(A) Except as provided in divisions (B)(2) and (C)(1) of this section, erosion and sedimentation control measures, structures, and devices shall be planned, designed, and constructed to provide protection from the calculated maximum peak rate of runoff from the ten-year storm. Runoff rates shall be calculated using the procedures in the latest edition of the United States Department of Agriculture (USDA), Natural Resources Conservation Service’s National Engineering Field Handbook or other acceptable calculation procedures.
(B) HQW zones. In high quality water (HWQ) zones, the following design standards shall apply.
(1) Limit on uncovered area. Uncovered areas in HQW zones shall be limited at any time to a maximum total area of 20 acres within the boundaries of the tract. Only the portion of the land-disturbing activity within a HQW zone shall be governed by this section. Larger areas may be uncovered within the boundaries of the tract with the written approval of the Director, upon providing engineering justification with a construction sequence that considers phasing, limiting exposure, self-inspection reports submitted weekly, and a more conservative design than the 25-year storm.
(2) Maximum peak rate of runoff protection. Erosion and sedimentation control measures, structures, and devices within HQW zones shall be planned, designed, and constructed to provide protection from the runoff of the 25-year storm that produces the maximum peak rate of runoff, as calculated according to procedures in the United States Department of Agriculture Natural Resources Conservation Service’s National Engineering Field Handbook, or according to procedures adopted by any other agency of this state or the United States or any generally recognized organization or association.
(3) Sediment basin design.
(a) Sediment basins within HQW zones shall be designed and constructed according to the following criteria:
1. Use a surface withdrawal mechanism, except when the basin drainage area is less than one acre;
2. Have a minimum of 1,800 cubic feet of storage area per acre of disturbed area;
3. Have a minimum surface area of 325 square feet per cfs of the 25-year storm (Q25) peak flow;
4. Have a minimum dewatering time of 48 hours;
5. Incorporate three baffles, unless the basin is less than 20 feet in length, in which case two baffles shall be sufficient.
(b) Upon a written request of the applicant, the Director may allow alternative design and control measures in lieu of meeting the conditions required in division (B)(3)(a)2. through 5. of this section, if the applicant demonstrates that meeting all of those conditions will result in design or operational hardships, and that the alternative measures will provide an equal or more effective level of erosion and sediment control on the site. Alternative measures may include quicker application of ground cover, use of sediment flocculants, and use of enhanced ground cover practices.
(4) Grade. Newly constructed open channels in HQW zones shall be designed and constructed with side slopes no steeper than two horizontal to one vertical, if a vegetative cover is used for stabilization, unless soil conditions permit a steeper slope or where the slopes are stabilized by using mechanical devices, structural devices, or other forms of ditch liners proven as being effective in restraining accelerated erosion. In any event, the angle for side slopes shall be sufficient to restrain accelerated erosion.
(C) Design and performance standards for land-disturbing activities of 20 acres or greater. In addition to any other requirements of state, federal, and local law, land-disturbing activity of 20 acres or more within Lincoln County or the City of Lincolnton shall meet all of the following additional design standards for sedimentation and erosion control.
(1) Sediment basins shall be planned, designed, and constructed to provide protection from the runoff of the 25-year storm that produces the maximum peak rate of runoff, as calculated according to procedures set out in the latest edition of the United States Department of Agriculture Natural Resources Conservation Service’s Engineering Field Handbook, found through nrcs.usda.gov, or according to procedures adopted by any other agency of the state or the United States.
(2) Construction entrances shall be planned, designed and constructed at a minimum length of 100 feet.
(3) Sediment fence (silt fencing) used along all watercourses shall planned, designed and constructed as double-row, high-hazard or super-silt fence.
(Ord. passed 1-22-2007; Ord. 2012-21, passed 10-1-2012; Ord. passed 12-18-2023)