Dredging continues on lower Snake River

WALLA WALLA, WA - Channel maintenance on the lower Snake River began Dec. 15 and will continue through February, according to U.S. Army Corps of Engineers officials.

The maintenance project will restore the 14-foot congressionally authorized channel depth in three key areas of the navigation channel and two port berthing areas that are clogged with sediment - the confluence of the Snake and Clearwater rivers, the navigation lock approaches to Lower Granite and Lower Monumental dams and the berthing areas at the ports of Clarkston, WA, and Lewiston, Idaho.

As of Jan. 25, dredging crews from the Seattle-based Manson Construction Company removed approximately 200,000 cubic yards - about 150-160 barge loads - of sediment from the navigation lock approaches at Lower Monumental and Lower Granite dams, the berthing areas at the ports of Lewiston and Clarkston and the Snake River portion of the federal navigation channel near Clarkston, WA.

Corps planners estimate a total of about 400,000 cubic yards of dredged material will be removed from the five sites. A portion of the cost is borne by the ports of Lewiston and Clarkston for dredging the berthing areas in front of their facilities.

Manson crews are working 24 hours a day in two 12-hour shifts, seven days a week, in an effort to complete dredging within the Dec. 15-Feb. 28 in-water work window. Crews took a break for the holidays, Dec. 24-Jan. 2, and then returned to round-the-clock operations.

The dredging vessel uses a 130-foot-tall, crane-like boom attached to a 15-cubic-yard hinged bucket that scoops up sediment from the channel and deposits it on a barge. Once filled, crews navigate the barge to a disposal site near Knoxway Canyon on the river between Lower Granite Dam and Clarkston where the sediment is placed to develop rearing and resting habitat for juvenile salmon.

Concerns prompted by the buildup of sediment drove the Corps' plans to begin clearing the Snake River channel.

"The Corps considers maintaining the authorized channel depth a priority for this region," said Jack Sands, project manager. "Shoaling in the channel is critical in some locations. Since early 2001, there have been reports of groundings in the channel."

In the past, the Corps dredged in the lower Snake River every three to five years to maintain the authorized channel depth and provide for safe, efficient navigation. The Corps has not performed maintenance dredging since the winter of 1998-99.

Over the years, economic costs to the region rose as the navigation industry tried to adapt to channel conditions. Depths as shallow as 8 to 10 feet were recorded in critical areas. Some shippers began "light loading" barges, Sands said.

"Without dredging, impacts to commercial navigation will continue to increase operations costs to get inland cargo to world markets," Sands added.

The lower Snake River is part of an inland channel system that provides navigation from the mouth of the Columbia River near Astoria, Ore., to port facilities on the rivers in Lewiston-Clarkston. Transporters shipped 19.5 million tons of products through the lower Snake River locks in 2004.

U.S. Army Corps of Engineers quality assurance inspectors and Manson Construction Company officials ensure safe operations Jan. 11 while removing built-up sediment from the berthing areas at the ports of Lewiston and Clarkston. (Photo courtesy of Manson Construction Company--taken by Kathleen Becker, MCC safety manager).