All detention basins shall be designed to remove stormwater pollutants, so as to be safe, aesthetically pleasing, and to provide recreational use whenever feasible. There is no depth limitation to basin design, other than that necessitated by impoundment volume safety and/or vegetative survivability and maintenance concerns due to longer drawdown times.
A. Wet Basin Depths: The normal water pool in wet basins shall be at least six feet (6') deep, excluding near shore banks and safety ledges and shall be at least ten feet (10') deep over twenty five percent (25%) of the normal water level surface area.
B. Permanent Pool Volume: The permanent pool volume at normal depth shall be equal to or greater than the runoff from its watershed for the 2-year event.
C. Life Saving Equipment: The subdivider shall install life- saving equipment at regular intervals around the perimeter of wet detention/retention ponds. The subdivider shall consult with the Police Department and the fire protection district regarding the type of equipment to be installed. The equipment shall be maintained by the entity that maintains the pond.
D. Dry Detention Ponds: Dry detention ponds shall be designed to have a high water depth of four feet (4') or less. Parking lots used for stormwater detention shall not allow ponding greater than six inches (6") deep for a period of four (4) hours. All slopes shall not be steeper than 4 to 1 (horizontal to vertical).
E. Dry Basins: Dry basins shall be designed so that at least eighty percent (80%) of the bottom area shall have standing water no longer than seventy two (72) hours for any runoff event less than the 100-year event. Underdrains directed to the outlet control shall be used to aid in keeping the pond bottom dry.
F. Aeration: All wet basins shall incorporate wind powered aeration systems to oxygenate the normal water pool. If it can be shown, based on a sheltered location of the basin, that wind powered aeration is not feasible, then an electric powered aeration system will be allowed.
G. Basin Slopes: The underwater side slopes of wet basins from the safety ledge to the high water elevation shall not be steeper than 4 to 1 (horizontal to vertical). All side slopes above normal water level shall be no steeper than 4 to 1 (horizontal to vertical). Backslopes on the side of a berm opposite the basin may be 3 to 1 if they are along the external boundary of a development and no/low maintenance groundcovers and landscaping are installed.
H. Safety Ledges: All wet detention basins shall have a level safety ledge at least five feet (5') in width from the normal water's edge and three feet (3') below the normal water level.
I. Desiltation Basins: Desiltation basins shall be provided at the pond's in-flow locations. Desiltation basin size shall be one hundred (100) cubic yards per acre of disturbed tributary area. Use of settlement basins or other sediment control practices upstream of the basins shall be taken into consideration when reviewing the proposed desiltation volume.
J. Embankment Protection: Embankment protection shall be provided and approved by the Village Engineer.
K. Velocity Dissipation: Velocity dissipation measures shall be incorporated into dry basin designs to minimize erosion at inlets and outlets and to minimize the re-suspension of pollutants.
L. Inlet And Outlet Orientation For Both Wet And Dry Detention Basins: To the extent feasible, the distance between detention inlets and outlets shall be maximized. If possible, they should be at opposite ends of the basin. (Ord. 2018-02-20, 2-20-2018)