§19-403.Stormwater Management District Implementation Provisions (Performance Standards)

1. General. Post-development 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 official stormwater management release rate map, Ordinance Appendix A, and other applicable ordinances.

2. Standards for New Development.

A. Standards for managing runoff for new development from each subarea in the Chester Creek watershed for the 2-, 5-, 10-, 25-, 50-, and 100-year design storms are shown in Table 403-1. Development sites located in each of the districts must control post-development peak runoff rates to the specified percentage of predevelopment peak runoff rates for the design storms as shown in the table.

TABLE 403-1 CONTROL CRITERIA FOR STORMWATER MANAGEMENT DISTRICTS

B.Ridley Creek watershed plan release rates and associated requirements, as outlined in the Ridley Creek Watershed Plan.

C. All other areas of the Township shall utilize a 100% release rate for the purpose of implementation of this Chapter.

3. Redevelopment projects within the Chester Creek Watershed shall meet peak discharge requirements based on the adjusted runoff control number (RCN) or "C " value illustrated by Figure B-3 in Appendix B.

4. 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 pre-development peak discharge for each 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.

5. 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.



6. Site Areas. Where the site area to be impacted by a proposed development activity differs significantly from the total site area, as determined by the Township Engineer, only the proposed development area and areas contributory to the proposed stormwater management facilities shall be subject to the release rate criteria.

7. 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 applicants. 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.

(Ord. 4-2004, 6/2/2004, §403)