(A) Generally. The following general performance standards are applicable to all development in a regulatory floodplain. The standards of this section apply except when superseded by more stringent requirements in the subsequent sections.
(1) No development except as allowed in § 164.066 shall be allowed in the regulatory floodplain that singularly or cumulatively creates an increase in flood stage or velocity off-site, or a damaging or potentially damaging increase in flood heights or velocity on-site or threat to public health, safety and welfare.
(2) For all projects involving a channel modification, fill, stream maintenance or a levee, the flood conveyance and storage capacity of the regulatory floodplain shall not be reduced.
(3) If the proposed development would result in a change in the regulatory floodplain or BFE as indicated in Appendix B, the applicant shall obtain a LOMR from FEMA. No buildings may be built in the existing or proposed regulatory floodplain until the LOMR receives concurrence from IDNR/OWR and is issued by FEMA and the building meets all the building protection standards (division (C) below). Proposed changes to the regulatory floodway delineation and the BFE must be submitted to IDNR/OWR for concurrence.
(4) If the development is located in a public body of water, as defined by IDNR/OWR (Appendix C), a permit or a waiver of a permit must also be received from IDNR/OWR.
(5) Prior to the commencement of any construction, modification or removal of a dam, the developer shall obtain an IDNR/OWR permit or letter indicating a permit is not required.
(6) (a) For public flood control projects, the floodplain management standards will be considered met if the applicant can demonstrate to IDNR/OWR and Chief Subdivision Engineer that each of the following conditions are met:
1. Demonstrate by hydraulic and hydrologic modeling that the proposed project will not singularly or cumulatively result in increased flood heights outside the project site or demonstrate that any increases will be contained in easements for all flood events up to and including the base flood event;
2. Demonstrate that the project will be operated and maintained by a public agency; and
3. Demonstrate that the project will reduce flood damage to an existing building or structure.
(b) These standards do not preclude the design, engineering, construction or financing, in whole or in part of a public flood control project by persons who are not public agencies.
(7) Proposals for new subdivisions, manufactured home parks, planned unit developments (PUDs) and additions to manufactured home park and additions to subdivisions shall include base flood or 100-year frequency flood elevation data and floodway delineations.
(8) Critical facilities shall not be permitted within the 500-year floodplain.
(B) Public health protection standards.
(1) New and replacement water supply systems, wells and sanitary sewer lines may be permitted if all manholes or other aboveground openings located below the FPE are watertight.
(2) New on-site waste disposal systems, such as septic systems, are allowed in the regulatory floodplain only if they meet all of the following conditions.
(a) The invert of any wastewater distribution lines shall be a minimum of two feet above the water surface elevation of the base flow of any perennial stream.
(b) The lateral distance from a ditch, creek or other riverine source to the wastewater distribution lines shall be a minimum of 75.
(c) The elevation of any areas which are to receive wastewater distribution shall be above the ordinary high water mark.
(d) The soil of the receiving field shall be of a type suitable for septic fields.
(e) The tank shall be placed out of the floodplain with the invert of the outlet above the BFE.
(3) New, substantially improved or replacement wastewater treatment plants shall have watertight openings for those openings located below the FPE. These facilities should be located to avoid impairment to the facility or contamination of floodwaters during the base flood.
(C) Building protection standards. The building protection standards apply to all buildings located in the regulatory floodplain; however, it should be noted that most new and replacement buildings are not appropriate uses of the regulatory floodway.
(1) The lowest floor including basements of all new residential structures, substantially improved structures and additions shall be elevated up to at least the flood protection elevation.
(a) If placed on fill, the top of the fill for the residential structure shall be at the flood protection elevation (FPE) or higher. The top of fill for an attached garage shall be at least 0.1 foot above the base flood elevation (BFE). The fill shall be placed at that elevation for a distance of ten feet out from the building unless the building design is certified by a registered structural engineer to be protected from damages due to hydrostatic pressures. Additionally, the fill shall not settle below the FPE for the residential structure and not below 0.1 feet above the base flood for an attached garage, and shall be adequately protected against erosion, scour and differential settlement. The fill shall not adversely affect surface drainage from or onto neighboring properties. All structures placed on fill in the floodplain shall meet the requirements of this chapter and FEMA Technical Bulletin 10-01, and the applicant’s design engineer shall certify that the land or structures to be removed from the special flood hazard area are reasonably safe from flooding.
(b) If elevated by means of walls, pilings or other foundation, the building’s supporting structure must be permanently open to flood waters and not subject to damage by hydrostatic pressures of the base flood. The permanent openings shall be no more than one foot above existing grade, and consist of a minimum of two openings. The openings must have a total net area of not less than one square inch for every one square foot of enclosed area subject to flooding below the BFE. The lowest inside grade must match the lowest existing outside grade adjacent to the structure. The foundation and supporting members shall be anchored and aligned in relation to flood flows and adjoining structures so as to minimize exposure to known hydrodynamic forces such as current, waves, ice and floating debris. All areas below the FPE shall be constructed of materials resistant to flood damage. The lowest floor (including basement) for the residential structure and all electrical, heating, ventilating, plumbing and air conditioning equipment and utility meters shall be located at or above the FPE. An attached garage must be elevated to at least 0.1 feet above the BFE. Water and sewer pipes, electrical and telephone lines, submersible pumps and other waterproofed service facilities may be located below the FPE. No area below the FPE shall be used for storage.
(2) The lowest floor including the basement of all new or substantially improved nonresidential buildings shall be elevated at least to the FPE as described above or be structurally dry flood proofed to at least the FPE. A nonresidential building may be structurally dry flood proofed (in lieu of elevation) provided that a professional engineer or registered structural engineer shall certify that the building has been structurally dry flood proofed below the FPE and the structure and attendant utility facilities are watertight and capable of resisting the effects of the base flood. The building design shall take into account flood velocities, duration, rate of rise, hydrostatic and hydrodynamic forces, the effects of buoyancy and impacts from debris or ice. Flood proofing measures shall be operable without human intervention and without an outside source of electricity. (Levees, berms, floodwalls and similar works are not considered flood proofing for the purpose of this division.)
(3) Manufactured homes and recreational vehicles to be installed on a site for more than 180 days shall be at or above the FPE and shall be anchored to resist flotation, collapse or lateral movement in accordance with the Illinois Manufactured Home Tie-Down Code (77 Ill. Adm. Code 870) as amended.
(4) (a) Accessory structures, such as tool sheds and detached garages which are not substantial improvements on an existing single-family lot, may be constructed with the lowest floor below the FPE in accordance with the following criteria.
1. The building shall not be used for human habitation.
2. All areas below the FPE shall be constructed with waterproof material. Structures located in a regulatory floodway shall meet the floodway standards in § 164.064.
3. The structure shall be anchored to prevent flotation and movement.
4. Service facilities such as electrical and heating equipment shall be elevated or flood proofed to the FPE.
5. The building shall be no greater than 600 square feet in floor size, and be valued at less than $7,500. The building shall meet the permanent opening criteria of division (C)(1)(b) above.
6. The building shall be used only for the storage of vehicles or tools and may not contain basements or other rooms, workshops, greenhouses or similar uses.
(b) Accessory structures that do not meet all of the above criteria may be constructed if they are dry flood proofed or elevated at least one-half of one foot above the BFE.
(D) Nonconforming structures. A nonconforming structure damaged by flood, fire, wind or other disaster may be restored unless the damage meets or exceeds 50% of its market value before it was damaged, in which case it shall conform to the building protection standards of this chapter.
(E) LOMR-F. A LOMR-F must be issued by FEMA before a building permit may be issued for structures built on fill in the floodplain. A permit shall not be issued unless the applicant has complied with all the following criteria.
(1) Compensatory storage shall be provided per § 164.063.
(2) The elevation of the lowest opening in the basement wall (i.e., window wells, access ways) shall be at or above the flood protection elevation (FPE).
(3) The lowest adjacent grade to the foundation shall be at or above the FPE for a minimum distance of ten feet beyond the outside face of the structure. However, if site conditions are such that this requirement cannot be met, the Chief Subdivision Engineer may waive the ten foot minimum setback if a state licensed professional engineer certifies that an alternative method to protect the building from damage due to hydrostatic pressure has been met. The certifications shall be in the form of a detailed soils and structural design analysis, which shall be submitted to the Chief Subdivision Engineer for review. The Chief Subdivision Engineer may require additional documentation as necessary to prove that the proposed shorter setback distance will keep the structure reasonably safe. In no case shall the setback distance be less than four feet.
(4) The grade around the perimeter of the structure, measured at a distance of 20 feet from the structure, shall be above the base flood elevation (BFE). However, if site conditions are such that this requirement cannot be met, the Chief Subdivision Engineer may waive the 20-foot minimum setback distance if a state licensed professional engineer certifies that an alternative method to protect the building from damages due to hydrostatic pressures have been met. A detailed soils analysis and structural design proving that a shorter setback distance will keep the structure reasonably safe from flooding, shall be submitted to the Chief Subdivision Engineer for review. In no case shall the setback distance be less than four feet.
(5) The ground around the building shall be compacted fill that meets all requirements of this division and is at least five feet thick under the basement floor slab. Nothing in this division shall be interpreted to require the removal or replacement of fill that was placed as part of a LOMR-F, if the fill consists of material, including soils of similar classification and degree permeability, as those classified as CH, CL, SC or ML according to ASTM standard D-2487, Classification of Soils for Engineering Purposes.
(6) The fill material must be homogeneous and isotropic; that is, soil must be all of one material, and the engineering priorities must be in the same direction.
(7) All fill material and compaction shall be designed, certified and inspected by a state licensed professional engineer, as warranted by the site conditions.
(8) The basement floor shall be at an elevation that is no more than five feet below the BFE.
(9) There shall be a granular drainage layer beneath the floor slab, and minimum of one quarter horsepower sump pump with a backup power supply shall be provided to remove seepage flow. The pump shall be rated at four times the estimated seepage rate and shall discharge above the BFE and away from the building in order to prevent flooding of the basement or uplift of the floor under the effect of the seepage pressure.
(10) The drainage system shall be equipped with a positive means of preventing backflow.
(11) All foundation elements shall be designed to withstand hydrostatic pressure in accordance with accepted engineering practices.
(12) If the applicant is unable to meet all of the requirements set forth in divisions (E)(1) through (E)(11) above, the Chief Subdivision Engineer may allow the construction of a basement below the BFE only if the applicant demonstrates that the proposed fill and structure meet the guidelines and requirements set forth in FEMA Technical Bulletin 10-01 and are reasonably safe from flooding. In order to demonstrate that the proposed structure is reasonably safe from flooding, the applicant shall submit a detailed engineering analysis of the proposed fill and foundation wall. The engineered basement study shall be completed in accordance with the latest edition of FEMA Technical Bulleting 10-01 with the analysis of the fill being prepared by a state licensed professional engineer.
(13) In order to provide the required compensatory storage on site, in no case shall the depth of excavation in the front and side yards of the lot exceed 18 inches, as measured from the previously existing natural grade. The rear yard shall be permitted to have a greater depth of excavation, if necessary. All excavation shall be constructed to drain freely and openly to the watercourse or storm sewer system. The use of mechanical means to drain the compensatory storage area will not be permitted.
(Ord. 10-164, passed 6-17-2010)