This chapter's protection standard is based on the flood insurance study for the city. If a base flood elevation or 100-year frequency flood elevation is not available for a particular site, then the protection standard shall be according to the best existing data available in the Illinois state water survey's floodplain information repository that has been approved by IDNR/OWR and FEMA. When a party disagrees with the best available data, he/she shall finance the detailed engineering study needed to replace existing data with better data and submit it to IDNR/OWR and FEMA for approval prior to any development of the site.
A. The base flood or 100-year frequency flood elevation for the SFHAs of Addison Creek shall be as delineated on the 100-year flood profiles in the flood insurance study of the city prepared by FEMA and dated August 19, 2008, and such amendments to such study and maps as may be prepared from time to time.
B. The base flood or 100-year frequency flood elevation for the SFHAs of those parts of unincorporated Cook County that are within the extraterritorial jurisdiction of the city or that may be annexed into the city shall be as delineated on the 100-year flood profiles in the flood insurance study of Cook County prepared by FEMA and dated August 19, 2008, and such amendments or revisions to such study and maps as may be prepared from time to time.
C. The base flood or 100-year frequency flood elevation for each SFHA delineated as an "AH zone" or "AO zone" shall be that elevation (or depth) delineated on the flood insurance rate map of the city. The base flood or 100-year frequency flood elevation for each of the remaining SFHAs delineated as an "A zone" on the flood insurance rate map of the city shall be according to the best existing data available in the Illinois state water survey floodplain information repository.
1. When no base flood or 100-year frequency flood elevation exists, the base flood or 100-year frequency flood elevation for a riverine SFHA shall be determined from a backwater model, such as HEC-RAS, HEC-2, or WSP-2.
2. The flood flows used in the hydraulic models shall be obtained from a hydrologic model, such as HEC-HMS, HEC-1, or TR-20, or by techniques presented in various publications prepared by the United States geological survey for estimating peak flood discharges.
3. Along any watercourses draining more than one square mile, the above analyses shall be submitted to IDNR/OWR for approval. Once approved it must be submitted to the Illinois state water survey floodplain information repository for filing.
4. For a nonriverine SFHA, the base flood elevation shall be the historic flood of record plus three feet (3'), unless calculated by a detailed engineering study and approved by IDNR/OWR for drainage areas greater than one square mile.
5. For an unmapped extended SFHA (with a drainage area less than 1 square mile) which has been identified by the city pursuant to subsection 12-1-5A1c of this chapter, the base flood elevation shall be determined by the applicant utilizing a method as approved in this subsection C, with concurrence of the city. (Ord. O-20-2008, 6-16-2008)