(A) The only development in a regulatory floodway which will be allowed are appropriate uses which will not cause an increase in flood heights or velocities for all flood events up to and including the base flood, and which will not create a damaging or potentially damaging increase in flood heights or velocity, or be a threat to public health and safety and welfare, or impair the natural hydrologic and hydraulic functions of the floodway or channel, or permanently impair existing water quality of aquatic habitat. Construction impacts shall be minimized by appropriate mitigation methods. Only those appropriate uses listed in 17 Ill. Adm. Code Part 3708 will be allowed in the regulatory floodway.
(B) Appropriate uses do not include the construction or placement of any new structures, fill, building additions, buildings on stilts, excavation or channel modifications done to accommodate otherwise non-appropriate uses in the floodway, fencing (including landscaping or planting designed to act as a fence) and storage of materials except as specifically defined below as an appropriate use. If the development is proposed for the regulatory floodway portion of the regulatory floodplain, the following standards apply in addition to the standards for the regulatory floodplain.
(1) The approved appropriate uses are as follows:
(a) Public flood control structures, dikes, dams and other public works or and private improvements relating to the control of drainage flooding, erosion, water quality or habitat for fish and wildlife;
(b) Structures or facilities relating to the use of, or requiring access to, the water or shoreline, such as pumping and treatment facilities, and facilities and improvements relating to recreational boating, commercial shipping and other functionally water dependent uses;
(c) Storm and sanitary sewer outfalls;
(d) Underground and overhead utilities;
(e) Recreational facilities such as playing fields, and trail systems including any related fencing (at least 50% open when viewed from any one direction) built parallel to the direction of flood flows, and including open air pavilions and toilet facilities (four stall maximum) that will not block flood flows nor reduce floodway storage;
(f) Detached garages, storage sheds, boat houses or other non-habitable structures without sanitary facilities that are accessory to existing buildings and will not block flood flows nor reduce regulatory floodway storage;
(g) Bridges, culverts, roadways, sidewalks, railways and taxiways and any modification thereto;
(h) Parking lots built at or below existing grade provided that either:
1. The BFE is less than one foot above the proposed parking lot; or
2. The parking lot is accessory to short-term outdoor recreational facilities and the owner agrees to restrict access during periods of inundation and agrees to accept liability for all damage caused by vehicular access during flooding events.
(i) Regulatory floodway grading, without fill, to create a positive non-erosive slope toward a channel;
(j) Floodproofing activities to protect previously existing lawful structures including the construction of water-tight window wells, elevating structures, or the construction of flood walls around residential, commercial or industrial principal structures where the outside toe of the floodwall shall be no more than ten feet away from the exterior wall of the existing structure, and, which are not considered to be substantial improvements to the structure;
(k) The repair, replacement or reconstruction of a damaged building, provided that none of the outside dimensions of the building are increased and if the building was damaged to 50% or more of the market value before the damage occurred, the building will be protected from flooding to the flood protection elevation; and
(l) Modifications to an existing building that would not increase the enclosed floor area of the building below the BFE and which will not block flood flows including, but not limited to, fireplaces, bay windows, decks, patios and second story additions. If the building is improved to 50% or more of the market value before the modification occurred (i.e., a substantial improvement), the building will be protected from flooding to the flood protection elevation.
(2) Additions or changes to the above list of appropriate uses must be approved by the Committee prior to the adoption by the County Board and IDNR/OWR.
(3) All development in the regulatory floodway shall require a permit from IDNR-OWR and must be in accordance with all provisions of this chapter.
(4) Within the designated floodway, the construction of an appropriate use will be considered permissible provided that the proposed project meets the following engineering and mitigation criteria and is so stated in writing with supporting plans, calculations and data prepared and signed by a professional engineer and provided that any structure meets the protection requirements of this chapter.
(a) All effective regulatory floodway conveyance lost due to the development of appropriate uses, other than bridge or culvert crossings or on-stream structures or dams, shall be replaced for all flood events up to and including the base flood.
(b) The following expansion and contraction ratios shall be used to determine transition sections in calculations of effective regulatory floodway conveyance.
1. Flowing water will expand no faster than at a rate of one foot horizontal for every four feet of the flooded stream’s length.
2. Flowing water will contract no faster than at a rate of one foot horizontal for every one foot of the flooded stream’s length.
3. Flowing water will not expand or contract faster than one foot vertical for every ten feet of flooded stream length.
4. All cross-sections used in the calculations shall be located perpendicular to flood flows.
5. Transition sections must be used to determine the effective conveyance areas on adjacent properties.
(c) Development of an appropriate use will not result in an increase in the average channel or regulatory floodway velocities or stage. However, in the case of bridges or culverts or on stream structures built for the purpose of backing up water in the stream during normal or flood flows, velocities may be increased at the structure site if scour, erosion and sedimentation will be avoided by the use of riprap or other design measures.
(5) In the case of on-stream structures built for the purpose of backing up water during normal or flood flows, the increase in flood stage when compared to existing conditions for all storm events up to and including the base flood event shall be contained within recorded easements or the channel banks. A dam safety permit or letter indicating a dam safety permit is not required must be obtained from IDNR/OWR for these structures.
(6) IDNR/OWR will issue permits for any IDNR/OWR projects, dams and the like and for all other state or local projects.
(Ord. 10-164, passed 6-17-2010)