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1. The Brodhead Creek Watershed has been divided into stormwater management districts as shown on the Watershed Map in Appendix D.

Standards for managing runoff from each subarea in the Brodhead Creek Watershed for design storms are shown in Table 225.1. Development sites located in each of the A, B, or C Districts must control proposed conditions runoff rates to existing conditions runoff rates for the design storms in accord with Table 225.1.

In addition to the requirements specified in Table 225.1 below, the water quality and streambank erosion (§223), groundwater recharge (§224), and erosion control (§228) requirements shall be implemented.

Table 225.1. Water Quantity Requirements

District

Proposed conditions

(reduce to)

Existing conditions

A

2-year

1-year

5-year

5-year

10-year

10-year

25-year

25-year

50-year

50-year

100-year

100-year

B-1

2-year

1-year

5-year

2-year

10-year

5-year

25-year

10-year

50-year

25-year

100-year

100-year

B-2

2-year

1-year

5-year

2-year

25-year

5-year

50-year

10-year

100-year

50-year

B-3

50-year

10-year

100-year

50-year

C

Provisional Direct Discharge District - development sites which can discharge directly to the main channel or major tributaries or indirectly to the main channel through an existing stormwater drainage system (i.e., storm sewer or tributary) which meets the “Downstream Hydraulic Capacity Analysis” in §225(8) and is shown by the design professional to not cause a downstream problem, may allow an increase in flow as long as no downstream farm is demonstrated. However, sites in District C shall comply with the criteria for water quality and streambank erosion (§223; and groundwater recharge (§224). If the proposed conditions runoff is intended to be conveyed by an existing stormwater drainage system to the main channel, assurance must be provided that such system has adequate capacity to convey the increased peak flows or will be provided with improvements to furnish the required capacity. When adequate capacity of the downstream system does not exist and will not be provided through improvements, the proposed conditions peak rate of runoff must be controlled to the existing conditions peak rate as required in District A provisions (i.e., 10-year proposed conditions flows to 10 year existing conditions flows) for the specified design storms.

2. General. Proposed conditions rates of runoff from any regulated activity shall not exceed the peak release rates of runoff prior to development for the design storms specified on the Stormwater Management District Watershed Map (Appendix D) and §222 of this Part.

3. District Boundaries. The boundaries of the stormwater management districts are shown on an official map that is available for inspection at the municipal office. A copy of the official map at a reduced scale is included in Appendix D. The exact location of the stormwater management district boundaries as they apply to a given development site shall be determined by mapping the boundaries using the two (2) foot topographic contours (or most accurate data required) provided as part of the drainage plan.

4. Sites Located in More than One District. If a development site is located within two (2) or more stormwater management district category subareas, the peak discharge rate from any subarea shall be the existing conditions peak discharge for that subarea as indicated in §222. The calculated peak discharges shall apply regardless of whether the grading plan changes the drainage area by subarea The Board of Supervisors may grant a waiver if discharges from multiple subareas recombine in proximity to the development site. In this case, peak discharge in any direction may be a one hundred (100%) percent release rate provided that the overall site discharge meets the weighted average release rate.

5. Off-Site Areas. Off-site areas that drain through a 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.

6. Site Areas. Where the development site area differs significantly from the total parent tract area, only the proposed impact area utilizing stormwater management measures shall be subject to the management district criteria. In other words, unimpacted areas bypassing the stormwater management facilities would not be subject to the management district criteria.

7. “No Harm” Option. For any proposed development site not located in a provisional direct discharge district, the applicant has the option of using a less restrictive runoff control (including no detention) if the applicant can prove that “no harm” would be caused by discharging at a higher runoff rate than that specified by the applicable Act 167 Plan. The “no harm” option is used when an applicant can prove that the proposed hydrographs can match existing hydrographs, or if it can be proved that the proposed conditions will not cause increases in peaks at all points downstream. Proof of “no harm” must be shown based upon the following “downstream impact evaluation” which shall include a “downstream hydraulic capacity analysis” consistent with §225(8) to determine if adequate hydraulic capacity exists. The applicant shall submit this evaluation of the impacts due to increased downstream stormwater flows in the watershed to the Township.

A. The hydrologic regime of the site must be maintained.

B. The “downstream impact evaluation” shall include hydrologic and hydraulic calculations necessary to determine the impact of hydrograph timing modifications due to the proposed development upon a dam, highway, structure, natural point of restricted streamflow or any stream channel section, established with the concurrence of the municipality.

C. The evaluation shall continue downstream until the increase in flow diminishes due to additional flow from tributaries and/or stream attenuation.

D. The peak flow values to be used for downstream areas for the design return period storms (2, 5, 10, 25, 50, and 100-year) shall be the values from the calibrated model for the applicable Act 167 Plan.

E. Applicant-proposed conditions 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 §225(8).

F. A financial distress shall not constitute grounds for the Township to approve the use of the “no-harm” option.

G. Downstream capacity improvements may be provided as necessary to achieve the “no harm” option.

H. Any “no harm” justifications shall be submitted by the applicant as part of the drainage plan submission per Part 2D.

8. “Downstream Hydraulic Capacity Analysis.” Any downstream hydraulic capacity analysis conducted in accordance with this Part shall use the following criteria for determining adequacy for accepting increased peak flow rates:

A. Existing natural or man-made channels or swales must be able to convey the increased runoff associated with a two (2) 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.

B. Existing natural or man-made channels or swales must be able to convey increased twenty-five (25) year return period runoff without creating any hazard to persons or property.

C. Culverts, bridges, storm sewers or any other facilities which must pass or convey flows from the tributary area must be designed in accordance with Chapter 105 (if applicable) and, at minimum, pass the increased twenty-five (25) year return period runoff.

9. Hardship Option. The applicable Act 167 Plan and its standards and criteria are designed to maintain existing conditions peak flows and volumes throughout the watershed as the watershed becomes developed. There may be certain instances, however, where the standards and criteria established are too restrictive for a particular applicant. The existing drainage network in some areas may be capable of safely transporting slight increases in flows without causing a problem or increasing flows elsewhere. If an applicant cannot meet the stormwater standards due to lot conditions or if conformance would become a hardship to an applicant, the hardship option may be applied. A financial distress shall not constitute grounds for the Township to approve the use of the hardship option. The applicant would have to plead his/her case to the Board of Supervisors with the final determination made by the Township. Any applicant’s pleading the “hardship option” will assume all liabilities that may arise due to exercising this option. A financial distress shall not constitute grounds for the Township to approve the use of the “no-harm” option. (Ord. 181, 10/11/2006, §305)