COLUMBIA RIVER - With one muscular arm, she can crush underwater rock with 230,000 pounds of breaking force.

Then, she scoops it up from the river bottom and dumps it onto a barge to clear the way for deep-draft ships.

Home ported at Tongue Point in Astoria, the floating dredge Megan-Renee is the largest excavator on the West Coast and a maritime rarity worldwide.

With a swiveling yellow arm and connected bucket, the 694-ton vessel can hold 12 yards of material 88 feet from the center pin on deck.

And she's quick too, throwing the equivalent of a dump-truck load every 35 to 40 seconds.

Her specialty in digging up dense, submerged material recently earned her parent company a $9.8 million contract with the U.S. Army Corps of Engineers to help out with the Columbia River Channel Improvement project.

Most dredges couldn't handle the eight-month deepening job she began this month. With instructions to remove 1.5 million cubic yards of rock from the riverbed, the Megan-Renee is extracting 8,000 cubic yards of hard mineral deposits per day along a one-mile stretch of the Columbia River near Vancouver.

Capt. Del Thompson, 28, an Astoria native, is nearly as specialized as the vessel itself. He spent two weeks in Holland and Germany learning how to operate the giant dipper dredge, which is one of about 10 of its kind worldwide, according to owner John McAmis.

The Megan-Renee employs 15 crew members from this area, and her projects are managed by Astoria resident Jim Campbell, who is the marine superintendent for J.E. McAmis, a Florida-based contractor with a corporate office in Chico, Calif.

But since it was completed in 2005, the vessel has had so many jobs up and down the coast, it hasn't spent much time at home.

The crew returned to the Lower Columbia in June after deepening California's Oceanside Harbor, only to leave a few weeks later to begin deepening work for the Corps upriver.

The Megan-Renee's excavation work near Vancouver will complete the river mile 91-105 portion of the Corps' deepening project, which is about half done and in line for $15 million in federal funding for 2008.

"This is one area in the upper channel that wasn't able to be completed with our dredge last year because of how hard the material is," said project manager Laura Hicks of the U.S. Army Corps of Engineers. "It's consolidated rock material that's sitting there from back in the day when old Troutdale Formation was formed. ... The (Megan-Renee) is able to go underwater and grab onto that material. It's got some real strength to it."

According to McAmis, who lives in Florida but was in Astoria recently to launch the deepening job, his company chose Tongue Point because it's a centrally located home port for the excavator, which has worked jobs from California to Alaska.

"It also makes sense with those (Thompson and Campbell) managing our rigs to have it home ported here," he said. "All our deck hands are from Astoria, and if there's any maintenance work to be done, we've got a good facility at Tongue Point."

Some precision features of the Megan-Renee make it one-of-a-kind, said McAmis, though there are a handful of similar dipper dredges on the East Coast and in Europe.

Three 70-foot tall metal piles - called "spuds" - jut up from the deck of the dredge. A hydraulic motor connected to the posts allows Thompson to raise and lower the vessel and plant the foot-like appendages for leverage and accuracy.

"The three spuds drive down and jack the barge up," he said. "It picks up, and you basically walk along the bottom and dredge."

A global positioning system on board maps the ground underwater and shows Thompson what areas need to be deepened.

"It tells me where my bucket is, where the material on the bottom is, what the tide is. It shows me theoretically exactly what the bottom looks like and exactly what my bucket is doing to the bottom," he said. "We can tell within a tenth (of a foot) where the material is."

One of the Megan-Renee's first jobs was to dig a trench through granite in the Gulf of Alaska for an offshore pipe, relying on GPS to avoid an existing crude oil pipeline nearby.

"It was definitely nerve-wracking," said Thompson.

The Astoria-based tug Norton Bay tows the dredge to its destinations. For the deepening project, two 1,800 square-foot dump barges will transport dredged riverbed material two miles down river for upland disposal.

So far, Thompson said, he hasn't found any rock the Megan-Renee can't cut through, "but I'm always looking."

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