The Iowa Flood Center (IFC) has released updated flood inundation maps for Decorah, Iowa following repeated flood impacts to the area.  In mid-August, 8.6 inches of rain fell in under 36 hours according to data from the National Weather Service, causing river levels to spike at over 10 feet. To better prepare for future events, local officials asked the IFC to update the flood inundation maps for Decorah to increase the maximum flood stage from 18.5 feet to 22 feet to allow for better planning scenarios in extreme flood conditions.  

The updated flood inundation maps are available to the public through the Iowa Flood Center’s publicly accessible Iowa Flood Information System (IFIS) online tool. Users can access the maps by visiting IFIS and clicking “inundation maps,” to select their community and view adjustable flood stage heights and flood extent and depth areas. These nonregulatory maps provide valuable information to help individuals and communities prepare for and respond to potential flooding. 

“I rely heavily on the partnership between the Iowa Flood Center and the Winneshiek County Emergency Management Agency, not only during times of flooding but also on ‘blue sky days’. Our continued partnership has evolved over the years to the point of the IFC being front and center in the preparedness phase of emergency management. They added two new bridge sensors that allow flood inundation modeling in the Decorah area, and at this juncture, I could not imagine flood preparation without the IFC.” 

 

Sean Snyder, emergency management coordinator for Winneshiek County.

Since the last maps were created in 2015, the IFC has collected more years of river flow data that can be used to estimate how often major floods occur. For example, what was considered a "100-year flood" in 2015 is now expected to happen more frequently.  New LiDAR, laser radar remote sensing technology used to measure distances and create 3D models of the environment, and more advanced computer modeling techniques have also improved the accuracy of flood inundation maps. These revisions help to better understand areas at risk and how communities can better prepare for flood hazards.  

Detailed community-based maps are available for dozens of cities and small towns in Iowa (with more added every year) to show how predicted flood extent and depth could affect property and critical infrastructure. These inundation map libraries are meant to supplement National Weather Service river stage flood forecasts by providing a visual representation of potential inundation extent based on predicted river stage at stream gage locations. In addition, the IFC provides high-resolution interactive flood maps for every Iowa stream in all 99 counties showing the 2-, 5-, 10-, 25-, 50-, 100-, 200-, and 500-year floodplain boundaries. The maps are also available through IFIS and provide critical information to evaluate flood risks and support decision-making, though they are considered non-regulatory. Maps that have completed review and become regulatory should be accessed through FEMA’s Flood Map Service Center. 

The Iowa Flood Center is part of the University of Iowa College of Engineering and is the first and only center in the nation focused solely on flood-related research and education. The IFC was established by the state of Iowa in 2009 following the devastating 2008 floods to help Iowans understand and reduce their flood risks. For more information, visit iowafloodcenter.uiowa.edu.