maximum pool elevation associated with the two- through twenty-five-year runoff events. A 0.5 foot freeboard shall be provided above the maximum pool elevation of the 100-year runoff event. The two- through 100-year storm events shall be controlled by the primary outlet structure. An emergency spillway for each basin shall be designed to pass the entire 100-year return frequency storm peak flow rate with a minimum 0.5 foot freeboard measured to the top of the basin. The spillway should function to control overflows in the event of a complete blockage of the basin outlet system. 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 100-year event.

J. The minimum circular orifice diameter for controlling discharge rates from detention facilities shall be three inches provided that as much of the site runoff as practical is directed to the detention facilities.

K. Proposed volume controls shall be designed with sufficient storage volume for a 100-year return period event unless proposed in combination with rate controls to achieve the required performance standard across all return periods. For the return period(s) to be solely controlled by the volume control, the storage volume shall equal or exceed the volume of the universal rational hydrograph for the drainage area to the volume control.

L. All predevelopment 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. All postdevelopment 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.

M. 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 may not be the same criteria that are used in the permitting of dams under the Dam Safety Program.

N. If the designer can substantiate through actual physical calibration that more appropriate runoff and time-of-concentration values should be utilized at a particular site, then appropriate variations may be made upon review and recommendations of the Municipal Engineer, provided that the Borough has the authority to require that computed existing runoff rates be reconciled with field observations and conditions. Calibration shall require detailed gauge and rainfall data for the particular site in question.

O. Calculation of water quality volume. The water quality volume (WQv) is the storage capacity needed to treat 90% of the average annual stormwater rainfall from the developed areas of the site. The following calculation is used to determine the storage volume, WQv, in acre-feet of storage.

WQv	=	(1.95) (Rv)(A) 12
WQv	=	Water quality volume
A	=	Area in acres
Rv	=	0.05 + 0.009 (I), where I is the percent impervious cover (example: I = 50 for 50% impervious cover)
1.95	=	A coefficient representing the 90% annual rainfall (PA Handbook of Best Management Practices for Developing Areas)

WQv shall be designed as part of a stormwater management facility which incorporates water quality BMPs as a primary benefit of using that facility, in accordance with design specifications contained in "Pennsylvania Handbook of Best Management Practices for Developing Areas," 1998.

P. Calculation of recharge volume. The recharge volume (Rev) is the volume of stormwater runoff from a developed site which shall be required to maintain existing predevelopment groundwater recharge at development sites. It may be part of the water quality volume, and is calculated on the basis of treatment and recharge by structural stormwater management practices, as follows:

Rev	=	(S)(Rv)(A) 12
Rev	=	Recharge volume
A	=	Area in acres
Rv	=	0.05 + 0.009(I), where I is the percent impervious cover (example: I = 50 for 50% impervious cover)

S is the soil-specific recharge factor and varies according to soil type, as follows:

Hydrologic Soil Group	Soil-Specific Recharge Factor (S)
A	0.38
B	0.26
C	0.14
D	0.07

Structural stormwater management facilities which provide treatment and recharge of the required recharge volume will be designed as part of a stormwater management facility which incorporates groundwater recharge BMPs as a primary benefit of using that facility, in accordance with design specifications contained in "Pennsylvania Handbook of Best Management Practices for Developing Areas," 1998.

§ 377-14 Erosion and sedimentation requirements.

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

B. Additional erosion and sedimentation control design standards and criteria that must be or are recommended to be applied where infiltration BMPs are proposed and include the following:

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

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

§ 377-15 Riparian buffers.

A. In order to protect and improve water quality, a riparian buffer easement shall be created and recorded as part of any subdivision or land development that encompasses a Riparian Buffer.

B. Except as required by Chapter 102, the riparian buffer easement shall be measured to be the greater of the limit of the 100-year floodplain or a minimum of 35 feet from the top of the streambank (on each side).

C. Minimum management requirements for riparian buffers.

(1) Existing native vegetation shall be protected and maintained within the riparian buffer easement.

(2) Whenever practical invasive vegetation shall be actively removed and the riparian buffer easement shall be planted with native trees, shrubs and other vegetation to create a diverse native plant community appropriate to the intended ecological context of the site.

D. The riparian buffer easement shall be enforceable by Jim Thorpe Borough and shall be recorded in the Carbon County Recorder of Deeds Office, so that it shall run with the land and shall limit the use of the property located therein. The easement shall allow for the continued private ownership and shall count toward the minimum lot area as required by Zoning, unless otherwise specified in the Borough Zoning Ordinance.

E. Any permitted use within the riparian buffer easement shall be conducted in a manner that will maintain the extent of the existing 100-year floodplain, improve or maintain the stream stability, and preserve and protect the ecological function of the floodplain.

F. The following conditions shall apply when public and/or private recreation trails are permitted within riparian buffers:

(1) Trails shall be for nonmotorized use only.

(2) Trails shall be designed to have the least impact on native plant species and other sensitive environmental features.

G. Septic drainfields and sewage disposal systems shall not be permitted within the riparian buffer easement and shall comply with setback requirements established under 25 Pa. Code Chapter 73.