(A) The BFE shall be delineated onto the site topography to establish the regulatory floodplain area limits for regulation under this chapter. Regulatory floodplains shall be delineated onto the site map from the current FEMA FIRM (see Appendix A), FBFM or LOMR and include those areas of the SFHA which are not regulatory floodplains. Each community, whether certified or not, remains responsible for maintaining the effective FIS and a list of FIRM panels for their respective communities.
(B) The BFE shall be:
(1) The elevation of the 100-year profile corresponding to the location of the development as indicated in the flood profiles in the FEMA Flood Insurance Studies listed in Appendix A, or as adopted by each community (which may be updated from time to time);
(2) In the case of FEMA delineated “AH Zones” the elevation noted on the map shall be the BFE. In the case of FEMA delineated “AO Zones” the BFE shall be the depth number shown on the map added to the highest adjacent grade, or at least two feet above the highest adjacent grade if no depth number is provided;
(3) (a) When no BFE information exists and the upstream tributary drainage area is 640 acres or greater, the BFE shall be determined using a site specific floodplain study by a professional engineer using appropriate hydrologic and hydraulic models as follows:
1. Hydrologic models: TR-20, HEC-1, HEC-HMS;
2. Hydraulic models: HEC-2, HEC-RAS, WSP-2; or
3. A technique approved by the Administrator and the IDNR/OWR.
(b) Where a channel has a tributary drainage area of 640 acres or more, the above analyses shall be submitted to the IDNR/OWR for concurrent approval.
(c) For a non-riverine regulatory floodplain, the historic flood of record plus three feet may be used for the BFE instead of performing a detailed hydrologic and hydraulic study.
(4) For floodplains that are not regulatory, are not draining more than 640 acres, and with
no BFE determined, the Administrator may require a site-specific floodplain study for the purpose of establishing an FPE for the development.
(C) (1) The location of the regulatory floodway shall be as delineated on the current effective regulatory maps maintain by each community. The location of the regulatory floodway boundary shall be scaled onto the site plan using references common to both the map and the plan (typically the center lines of adjacent roadways). Where an interpretation is needed to determine the exact location of the regulatory floodway boundary, IDNR/OWR should be contacted.
(2) Note: If an area of the site is located in the regulatory floodway that is higher than the BFE, that area is subject to the floodway standards of § 151.064, including the appropriate use criteria, until a time as a LOMR is received from FEMA with concurrence by IDNR/OWR.
(3) General criteria for analysis of flood elevations in the regulatory floodway are as follows.
(a) The flood profiles, flows and data in the current effective FIS must be used for analysis of the base conditions. If the study data appears to be in error or conditions have changed, FEMA and IDNR/OWR shall be contacted for approval and concurrence on the appropriate base conditions data to use. The Director shall be copied on all related correspondence.
(b) If the BFE at the site of the proposed development is affected by backwater from a downstream receiving stream with a larger drainage area, the proposed development shall be shown to meet the requirements of this section with the receiving stream at both the normal water and BFEs.
(c) If the applicant is informed by IDNR/OWR, local governments, or a private owner that a downstream or upstream restrictive bridge or culvert is scheduled to be removed, reconstructed, modified or a regional flood control project is scheduled to be built, removed, constructed or modified within the next five years, the proposed development shall be analyzed and shown to meet the requirements of this section for both the existing conditions and the expected flood profile conditions when the bridge, culvert or flood control project is built, removed or modified as applicable.
(d) If the appropriate use will result in a change in the regulatory floodway location or a change in the BFE, the applicant shall submit the information required to be issued a conditional letter of map revision (CLOMR) to IDNR/OWR and FEMA. A public notice inviting public comment on the proposed change in the BFE or location of the regulatory floodway will be issued by IDNR/OWR or its designee before a CLOMR is issued. Filling, grading, dredging or excavating may take place upon issuance of a conditional approval from IDNR/OWR and the Administrator. No further development activities shall take place in the existing or proposed floodplain until a letter of map revision (LOMR) is issued by FEMA unless the activities meet all the requirements of § 151.062 of this chapter. The Director shall be copied on all related correspondence.
(e) For those circumstances listed below and located in a regulatory floodway, at a minimum, the following information shall be submitted to IDNR/OWR for their review and concurrence:
1. Analysis of the flood profile due to a proposed bridge, culvert crossings and roadway approaches;
2. An engineer's determination that an existing bridge, culvert crossing or approach road is not a source of flood damage and the analysis indicating the proposed flood profile;
3. Alternative transition sections and hydraulically equivalent compensatory storage; and
4. Stormwater management permits to local units of government for regulatory floodway and floodplain development.
(f) IDNR/OWR will issue permits for any IDNR/OWR projects, dams and the like all other state, Federal or WCSMC or certified community projects.
(Ord. 18-08, passed 1-14-19)