Aug. 31, 2025
VIROQUA, Wis. – A veteran Iowa engineer is urging Vernon County and other parts of Wisconsin’s Driftless Area to consider adopting on-road flood mitigation structures, a tool he says has proven effective in reducing flood damage across Iowa’s rural landscapes. Lee Bjerke, a research engineer with the Iowa County Engineers Service Bureau and former Winneshiek County engineer, presented his findings to the Vernon County Flood Mitigation Alliance this week.
The presentation grew out of a recent visit by watershed conservationists, engineers, farmers, and community members from Wisconsin organized by the Coon Creek Community Watershed Council that connected in Postville, Iowa for an informational exchange around innovative watershed management strategies. You can read our story about that trip here.
Bjerke, who spent more than two decades overseeing roads and bridges in northeast Iowa, described how earthen embankments known as “on-road flood mitigation structures” built on or near roadways can temporarily hold back floodwaters, reducing peak flows and protecting both infrastructure and communities.
“These structures are designed to slow down water during storm events, typically holding it for about 24 hours before releasing it gradually,” Bjerke said. “They’re not new, but we’ve refined the approach to maximize their impact on flood-prone watersheds.”
Bjerke said the typical design includes pipes that handle normal drainage, with additional capacity to manage overflow during heavy rains. Unlike permanent ponds, these structures are usually dry except after storms. Each structure is tailored to the specific site, taking into account local topography and watershed characteristics.
Bjerke explained that while the initial construction costs can exceed those of simply replacing a culvert or bridge, the long-term benefits — including reduced maintenance, improved road safety, and less frequent flood damage — make the investment worthwhile. In Iowa, the average cost of such a structure is about $550,000, comparable to the price of a new bridge. The structures, sometimes called “on-road impoundments,” are most effective in areas with steep valleys and clay soils, like those found in Bear Creek, Iowa, and much of Vernon County.
Bjerke noted that in Bear Creek, about 15% of the watershed’s runoff passes through these structures, significantly lowering flood peaks downstream.
“Every site is unique, but the principle is the same: slow the water, reduce the damage,” Bjerke said. “We’ve seen firsthand that these structures can make a real difference, especially when combined with public-private partnerships and permanent easements.”
Bjerke acknowledged that not every location is suitable, and landowner cooperation is essential since an easement is typically needed to impound the water on private property. Property owners are free to use the land however they like and are compensated for the time water would be impounded based on modeling and impact to the property.
Bjerke also emphasized the importance of high-level watershed modeling and state support, pointing to Iowa’s statewide approach as a model for Wisconsin.
“I really struggle to find a downside,” Bjerke said. “If you want to see if it works, build one and measure the results. The benefits may not be immediate, but over time, they can be transformative for communities facing repeated floods.” Bjerke’s presentation comes as Vernon County and other Driftless Area communities grapple with aging dams, frequent flooding, and the need for new approaches to watershed management.
As the group considered whether the approach would work in Vernon County, some members expressed optimism, while others emphasized the need for careful, site-specific evaluation.
“You really just have to look at each site individually and decide, is this worth putting in? Can I make it work?” Bjerke said. “My advice would be just try one and see how that works.”
Local ordinance becomes tool to get FEMA to approve upgrades to infrastructure
Bjerke explained that some Iowa counties, such as Winneshiek County, adopted local ordinances requiring the use of improved drainage structures—like box culverts or on-road impoundments—when replacing damaged infrastructure. Bjerke said one of the biggest challenges after a disaster, including floods, is to get FEMA to approve infrastructure improvements that go beyond what had previously been in place. One of the common problems is local officials see the areas that get repeatedly damaged and it is often more cost effective to upgrade that piece of infrastructure to prevent future damage, but FEMA’s policy is to only pay for the existing design and not upgrades.
Bjerke said by passing the local ordinance and making it their official policy and consistently following it, counties could demonstrate to FEMA that these upgrades were standard practice, not just post-disaster enhancements. As a result, after a disaster, FEMA was required to fund the improved structures rather than only paying for like-for-like replacements. Bjerke emphasized that having a clear ordinance and a track record of implementation was key to compelling FEMA’s approval for infrastructure improvements.
Despite questions about the tools Bjerke presented, Alliance members agreed that new solutions are needed as the region faces more frequent and severe flooding and the options should be explored further.
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