Hopper dredge Westport busy in Alaska

All summer long, a crimson and white boat moves back and forth through the waters near the Port of Alaska collecting silt, sand and gravel off the seafloor to allow vessels to navigate the harbor in Anchorage.

The boat is a dredging vessel called the Westport, operated by Manson Construction of Seattle, Wash., which the U.S. Army Corps of Engineers – Alaska District contracted to maintain the mooring areas for the past three years.

An estimated 2,400 to 2,600 cargo containers arrive at the port each week to keep stores supplied with consumer goods throughout the Interior and Southcentral Alaska, said Julie Anderson, operations branch chief for the Alaska District.

For the Port of Alaska, the Westport, a 2,000-cubic-yard hopper dredge, maintains the seafloor to the congressionally approved depth of -35 feet for safe navigation.

Its onboard hold area carries the sediment load until it can be deposited by opening the split hull at least 3,000 feet offshore where currents will not bring the material back to the port.

“We use a hopper dredge, which has two heads that suction off the bottom and never stop as the dredge moves one to two knots through the harbor,” Anderson said. “If a ship comes in that is not on schedule, then the dredge can quickly move out of the way or if there is a concern about a certain spot in the channel, then the dredge can move to that location to meet the needs of the harbor’s users.”

“The usual dredging season is from May 1 to Nov. 1, when the port is ice-free,” said Donna West, project manager for the Operations Branch. “However, to address winter shoaling in Terminal 3, the contract has an option to start work early as April 1.”

At full federal expense, dredging at the port starts 5 feet from the dock face and extends 1,000 feet seaward. An estimated 183,500 cubic yards of material have been collected this year (as of June 22) with an estimated 1.1 million cubic yards of material expected to be collected in the 2020 dredging season.

“An important aspect of the Anchorage maintenance dredging contract is hydrographic surveying. Two hydrographic surveys are conducted each week to monitor project conditions,” West said.

Once the results of the surveys are complete, they are provided to the port, U.S. Coast Guard, shippers, marine pilots and other interested parties for their use.

After the earthquake on Nov. 30, 2018, these surveys were completed within 24 hours to provide shippers with updated navigation data in advance of their scheduled arrival.

Photo: USACE