MONROE, Conn. (AP) On Oct. 16, dignitaries gathered to open the new Colorado River Bridge, the graceful 1,900-ft. (579 m) span that replaced the creeping two-lane road over the Hoover Dam on the Arizona-Nevada border.
Up until then, the Hoover Dam carried U.S. Route 93 on its back, a sleepy route to nowhere in the 1930s. But by the 1960s it was a huge tourist attraction carrying thousands of vehicles every day.
There aren’t many major highways left in the United States that still ride over concrete dams. One of those that remains is the Stevenson Dam Bridge, which carries Route 34 between Monroe and Oxford.
Now 91 years old, the Stevenson Dam Bridge, which sits on 24 concrete arches that rest atop the Stevenson Dam, is regarded as a dangerous antique by traffic engineers.
There are sharp corners at both approaches, and the deck offers no room for bicycles or pedestrians. Two tractor-trailers, passing in opposite directions, can barely get by.
There has been talk about building a stand-alone bridge to replace it, but these discussions have been going on for the past two or three decades with little to show for it.
The bridge and the dam are regarded as separate structures and, in fact, have separate owners. The dam is owned by FirstLight Power and the bridge is owned and maintained by the state Department of Transportation. The DOT does not pay FirstLight any compensation for, in effect, carrying the bridge on its shoulders, DOT and FirstLight officials said.
“Our position has been that the bridge and the roadway is beyond its useful life,” said Chuck Burnham, a spokesman of FirstLight. “We’d like to see a bridge that’s not on top of our dam. Our position had been they’ve done as much repair work as possible.”
The bridge underwent extensive rehabilitative work in 1957, 1977, 1979, 1987 and 2005. In the 1979 widening project, the bridge was closed entirely to traffic for about six months. The bridge deck has been repaved and patched countless times since the 1920s, the most recent resurfacing completed two months ago.
But Burnham said that while the power company would rather see a standalone bridge, the bridge over the dam doesn’t significantly affect the power generation operations, nor the integrity of the dam.
“We do have a design process that is taking place on what to potentially build to replace the bridge going over the dam,” said Kevin Nursick, a spokesman of the state DOT. “The one that we were looking at building is a new, standalone structure upriver, but make no mistake about it, it’s a very expensive proposition.”
How expensive, the DOT can’t say, although the $34 million estimate for a replacement bridge made years ago is viewed as inadequate today.
Nursick said that the state simply doesn’t have money at the moment for a new Route 34 bridge across the Housatonic River. “At the moment, we’ll only have money for design work,” he said.
Officials note that the DOT is now engaged in two huge bridge construction projects on Interstate 95 — the $1 billion Pearl Harbor Memorial Bridge, or “Q Bridge” in New Haven, and the $500 million span over the Housatonic River between Stratford and Milford, also known as the Moses Wheeler Bridge.
Nursick noted that much of the state’s bridge and road infrastructure was built between 1920 and 1940, and just about all are past their design lifetimes, as least for what hasn’t been replaced already.
The Stevenson Dam Bridge carries about 10,300 vehicles per day, according to the DOT’s most recent traffic count, published in 2009.
The bridge, last inspected earlier this year, received a “fair” rating score of 5 for the deck, and the superstructure received a “poor” rating of 4.
Bridges in the state are scored between 0 and 10, with 0-1 being “critical,” 2-4 as “poor,” 5 to 8 as “good,” and 9-10 as “excellent.” As is the case with all major bridges it’s inspected every year. The state has more than 3,400 bridges, large and small.
Nursick said that the ratings for the Stevenson Dam Bridge are typical of bridges of that vintage. “Structurally, the bridge is safe,” he said. “Just about all of the bridges constructed in the 1920s and ’30s get ratings of 4 to 6.
The dam is by no means the only concrete dam that carries a major highway. The Norfork Dam in north-central Arkansas carries Route 177S, for example. Connecticut’s picturesque Saville Dam in Barkhamsted carries Route 318, but that is an earthen, embankment-type structure.
There are about 75,000 dams in the United States.
When the dam and bridge were constructed in 1917-19, it was one the largest projects going on at the time in Connecticut. According to historical records, about 750 men worked on it. The contractor, United Gas Improvement, wanted 200 more men on the job, but laborers were hard to find because of World War I. Occasional strikes over wages also slowed progress. One of the major subcontractors was the C.W. Blakeslee Co. of New Haven which, as Blakeslee Aepaia Chapman, remains today a major player in the heavy construction industry.
The dam is anchored in gneiss, which is very hard bedrock in what is the Collinsville Formation that was laid down about 400 million years ago. This was one of several formations that make up what is now much of western Connecticut, which was “assembled” from various plate collision events.
So strong is this rock that the gravity-type dam wasn’t physically anchored to the bedrock until 1987, when 80 “post tensioned” anchor cables were installed to give the dam improved resiliency in the event of a major earthquake. Hundreds of concrete dams in the United States were similarly stabilized beginning in the late 1970s; this work continues to this day.
To build the dam, about 212,000 cu yds. (162,086 cu m) of rock were excavated, or about the same volume as a cube with 180-ft. (55 m) sides. The construction camp for the men included a church, and nearly 2 sq. mi. of forest was leveled to make room for the project.
The camp also included two blacksmith shops, a coal-fired electric powerhouse, four carpenter shops and two cement plants. Between the dam and the attached powerhouse, 156,000 cu yds. (119,270 cu m) of concrete was poured.
A railway also was built into the site, and 13 locomotives were used to haul in equipment and roll away the overburden. A cemetery that would have sat at the bottom of the future Lake Zoar had to be relocated.
The bridge on the top of the dam replaced a rickety wooden suspension bridge, the Zoar Bridge, that was about three-fourths of a mile upstream from the dam. Other bridges and roads upstream had to be reconfigured, too.
Zoar was the name given by white settlers to the portion of the valley formed by the Housatonic River that would later become Lake Zoar. The name probably refers to the biblical city by the same name in land of Canaan, according to Oxford town historian Dorothy DeBisschop.
“Beyond that, we really don’t know much about where the name ’Zoar’ came from,” she said.
Despite the dangerous curves and the narrow roadbed, the drive to the dam offers lovely views on a crisp autumn day. Most of the cars and trucks on the bridge are traveling between Monroe and Derby, rather than Monroe and Oxford.
The business that’s closest to the dam is the Lake Zoar Drive In, whose owner, Mike Basso, has been cooking up the “World Famous Zoar Burger” for customers since he bought the place in 1993. The restaurant has been there since the 1920s. He said that concerns of stirring up PCB, or polychlorinated biphenyls, will likely force any replacement bridge south of the dam. The PCB pollution is from the Pittsfield, Mass., General Electric plant, which dumped the chemicals into the Housatonic between 1932 and 1977.
He explained that reconfiguring the road to make the approaches to the new bridge safer will be an expensive proposition.
The geology that made the dam possible — a rock gorge — also means that moving the Monroe-side approach road a little to the south to make the approach easier to navigate will involve blasting out unknown tons of solid rock. Originally, Basso said, they were going to move Route 34 almost to the railroad tracks that rest on top of the cliff which overlooks the Oxford side of Route 34, also known as Roosevelt Drive.
As for the new bridge in Nevada, Basso said that there’s a connection between the Hoover and Stevenson dams.