Even as city officials work to restart the stalled Port of Anchorage improvement project -- a decade-long boondoggle that has already cost hundreds of millions of dollars -- another persistent and immediate problem is being scraped away at the port's docks: a buildup of silt and mud. Ships that dock there each Tuesday and Sunday deliver up to 85 percent of the goods that come into Alaska. When loaded, the massive barges require a draft -- the depth of water needed to keep the ships afloat when loaded -- of about 28 feet. The port's operation plans call for the entire dockside to be kept at a minimum of 35 feet of water at mean low tide, also called zero tide.
But at times this winter, the buildup of silt and mud has seen the depth at the dock get as shallow as 26 feet. Now, dredge barges contracted by the U.S. Army Corps of Engineers are scooping out the debris to restore 35 feet of depth. And they didn’t arrive a moment too soon.
The waters of Cook Inlet see monstrous tides, among the largest in the world. The tides can scour the seafloor, creating new channels and covering old ones. But the problem at the port is a function of the water there, not the tides. Cook Inlet is a silty body of water, and while some of that silt is picked up and suspended by the Inlet's tidal action, most comes from surrounding glaciers and the rivers they feed. Silt, mud, and particulates are suspended in its waters throughout the year. When that suspended material settles near the Port of Anchorage, it builds up until it threatens the loading and unloading operations of the container ships that are the state's lifeline, delivering from Outside. The dredging ships arrived this month and immediately began to dig out the area next to the port, so that it can continue to handle deep-drafting container ships.
Silt buildup differs year to year. The weather probably has the most to do with seasonal changes at the port. Warm weather can rapidly melt Cook Inlet sea ice, sending additional silt into the water. That's what port managers and engineers believe happened this year, causing the depth of the water alongside the port to become as shallow as 26 to 29 feet in February.
"We had a warm fall," said Julie Anderson, port operations project manager for the Corps. "The January warm-up we had also caused the tidal flats to form later than usual."
That unusual weather may have helped the sediment build up around the port. Anderson said the problem this year is among the worst in years.
If the sea floor at the dockside rises above the minimum depth required to unload a ship at low tide, problems could mount for shippers and most everyone else in Alaska, since the Port of Anchorage serves as the main receiving area for products brought into Alaska. From new cars to cereal, almost everything on store shelves in the Last Frontier entered Alaska through the port. If the silt isn't dug away each year, ships might be forced to stop in the middle of the unloading process and go farther out into the Inlet to await a higher tide. That could cost thousands of dollars and delay the ship on its return to Tacoma, Wash. -- which would, in turn, possibly delay its return to Alaska the following week. According to muncipal officials and Totem Ocean Trailer Express -- the main shipper at the Port of Anchorage -- the city came close to that scenario this year.
"But, the dredge got us back down to 35-feet depth, so we are OK now," said TOTE's Alaska Director George Lowery.
The U.S. Army Corp of Engineers' barge arrived in Anchorage on March 14. It was towed to Alaska by tug and continues to dig out the seabed around the port's docks, using its bucket to bring up the thick, smelly mud and silt, transferring it to a scow. When full, the scow will be taken out into the middle of the Inlet and dumped so it can be re-filled again. The dredging -- depending on the amount of silt build-up -- can cost between $10 million and $14 million annually. It will have to be done each year, for the rest of the port's lifespan.
"It's a pretty unique situation for Alaska," Anderson said of the silt problem. "Most places have sandier bottoms."
Contact Sean Doogan at sean(at)alaskadispatch.com.
Correction: This story originally reported that the annual cost of dredging the port is $1 million to $4 million. The correct range is $10 million to $14 million.