In addition to the other requirements of this chapter, dry basins shall be designed to remove stormwater pollutants, to be safe, to be aesthetically pleasing and as much as feasible to be available for multiple uses.
(A) Dry basin drainage.
(1) Dry basins shall be designed so that 80% of their bottom area shall have standing water no longer than 72 hours for any runoff event less than the 100-year, 24-hour event. Grading plans shall clearly distinguish the wet portion of the basin bottom.
(2) Underdrains directed to the outlet may be used to accomplish this requirement.
(B) Minimum bottom slope. Dry bottom basins shall have 2% minimum bottom slopes or underdrain systems as approved by Zoning and Building Director, or his or her designee.
(C) Low flow channel. Dry bottom basins may include a low flow channel with some form of erosion protection.
(D) Velocity dissipation. Velocity dissipation measures shall be incorporated into dry basin designs to minimize erosion at inlets and outlets and to minimize re-suspension of pollutants.
(E) Dry basin inlet and outlet orientation. Dry basin inlet and outlet orientation shall be the same as for wet basins.
(F) Temporary sediment trap. A sediment trap shall be constructed at each major inlet to a dry basin during construction. The temporary sediment trap should be designed in accordance with criteria in the Illinois Urban Manual.
(Ord. passed - -)