Flood control with trees

Trees are a powerful tool to help control flooding. Roots have the highest infiltration capacity of any vegetation to soak up water when it rains and allow it to be slowly sent to a stream. They also add nutrients, carbon, and increase soil cohesion which reduces erosion.

Billy Beck is an extension forestry specialist at Iowa State University. He says trees should be viewed as an on-farm asset. Reforesting riparian buffers in our flood plains has many benefits for landowners.

"These are really great for reducing flood plain scour. They’re a two-way filter so yes, they filter runoff, surface runoff and shallow groundwater from the uplands," says Beck. "But, they also kind of work in reverse. Landowners tend to love this and tell me this a lot, that they block flood debris from entering their fields during flood events."

A stream channel adapts to surging amounts of water. It becomes deeper, the banks collapse and the channel widens. When that happens, trees on the bank fall in. Beck says it’s ugly but beneficial.

"Trees do a lot of interesting things that are positive for the hydrology, trapping sediment, and whatnot when they do topple in and when they do kind of jam up like this. Those jams reduce flow velocity in the channel, acts to trap nutrients and sediment, provides aquatic habitat," he says. "So, there’s a lot going on here that looks bad. But in the context and in the scenario of adjustment, it’s actually doing quite a lot of good."

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