(A) Mapping of stormwater management districts. To implement the provisions of the Bushkill Creek watershed stormwater management plan, the borough is hereby divided into stormwater management districts consistent with the Bushkill Creek release rate map presented in the plan update. The boundaries of the stormwater management districts are shown on an official map which is available for inspection at the borough office. A copy of the official map at a reduced scale is included in Appendix A for general reference.
(B) Description of stormwater management districts. Two types of stormwater management districts may be applicable to the borough, namely conditional/provisional no detention districts and dual release rate districts as described below.
(1) Conditional/provisional no detention districts. Within these districts, the capacity of the “local” runoff conveyance facilities (as defined in § 153.020) 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 (as defined in § 153.020), these watershed areas may discharge post-development 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 § 153.040(P). 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 § 153.040(D). By definition, a storm drainage problem area associated with the “local” runoff conveyance facilities indicates that adequate capacity does not exist. Sites in these districts are still required to meet all of the water quality requirements in § 153.038.
(2) Dual release rate districts. Within these districts, the two-year post-development peak discharge must be controlled to 30% of the pre-development two-year runoff peak. Further, the ten-year, 25-year and 100-year post-development peak runoff must be controlled to the stated percentage of the pre-development peak. Release rates associated with the ten- through 100-year events vary from 50% to 100% depending upon location in the watershed. (For the Monocacy Creek and Nancy Run Watersheds, the original single release rate districts become dual release rate districts due to the channel protection standard requiring developments to meet a two-year 30% release rate.)
(Ord. 226-2007, passed 5-7-2007)