Dredging to Begin Next Weekby Eric Barker
Lewiston Tribune, December 12, 2005
Corps of Engineers awards contract for work on Snake and Clearwater rivers
Sand and silt will be excavated from the shipping channel of the lower Snake and Clearwater rivers for the first time in seven years beginning next week.
The U.S. Army Corps of Engineers awarded a $5.1 million contract to the Manson Construction Company of Seattle to remove about 400,000 cubic yards of material from the bottom of the two rivers. The company also will remove sediment from the berthing areas of the ports of Lewiston and Clarkston.
The work can officially begin Thursday and must be completed by the end of March.
Two crews will work around the clock in 12-hour shifts during the three-and-a-half month work window. A clamshell dredge, known as The Vulcan, will perform the work. The dredge has a crane-like boom that will lift and lower a 15-cubic-yard hinged bucket. The bucket will be lowered to the bottom of the river, scoop up sediment and bring it to the surface.
Jack Sands, project manager for the corps at Walla Walla, said a hydraulic dredge that sucks sediment through a submerged pipe could not be used.
"We are not allowed to use that (type of dredge) because of environmental concerns and endangered species," he said. "They don't want it sucking up endangered salmon."
When the bucket is raised the sediment will be placed on a barge. When full, a tug will push the barge 23 miles down river near Noxway Canyon. There the barge, with a hinged bottom, will release the sediment near the south shore where corps officials want to create shallow water rearing habitat for juvenile salmon and steelhead.
"We are taking essentially a mid-depth area and bringing it up to a shallow depth so it's better habitat," Sands said.
The dredge likely will produce a sediment plume, but Sands said it shouldn't turn the entire river muddy. "We don't anticipate any problems," he said. "Most of the material we will be removing will be of a sandy consistency instead of a fine silt or clay."
Corps officials will monitor the work to ensure it does not violate state and federal standards for turbidity and levels of pH, ammonia and dissolved oxygen.
The work eventually will be visible from the Lewiston levee. But the dredge is not expected to make an appearance in the confluence area until the following week. Sands said the work crew and dredge will begin its work at the downstream navigation approach to Lower Monumental Dam, about 97 miles west of Lewiston and then move the navigation approach to Lower Granite Dam, 35 miles west of Lewiston. When that work is finished the dredge will begin work in Lower Granite Reservoir. Sands said that could be as soon as Dec. 20.
Each year spring floods carry sediments down river. The sand and silt settle out when the flow of the river slows as it enters the slackwater reservoir. The corps is mandated by Congress to maintain a 14 foot shipping channel.
But the channel and port berthing areas are as shallow as 8 feet in some places. That has caused port officials and barge operators to refrain from filling barges to capacity. Last spring two barges became stuck, one each at the port of Lewiston and Clarkston.
"We won't have to contend with that for a couple of years," said Arvid Lyons, general manager of Lewis-Clark Terminal at the Port of Lewiston.
Lyons said the dredging will make the loading and off loading of barges faster and more efficient.
"We can load them full," he said. "We won't have to worry about light loading them."
The shallow shipping channel and port areas also have caused problems for some cruise ships that call on the Port of Clarkston. Some of those ships now dock at the Port of Wilma to avoid the shallow water.
Both ports will be billed for the dredging work in berthing areas. Dredging is expected to cost the Port of Lewiston about $200,000 and the Port of Clarkston $180,000 to $225,000.
Dredging was made possible when the corps and environmental groups opposed to the work reached a settlement agreement. The National Wildlife Federation and other environmental groups agreed not to sue the corps over the work this winter in exchange for corps officials promising to perform a long-term study of sediment problems in the river.
The groups sued and successfully blocked work planned for the winters of 2002 and 2004. The corps voluntarily withdrew its dredging plan in 2003 when officials were unable to complete necessary paper work.
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