Complicated Waters: Mapping Kalona

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.