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University Of Iowa Scientists Studying Flood Control In Northwest Iowa Lakes

Tom Gustafson
Courtesy of Okoboji Tourism
The Iowa Great Lakes

A University of Iowa scientist is studying different ways to manage flooding in northwest Iowa’s great lakes.
Larry Weber, the executive associate dean for University of Iowa’s College of Engineering, will use computer models to estimate how much the Iowa Great Lakes, particularly the Lower Gar Lake outlet, will rise in different amounts of rainfall. He’s also studying how much water can pass through channel structures called culverts at the outlet that currently restricts flow.

His team will look at sharing a number of options with lake enthusiasts and area officials, such as adding more culverts, using different types and shapes of culverts, or getting rid of them entirely and replacing them with a bridge or a dam to allow more water to flow out of the lakes.

“We want to make sure we design something that has the utility and lifespan of many decades,” Weber said. “So we want to make sure we think of increasing intensity of rainfall in the future.”

Rains were so heavy this past summer that they caused shoreline erosion and temporarily shut down the Iowa Great Lakes in July. Iowa Great Lakes Association President Bill Van Orsdel says shutting down the lakes causes economic damage to a community that thrives on recreation and tourism.

“Whatever it costs to rent a room, or a condo for a week or two weeks, it’s right down the drain,” Van Orsdel said. “…It’s devastating to the homeowners, to the residents and to the vacationers.”

Scientists project that over time, rains will get heavier and the risk of flooding will increase, so the association wanted to do something about it. They contacted Weber to ask if he could study how flooding affects the area.

When rain falls, it flows into Spirit Lake and East and West Lake Okoboji, the water combines and flows into the Upper Gar and Lower Gar Lake areas and flows out of the area through Lower Gar, Weber said. The Lower Gar area currently has around 10 culverts that restrict the amount of water that can flow through.

Weber compared the model he and his team are using to SimCity, the popular simulation-based video game where players build a city.

“This is kind of similar in that our model includes all the land cover and land use, the location of buildings and urban areas in the watershed,” he said. “As we're looking to the future, we could look at the benefit of building wetlands out in the landscape and capturing the water or holding the water back out in the rural landscape before it even flows into the lakes.”

Wetlands can trap rainfall and even uptake nutrients like phosphorous to prevent that from traveling in the lake.

The scientists will show the association as well as officials and residents the different ways they can better control flooding early next year. Van Orsdel said he’s confident that a long term solution can be found. He said they’ll have to fundraise and look to partnerships to cover costs.

Katie Peikes was a reporter for Iowa Public Radio from 2018 to 2023. She joined IPR as its first-ever Western Iowa reporter, and then served as the agricultural reporter.