The City of Joliet, Illinois has enacted a Stormwater Management Ordinance in order to diminish threats to public health, safety and welfare caused by runoff of excessive storm water from new development and redevelopment. The City of Joliet is the permitting authority for all land disturbing activities and requires the land owner to maintain all on-site stormwater control facilities and all open space areas (e.g. parks or “green” areas) required by the approved stormwater control plan. The City of Joliet will only provide construction permits to projects that establish a plan to manage stormwater runoff occurring during the construction process. The City of Joliet, under the NPDES program, also has the authority to inspect properties for noncompliance and can issue a notice of violation (NOV) for any deficiency or infraction onsite. Property owners are responsible for the maintenance of any stormwater facilities or practices located on the property. The City of Joliet has the authority to inspect stormwater facilities and practices in order to ascertain that they properly maintained and functioning.
General regulations
(1) The peak discharge rate from a storm detention facility shall be controlled for the two year 24-hour storm event and the 100 year 24-hour storm event to levels that will not cause and increase in flooding or channel instability downstream when considered in aggregate with other developed properties and downstream drainage capacities. The peak discharge from events less than or equal to the two-year event shall not be greater than 0.04 cfs per acre of property drained. The peak 100 year discharge shall not be greater than 0.15 cfs per acre of property drained.
Design Objectives
(1) The drainage system should be designed to minimize adverse water quality impacts downstream and on the property itself. Detention basins shall incorporate design features to capture storm water runoff pollutants. In particular, designers shall give preference to wet bottom and wetland designs and all flows from the development shall be routed through the basin (i.e., low flows shall not be bypassed). Retention and infiltration of storm water shall be promoted throughout the property's drainage system to reduce the volume of storm water runoff and to reduce the quantity of runoff pollutants.
(2) The drainage system should incorporate multiple uses where practicable. Uses considered compatible with storm water management include open space, aesthetics, aquatic habitat, recreation (boating, trails, playing fields), wetlands and water quality mitigation. The applicant should avoid using portions of the property exclusively for storm water management.
Wet Detention Basins
(1) Wet detention basin design. Wet detention basins shall be designed to remove storm water pollutants, to be safe, to be aesthetically pleasing, and as much as feasible to be available for recreational use.
(2) Wet detention depths. Wet basins shall be at least three feet deep, excluding near shore banks and safety ledges. If fish habitat is to be provided, they shall be at least ten feet deep over twenty-five percent of the bottom area to prevent winter freeze out.
(3) Inlet and outlet orientation. To the extent feasible the distance between detention inlets and outlets shall be maximized.
Wetland and Dry Detention Basin Design:
In addition to the other requirements of this ordinance, wet and dry basins shall be designed to remove storm water pollutants, to be safe, to be aesthetically pleasing and as much as feasible to be available for multiple uses.
(1) Wetland and Dry Basin Drainage: Wetland and dry basins shall be designed so that the portion of their bottom area which is intended to be dry shall have standing water no longer than seventy-two hours for all runoff events less than the 100-year event. Under drains directed to the outlet may be used to accomplish this requirement. Grading plans shall clearly distinguish the wet/wetland, portion of the basin bottom from the dry portion.
(2) Velocity dissipation: Velocity dissipation measures shall be incorporated into dry basin designs to minimize erosion at inlets and outlets and to minimize the resuspension of pollutants.
(3) Inlet and Outlet Orientation: 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. There should be no low flow bypass between the inlet and outlet.
(4) Stilling/Sedimentation Basins: A stilling/sedimentation basin should be constructed at each major inlet to a wetland or dry basin. The volume of the basins should be at least 500 ft. per acre of impervious surface in the drainage area. Side slopes of the basins shall be no steeper than 3 horizontal to 1 vertical and basin depths should be at least 3 feet to minimize resuspension of accumulated sediment.
Detention in floodplains
The placement of detention basins within the floodplain is strongly discouraged because of questions about their reliable operation during flood events. However, the storm water detention requirements of this ordinance may be fulfilled by providing detention storage within flood fringe areas on the project site provided the following provisions are met:
(1) Detention in flood fringe areas: The placement of a detention basin in a flood fringe area shall require compensatory storage for 1.0 times the volume below the base flood elevation occupied by the detention basin including any berms. The release from the detention storage provided shall still be controlled consistent with the requirements of this section. The applicant shall demonstrate its operation for all stream flow and floodplain backwater conditions. Excavations for compensatory storage along watercourses shall be opposite or adjacent to the area occupied by detention. All floodplain storage lost below the ten-year flood elevation shall be replaced below the ten-year flood elevation. All floodplain storage lost above the existing ten-year flood elevation shall be replaced about the proposed ten-year flood elevation. All compensatory storage excavations shall be constructed to drain freely and openly to the watercourse.
(3) On-stream detention: On stream detention basins are discouraged but allowable if they provide regional public benefits and if they meet the other provisions of these regulations with respect to water quality and control of the two-year and 100 year, 24-hour events from this property. If on-stream detention is used for watersheds larger than one square mile, it is recommended that the applicant used dynamic modeling to demonstrate that the design will not increase stage for any properties upstream or downstream of the property. Also, impoundment of the stream as part of on-stream detention:
Protection of Wetlands and Depressional Storage Areas
Wetlands and other depressional storage areas shall be protected from damaging modifications and adverse changes in runoff quality and quantity associated with land developments. In addition to the other requirements of this ordinance, the following requirements shall be met for all developments whose drainage flows into wetlands and depressions] storage areas (as appropriate):
Detention in Wetlands and Depressional Storage Areas: Existing wetlands shall not be modified for the purposes of storm water detention unless it is demonstrated that the existing wetland is low in quality and the proposed modifications will maintain or improve its habitat and ability to perform beneficial functions. Existing storage and release rate characteristics of wetlands and other depressional storage areas shall be maintained and the volume of detention storage provided to meet the requirements of this section shall be in addition to this existing storage.
Alteration of drainage patterns: Site drainage patterns shall not be altered to substantially decrease or increase the existing area tributary to the wetland.
Vegetated Buffer Strip: A buffer strip of at least 25 feet in width, preferably vegetated with native plant species, shall be maintained or restored around the periphery of the wetland.
Streets and parking lots
Infiltration Practices
Infiltration practices including basins, trenches and porous pavement may be allowed if the following conditions are met:
Maintenance Considerations
The stormwater drainage system shall be designed to minimize and facilitate maintenance. Turfed side slopes shall be designed to allow lawn mowing equipment to easily negotiate them. Pre-sedimentation basins shall be provided with easy methods for removing sediment. Access for heavy equipment shall be provided to the pre-sedimentation basins. In addition, all applicants shall be required to establish a restrictive covenant by notation on the record plat stating that the maintenance of the detention area is the responsibility of all property owners in the subdivision, including bank stabilization, bank maintenance, future sediment removal, or dredging, stabilization of water levels, outfall structures and storm sewer pipes within the detention easement.
Maintenance responsibility
The maintenance of storm water detention facilities shall be provided by the property owner(s) of the site. The owner(s) of the property shall grant an easement to the City of Joliet in the event that Joliet needs to enter the property to correct deficiencies in the maintenance provided by the owner(s). Presedimentation facilities, inlet control structures and outlet structures shall be maintained by the City of Joliet to assure adequate functioning of the facility.
City of Joliet Stormwater Management Plan