What you need to know about Vermont’s Wrightsville Dam

Flood waters approached the top of the Wrightsville Dam near Montpelier, Vt., on Tuesday morning.Montpelier, Vt., Police Department

Officials in Montpelier, Vt., were closely watching the Wrightsville Dam near the capital city’s northern edge Tuesday, as the flood waters that have spread across much of Vermont threatened to overwhelm the barrier.

Waters reached about a foot below the dam’s spillway in the morning and held steady into the afternoon, and officials said they will continue to monitor the situation through the night.

Here’s what you need to know about the Wrightsville Dam.

Where is it?

The dam is part of the Wrightsville Reservoir Flood Risk Management Project and is located on the north branch of the Winooski River, about 40 miles southeast of Burlington and three miles north of Montpelier on Route 12, according to the US Army Corps of Engineers.

How old is it?

About 90 years old. The dam was constructed by the Civilian Conservation Corps from August 1933 to October 1935, according to the Corps of Engineers, during the Great Depression-era boom of federal construction projects intended to help the economy.

How big is it?

The dam is 1,525 feet long and 115 feet high and is constructed of earthfill with a stone slope protection, according to the Corps of Engineers.

What could happen if it overflows?

“If water exceeds capacity, the first spillway will release water into the North Branch River,” Montpelier City Manager William Fraser said in a statement Tuesday. Fraser warned that such an overflow has never happened before, so it wasn’t clear how much damage it might cause.

“There would be a large amount of water coming into Montpelier which would drastically add to the existing flood damage,” he said. “This will be particularly bad along the North Branch River corridor and into the downtown.”

How likely is an overflow?

The chances appear to be diminishing. On Tuesday morning, Fraser cautioned residents that the dam had only six feet of storage capacity remaining, and by 11:30 a.m. waters were only about 1 foot from the spillway, police said.

But at 1:30 p.m., police said they had seen no significant changes in the water level and that a representative for the Vermont Dam Safety Program “believes minimal increases can be expected.”

At 4 p.m., the dam was “holding at maximum capacity,” Montpelier officials said in a statement.

“We will continue to monitor the dam throughout the night,” police said.