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Township of Bethlehem, PA
Northampton County
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Table of Contents
Table of Contents
Code
New Laws (4) Index
[1]
Editor's Note: See also Part 2, Bushkill Creek, Fry's Run, Monocacy Creek and Nancy Run Watersheds, of this chapter.
A. 
This article shall only apply to those areas of the Township which are contained within the Bushkill Creek, Fry's Run, Monocacy Creek and/or the Nancy Run drainage basins as delineated on the official maps available for inspection at the Township Building, and which are incorporated herein by reference.
[Amended 5-1-2000 by Ord. No. 2-00]
B. 
This article shall only apply to permanent stormwater management facilities constructed as part of the activities listed in this section. Stormwater management and erosion and sedimentation control during construction involved with any of these activities are specifically not regulated by this article.
C. 
This article contains only those stormwater runoff control criteria and standards which are necessary or desirable from a total watershed perspective. Additional stormwater management design criteria (e.g., inlet spacing, inlet type, collection system details, etc.) are regulated by Article III of this Part 1.
(1) 
The following activities are defined as regulated activities and shall be regulated by this article, except those which meet the waiver specifications presented hereafter:
[Amended 6-21-1993 by Ord. No. 6-93]
(a) 
Land development.
(b) 
Subdivision.
(c) 
Construction of new or additional impervious surfaces (driveways, parking lots, etc.).
(d) 
Construction of new buildings or additions to existing buildings.
(e) 
Diversions or piping of any natural or man-made stream channel.
(f) 
Installation of stormwater systems or appurtenances thereto.
(2) 
This article shall not apply to any development located entirely within the general stormwater management district.
(3) 
Any proposed regulated activity, except those defined in Subsection C(1)(e) and (f), which would add less than 5,000 square feet of additional impervious cover (provided that all additions of impervious cover on the development site within the five-year period preceding the application shall be included in determining the area of additional impervious cover) is exempt from meeting the provisions of this article. For development taking place in stages, the entire development plan shall be used in determining conformance with this criteria. Additional impervious cover shall include, but not be limited to, any roof, parking or driveway areas and any new streets and sidewalks constructed as part of or for the proposed regulated activity. Any areas which may be designed to initially be semipervious (e.g., uncompacted aggregate) shall be considered impervious areas for the purpose of waiver evaluation. No waiver shall be provided for regulated activities as defined in Subsection C(1)(e) and (f).
A. 
Mapping of stormwater management districts. The Township is hereby divided into stormwater management districts consistent with the Stormwater Management Release Rate Map presented in Appendix B.[1] The boundaries of the stormwater management districts are shown on an official map which is available for inspection at the Township Building.
[1]
Editor's Note: Appendix B, Stormwater Management Districts Release Rate Map, is included at the end of this chapter.
B. 
Description of stormwater management districts. Four types of stormwater management districts may be applicable to the Township, namely Single Release Rate Districts, Provisional No Detention Districts, Dual Release Rate Districts and the General District as described below.
(1) 
Single Release Rate Districts. There are five Single Release Rate Districts which differ in the extent to which postdevelopment runoff shall be controlled. The release rates and districts are 50%, 60%, 80%, 90% and 100%. Within a given district, the postdevelopment peak rate of stormwater runoff shall be controlled to the stated percentage of the predevelopment peak rate of stormwater runoff in order to protect downstream watershed areas.
[Amended 6-21-1993 by Ord. No. 6-93]
(2) 
Provisional No Detention Districts. These watershed areas may discharge postdevelopment peak runoff without detention facilities without adversely affecting the total watershed peak flow. In certain instances; however, the "local" runoff conveyance facilities, which transport runoff from the site to the main channel, may not have adequate capacity to safely transport increased peak flows associated with not providing detention for a proposed development. In those instances, the developer shall either use 100% release rate control or provide increased capacity of downstream drainage elements to convey increased peak flows consistent with § 218-38H. In determining if adequate capacity exists in the local watershed drainage network, the developer shall assume that the entire local watershed is developed per current zoning and that all new development would use the runoff controls specified in this Part 1. Similarly, any capacity improvement shall be designed to convey runoff from development of all areas tributary to the improvement consistent with the capacity criteria specified in § 218-38H.
(3) 
Dual Release Rate Districts. The anticipated postdevelopment runoff from these areas can only be controlled across the range of return periods from two years through 100 years by implementing a dual system of release rates. Within this district, the two-year postdevelopment runoff shall be controlled to 30% of the predevelopment two-year runoff peak. Further, the ten-, twenty-five-, fifty-, and one-hundred-year postdevelopment runoff shall be controlled to the stated percentage of the predevelopment peak. Release rates associated with the ten-year through one-hundred-year events vary from 60% to 100% depending upon the location in the watersheds.
[Amended 6-21-1993 by Ord. No. 6-93]
(4) 
General District. This district is defined as all land located outside of the Bushkill Creek, Fry's Run, Monocacy Creek and Nancy Run Watersheds. The release rate shall be 100%. The "no harm" provision (§ 218-38F) shall not apply to the General District.
[Amended 5-1-2000 by Ord. No. 2-00]
A. 
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 the intersection of the watercourse and a physical feature (such as the confluence with another watercourse or a potential flow obstruction, e.g., culvert, bridge, etc.) to the topographic divide consistent with topography.
B. 
Any downstream capacity analysis conducted in accordance with this Part 1 shall use the following criteria for determining adequacy for accepting increased peak flow rates:
(1) 
Natural or man-made channels or swales shall be able to convey the increased runoff associated with a twenty-five-year and more frequent return period events within their banks at velocities consistent with protection of the channels from erosion. All conveyance swales shall be capable of conveying the one-hundred-year and more frequently occurring storms within their banks at velocities consistent with protection of the channels from erosion. Acceptable velocities shall be based upon criteria included in the DEP Soil Erosion and Sedimentation Control Manual (April 1990, or most recent edition).
[Amended 5-1-2000 by Ord. No. 2-00]
(2) 
Culverts, bridges or any other facilities which must pass or convey flows from the tributary area shall have sufficient capacity to pass or convey the increased flows associated with the fifty-year-return period runoff event, except for facilities located within a designated floodplain area which shall be capable of passing or conveying the one-hundred-year-return period runoff. Any facilities which constitute stream enclosures per DEP Chapter 105 regulations shall be designed to convey the one-hundred-year-return period runoff.
[Amended 5-1-2000 by Ord. No. 2-00]
C. 
For a proposed development site located wholly within one release rate category area, the total runoff from the site shall meet the applicable release rate criteria. For development sites with multiple points of concentrated runoff discharge, individual drainage points 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.
D. 
For a proposed development site located within two or more release rate category areas, the maximum peak rate of runoff that may be discharged at any point shall be limited to the predevelopment peak rate of runoff at that point multiplied by the applicable release rate. The control rates shall apply regardless of any grading modifications which may change the drainage area which discharges at a given point.
[Amended 6-21-1993 by Ord. No. 6-93]
E. 
For the proposed development sites located partially within a release rate category area and partially within a provisional no detention area, a significant portion of the site area subject to the release rate control shall not be drained to the discharge point(s) located in the no detention area.
F. 
No harm option. For any proposed development site located within the General Stormwater Management 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 this article. Proof of no harm would have to be shown from the development site through the remainder of the downstream drainage network to the confluences of the Bushkill Creek and/or Fry's Run and/or Monocacy Creek and/or the Nancy Run with the Lehigh River. Attempts to prove no harm based upon downstream peak flow versus capacity analysis shall be governed by the following provisions:
[Amended 5-1-2000 by Ord. No. 2-00]
(1) 
The peak flow values to be used for downstream areas for the design return period storms (two, 10, 25, and 100 years) shall be the values from the calibrated Penn State Runoff Model for the Bushkill Creek and/or Fry's Run, Monocacy Creek and/or Nancy Run Watersheds. These flow values will be supplied to the developer by the Township Engineer upon request.
(2) 
The capacity of downstream conveyance facilities for increased peak flows shall be based upon the capacity criteria as specified in Subsection B.
(3) 
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 site area is 10% of the upstream undeveloped acreage, then up to 10% of the documented downstream available capacity may be used to convey additional runoff from the site.
(4) 
Developer proposed runoff controls which would generate increased peak flow rates at documented storm drainage problem areas shall, by definition, be precluded from successful attempts to prove no harm, except in conjunction with proposed capacity improvements for the problem areas consistent with Subsection H.
(5) 
Any no harm justifications shall be submitted by the developer as part of the drainage plan submission.
G. 
Regional or subregional detention alternatives. For certain areas within the watershed, it may be more cost effective to provide one control facility for an entire subarea, group of subareas or portion of a subarea incorporating more than one development site than to provide an individual control facility for each development site. The initiative and funding for any regional or subregional runoff control alternatives are the responsibility of prospective developers. The design of any regional control basins shall 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 applicable version of the Penn State Runoff Model as developed for the stormwater management plan (LVPC).
[Amended 5-1-2000 by Ord. No. 2-00]
H. 
Capacity improvements.
(1) 
Any capacity improvements proposed to meet the requirements of this article shall be designed based upon the assumption of development of all areas tributary to the proposed improvement and the capacity criteria specified in Subsection B. In addition, all new development upstream of a proposed capacity improvement shall be assumed to implement the applicable runoff controls consistent with this article except that all new development within 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 or subregional detention alternatives or to implement a modified no harm option which proposes specific capacity improvements to document the validity of a less stringent discharge control which would not create any harm downstream.