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60 <br />Article 6: development Standards <br />Section 6.14: Stormwater Management <br />(a) Increase in peak flow between pre- and post- development <br />conditions does not exceed 10% (ten per-Gen -. <br />(b) Proposed new development meets all of the following criteria: <br />(i) total impervious surface is less than 15% (fifteen <br />pement), and <br />(ii) remaining pervious surface maximizes stormwater runoff <br />control and conveyance. <br />(c) Detention will cause further flooding on lands that have <br />experience flooding during previous storm events. <br />(2) This request for exemption must be prepared by a North Carolina <br />registered professional engineer and submitted in writing to the Planning <br />Director or Designee. Appeals of this decision will follow Section 7-€ <br />2.24 of this Ordinance. <br />(C) Calculating Peak Runoff Volume <br />(1) The following are acceptable methodologies for computing the pre- and <br />post- development conditions for the 1 year, 24 hour storm. <br />(a) Rational Method <br />(b) Peak Discharge Method as described in the USDA Soil <br />Conservation Service's Technical Release Number 55 (TR -55). <br />(c) Putnam Method <br />(d) Alternative methods must be approved by the County and the <br />EMC <br />(2) The same method must be used for both the pre- and post- development <br />conditions. <br />(3) Raleigh Rainfall Depths <br />Orange County, North Carolina — DRAFT Unified Development Ordinance Page 6 -151 <br />