Inundation Maps Released for Waverly

The Iowa Flood Center has released newly updated flood inundation maps for the community of Waverly. These maps are accessible on the Internet through the Iowa Flood Information System (IFIS), an interactive Google Maps-based online application. The inundation maps are frequently used by local authorities for planning and real-time flood mitigation, but are also useful for homeowners, business owners, and others.

The City of Waverly, perched on the banks of the Cedar River, is prone to seasonal flooding. Like many Iowa communities, Waverly experienced severe flooding in 2008 that inundated the downtown, including city offices.

An unusually wet spring in 2013 brought additional flooding to residential areas of the city and reinforced the community’s need for tools to better understand flood risks.

The Iowa Flood Center, created in 2009, was charged with developing inundation maps for those communities most affected by the floods of 2008. IFC Water Resources Engineer Dan Gilles says that the maps creation process begins with data collection. Typically, the team will collect measurements of the river bed and any structures in the floodplain that affect how the river flows. These structures could include dams, bridges, levees, or even buildings. All of these data are used to create a computer model of the river and surrounding floodplain. In this particular case, the team was able to make use of an existing FEMA flood model and make some minor updates. Once a satisfactory model is developed, the team then selects the flow simulation scenarios, conducts post-processing of simulation results, gathers and applies feedback from the city and county, and finally releases the maps.

This is the second release of maps for the Waverly community, which have been revised following additional feedback from the city. “After receiving some valuable data from the City of Waverly, we chose to process some of the high flow simulation results differently to reflect their observations during the 2013 flooding event,” Gilles says.

In addition, the city’s recent installation of an inflatable dam, which can be adjusted to regulate the upstream pool height, significantly altered the model. Gilles explains that while the U.S. Geological Survey’s gauges use the river’s stage to estimate flow, the new dam disrupts that relationship and has caused the USGS to deploy different techniques to estimate flow through Waverly. These most recent revisions more accurately reflect the relationship between flow and inundation extent on the maps.

Waverly City Administrator Phil Jones described IFIS as a great way to see both real-time precipitation and river information. He adds that during last May’s flooding, the system allowed city officials to see the rainfall in the upper part of the watershed and the changes in stream levels as the high water flowed south. They were able to then apply that data to the inundation maps to get an idea of the potential impact on Waverly.

The IFC team has created an ever-expanding library of inundation maps; currently maps exist for 12 Iowa communities. The IFC continues to improve these maps in response to feedback from local officials and new flood mitigation systems installed by these communities.

MEDIA CONTACT: Jackie Stolze, Iowa Flood Center, 319-335-6410, jackie-stolze@uiowa.edu