Iowa Statewide Floodplain Mapping Project
In 2010, the Iowa Flood Center and Iowa Department of Natural Resources (IDNR) began a six-year, $15 million program to create and update floodplain maps throughout the state. Funded by the U.S. Department of Housing and Urban Development in response to the devastating 2008 flood, the Iowa Statewide Floodplain Mapping Program helped to identify and communicate Iowa’s flood hazards, providing communities and individuals with information needed to make informed decisions on managing floodplain areas. Working the IDNR, the U.S. Army Corps of Engineers (USACE), Federal Emergency Management Agency (FEMA), and the Iowa Natural Heritage Foundation, the IFC team created maps showing probability, extent, and depth of flooding for every Iowa stream draining more than one square mile. The project was completed in December 2016.
Visit http://www.iowafloodmaps.org to view maps from this project.
Example of floodplain maps available at www.iowafloodmaps.org.
Floodplain maps for each of Iowa’s 85 counties declared Presidential Disaster Areas in 2008 were completed by IFC. The remaining 14 Iowa counties not included in the 2008 Presidential Disaster Areas were completed by the USACE.
IFC researchers utilized statewide light detection and ranging (LiDAR) data recently collected by the IDNR to accurately describe Iowa’s river and stream networks, develop computer-based flood simulations, and delineate floodplains. The mapping follows specific guidelines that adhere to standards established by the FEMA.
Step 1: Hydrography
Hydrography describes the geometry of Iowa’s network of streams and rivers. The DNR’s statewide LiDAR data is used to locate stream channels and create a digital stream network map.
Step 2: Hydrology
Hydrology is used to predict the amount of water flowing in Iowa’s streams. Stream gage data and mathematical relationships from the United States Geological Survey (USGS) are used with LiDAR and hydrography data to estimate stream flows.
Step 3: Hydraulics
Hydraulics use physics to calculate flood depths and extents based upon stream flow. Computer models are constructed using LiDAR and hydrography data, and used to simulate flow behavior and estimate flood elevations.
Step 4: Mapping
The results of hydraulic computer models are used to create maps showing flood depths and extents. Model results are combined with LiDAR data and analyzed to identify floodplain boundaries.
Step 5: DFIRM
Digital Flood Insurance Rate Maps (DFIRMs) are created and formatted according to FEMA requirements. Upon completion, the DFIRMs are provided to the DNR who will make the maps available for community review.