(A) Except as provided for in § 154.09(B)(2) below, 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 10-year storm.
(B) In High-Quality Water (HQW) zones the following design standards shall apply:
(1) Limit on uncovered areas. 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.
(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 calculated maximum peak rate of runoff from the 25 year storm.
(3) Settling efficiency. 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 calculated maximum peak rate of runoff from the 2 year storm.
(4) Grade. Newly constructed open channels in HQW zones shall be designed and constructed with side slopes no steeper than 2 horizontal to 1 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 acceptable ditch liners. In any event, the angle for side slopes shall be sufficient to restrain accelerated erosion.
(5) Ground cover. 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 60 calendar days following completion of construction or development, whichever period is shorter.
(1989 Code, § 154.09) (Ord. 1185, passed 6-14-2005)