Erosion, Flood, Stormwater & Watershed Standards 12.5 Stormwater Management
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associated riparian buffers are not compromised by erosive flows, stormwater flows from the development shall not contribute to degradation of waters of the State. At a minimum, the development shall not result in a net increase in peak flow leaving the site from pre-development conditions for the one-year, 24-hour storm event. D. Sediment Basin Design: Basins shall be planned, designed, and constructed so that the basin will have a settling efficiency of at least 70% for the 40 micron size soil particle transported into the basin by the runoff of the two-year storm that produces an maximum peak runoff as calculated according the procedures in the United State Department of Agriculture and Soil Conservation Services “National Engineering Field Manual for Conservation Practices” or accordi ng to procedures adopted by any other agency of the State or the United States. E. Open Channels: Newly constructed open channels shall be planned, designed, and constructed with side slopes no steeper than two foot horizontal to one foot vertical if a vegetative cover is used for stabilization unless soil conditions permit steeper side slopes or where the side slopes are stabilized by using mechanical devices, structural devices, or other ditch liners sufficient to restrain accelerated erosion. The angle for side slopes shall be sufficient to restrain accelerated erosion. F. Partial Offset of Nutrient Control Requirements: Development subject to this section shall attain nitrogen and phosphorus loading rate reductions on-site, as determined by the Administrator, that meet the following criteria prior to using an offsite offset measure: 1. 30% or more reduction in both nitrogen and phosphorus loading from the untreated conditions for any single-family, detached and duplex residential development disturbing more than ½ acre but less than 1 acre. 2. 50% or more reduction in both nitrogen and phosphorus loading from the untreated conditions for any single-family, detached and duplex residential development disturbing more than 1 acre. 3. 30% or more reduction in both nitrogen and phosphorus loading from the untreated condition for other development, including multifamily residential, commercial, and industrial development disturbing more than 12,000 square feet but less than one acre. 4. 50% or more reduction in both nitrogen and phosphorus loading from the untreated condition for other development, including multifamily residential, commercial, and industrial development disturbing more than 1 acre. G. Offset Payments: An applicant subject to this section may achieve the additional reductions in nitrogen and phosphorus loading required by this section by making offset payments to the NC Ecosystem Enhancement Program contingent upon acceptance of payments by that program. Applicants may use an offset option provided by the Town of Wake Forest. Applicants may propose other offset measures to the Town of Wake Forest, including providing his or her own offsite offset or utilizing a private seller. All offset measures permitted by this ordinance shall meet the requirements of 15A NCAC 02B .0282 and 15A NCAC 02B .0240. 12.5.5. Standards For Stormwater Control Measures A. Evaluation According to NC Stormwater Design Manual 1. All stormwater control measures and stormwater treatment practices (also referred to as Stormwater Control Measures, or SCMs) required under this ordinance shall be evaluated by the Administrator according to the policies, criteria, and information, including technical specifications and standards and the specific design criteria for each stormwater practice, in the Stormwater Design Manual published by the NCDEQ (hereafter referred to as “SCM Manual”). The
Town of Wake Forest Unified Development Ordinance – July 19, 2022
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