Epic Rebirth

Watershed approach: Invest in prevention, cut flooding costs

Ponds, wetlands, terraces retain and slow water, reduce flood risk

Adam Rodenberg, project coordinator for the Middle Cedar Watershed Management Authority, points out a feature to Kristina TeBockhorst, of Iowa State University Extension during a watershed program May 31 at the ISU Borlaug Learning Center outside of Nashua. Nashua is in the Upper Cedar Watershed. (Photo by Kate Giannini/Iowa Flood Center)
Adam Rodenberg, project coordinator for the Middle Cedar Watershed Management Authority, points out a feature to Kristina TeBockhorst, of Iowa State University Extension during a watershed program May 31 at the ISU Borlaug Learning Center outside of Nashua. Nashua is in the Upper Cedar Watershed. (Photo by Kate Giannini/Iowa Flood Center)
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Eastern Iowa has a lot of experience spending money after a flood to help communities recover.

The Iowa Watershed Approach, though, is about focusing intensive conservation strategies on watersheds to reduce the risk of flooding — before it happens.

“Rather than spending a lot of money post disaster, invest money upstream where flooding events start,” said Adam Rodenberg, project coordinator for the Middle Cedar Watershed Management Authority. “The long-term impact is reducing flood risk and developing more resiliency to flooding.”

The U.S. Department of Housing and Urban Development awarded Iowa nearly $97 million in 2016 for a watershed improvement program called the Iowa Watershed Approach.

Iowa received the fourth-largest grant in the nation, in part because the project focuses on quantifying the benefits of practices to see if they work, said Larry Weber, a University of Iowa hydraulic engineer and executive associate dean for the College of Engineering.

“We hope we can inspire people to do this in other areas,” said Weber, who spearheaded the proposal for the grant, which continues through 2021.

Smaller demonstration projects provided early evidence the watershed approach could reduce flood risks.

measuring impact

One of those projects was on the Soap Creek Watershed, which drains 258 square miles of southeast Iowa, with water eventually going into the Des Moines River.

Landowners agreed to have ponds and other water retention structures built on their land to hold rain, allowing it to slowly drain rather than rushing into the river where it could cause flooding downstream.

Hydrologic modeling of 132 Soap Creek watershed projects showed peak discharge was 40 percent to 95 percent lower than before the structures were installed, according to a project evaluation done by the Flood Center in 2016.

Even as the water left the watershed, peak discharge was 20 percent to 30 percent lower, which lessens the amount of water that goes out of the river banks across the flood plain.

Middle Cedar Watershed

Middle Cedar Fact Sheet and Map by Source Media Group News on Scribd

voluntary

A big part of the Iowa Watershed Approach is getting landowners on board for this voluntary program.

The grant pays for 75 percent of approved projects — such as ponds, wetlands, retention basins and terraces — and the landowner pays the rest. The structures reduce erosion and provide the landowner with a fishing or swimming spot that draws wildlife, but projects also may take land out of agricultural production, Rodenberg said.

The grant provides $8.5 million for projects in targeted areas of Benton, Buchanan and Tama counties.

“There’s been a pretty decent amount of interest,” Rodenberg said. “The limiting factor is will it be conducive to the landowner’s farming operation.”

Many of these conservation structures also improve water quality, filtering out fertilizer and other contaminants, Rodenberg said.

linn county

Linn County voters in November 2016 overwhelmingly passed a $40 million conservation bond to pay for wetland development and natural flood protection along the Cedar River.

About 55 percent of the bond will go toward water quality and land protection projects, 30 percent for parks and 15 percent for trails.

Public-private partnerships have helped bring about other watershed improvements.

The Nature Conservancy in Iowa teamed up with the Linn County Conservation Department and the Cedar Rapids Water Division to create or restore wetlands in the Cedar River basin, including an oxbow that was once part of Silver Creek.

More than 1,100 cubic yards of soil and sediment were removed from the oxbow channel, which provided an estimated 240,000 gallons of floodwater storage, according to the Nature Conservancy.

Oxbows also remove nitrate from water draining from nearby farm fields and create wildlife habitat, the group reported.

l Comments: (319) 339-3157; erin.jordan@thegazette.com

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