Wetlands save Middlebury millions of dollars by softening damage from floods
MIDDLEBURY — Wetlands like the Cornwall swamp and floodplains like those near the Salisbury flats have saved the town of Middlebury between $126,000 and $450,000 a year in flood damage over the past 80 years, plus up to $1.8 million when Tropical Storm Irene struck in 2011, according to a unique University of Vermont study recently made public.
And, said lead study author Keri Bryan Watson, those figures include only private property that would have been flooded without buffering and water absorption from wetlands and floodplains along Otter Creek between Rutland and Middlebury.
Watson said in an interview with the Independent that the study only measured damage from “inundation of buildings” using federal flood insurance models, and not what floodwaters could have done to public infrastructure such as roads, bridges and utilities.
She called the damage estimates “really conservative.”
“What we know is that in Vermont most damages are occurring from erosion that occurs in flood events or from damages to infrastructure,” said Watson, a Ph.D. candidate in UVM’s Gund Institute and Rubenstein School of Environment and Natural Resources. “We just didn’t have the ability with our methodology to measure that kind of damage.”
One of the central goals of the study, published in the May edition of Ecological Economics, was to demonstrate the value not only of wetlands, but also of regional planning for wetlands conservation.
In many cases after flooding, including in Vermont after Irene, communities “armor” streams and rivers that run through them to make them flow faster and more smoothly. This tactic, Watson said, typically makes things much worse overall for towns further along waterways that will feel the brunt of the swifter waters.
“When you straighten a river, what you’re doing is forcing water to move quickly downstream,” Watson said. “That might provide benefits in reducing flooding where you straighten the river. But making water move quickly downstream is exactly what causes extreme flooding.”
By demonstrating the economic benefits of the wetlands and floodplains, the study’s authors hope to support planners and lawmakers who want to look at the big picture and take steps to prevent floods by supplying evidence of, according to the study, “the economic value of flood mitigation” of wetlands and floodplains.
“In order to responsibly allocate conservation resources to protect wetlands and floodplains, we need to know when expected returns on that conservation investment will be positive,” the study states.
Watson said and the other authors — Taylor Ricketts, Gillian Galford, Stephen Polasky and Jarlath O’Niel-Dunne — had good reasons to study Middlebury.
Middlebury was well known after Irene as a town that, unlike others in Vermont, dodged widespread damage from the tropical storm that dumped as much as a dozen inches of water on parts of Vermont in a short amount of time. Watson said the 18,000 acres of Otter Creek wetlands and related floodplains were credited with reduced flooding in Middlebury.
And the U.S. Geologic Survey has for decades had water-level gauges in northern Rutland County and just above the falls in Middlebury, thus bracketing the wetlands and floodplains between the two towns and making for what Watson called a “really clean” comparison.
“That made this case study really a unique opportunity to look at those water levels and the difference in the pattern of flooding between them and really say that difference was largely explained by the wetlands and floodplains between the two points along the river,” she said. “We had really good data.”
Essentially, the meters allowed researchers to measure how much water would have reached Middlebury without wetlands to sponge up water and floodplains to siphon off overflow. They then could estimate how high flood waters would have reached in Middlebury, and thus how much damage would have been done in Irene’s aftermath.
And because the U.S. Geologic Survey keeps records of meter readings dating back decades, the researchers also chose nine other floods between 1936 and the present and ran the same numbers.
Using slightly different assumptions on water coming into the creek from north and south of the Rutland gauge, they came up with a range of $525,900 to $1.8 million in savings for Irene and the averages of at least $126,000 and at most $450,000 a year for Middlebury — again, not including damage to public infrastructure.
In percentage terms, the study estimates the wetlands and floodplains associated with Otter Creek reduce damages by between 54 and 78 percent.
The study also concludes those savings are roughly equal to 26 percent of the cost of conserving the wetlands: “That flood mitigation alone could pay back over a quarter of the costs of conservation is remarkable since conservation would also protect biodiversity and a number of other ecosystem services that provide quantifiable benefits to people, such as hunting, bird watching, recreation and water filtration.”
A UVM press release quoted Deb Markowitz, Secretary of Vermont’s Agency of Natural Resources, on this issue.
“This study shows policy makers the importance of conservation investments that make communities more resilient to the impacts of climate change,” Markowitz said. “By putting a price tag on wetlands and floodplains, we can demonstrate the value of natural infrastructure to protect communities from the increased risks of flooding from climate-related storms.”
That is the other central issue hanging over this study and the larger wetlands preservation issue in Vermont, the U.S. and around the world — global warming. Watson said the Vermont flood data over the years already shows a pattern.
“It’s very clear that flooding is getting more intense and more frequent already and will continue to,” she said.
As rainstorms and floods worsen, wetlands and floodplains will become even more critical, Watson said — the UVM press release notes the Vermont Department of Environmental Conservation is working on a river corridor program to allow rivers to recreate protective floodplains.
“These findings show the huge benefits of ‘natural infrastructure,’” she said, adding, “Protecting these wetlands and floodplains so that they can continue to protect us is extremely important.”
Watson also has personal, anecdotal experience with how floodplains and wetlands work. She lived in Baton Route, La., when Hurricanes Katrina and Rita hit, but said she was even more struck by typical river flooding on 10 acres of conserved floodplain next to her home.
“I would kayak through the floodwaters. And you could see as soon as you got out of the woods into the main channel of the river the water was moving really quickly. But on that flood plain that was protected by the state and allowed to flood, the water was completely still,” she said. “And so that is my visual of this effect, still, that water essentially overflows and is stored in these floodplain areas.”
Andy Kirkaldy may be reached at [email protected].
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