Identification of Unmapped Special Flood Hazard Areas in Illinois
Presented here are maps of each of Illinois’ 102 counties illustrating stream reaches with potential flood risk for which Special Flood Hazard Areas (SFHAs) have not been identified on Federal Emergency Management Agency (FEMA) Flood Insurance Rate Maps (FIRMs) as of July 1, 2007. Tabular data providing stream names and number of unmapped stream miles are listed here. More on our study approach is listed in the contract report.
Select a county of interest to view and/or download the map. Please see our disclaimer.
FEMA publishes FIRMs showing SFHAs, which have a 1 percent chance of being inundated in any given year. The nationwide identification of SFHAs was initiated with the signing of the Flood Insurance Act of 1968. Illinois Administrative Code defines state oversight of floodways for streams that drain 10 square miles (sq. mi.) or more in rural areas or 1 sq. mi. or more in urban or urbanizing areas. This general guidance has been used in preparing Illinois FIRMs to identify streams that pose a flood hazard. Many SFHAs for streams meeting these criteria have not been identified on Illinois FIRMs, however. There are streams in rural and urban areas meeting the criteria for which SFHAs have never been identified, and there are urban areas where community annexation is expanding into areas mapped according to rural guidelines of a 10 sq. mi. drainage area. Unmapped SFHAs pose a flood risk that is has not been communicated to the public, floodplain managers, or elected officials. In order to bridge this gap in Illinois, a screening process was developed, and streams having potential flood risk for which SFHAs have not been mapped were identified for each Illinois county.
This project was sponsored by the Federal Emergency Management Agency, through the Map Modernization Management Support Best Practices Award for Federal Fiscal Year 2006, awarded to the Illinois Department of Natural Resources under Cooperating Technical Partner (CTP) Agreement EMC-2006-CA-7023.