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Silt from the Rappahannock River is deposited into a large disposal pit near Bragg Road in Fredericksburg, as earthmovers arrange it to allow for more dredge spoil to accumulate at the bottom. Eventually, the pit will be filled with silt dredged from the river nearby.
A meter on the front of the Ellicott 370 dredge barge tracks |
Dan Miller sits in the cab of a most unusual machine that does its digging not on land, but under water.
A signal from shore crackles over his radio, and he starts the engine on the Ellicott 370 dredge barge. A giant pump roars to life, and Miller positions a protruding steel snout on the bow--outfitted with a giant suction hose and augur--into place just above the Embrey Dam in the Rappahannock River. The barge shimmies noticeably as the dredge head bites into the river bottom.
Miller smiles, shouting something over the roar of the engine that sounds like: "I love my job."
After months of preparation, the formidable task of removing a vast shoal of silt from behind the dam began yesterday.
Since May, Woodside Construction Corp. of Dayton, Md., has been moving equipment into place and preparing a massive hole along the Fredericksburg shore where decades of river muck will be deposited. Woodside is doing the dredging project under contract with the Army Corps of Engineers.
Company Vice President Russell Smith says this is not a typical silt-removal job because of the sheer volume of the material to be moved. An estimated 250,000 cubic yards of sediment has built up behind the dam since it was completed in 1910.
And, Smith says, "We'll be pumping material 170 feet up a hill," which is a technical challenge.
Normal dredging projects operate on a level plane. Deepening a channel in the Chesapeake Bay, for example, entails removing material from one spot and pumping it a short distance away.
There's one advantage here over tidal water, Smith says. On the bay, "You're always watching the tide" because the depth of the dredging is affected by the level of the boat relative to the bottom.
Underwater vacuumThe silt, gravel, clay and water sucked from behind Embrey Dam flows through a 12-inch-diameter flexible pipeline to a 400-horsepower booster pump on shore that propels the mixture uphill to the 13-acre disposal pit. The whole line runs more than 3,000 feet.
The dredge operates like a giant underwater vacuum cleaner. Miller, known in the trade as a leverman, slowly sweeps the hose snout in an arc along the bottom. He works a grid marked by white poles; each section to be dredged has been carefully surveyed in the three-quarter-mile section of river from the dam upstream to the Interstate 95 bridge. (That part of the river is closed to public use until the removal of the dam is completed sometime early in 2006.)
The dredge is secured and maneuvered by steel cables, one attached to a 500-pound anchor off the bow and another to a tree on shore. A third anchor secures the stern. A small tender boat outfitted with a winch and crane repositions the anchors and pipe sections as needed.
The pipe, fitted with flotation collars, runs in a sweeping "S" pattern from the barge to the shore.
The Mudcat can pump about 100 to 200 cubic yards of material an hour. "It really depends on the type of material," Smith says. Gravel and heavier materials take longer; fine silt moves much faster.
Miller controls the silt-water mixture from his console. "We like to run about 60 percent water to 40 percent solids," Smith says.
The biggest challenge is not clogging the pipe.
"That's every dredger's worst nightmare. You get it clogged, and you have to pick up the pipe and shake it out," Smith says.
The dredge and booster pump on shore consume about 600 gallons of diesel fuel per shift, so a tanker truck holding 3,200 gallons is positioned on shore. Fuel is ferried to the dredge on a pontoon boat fitted with a large yellow tank.
The dredge draws about 2.7 feet of water, which Smith says will be close to the bottom on some areas along the silt-clogged Stafford County shoreline.
Mountain of silt
On shore, at the bottom of a 50-foot-deep disposal pit, a geyser of black water spews from the pipe where bulldozer driver Melvin "Bobo" Yates--the dump man--shoves material away as it accumulates. By winter, the silt from the river will nearly fill the hole.
Yates tells Miller by radio if the mixture of silt and water is too thin or too thick. That's important, because too much silt can clog the pipe.
"He's my eyes and ears on the ground," says Miller, 42, a Louisiana native who's been doing dredging work for more than 20 years up and down the East Coast. His most recent job was in Florida.
In the pit, "Gravels drop out first, then clays and silts," Smith says. Water, minus the silt, eventually channels back into the river through a weir box on the opposite end of the pit.
Dredging will continue 24 hours a day, six days a week. "Sunday is laundry day," Smith says.
January deadlineWoodside specializes in heavy construction. In April, the company won the Embrey Dam project with a $2.7 million bid. The company has done other dredging work in the bay, tidal rivers and around dams.
Dismantling the dam has been a hot topic for more than a decade. It has long since outlived its purpose and is considered a safety hazard. In 1999, Congress authorized $10 million for the project under the Water Resources Development Act.
Work on the Rappahannock is supposed to be completed by mid-January so that the aging dam can be breached sometime in February to allow migrating fish upstream.
The opening will lower the river water level to expose an 1850s-era crib dam, which will be studied by archaeologists with the Virginia Department of Historic Resources next year between March 1 and June 30.
About the only unknown is the weather.
"If we get a normal rain--say an inch or so--it's not that big a deal" for the operators, Smith says. Heavier rains are difficult to handle because it's difficult to work in high water.
Dredging was supposed to have begun in mid-July, but frequent rains slowed preparations of the shore disposal site.
Next summer, a causeway will be built into the river, and then the remaining concrete from the Embrey Dam, as well as the crib dam, will be removed.
To reach RUSTY DENNEN: 374-5431 rdennen@freelancestar.com
