Community-based Flood Inundation Maps

During recent flood events, many Iowans found it difficult to relate flood forecast information to risks within their community. To help translate flood forecasting information into an easy-to-use format, the Iowa Flood Center is developing flood inundation maps for select Iowa communities.

IFC researchers are creating physics-based computer models to predict how a flood wave travels through urban floodplains. These high-resolution models can illustrate the extent of flooding under different conditions allowing Iowans to see how predicted flood levels could affect their property, and in turn helping them make informed decisions.

Communities

Individuals filled sandbags across Iowa as river levels rose in June of 2008.

Inundation maps are available for eight Iowa communities — AmesCedar Falls/Waterloo, Cedar Rapids, Charles City, Des Moines, Elkader, Hills, Iowa CityMason City, OttumwaSpencer, and Waverly.

Click on a community above or launch IFIS to view the completed inundation maps.

Methodology

Step 1: Geometric data

Geometric data includes bathmetry (riverbed) and topography (land surface). Bathrymetry is measured using advanced sound navigation and ranging (SONAR) while topography is measured using airplane-based stereoscopic imaging and LiDAR technologies.

What is LiDAR? (NOAA)

Step 2: Digital Elevation Model (DEM)

Topography and bathymetry are combined to create a continuous, high-resolution DEM. In addition, data describing the land use patterns, geometry of buildings in the floodplain, bridge piers, culverts, and low-head dams is acquired.

Step 3: 2-D Mesh – Numerical Modeling

The building, bridge, culvert, and dam geometry are combined with the DEM to construct the numerical model geometry (mesh). Land use data are used to define roughness parameters for the model. Flow rates of water entering the model are determined with USGS river gauge data.

Step 4: Inundation Map

A completed map is prepared but must undergo validation before predicting the flooding extent of the river under different conditions so inundation maps for virtually any possible flow rate can be created.

Step 5: Validation

To ensure model parameters are correct, the model must be calibrated to measured water surface elevations for a given flow rate at numerous locations.

To confirm the model is properly calibrated, its performance is compared with an additional independent set of measured water surface elevations.

Project Personnel:
, Associate Director
, Water Resources Engineer
Funding Source
Iowa State SealState of Iowa
Related Content
Iowa River Inundation Maps and the National Weather Service