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Complicated Waters: Mapping Kalona

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A preliminary inundation map of Kalona, Iowa.

On June 15, 2010, the city of Kalona, Iowa, was soaked with more than two inches of rain in about an hour. Flash flooding from a nearby drainage ditch forced the evacuation of a mobile home park, where residents found themselves suddenly knee-deep in water.

The floodwaters receded quickly, and, compared to other floods in Iowa, this event could be considered minor. But Kalona is facing flooding issues that are actually quite complex. For more than two years, the city has been working to understand and modify a proposed floodplain map of the community presented by FEMA, the Federal Emergency Management Agency. The original FEMA maps, which delineate the 100-year-floodplain (areas with a 1 percent chance of flooding each year, independent of previous years), would have cost Kalona property owners over $1 million in annual flood insurance premiums.

Shortly after the FEMA maps were initially released in 2010, the Kalona City Council invited the Iowa Flood Center (IFC) to help evaluate the maps. IIHR Director Larry Weber and IFC Associate Director Nathan Young met with the Kalona City Council several times over the ensuing year and a half to explain the floodplain mapping methodology and discuss opportunities to refine the Kalona map.

The IFC team studied the methods used to create the maps and reran the models. At the Sept. 19, 2011, Kalona City Council meeting, Weber presented the results of IFC’s own 2D modeling of the Kalona area. The map looked quite a bit different than the FEMA original. Using LiDAR (laser radar) data to develop a digital elevation model, the IFC team modeled the geometry of the river and creek beds, as well as the surrounding area.

“This is a more advanced engineering approach,” Weber explained. “And it’s more appropriate.”

The new maps underwent another round of revisions when the IFC team applied a major precipitation event to the model. This added layer of complexity better shows where the true risk is, Weber explained. “We wanted to be able to provide the best kind of map.”

Working with FEMA and the Iowa Department of Natural Resources, the maps underwent a thorough review process and were presented to the public for comment on October 4, 2012. The new maps became effective last month, January 2013.

Using the new map, Kalona’s flood insurance tab has been cut in half. The services of the Iowa Flood Center have been crucial to Kalona as the town finds its way through a complicated and costly situation, says City Administrator Ryan Schlabaugh. “The goal was to have the most accurate map possible,” he says, “and the Iowa Flood Center helped us do that.”

Although the process has by no means been a simple one for Kalona, the community is in effect leading the way through complicated waters.

Maps delineating the 100-year floodplain in Kalona can be viewed by visiting the City of Kalona website.

 

Mapping the Future

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The Iowa Floodplain Mapping team.

The Iowa Floodplain Mapping team.

Accurate scientific information will be one of Iowa’s best defenses against future floods, says Iowa Flood Center Associate Director Nathan Young.

He is leading an effort to update floodplain maps for 85 of Iowa’s 99 counties. Young, who is also an IIHR research engineer, says that the new floodplain maps provide a direct and easy-to-understand way to communicate flood risk to Iowans.

The IFC, located at the University of Iowa’s IIHR—Hydroscience & Engineering, is about one year into the four-year Iowa Floodplain Mapping Project, funded with $10 million from the U.S. Department of Housing and Urban Development. Working closely with the Iowa Department of Natural Resources (DNR), the IFC will develop floodplain maps for the Iowa counties that were declared federal disaster areas after the 2008 floods. Some or all of the maps will eventually be adopted by the Federal Emergency Management Agency (FEMA) as regulatory maps.

“We’re excited to partner with the DNR on this important statewide project,” Young says. “These maps will provide Iowans with new information concerning flood risk in their own communities, so they are empowered to make informed land use and land management decisions.”

DNR Floodplain Mapping Coordinator Scott Ralston agrees. “We look forward to delivering quality flood hazard data to Iowans to increase public awareness and help protect life and property into the future.”

A Herculean Task

The scope of the project is huge. IFC researchers are mapping all streams draining one square mile or more. To accomplish this, they rely heavily on statewide LiDAR (laser radar) data recently collected by the DNR. LiDAR is a remote-sensing technology that researchers use to develop digital elevation models of the land surface. The availability of LiDAR was a major reason mapping funds were allocated to the state, Young says. “LiDAR data allow for more precise delineation of floodplain boundaries.” With these data, the team will be able to describe Iowa’s river and stream networks, develop computer-based flood simulations, and delineate floodplains with reasonable accuracy.

The project involves digitizing the state’s stream network, performing hydraulic and hydrologic analyses, and using the results to create maps. After a successful pilot project in Poweshiek County, the team turned to the statewide effort. The extent of the project requires the development of innovative, efficient new floodplain mapping tools, and the new data products will offer value beyond the mapping projects.

“Scaling the project up to the entire state and developing and managing such a large volume of data is daunting,” Young says. “We have hired a large number of engineers, GIS staff, and students dedicated specifically to the project. Our partnership with the DNR has also been a great help in that regard.”

“It has been rewarding to utilize the technical expertise of the IFC in the areas of hydrology, river hydraulics, and state-of-the-art GIS technology,” Ralston says. “The task ahead—to provide state-of-the-art floodplain mapping for Iowa—is daunting and challenging. … But we are confident that our partnership with the IFC will be successful.”

A Great Place to Be

University of Iowa students, too, will benefit. Their work is essential to the project, and they will take away tremendous practical applied engineering experience. Graduate student Nick Thomas came to Iowa with an undergraduate engineering degree from the University of Minnesota in the fall of 2010, just in time to get in on the start of the floodplain mapping project.

Thomas believes this experience will serve him well no matter where his career leads. “No matter what I do, this knowledge will be useful,” he says. “As a student, the flood center is a great place to be. Flooding is a problem for many people, and as part of a community of researchers all working toward a common goal through different means, it can be very exciting.”

He adds, “The flood center is creating great tools and technologies to better study and mitigate flood devastation, so yes, I do feel that it is important.”

When the maps are complete, Young says, they will guide floodplain regulation and management. Iowans will be able to access them on the Internet to better understand and identify their flood risks.

This project is exactly the kind of public service the Iowa Flood Center was established to provide, Young says. “This is an excellent opportunity for us to produce research that will benefit of the people of Iowa.”

Read more about the statewide floodplain mapping project.