The Old Mouth of the Cowlitz River channel at Longview, Wash. is authorized to 8 feet deep and 150 feet wide, from deep water in the Columbia River through the Old Mouth of the Cowlitz River, to a point about 3,000 feet upstream from the old harbor line.
The navigation channel supports commercial barges shipping 288,000 tons of wood chips per year. Those chips are used to produce 144,000 tons of products worth over $84 million.
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The vertical plane of reference is adopted low water. The project is subject to tidal influences and annual river freshets. A large shoal regularly forms at the Old Mouth of the Cowlitz River where it meets the Columbia River. Dredging by a contract clamshell dredge is required every 2-to-3 years to allow adequate depth for commercial barge traffic.
This shoal was last dredged by the Corps in 2002 and the material was placed at an in-water site. Limited advanced maintenance width dredging outside the authorized channel width and up to 2 feet of advanced maintenance dredging below the authorized channel depth is practiced in order to maintain adequate depth for commercial barges between dredging events.
The Rivers and Harbors Act of March 2, 1945, as part of the overall Columbia and Lower Willamette Rivers Project.