Soil Matters: Wetlands and Healthy Soil Are Keys to Reducing Flooding

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Flooded neighborhood

Widespread flooding in 2018 and 2019 caused billions of dollars of damage in many parts of the country. The Kankakee River watershed is one of many places where local officials are looking for solutions to flooding. Part of the solution is actually right under their feet.

The Kankakee River flows from north-central Indiana into northeastern Illinois. The river was once surrounded by the Grand Kankakee Marsh – one million acres of marshland, wetlands, wet meadows, prairie, and forested swamps that stretched for nearly 100 miles. The marsh teemed with fish, waterfowl, beaver, mink, deer, and bison.

“It was one of the richest wildlife habitats in all of North America,” says Jim Sweeney, an IWLA member who has worked for decades to protect and restore some of the last vestiges of the Grand Kankakee Marsh. Its size and bounty of wildlife earned the marsh the nickname “Everglades of the North.”

Yet decades of work to drain and fill the marsh destroyed 99 percent of the original wetlands by the 1920s. Much of that former swampland is now cropland and pasture, flat fields crisscrossed with thousands of miles of drainage ditches and underlain with tile drain systems to quickly carry rainfall away. Indiana’s portion of the Kankakee River was also straightened and dredged, turning a meandering 250-mile-long river into an arrow-straight canal just 82 miles long. It should be no surprise that a system designed to carry water quickly downstream would result in flooding.

Flooding was made even worse in recent decades by farming practices that reduced the soil’s organic matter, and with it, the water storage capacity of the soil. Wetland soil is naturally high in organic matter such as dead leaves and roots. When wetlands are drained, plowed, and farmed, much of that organic matter is lost.

Healthy, biologically active soil has pockets of air space that can absorb water quickly. The pockets are the result of worms, nematodes, beneficial bacteria, and other critters that create space and the tiny fungi that glue the structure together. Healthy topsoil is about half minerals (sand, silt, and clay) and half air, water, and organic matter.

Losing just one percent of the soil’s organic matter cuts its water-holding capacity by 20,000 to 40,000 gallons per acre. In a landscape the size of the Kankakee River basin, a drop in organic matter from four percent to two percent – a conservative estimate of what actually happened in the Indiana part of the watershed – could translate into the loss of billions of gallons of water-holding capacity. That is more than enough water to flood downstream communities.

It should be no surprise that a system designed to carry water quickly downstream would result in flooding.

Persistent and worsening flooding is prompting communities to look for new solutions.

The Izaak Walton League explained the importance of soil health and its water-holding capacity to consultants hired by the Kankakee River Basin Commission to study flooding problems. The Commission’s past focus has been on engineering solutions, but recommendations in the new consultants’ report included incentives for soil health practices in the watershed. The League also emphasized the need to restore some of the wetlands and wet meadows that once held the Kankakee’s floodwaters back while also providing fish and wildlife habitat, filtering polluted runoff, and recharging groundwater.

Purdue University expects rainfall amounts in Indiana to continue to increase due to climate change. Unless Indiana, Illinois, and local communities begin to restore wetlands and healthy soils, they will likely face even worse flooding in the future.

“We have the potential to do something really significant in the Kankakee basin,” says Sweeney. “We can improve water quality, decrease flooding and erosion, and help fish and wildlife. It starts with restoring wetlands and soil health.” The same is true for communities across the country.

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