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Article 6: Development Standards <br /> Section 6.14: Stormwater Management <br /> <br /> <br />Orange County, North Carolina – Unified Development Ordinance Page 6-106 <br /> <br />(E) Permanent Nutrient Export Reduction Best Management PracticesStormwater <br />Control Measures <br />(1) Allowable on-site structural stormwater BMPsSCMs for nutrient reduction shall <br />include those listed in the current NC DWQ DEQ Stormwater Best Management <br />Practices ManualDesign Manual (Stormwater BMP ManualMinimum Design <br />Criteria)12 or others approved on a case by case basis. <br />(2) Design, maintenance and operation of stormwater BMPsSCMs shall follow <br />standards provided in the Stormwater BMP ManualDesign Manual.13 <br />(3) Deviations from these standards may be allowed as approved on a case by case <br />basis. <br />(F) Total Nutrient Removal Rates <br />Total nutrient removal rates of stormwater BMPsSCMs and BMPs SCMs in a series will <br />be calculated pursuant to the approved accounting tool. <br />6.14.8 Peak Runoff Volume <br />(A) Standard <br />(1) Falls Lake Watershed <br />(a) For all new development, there shall be no net increase 14 in peak flow <br />leaving the site from the predevelopment conditions for the 1 year, 24 <br />hour storm for the Falls Lake Watershed.15 <br />(2) Jordan Lake Watershed <br />(a) For all new development there shall be no net increase greater than 10% <br />in peak flow leaving the site from the predevelopment conditions for the <br />Jordan Lake Watershed.16 <br />(B) Calculating Peak Runoff Volume <br />(1) The following are acceptable methodologies for computing the pre- and post- <br />development conditions for the 1 year, 24 hour storm: <br />(a) Rational Method, <br />(b) Peak Discharge Method as described in the USDA Soil Conservation <br />Service’s Technical Release Number 55 (TR-55), <br />(c) Alternative methods must be approved by the County. <br />(2) The same method must be used for both the pre- and post- development <br />conditions. <br /> <br />12 New Stormwater Design Manual is compatible with the new Minimum Design Criteria that are codified in the <br />new stormwater rules (15A NCAC 02H) which went into effect on January 1, 2017 <br />13 New Stormwater Design Manual is compatible with the new Minimum Design Criteria that are codified in the <br />new stormwater rules (15A NCAC 02H) which went into effect on January 1, 2017 <br />14 The ten percent rule, as noted in 15 A NCAC 02H.1002 (44) and approved of in the NCDEQ Stormwater Design <br />Manual revised on April 3, 2017, addresses the quantity assessment that is required for pre- and post- <br />development analysis to ensure that detention ponds maintain pre-development peak flows through downstream <br />conveyance systems. This is a clarification for the Jordan Lake Watershed <br />15 Clarification for the Falls Lake Watershed <br />16 The ten percent rule, as noted in 15 A NCAC 02H.1002 (44) and approved of in the NCDEQ Stormwater Design <br />Manual revised on April 3, 2017, addresses the quantity assessment that is required for pre- and post- <br />development analysis to ensure that detention ponds maintain pre-development peak flows through downstream <br />conveyance systems. This is a clarification for the Jordan Lake Watershed <br /> 13