ADDISON COUNTY — Seventeen Addison County bridges will fall under increased scrutiny in coming years as the Vermont Agency of Transportation (VTrans) complies with a federal ramp-up in bridge safety efforts.
The 17 bridges are on a list of around 300 spans across the state now considered “scour critical,” or particularly vulnerable to erosion during high-water events that can eat away the footings or foundation of a bridge.
VTrans sent out a team of structural, hydrology and geotechnical engineers to survey all of the at-risk bridges, and the agency has been developing plans for monitoring the spans. Those plans went out to municipalities earlier this month.
Now the bridge owners — in some cases the state, and in others local towns — have a year to put those plans into place.
Each plan is a little different, said VTrans spokesman John Zicconi, but the idea boils down to this: Scour-critical bridges are at their most vulnerable during high-water events, like big storms or especially heavy spring runoff. During those times, Zicconi said, the bridges don’t necessarily need to be closed, but they do need to be monitored.
“We’re not asking the towns to sit there 24/7 (watching the bridges),” Zicconi said. “They have to understand the type of weather and conditions … that could potentially be a threat to a bridge during a high-water event.”
If the water is too high, or draws too close to bridge beams, Zicconi said scour-critical bridges may need to be temporarily closed during these weather events. If that is the case, the state will send out a team of inspectors after the storm to look over the bridge, a process that Zicconi said would likely take, at its very longest, 24 to 48 hours.
The Nash Bridge in New Haven, located on River Road and spanning the New Haven River, is one of the 17 Addison County bridges deemed “scour critical.”
Katie Reilley, who works on the highway staff for the town of New Haven, said that New Haven learned about the scour issues in a Dec. 3 letter the town received from the state. Riley and the town are working with VTrans officials to set up a plan for addressing the risk.
“We’re just beginning to get involved in what the state has embarked on,” Reilley said, estimating it would take the town about a year before a program for monitoring the Nash Bridge was set up and operational.
In that bridge’s case, if water rises to within five feet of the lowest bridge beam, the River Road span may be closed.
Meanwhile, other towns have found that the state records might not necessarily line up with the actual conditions of their bridges. Two bridges in Middlebury — one owned by the state, the other by the town — wound up on the scour-critical list. But Dan Werner, the director of operations for the Middlebury public works department, pointed out that the town-owned Lower Plains Bridge was rebuilt earlier this year. The scour plan, on the other hand, indicated the bridge hadn’t been repaired since 1973.
Zicconi said that towns will need to take the scour plans seriously. High water is one of the conditions that can take a bridge out, he said, pointing to the Flood of 1927 as an example of the destruction high water can cause.
“Rushing water can take bridges away, and obviously you don’t want people on the bridge when that happens,” he said. “If you think there’s danger, you need to close it.”
But he also pointed out that just because a bridge is on the “scour critical” list doesn’t mean the structure is dangerous.
“It just means it’s a bridge you have to keep an eye on,” Zicconi said.