It might have been the most impressive engineering feat seen here since the opening of the Erie Canal.
A new steel bridge weighing 1.1 million pounds was floated a short distance down the canal Thursday on the barge upon which it had been assembled over the last few months.
The 270-foot-long span then was lowered into place by filling the barge with thousands of gallons of canal water. That made it sink enough to bring the bridge to rest on stacks of wood resting atop the newly poured concrete bridge abutments.
By evening, workers for Holmes & Murphy of Orchard Park, the company that won a $5.5 million contract for the project, were ready to begin the process of removing the barge and the two steel frames supporting the bridge.
"Now it's going to be some tedious work," said Susan Surdej, spokeswoman for the state Department of Transportation.
The gray truss span is to be slowly brought down to the concrete abutments by jacking up the ends just enough to remove a piece of wood from the pile, called a "crib wall." Then the process will be repeated until the wood is gone and the bridge can be attached to the concrete.
During the afternoon, a fascinated crowd of more than 100 residents, local politicians and DOT engineers, many armed with cameras and camcorders, came and went.
"We videotaped it so we could show it to the engineers who weren't there," Surdej said, adding that this installation method seems to have been a first in the state.
The original plan had been to use a crane to pluck the bridge off the barge, but fears that it would touch overhead electrical wires ruled out that idea.
The bridge, which the DOT is calling the Stevens Street Bridge until the city chooses an official name, replaces the Prospect Street Bridge. The latter was built in 1910 and closed in December 1991 because of deterioration.
A steel truss design was used at the insistence of the state Office of Historic Preservation,, which ruled that the new bridge must look as much like the old one as possible.
However, the old bridge had one traffic lane and a steel deck. The new one will have a concrete deck, which will not be poured until next spring. It will have two traffic lanes and two bicycle lanes, along with duplicating the sidewalks outside the railings that the old bridge had.
The new span, like the old, will carry a 24-inch water main beneath the deck on one side. Surdej said that once the new span is in place, the contractors will connect the new water main and remove the old bridge nearby.
The Sand Pebble, a flat-prowed tugboat, began pushing the barge west on the canal about 1 p.m. as a worker scrambled atop the steel truss and raised the American flag. Other workers on both banks of the canal pulled on ropes to keep the bridge in line.
After about 10 minutes, the bridge was near where they wanted it to be, but it needed to be turned about 45 degrees clockwise to make the diagonal connection with the abutments at the feet of Stevens and West High streets.
It took nearly an hour of welding cables onto the barge before the winches and manpower could make the turn. That took only a few minutes.
After another hour, the workers were ready to begin using four pumps on the barge to pull water through fire hoses into slots in the barge.