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Suctioning up a century of sediment

Workers begin the technical challenge of dredging silt from behind Embrey Dam, the first step toward removing the outdated structure next year.

By RUSTY DENNEN

Date published: 8/27/2003

By RUSTY DENNEN

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 vacuum

The 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.