Published 9:37 am Wednesday, October 23, 2013
By Elizabeth Baier
Minnesota Public Radio News
SPRING GROVE — Southeast Minnesota’s high, sandy river bluffs make trout fishing beautiful here — but that beauty comes at a cost.
The bluffs routinely send tons of sediment sliding into the cold-water trout streams, threatening water and fish.
When severe flooding this summer worsened erosion around many of the region’s cold-water trout streams, environmentalists searched for ways to keep soil out of the water without breaking local government budgets.
They decided to try walls of trees.
That’s why on a recent fall day, workers splashed into Riceford Creek to pound long, steel cables into its muddy, 10-foot bank. The cables will help hold in place a barrier of cedar trees stacked three or four high, lining the creek for several hundred feet. The trees, hopefully, will slow the bluff erosion on the banks.
“They’re going to help trap sediment, help allow vegetation to get established and vegetation can go a long way,” said Toby Dogwiler, a geosciences professor at Winona State University.
Runoff from heavy rain and floods pushed water over river and stream banks across the region this summer. At some places in Riceford Creek, the water chisels slowly at the sandy banks. At other spots, the banks rise 20 to 30 feet.
Left unbuffered, the stream would gradually eat away at the bank, distributing more sediment and widening the creek. Much of that sediment finds its way to the Root River, and eventually, it empties out into the Mississippi River.
Bank erosion is a natural process, but it’s happening at a much faster rate than rivers and streams can handle, said Dogwiler.
If the cedar barrier, known as a tree revetment, works, it should help the banks stabilize naturally, added Dogwiler, who’s mapping the banks to measure the effectiveness of the cedar tree revetment for future use.
“If you can get the right species in there, grasses and so forth that have deep roots and certain types of trees, we can think of those as a bandage that can help stabilize the stream while the stream heals itself,” he said.
That’s especially important in southeastern Minnesota, where much of the local economy depends on outdoor recreation and tourism.
The cedar barriers may also bring a benefit to the bluffs above the river.
“The cedar trees are coming off of local bluff prairies that are overrun,” said Dustin Looman, Conservation Corps Minnesota’s southern district assistant manager. “So this is kind of a one-two punch to get those (cedars) out and to actually utilize them versus cut, pile and then burn them.”
Using trees to stabilize river banks is significantly less expensive than using heavy rocks or other material, said Rich Biske, southeast Minnesota coordinator for The Nature Conservancy. The Riceford Creek project, which covers about a half mile, cost $40,000.
The barrier, he said, will help create a narrower stream with higher energy that can push the sediment and expose nice limestone cobble and rock, which is good habitat for insects and trout.
It also comes with some uncertainty, he acknowledged.
“It’s a risky practice because of just the frequency of the floods that we have here that this could very easily be wiped out a week from now,” Biske said. “But we have such a problem in the southeast with these eroding banks and this endless supply of sediment that we need to think of low-cost alternatives to try to get at this larger issue of eroding stream banks.”