Storage facilities shall be designed and constructed with the following characteristics:
(A) The site runoff storage facility shall provide one foot of freeboard above the design high water elevation.
(B) The storage facilities shall be accessible and easily maintained. Side slopes above the NWL shall not exceed 4:1 (horizontal to vertical) under any circumstances. For storage facilities with a bounce of greater than four feet the maximum side slope shall not exceed 5:1 (horizontal to vertical). For industrial or commercial areas that do not adjoin schools, residential, or planned residential areas the administrator may approve 4:1 side slopes for bounces up to six feet. The Administrator may require that access roads or paths on the top of berms shall be provided with an H10 design load rating and meeting village design criteria.
(C) Storage facilities shall facilitate sedimentation and catchment of floating material. Unless specifically approved by the Administrator, concrete lined low-flow ditches shall not be used in detention basins.
(D) Storage facilities shall minimize impacts of stormwater runoff on water quality by incorporating best management practices.
(E) Storage facilities shall maximize the normal flow distance between detention inlets and outlets, to the extent possible.
(F) Storage facilities shall be designed such that the existing conditions pre-development peak runoff rate from the 100-year, critical duration rainfall will not be exceeded assuming the primary restrictor is blocked.
(G) Storage facilities with single pipe outlets shall have a minimum inside diameter of 12 inches. If design release rates necessitate a smaller outlet, structures such as perforated risers, or flow control orifices shall be used.
(H) The following criteria are proposed as moderately conservative standards for design of stormwater basins within the village. If a developer wishes to exceed the standards, we recommend that they (via their landscape contractor/designer) bear the burden of proof that the landscape will be successful. The following limits of acceptable fluctuation and drawdown times are based on best professional judgment for landscape treatments typical to wet and dry stormwater basin designs.
(1) Wet bottom pond.
Minimum area | 1.0 acre at NWL |
Maximum area | No maximum |
Depth | Over 25% of the bottom area at least 10.0 ft. deep |
Maximum bounce | 100-year: 4.0 ft. - residential (industrial/commercial may be greater based on approval by Administrator) |
2-year: 1.0 ft. | |
Maximum drawdown time | 100-year: above NWL by 0.5 ft. for 72 hrs |
2-yr: above NWL by 0.5 ft. for 36 hrs | |
Maximum slopes | Freeboard elevation to 2-yr water level: 4:1 |
2-yr water level to NWL: 8:1 | |
NWL to 1.5 ft. below NWL: 20:1 (safety shelf) | |
>1.5 ft. below NWL: 2:1 | |
Freeboard to 1.5 ft. below NWL: 5:1 avg. max. | |
Safety shelf | 0.5 to 1.5 ft. inundation at NWL, 10.0 ft. avg. width (variable 8.0 to 12.0 ft.), with 25% of the shoreline 2.0 ft. shorter than maximum width |
Shoreline protection | Natural vegetation (shall be used unless otherwise approved); armoring (conditioned upon village review and approval); biotechnical stabilization (depending on site-specific conditions); erosion control measures |
Water quality enhancements | Maximize distance between inlets and outlets; no low-flow channel to be provided; energy dissipation measures at outlets; measures such as aerators, cascading streams, water falls, etc. are recommended for aesthetic appeal and to promote water circulation and aeration |
Landscape options | Natural, ornamental hybrid, low maintenance turf, and turfgrass (depending on site conditions and adjacent/adjoining land uses); public access via stone outcroppings, groomed areas, etc. are recommended |
(2) Naturalized detention basin.
Minimum area | 8,000 s.f. at NWL |
Maximum area | No maximum |
Depth | Ranging from 0.5 to 5.0 ft. (average 3.0 ft.); at least 5% of the area below NWL having pockets up to 5.0 ft. deep |
Maximum bounce | 100-year: 4.0 ft. residential (industrial/commercial may be greater based on approval by Administrator) |
2-year: 1.0 ft. | |
Maximum drawdown time | 100-year: above NWL by 0.5 ft. for 72 hrs |
2-yr: above NWL by 0.5 ft. for 36 hours | |
Maximum slopes | Freeboard elevation to 2-yr water level: 4:1 |
2-yr water level to 0.5 ft. below NWL: 8:1 | |
0.5 to 1.5 ft. below NWL: variable 8:1 to 12:1 (safety ledge) | |
>1.5 ft. below NWL: 2:1 | |
Freeboard to 1.5 ft. below NWL: 5:1 avg. max. | |
Shoreline protection | Natural vegetation; biotechnical stabilization (depending on site-specific conditions); erosion control measures |
Water quality enhancements | Maximize distance between inlets and outlets; no low-flow channel to be provided; energy dissipation measures at outlets; measures such as aerators, cascading streams, water falls, etc. are strongly recommended to maintain cooler water temperatures, promote water circulation and aeration, and provide aesthetic appeal |
Minimum topsoil | 18" |
Landscape options | Natural, ornamental hybrid, and low maintenance turf; public access via stone outcroppings, groomed areas, etc. are recommended. A planting and maintenance report, provided by a recognized wetlands firm, must be submitted and approved. |
(3) Dry basin design.
Minimum area | No minimum |
Maximum area | 8,000 s.f., unless approved by the Administrator |
Safety shelf | Not applicable |
Maximum bounce | 4.0 ft. residential (industrial/commercial may be greater based on approval by Administrator) |
(Ord. 06-0383, passed 3-15-06; Am. Ord. 19-1532, passed 1-16-19)