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Floodplain Mapping

Program Overview

DuPage County has grown dramatically over the last half decade. From 1950 to 2002 DuPage County saw a 600% increase in population alone. This rapid urbanization from what was mostly agricultural land to large residential, commercial, and industrial areas has had a profound impact on many of DuPage County's rivers and streams. The Stormwater Management Program was established to address existing flooding issues and prevent future flood damages along the county's waterways. Since its inception, the Stormwater Management Department has strived to provide accurate flood plain information to property owners, regulators, and developers.

The first Flood Insurance Rate Maps (FIRM) that established the 1% annual chance (100-year) floodplains for DuPage County were issued by the Federal Emergency Management Agency (FEMA) in the late 1970s and early 1980s. These maps have become outdated and inaccurate due to changes in land use, topography, and modeling technologies. The Stormwater Management Department has been conducting new watershed studies that incorporate more current land use and topographical conditions and meet today's standards and practices in hydrologic and hydraulic analysis.

In 2008, DuPage County Stormwater Management received a $2,050,000.00 grant from FEMA to restudy and remap the floodplains for 24 watersheds in DuPage County. In cooperation with the Illinois State Water Survey (ISWS), this project resulted in a new Countywide floodplain map that became effective on August 1, 2019.

This countywide project incorporated new flood hazard information (base flood elevations, Special Flood Hazard Area (SFHA) boundaries, floodway boundaries, and flood insurance zone designations) in the following watersheds:

  • Salt Creek Mainstem and its tributaries that include Spring Brook, Devon Avenue, Westwood Creek, Ginger Creek, Sugar Creek, Oak Brook Tributary and Bronswood Tributary
  • East Branch DuPage River Mainstem and its tributaries that include Swift Meadows/Army Trail Road, Armitage Creek, Glencrest Creek, Tributary No. 2, Rott Creek, Lacey Creek, Prentiss Creek, St. Joseph Creek, Crabtree Creek and Willoway Brook
  • Steeple Run Tributary, Spring Brook No. 1
  • Sawmill Creek, Wards Creek

The project also incorporated flood hazard information from effective FIS reports, FIRMs and Flood Boundary, and Floodway Maps for the remaining watersheds in DuPage County that were not were not re-studied. Fifty-six Letters of Map Revision (LOMR) and one multi-lot Letter of Map Amendment (LOMA) were also incorporated.

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