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The County of DuPage
Wheaton, Illinois

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 have had a profound impact on many of DuPage County's rivers and streams. The Stormwater Management Program was therefore established to address existing issues and to prevent future flood damages along the county's waterways. Since its inception, the Stormwater Management Division has striven to provide accurate flood plain information to property owners, regulators, and developers.

In the late 1970s and early 1980s the Federal Emergency Management Agency issued Flood Insurance Rate Maps (FIRM) that established the 1% annual chance (100-year) floodplains for DuPage County. These and other FIRMs have since been rendered obsolete due to changes in land use, topography, modeling standards and technologies but can still be viewed at FEMA's Map Service Center website by using the "Product Catalog". The Stormwater Division has been conducting new watershed studies that will conform to current topographical conditions and meet today's standards and practices in hydrologic and hydraulic analysis.

DuPage County effective FEMA issued Digital Flood Insurance Rate Maps (DFIRM)

County Mapping Update Overview

In 2008, DuPage County Stormwater Management received a $2,050,000.00 grant from the Federal Emergency Management Agency (FEMA) to restudy and remap the floodplains for 24 watersheds in DuPage County.  In cooperation with the Illinois State Water Survey (ISWS), this project will result in a new Countywide floodplain map updating the current FEMA Digital Flood Insurance Rate Map (DFIRM) map dated December 16, 2004.  

This countywide project incorporated new flood hazard information 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 new study information has resulted in new and modified: base flood elevations, Special Flood Hazard Area (SFHA) boundaries, floodway boundaries, and food insurance zone designations.  The revision also incorporated non-revised flood hazard information from effective FIS reports, FIRMs and Flood Boundary and Floodway Maps as appropriate for the remaining watersheds in DuPage County.  Fifty-six Letters of Map Revision (LOMR) and one multi-lot Letter of Map Amendment (LOMA) were also incorporated.

Watershed Planning and Modeling

The Stormwater Management Division utilizes a specific methodology when developing watershed plans. The Hydrologic Simulation Program (HSPF) is used to create the required hydrologic inputs. The hydraulic analysis is achieved using the dynamic flood routing model known as Full Equations (FEQ) to determine flood elevations. Once the hydrologic and hydraulic analysis is complete the results are used as inputs to a statistical program called Peak To Volume Statistics (PVSTATS) which then determines the 100-year and other frequency flood elevations. View a detailed explanation and a map showing model progress.

Request for Information

  • Flood Elevation Request Form (PDF) - Please download this form to your computer. Opening the form within a web browser will DISABLE the "Send via Email" button.
  • Data/Map Request Form (PDF) - Please download this form to your computer. Opening the form within a web browser will DISABLE the "Send via Email" button.