Last month, the town of Johnson got lucky. When the Lamoille River overflowed its banks for the third time in a year, the river didn’t reach the town’s wastewater plant. Only a few inches of water got into the new post office. Most homes and businesses were spared.
“We dodged the bullet,” said Erik Bailey, the town manager. “By the skin of our teeth, basically.”
Bailey says three recent floods — last summer, in December, and again this July, are among the top five biggest floods in Johnson on record. He has a theory about why so many of the worst floods have happened so recently.
“Everyone's gonna say climate change, and I'm sure it might have something to do with it,” he said. “But the biggest thing, I'm fully convinced, is because the rivers are so shallow now, because we stopped dredging.”
This idea of digging our rivers deeper as a way to protect places like Johnson in some ways feels obvious.
“Intuitively, it makes all the sense in the world. If our buildings are getting wet, then let's make the channels deeper, let's make the pipe bigger, and transport that water downstream,” Shayne Jaquith, a river scientist with The Nature Conservancy, said on Vermont Edition last month.
“That's what the early European settlers started doing, and that's what we kept doing.”
Dredging prevents flood waters from rising as often. But it comes with a big tradeoff. When rivers do flood, they’re a lot more destructive.
“The channel just explodes, it just enlarges, really,” Jaquith said.
When you make a stream deeper, it becomes more powerful — sort of like a firehose. Eventually, that pressure will release. That’s when roads and bridges wash out, and homes get swept away. Not from rivers rising, but from the sheer force of water. That’s what happened in East Burke this week.
“It was just the pummeling — the pummeling that the bridge abutments are taking right now — that's what’s causing the damage,” said town administrator Jim Sullivan, as he watched Dish Mill Brook pound into Mountain Road Tuesday morning.
This type of damage — from erosion — is so widespread because people have messed with some 75% of Vermont’s rivers over the last few hundred years, according to state assessments. Jaquith, with The Nature Conservancy, has looked into some of this history.
“Some of the images of the dredging that happened — it's just mind boggling,” he said. “Like 15 feet of digging downward and it’s just like, how did they think those vertical banks are not just going to collapse,” he asked.
“Then, of course, there's dynamiting the rivers to straighten them out.”
In recent decades, there’s been a big push to counteract this legacy of dredging by cutting into river banks and leaving space for rivers to spill out and release some of their energy — creating floodplains.
It’s well established floodplains slow down rivers and can prevent damage during storms: Having wetlands upstream of Middlebury saved the town up to $2 million in damage during Tropical Storm Irene, according to a University of Vermont study. More recently, a five-acre floodplain in Northfield reduced flood levels by six inches last year, according to the Friends of the Winooski River.
But in some areas, floodplains alone aren't enough.
“Restored floodplains doesn't change the fact that so many of our village centers are just built in floodplains, where it's going to naturally flood, especially in light of a changing climate,” said Rob Evans, who runs the rivers program at the Vermont Department of Environmental Conservation.
We can’t dredge our way out of flood damage either — at a recent press conference, state officials said to replace historic floodplain capacity in Barre City, you would need to dig 100 feet down in the Stevens Branch.
But despite its risks, dredging still has a place to protect existing homes and businesses and roads.
The state approved hundreds of dredging permits last year, and they’re sure to approve more after this summer’s flooding.
“We accept that's going to inevitably bring about some issues,” Jaquith said. “We have to protect those areas that are already developed.”
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