BRATTLEBORO — Pop quiz: What percentage of Vermont rivers do river engineers consider stable?
“Twenty-five percent,” said Marie Levesque Caduto, the watershed coordinator for the Vermont Agency of Natural Resources (ANR).
And that was before Tropical Storm Irene's rains flooded swaths of Vermont on Aug. 28.
Caduto joined state Rep. David Deen, D-Westminster, and Windham Regional Commission (WRC) Executive Director Christopher Campany to explain how high-water events like Irene's floods and human interference affect rivers and aquatic habitats.
The Brattleboro Conservation Commission sponsored the Dec. 13 presentation, aimed to educate people about considering rivers when repairing Irene's damage.
The trio also said that communities might want to rethink whether they rebuild or develop near flood zones.
Recovering from Irene will also mean that some difficult emotional decisions will have to be made, said Campany.
“You're talking about real lives. This isn't a clinical one-size-fits-all type of decision to make,” he said.
A healthy river
“I just want to put a face on a healthy river,” said Deen, who has served in the Legislature for 24 years and works as a river steward for the Connecticut River Watershed Council. He also is a professional fishing guide.
According to Deen, Vermont's native fish, the brook trout, are the “canary in the coal mine” for identifying healthy rivers.
Brook trout demand the hallmarks of vibrant rivers: the coldest water, most highly dissolved oxygen levels, and cobbled river bottoms.
And healthy rivers are stable rivers, he said.
Stable rivers contain features like a meandering channel, riffles, and pools.
Riffles, like a stretch of little falls, are areas in a river where the bed contains obstructions or slopes. Deeper pools often form on the other side of riffles.
“Wiggly rivers are healthy rivers,” said Deen. “And that's what they'll do with themselves after Irene, and when we stop messing in the streams.”
“Rivers should not be neat and clean,” he continued, adding that the woody vegetation they require provides habitat for aquatic life.
Vermont fishing regulations allow for catching more brook trout than other fish species, Deen said in a separate interview.
Prior to Irene, populations of brook trout in “undisturbed” streams were “pretty healthy,” said Deen.
According to Deen, brook trout populations historically plummet 60 percent after floods, and the fish population might take two to three years to recover.
High-water events affect fish in two ways, he said.
First, the swift water, and the debris it carries, pummel the fish as it sweeps them downstream. Bouncing off rocks and trees injures or kills the fish, Deen explained.
Second, silt swirling through floodwaters can scrape fishes' gills, leading to infections.
But the disturbance of waterways by floods or human construction- like sediment filling in riffles or pools - also destroys habitat, Deen said.
Good flood mitigation measures can protect infrastructure and rivers, he added. Such measures include larger culverts that are less likely to blow out during a flood, or higher bridges that offer space for ice flows and debris to pass beneath.
Deen expressed concern that towns, looking to save money, might avoid replacing damaged road infrastructure with larger culverts or bridges.
In post-Irene Vermont, Deen has witnessed instances where the Federal Emergency Management Agency (FEMA) agreed to pay to replace pre-flood-level infrastructure.
That's the infrastructure that failed, he said.
Also, Deen wonders if agencies like FEMA have given people the “wrong incentive” for rebuilding in floodplains. According to Deen, FEMA pays floodplain-dwelling homeowners 75 percent of the value of their homes to rebuild.
The agency should pay people 100 percent of the value of their homes plus a bonus to not rebuild in the flood plain, he said.
100 years (and Irene's floods) later...
Rivers flow. Rivers support habitat. They also erode their banks, ice up, ice out, shift their channels, carry debris. And they flood.
“All the things we do on the landscape have an impact on the rivers,” Caduto said.
Caduto reinforced Deen's assertion that healthy rivers are stable. They have a balanced mix of water and sediment, follow a meandering channel, and deposit extra water or sediments onto open floodplains.
But floods, development, dredging, and construction can knock rivers out of balance, Caduto said. The effort to stabilize rivers can cause them to jump their channels, erode riverbanks, or erode deep trenches, she said.
Vermonters dug in to restore roads and homes after Irene, she said, but some of the reconstruction, like measures that brought excavators into the middle of the river, might create more problems.
People may need to go back and fix the repairs, she warned.
Some of Irene's flood damage stemmed from the November 1927 flood - still Vermont's worst natural disaster in terms of damage and loss of life - and more than 100 years of manipulating rivers, Caduto added.
Vermont has a history of forcing rivers to change course by filling channels, building downtowns at the water's edge, and removing heavy boulders. thus exposing river beds of light silt, she said in a separate interview.
All these factors contributed the magnitude of Irene's floods, she said. “Every time we go through this cycle, we are spending more and more money on what will be destroyed.”
She said more communities and developers are trying to base decisions on the science of fluvial erosion, a river's natural movement of water and sediments, which in proper balance helps a river maintain equilibrium.
Tipping this ratio toward too much silt, or too much water, bounces a river out of balance, Caduto said.
For example, she said, if people remove too many sediments, then the water builds extra energy and picks up speed. The faster water will find sediment to move from elsewhere - like a property owner's back yard.
According to Caduto, a disturbed river moves through several stages:
• Incision: The river digs deeper into its channel until the weight of its banks cave in.
• Widening: The collapse of the banks widens the riverbed, and the water forms a new path.
• Narrowing: As the water flows, it settles into a new channel.
• Equilibrium: The river has dug a new, meandering riverbed. The old, collapsed riverbanks and riverbed settle into a new floodplain.
When people interrupt this cycle, they knock the transition backward, she said.
According to Caduto, some flood mitigation measures can boomerang, increasing future flood damage.
For safety, FEMA requires houses in a flood zone be at least 1 foot above the base flood elevation, she said.
The water that had filled that floodplain still must flow somewhere, Caduto said, like across the opposite riverbank and into a neighbor's formerly “high and dry” house.
Caduto hopes that as Vermont rebuilds, communities will incorporate better river management practices, such as removing berms that don't protect anything and stepping structures back from floodplains.
She also hoped property owners would evaluate their own land for flood hazards, such as erosion-prone treeless river banks.
Recovering from Irene won't end when the last excavator is removed from the river before the January snows. After the spring thaw, this past autumn's repairs to roads, bridges, and culverts will require re-evaluation, Caduto said.
And communities will have to ask tough zoning questions like whether they will let owners replace houses wiped out by the floods, she said.
“They're really difficult decisions,” Caduto said. “Because they deal with people's lives [and] people's homes, and people don't want to be displaced.”
Upstream, downstream
“Do unto those downstream as you'd have those upstream do unto you” said Campany, quoting author Wendell Berry's “Watershed and Commonwealth” essay from his book, Citizenship Papers.
The Windham Regional Commission found itself in a new position of disaster response after Irene, said Campany.
On a normal day, the commission coordinates planning projects or evaluates Act 250 permits in the 27 towns in its region, he said.
After Irene, the commission worked on response projects like creating a live, web-based map of open, closed, and damaged roads and bridges.
The map received 16,000 hits after the storm, more than the WRC's website gets, Campany said.
According to Campany, a lot of the flood damage occurred where the rivers reclaimed their old channels.
“Those channels are visible if you know what to do,” he said.
He wants to create a “pattern book” showing the signs of old river beds. Planners and homeowners can use the book to identify flooding hazards in the landscape and construct away from a river's tracks.
Campany, who came to the WRC from Mississippi State University, his alma mater, where he worked as an assistant professor of planning, expressed gratitude that Irene's winds fell short of hurricane speeds.
“This [storm] could have been much, much worse,” he said.