(A) Except as provided in subsection (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. Runoff rates shall be calculated using the procedures in the USDA, Natural Resources Conservation Service’s National Engineering Field Handbook, or other acceptable calculation procedures.
(B) In high quality water (HQW) zones 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 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) Erosion and sedimentation control measures, structures and devices within HQW zones shall be so planned, designed and constructed to provide protection from the runoff of the 25-year storm which 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 basins within HQW zones shall be designed and constructed according to the following criteria:
(a) Use a surface withdrawal mechanism, except when the basin drainage area is less than 1.0 acre;
(b) Have a minimum of 1800 cubic feet of storage area per acre of disturbed area;
(c) Have a minimum surface area of 325 square feet per cfs of the twenty-five year storm (q25) peak flow;
(d) Have a minimum dewatering time of 48 hours;
(e) Incorporate three baffles, unless the basin is less than 20 feet in length, in which case two baffles shall be sufficient.
Upon a written request of the applicant, the City Engineer may allow alternative design and control measures in lieu of meeting the conditions required in subparagraphs (3)(b) through (3)(e) of this sub-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) Newly constructed open channels in HQW zones shall be designed and constructed with side slopes no steeper than two horizontal to one vertical (2:1) 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 sufficient to restrain erosion must be provided for any portion of a land-disturbing activity in a HQW zone within 90 calendar days following completion of construction or development.
(Ord. No. 98-7, passed 1-8-1998; Ord. No. 23-040, § 1, passed 5-11-2023)