(A) Except as provided in division (B)(2) of this section, erosion and sedimentation control measures, structures, and devices shall be so planned, designed, and constructed as to provide protection from the calculated maximum peak rate of runoff from the ten-year storm. Run-off rates can be calculated using the rational method, the Natural Resources Conservation Service (NRCS) peak discharge method, or other acceptable methods.
(B) In high quality water zones (HQW) the following design standards shall apply:
(1) Uncovered areas in HQW zones shall be limited at any time to a maximum total area within the boundaries of the tract of 20 acres. Only this section shall govern the portion of the land-disturbing activity within a HQW zone. Larger areas may be uncovered with the written approval of the Director.
(2) Erosion and sedimentation control measures, structures, and devices within HQW zones shall be so planned, designed and constructed to provide protection from the run-off of the 25 year storm which produces the maximum peak rate of run-off as calculated according to procedures in the USDA, Natural Resource Conservation Service's "National Engineering Field Manual for Conservation Practices," 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 basins within HQW zones shall be designed and constructed such that the basin will have a settling efficiency of at least 70% for the 40 micron (0.04 mm) size soil particle transported into the basin by the run-off of that two-year storm which produces the maximum peak rate of run-off as calculated according to the procedures in the USDA, Natural Resources Conservation Service's "National Engineering Field Manual for Conservation Practices" or according to procedures adopted by any other agency of this state or the United States or any generally recognized organization or association.
(4) 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 or other acceptable ditch liners. In any event, the angle for side slopes shall be sufficient to restrain accelerated erosion.
(5) Ground cover sufficient to restrain erosion must be provided for any portion of a land-disturbing activity in a HQW zone within 15 working days or 30 calendar days following completion of any phase of construction or development, whichever period is shorter.
(Ord. 13-34, passed 11-26-2013)