Iowa City Press Citizen: Flood Models Will Better Prepare Cities, Residents

Tuesday, May 25, 2010

Iowa Ciy Press Citizen

by Josh O'Leary

In the days leading up to the 2008 flood, Iowa City and Coralville officials could only approximate the potential reach of the Iowa River as it began spilling over its banks.

They had 100-year and 500-year floodplain maps and data from the National Weather Service, but no tools that could tell them precisely which homes, which business and which streets would be in the floodwater's path.

As the second anniversary of the disaster approaches in June, a new flood modeling program developed by the Iowa Flood Center, based at the University of Iowa's hydraulics laboratory, will allow city leaders and residents to pinpoint where the water will flow in the event of future flooding.

Prototype flood inundation maps for the Iowa City and Coralville area, Waterloo and Charles City are available for public use at the Iowa Flood Center's website, The center also is in the early stages of a four-year project to generate flood models for the 85 counties in Iowa that were declared disaster areas because of flooding in 2008.

The models, which are built on a Google Maps platform, allow users to adjust river stages to see what areas will be inundated based on the height of the water. The models also use a risk calculator that determines the probability an area will be flooded.

"What a valuable tool it would have been in 2008, if on Wednesday we could have said, 'Here's what the flow looks like today, and three days from now this is what it's going to look like,'" said Larry Weber, director of UI's Hydraulic Research Laboratory, known as IIHR.

Witold Krajewski, director of the Iowa Flood Center, said the maps will one day be linked to real-time river data and forecasts to provide a visual depiction of how the river will react.

"The forecasts as they exist today and are reported by the media are often not very meaningful because they are just quoting stages -- '16 feet' doesn't really tell people much," Krajewski said. "But this way, there will be this link between the forecast and the extent of potential flooding."

Iowa City Public Works director Rick Fosse said in addition to being a benefit to the public, the inundation maps will help cities anticipate where their resources will be most needed during a flood.

"We now have maps that show how far it's supposed to get for a 100-year event or for a 500-year event, but for those intermediate events, we don't know the exact extent," Fosse said. "That's where this tool is going to be nice; we'll know where to focus our efforts."

The project began as result of the post-flood collaboration between UI and the cities of Coralville and Iowa City to create a unified model of the Iowa River rather than each hiring a consultant to create separate programs. UI took the leadership role in the project and worked with Ayres Associates of Fort Collins, Colo., to build the hydraulics model.

In addition to the public inundation maps, Coralville and Iowa City can use the model to examine the effects of proposed flood mitigation projects. Before Iowa City elevates Dubuque Street along the river and raises the Park Road Bridge in the coming years, for instance, the changes will have first been plugged into the model to see how the river is altered.

Coralville city engineer Dan Holderness said the level of cooperation between the three entities -- Iowa City, Coralville and UI -- is unique, and the partnership has benefited the area as it applies for state and federal help for mitigation projects. Knowing what the specific effects will be for cities and their neighbors has been a strong selling point, he said.

"It's a great predictive tool of what's going to happen and what can happen," Holderness said. "We can adjust our designs accordingly to not negatively impact our neighbors."

Holderness said the model has proven that flood mitigation improvements do not have an adverse impact on downstream areas, meaning Coralville's projects will not create problems down the river in Iowa City. He likened it to a bottleneck that, by constricting the outflow, can increase the liquid in the bottle but does not increase the water coming out of the bottle.

The Legislature established the Iowa Flood Center at UI in the spring of 2009 with a $1.3 million allocation. The center received the same amount of funding for the coming fiscal year, and $10 million of federal Community Development Block Grant money for flood plain mapping was moved from the Department of Natural Resources to the Flood Center.