The U.S. Army Corps of Engineers-Alaska District began dredging the Cook Inlet Navigation Channel yesterday for the first time since its construction in 1999-2000 to maintain safe ship passage between the Knik Arm Shoal and the Port of Anchorage.
This year’s $5 million project continues through June and is the first phase of a multiple-year maintenance program to restore the channel’s capacity. The area is located almost six miles from the Port of Anchorage within Knik Arm of Cook Inlet, west of Anchorage and northeast of Fire Island.
“The project won’t change ship traffic, but will improve pilots’ timing coming across the inlet and improve safety,” said Allen Churchill, chief of Alaska District’s Operations Branch.
Since the original dredging of the channel, maintenance was unnecessary until a sudden surge in shoal material in the channel during the past two years reduced depths and affected navigation.
If the shoal continues to grow without maintenance dredging, deeper draft vessels will have a shorter window of opportunity to access the Port of Anchorage upstream of the shoal on high tide cycles.
Last year, a condition survey found shoal material 10 feet above an acceptable depth for safety, which cut the channel usability by half and required shippers and their pilots to take special measures to avoid running aground while moving through the channel.
Maintenance dredging of the existing channel to a depth of 43 feet, width of 1,100 feet and length of 11,000 feet consists of hydraulic suction dredging of accumulated sands and gravels into a hopper dredge, dewatering during dredging and releasing collected materials into the water at the Fire Island disposal site.
Dewatering is necessary to help move the largest amount of dredged material per hopper or scow load, which minimizes dredging vessel traffic.
All dredged material and overflow water will be discharged beneath the surface to avoid impacts on juvenile salmon feeding. To protect beluga whales, dredging activities will be suspended any time they swim within 165 feet of the activity.
The Corps-owned and operated hopper dredge Essayons from the Portland District will remove about 25 percent of the available material this year. Manson Construction Company may also dredge on days when it is not performing maintenance dredging at the Port of Anchorage.
The Corps plans to eventually remove the 4 million cubic yards of accumulated material in the channel. Seasonal removal amounts will vary depending on the rate of accumulation.
Cook Inlet Navigation Channel is the only Coast Guard marked route for all cargo and fuel ships supplying the Port of Anchorage.
Press Release, May 15, 2013