Statewide Floodplain Maps
In partnership with the Iowa Department of Natural Resources (DNR), the Iowa Flood Center (IFC) is preparing new floodplain maps for the 85 Iowa counties that were declared Presidential Disaster Areas following the 2008 floods.
The Iowa Flood Center's role includes creating the maps for each county that include all streams in Iowa draining one square mile or more. IFC researchers are utilizing statewide light detection and ranging (LiDAR) data recently collected by the DNR to accurately describe Iowa’s river and stream networks, develop computer-based flood simulations, and delineate floodplains. All county maps will follow specific guidelines that adhere to standards established by the Federal Emergency Management Agency (FEMA).
Sequence for Mapping
Floodplain maps for each of Iowa's 85 counties declared Presidential Disaster Areas in 2008 will be completed over the next 3-4 years.
Note: Floodplain maps for the 14 Iowa counties not included in the 2008 Presidential Disaster Areas will be completed through US Army Corps of Engineers (USACE) Section 22 Planning Assistance to States (PAS) funds.
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.