A hundred years from now they might like to know that it was three laborers from Mexico, one from Guatemala, a supervisor from India and an engineer from the Army who ably doctored the Great Falls floodgate on the C&O canal yesterday.

They might like to hear how the workers in hard hats and waders stood in chilly, waist-deep water and how they wrestled 20-foot slabs of aluminum dangling from a crane into slots hewn into the rock more than a century before.

And sometime in the next millennium they might want to learn that there were many sighs of relief when the 1990s slabs fit almost perfectly into the 1820s stonework.

The last major piece of damage repair on the historic canal following the twin floods of 1996 neared completion yesterday as laborers and engineers began installing a state-of-the-art floodgate to replace the one shattered in 1996.

The previous gate, also called a "stop lock," was made of huge timbers that were fitted into the slots in a stack like the wall of a log cabin.

The stop lock, part of the C&O's early construction from the 1820s and '30s, was designed as a kind of huge door, anchored by two stone abutments, to divert damaging flood water back to the Potomac River, which runs alongside the canal.

But the January 1996 flood battered the wooden gate with tons of water until it splintered, and the National Park Service wanted a new one that would be much stronger.

The new gate will be made up of six slabs of aluminum, seven of wood reinforced with aluminum and seven that are all wood, according to Dan Copenhaver, the canal's chief engineer. The first seven will stay in place more or less permanently. The rest will be stored until the next flood threatens.

Yesterday, the repair workers used a truck crane to carry 300-pound pieces to the lock site, about a mile below Great Falls. The pieces were then gingerly lowered into the hands of Rosario Limon, 49, and Jaime Godoy, 26, both of Glen Burnie, who tried to guide them into place.

The work on the canal--an engineering marvel in its day--took place on a sunny fall morning. Leaves glided gently to the water. A huge, gray heron turned away from the racket. A lone turkey buzzard circled nearby.

"It's quite an honor, to be honest with you, to work on something that was a civil engineering landmark and also something that is so beautiful and historic," said David Worthington, a project engineer for the Army Corps of Engineers, who was overseeing the job. "It's quite an honor."

The workers first installed an aluminum channel, backed by rubber, into the old slots that had been cut into the stone a century and a half ago. The crane then lifted the slabs off the truck and lowered them to Limon and Godoy, who guided them into the place.

At first, the slabs caught at odd angles in the slots, but the workers tapped them into place with long crowbars. As the first one splashed into the canal, Kirit Patel, a supervisor with Pioneer Contracting Co., of Odenton, whose men were in the water, smiled broadly and gave a thumbs up.

Then came a problem. The slabs are hollow, and when the first one hit the water, it floated. The slabs were made without holes to allow water in and air out--holes that would have allowed them to sink.

But it was not a big problem. Patel's men procured a drill and quickly bored holes in the metal. As the first slab, and the second, dutifully sank, Worthington smiled. "Sometimes things work," he said.

Five of the slabs were installed yesterday. The rest will be fitted tomorrow and early next week.