Thomaston Dam Facts:
- 142 feet high, 2,000 feet long
- Made of compacted earth and impervious clay
- Highest water mark since its construction: 87.2 feet in June 1984
- 960 acres: the size of its flood storage area
- 13.7 billion gallons: how much the dam can hold
In the Naugatuck River basin, the Army Corps of Engineers also operates the Black Rock and Northfield dams in Thomaston, Colebrook Dam in Colebrook, Hancock Brook Dam in Plymouth and Hop Brook Dam in Middlebury. The state operates the East Branch and Hall Meadow dams in Torrington, and the Mad River and Sucker Brook dams in Winsted.
All of these dams were built by the Corps between 1961-1971 at a total cost of $49.9 million.
Vincent Gualtieri pulled a palm-sized spiral notepad out of his uniform pocket and flipped to a page where he had jotted down figures.
“This dam,” said Gualtieri, “has prevented $836 million in property damage. It cost $14 million to build. I’d say that’s a pretty good return.”
Gualtieri is the Army Corps of Engineers’ project manager at the Thomaston Dam, the No. 1 reason why the devastating Flood of 1955 has never been repeated.
Each day, Gualtieri confers with what’s called the Corps’ Reservoir Regulation team in Concord, Mass. about how much water to allow through the dam’s 455-foot, horseshoe-shaped conduit.
If it’s been raining heavily, the dam’s two hydraulic gates pinch off flow so downstream levels don’t rise too rapidly. Once they start to drop, more water stored behind the dam is allowed to tumble through.
When to raise and lower the gates is based on stream flow information gathered from 100 data collection sites on rivers and dams in five New England states.
The data is transmitted every 15 minutes to satellites, which bounce it to Concord, where hydro-engineers also evaluate reports from the U.S. Geological Survey and the U.S. Weather Service.
After major storms, computer modeling plots the severity of any flooding that might have occurred if not for the dam. The Corps’ finance division estimates the potential property damage.
The damage prevented by the Thomaston Dam since its completion in 1960 “is far and above any other Corps dam in New England,” said Gualtieri, who also oversees dams at Northfield and Black Rock and the Goshen radio relay station.
Traveling more than 40 miles from its headwaters in Norfolk and Winchester to its confluence with the Housatonic in Derby, the Naugatuck is the longest river fully contained within state borders.
During that trip, it drops approximately 540 feet in elevation, a gradient of 13 feet per mile, making it the steepest, most powerful and most dangerous river in Connecticut.
“The Naugatuck is our flashiest basin, which is good and bad,” said Jack Keenan, the Corps’ chief of reservoir regulation in New England.
The steady current was good for powering the industry that sprang up along its banks in the late 1700s and flourished for two centuries. But there was a downside: The steep geography made it prone to flooding.
Flood-control dams on the Naugatuck were first considered following the Hurricane of 1938, “but World War II got in the way,” said Christopher Way, the Corps’ operations manager for the Naugatuck basin.
Then came Aug. 19, 1955, and the worst natural disaster in state history. The torrential downpours of Hurricane Diane, on the heels of Hurricane Connie a week earlier, caused the swollen Naugatuck to angrily escape its banks.
The Mad, Still, Shepaug and Farmington rivers also wreaked havoc as downtowns from Winsted to Washington Depot to Collinsville to Derby were turned into rubble.
When the floodwaters receded, 47 people had been killed in Connecticut and $370 million in property damage ($1.5 billion in today’s dollars) had been wrought.
Construction began in May 1958 and finished in November 1960 at a total cost of about $14 million. Portions of Routes 8 and 222 as well as the railroad were relocated to accommodate the work.
O&G Industries of Torrington won the $4 million contract for the dam itself, the company’s first project of that magnitude.
O&G also constructed the East Branch Dam in Torrington, the Colebrook Dam, the West Thompson Dam and the river levees in Ansonia and Derby. The work helped to turn O&G into one of the largest construction firms in the state.
In all, the Corps erected 12 dams in Connecticut in the early 1960s. It still owns and operates eight of them, while turning four over to state control.
The keystone project, though, is the 142-foot high, 2,000-foot long Thomaston Dam, made of compacted earth and impervious clay.
“This is the Big Kahuna,” Way said.
The flood storage area covers 960 acres spread across the towns of Thomaston, Plymouth, Harwinton and Litchfield, and can store up to 13.7 billion gallons of water.
For much of this summer, the Naugatuck River has been a meandering trickle through the meadows behind the dam. Dirt-bike riders, picnickers and the model airplane flying club that use the property haven’t seen their recreation inconvenienced.
But that isn’t always the case.
The high-water mark for the dam came in June 1984, when it filled to 87.2 feet.
For Gualtieri, the highest level during his 20 years at the dam occurred after Hurricane Irene drenched the state in 2011. Some 9.31 inches of rain fell on Aug. 28, 2011, causing the water to crest at 83.8 feet on the dam’s scale.
Still, neither time did the dam fill to even half of its capacity.
“We have enough capacity to handle anything we’re going to see,” said Keenan.
“If it ever does (fill up),” joked Way, “start building an ark.”
Hurricane Irene was an example of the value of the dam. In Vermont, Irene caused an estimated $733 million in property damage, and floods damaged and destroyed around 500 miles of roads and bridges in that state.
Dams in northern New England needed two weeks to discharge the excess water in the reservoirs.
At the Thomaston Dam, the rain that fell was funneled harmlessly downriver in about five days.
*Photos Courtesy of O&G Industries.