1. (a) The purpose of this section is to protect channels, downstream receiving waters, and wetlands from erosion and associated sedimentation resulting from urbanization within a watershed.

2. (b) The combined flow to a channel, downstream receiving water, or wetland from a project site shall meet one of the following criteria:

   1. (1) The 2-year, 24-hour post-development peak flow rate generated from the proposed disturbance shall be equal to or less than the 2-year, 24-hour pre-development peak flow rate and:

      1. a. The 2 year, 24-hour post-development storm volume, directed to a channel, downstream receiving water, or wetland has not increased over the pre-development volume by more than 0.1 acre-feet;
      2. b. The 2-year, 24-hour post-development peak flow rate directed to a channel, downstream receiving water, or wetland is less than 2 cfs; or
      3. c. The area directly discharges into a fourth order or greater river, a pond or lake greater than 10 acres, or tidal water;
   2. (2) The 2-year, 24-hour post-development peak flow rate shall be less than or equal to 50% of the 2-year, 24-hour pre-development peak flow rate; or
   3. (3) The 2-year, 24-hour post-development peak flow rate shall be less than or equal to the 1-year, 24-hour pre-development peak flow rate.
3. (c) When determining “equal to or less than”, allowances shall be made for scientific uncertainty and mathematical rounding.

Source. #9343, eff 1-1-09; amd by #9817-A, eff 12-1-10; ss by #12342, eff 8-15-17; ss by #13758, eff 9-28-23; ss by #14472, eff 1-19-26, EXPIRES: 1-19-36