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Sonar shows corrosion at Port of Alaska with new clarity

Recent sonar scans show corrosion on underwater pilings, both with (Right) and without (Left)...
Recent sonar scans show corrosion on underwater pilings, both with (Right) and without (Left) reinforced steel jacketing. Courtesy: Port of Alaska (KTUU)
Published: Aug. 5, 2019 at 7:30 PM AKDT
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Corrosion under the docks is nothing new at the Port of Alaska. Engineers have been working for years to extend the life of around 1,400 wharf pilings that currently sit in what port officials refer to as a "high corrosion zone." Until now, routine inspections at low-tide have been the only way to locate and assess the progression of the damage.

But now they have a new way of looking at the damage: sonar.

At the end of last month, a dive team equipped with sonar technology scanned an area of known damage. Once the results matched up with what had already been reported, the port knew that sonar would be a viable option for accurately locating new damage. Sharen Walsh is an engineer serving as Deputy Director at the Port of Alaska. On Monday, she told KTUU that the scans didn't uncover any damage worse than what had been verified prior to the sonar inspection.

"What we couldn't see before was what's below the water," she said. "What we learned -- which is a good thing -- is that it doesn't get worse and worse as you go down."

According to Walsh, the worst areas of damage exist around the area of low-tide, where the pilings are routinely covered and uncovered as water-levels rise and fall. Apart from verifying this fact, the port also got it's first clear look at exactly what's happening under the silty water of Cook Inlet. This will allow for more accurate assessments of the remaining life for certain pilings. Information like this is particularly useful for deciding where to utilize steel jacketing, which can extend a piling's useful life for about 10 years. On average, the port can install this reinforced jacketing on 25-50 pilings per year.

Already in portions of the port known as "POL 1" and "POL 2," weight ratings have been lowered from the standard 600 lbs per square foot down to as low as 200 lbs per square foot. These docks are responsible for regularly receiving large amounts of the state's food supply, as well as 80% of the concrete used in Alaska and 80% of the fuel used in Southcentral. While work is being done to extend the life of the current facilities, the port already has its eyes on the future.

The municipality recently approved a $42 million contract to begin construction of the new (PCT) petroleum and cement terminal. It will ultimately take an additional $100 million to complete the terminal, but once funding is procured, the port estimates that the PCT could be functional by the end of 2020.

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