Dredge Westport Finishing Up First Year of Anchorage Contract
The dredge Westport is finishing up the first year of Manson Construction Company’s three-year contract for maintenance dredging in the Port of Anchorage, Alaska.
The unique $22-to $24-million job includes constant dredging during the June through October season, removing siltation as it settles in the channel and berths.
On September 11, Don Johnson, dredge captain, hosted visitors to the dredge through a dredging and disposal cycle. He explained that the huge tidal action in Cook Inlet and the Knick and Turnagain Arms, which can reach 40 feet and cause conflicting currents and eddies, contains an enormous load of fine, suspended silt, which is constantly dropping out and re-suspending. The Westport’s job is to keep the channel and berths at depth, emptying its load of up to 1,700 cubic yards a short sail to the west of the channel, where much of it re-suspends immediately.
The Westport is a 1,700-cubic-yard trailing suction hopper dredge, which is propelled by the tug Gladys M. The size of the dredge and the equipment arrangement is perfect for Anchorage, said Bob Richardson, Manson’s manager of Northwest Dredging operations. Because the job is essentially removing infill on an ongoing basis, a larger dredge would be idle too much of the time and a smaller one would not keep up with the rate of sedimentation, he said.
His son Rob is project manager, making the fourth generation of their family to dredge in Alaska for Manson.
The tour began at Manson’s trailer on the Port of Anchorage POL2 (petroleum oil and lubricants) dock. Johnson provided a hard hat and a PLB – personal location beacon – to each visitor, which activates in water and guides rescuers to a person in the water, and he described potential hazards that would be encountered on the crewboat and dredge. The survey boat Lester M doubles as a crewboat, and operator Michael Syron ferried the group out to the dredge, which was working a half mile up the channel. Dan Garrett, field engineer and surveyor, was operating the Odom MKIII single beam sounder during the trip.
The Port of Anchorage has four ship berths and draft of -35 feet mean lower low water (MLLW). There are four bulk carrier berths and two petroleum berths along one quay, and 90 percent of all commerce into and out of Alaska passes through the port.
“Anchorage is the only deepwater port in the U.S. where the federal government dredges up to the dock face,” said Allen Churchill, chief of the Corps Anchorage District Operations Branch. “This is because the dock was originally built by the Army for the Army, and was subsequently taken over by the Municipality of Anchorage in 1959. The congressional authorization kept the federal project limits ‘at the dock face’ and did not specify coordinates. Our Corps District is responsible for maintaining all the federally authorized and constructed navigation projects in Alaska (about 56 now). Some require dredging on annual basis, and others don’t require any at all,” he said.
On September 11, the dredge was working alongside sheetpile bulkheads of the unfinished expansion the port is building, but which has been stalled. A short ride brought the visitors to the Westport, and up the ladder to the bridge, where operator Jess Garvin was maneuvering the dredge into the cut, in constant contact with leverman Russ Woodruff at the other end of the dredge. Slurry was flowing into the hopper from pipes connected to the 20-inch starboard line and 16-inch port line, digging to 39 feet.
Garvin explained that it is a constant challenge to keep the dredge moving at the 3/10 of a knot required to keep the dragheads in the cut. Treacherous currents and back eddies with different elevations and strengths require constant attention, and when the tide is moving, the currents in the channel and along the dock face can be running in opposite directions.
Garvin pointed out the HYPACK® navigation screen which shows a picture of the channel with a blue line depicting the current dredge cut. A screen image of the dredge and tug in real-time moves onto the line, and he signals the leverman, who lowers the dragheads and begins pumping.
The Hypack program also provides information on the depth of the bottom in the surrounding area, with high spots to target. The leverman sees this screen plus a DredgePack® screen which shows the amount of material in the barge, draft of all four corners of the barge, depth of the dragarms, rpms of the pumps, velocity and density of the material, and opening and closing information on the split hull barge and all other DQM (Dredging Quality Management, formerly Silent Inspector) information.
Manson’s survey boat does daily condition surveys that are downloaded into Hypack for the information of the dredge and boat operators, and to double check the twice-weekly pay surveys performed by third-party surveyor eTrac. eTrac’s surveys go to both Manson and the Corps.
The Westport started life as a split hull hopper barge, which was transformed into a dredge in 1978 when the company installed the starboard dragarm with 20-inch Thomas pump, lever room and other dredging equipment. Later they installed the 16-inch port dragarm, with the pump and C18 Caterpillar engine mounted on the arm, modified to operate at a 45-degree angle. Two monitors are available to break up consolidated material in the hopper, and the dragheads include multiple jets for use during digging.
The lever room is forward on the starboard side of the dredge, and faces aft so the operator has a view of the hopper and the tug. Russ Woodruff explained that besides the split hull operation, the dredge can be emptied using valves operated from a control box in the lever room. A computer screen shows him both the navigation and bottom images from Hypack, and the DredgePack images.
In the midst of the visit, the Lester M approaches with the second crew. The operation is 24 hours a day, seven days a week, with two 12-hour shifts, changing at 11:30 a.m. and p.m. Relief leverman Dan Griffin climbs into the lever room and poses for a picture with Woodruff before taking over the controls. They are training a third leverman – Woodruff’s son Cody Woodruff.
The operation runs with four crew members – a captain and engineer on the boat, and a leverman and deck engineer on the dredge. As dredge captain, Don Johnson is on call 24 hours a day, and tries to spend six hours of each shift on the dredge.
Rob Richardson, project manager, explained that they had previously dredged the area next to the expansion as a new work contract called the transitional area, which is now part of the maintenance contract. The north end of this area is 800 feet wider than the rest of the project, with 18, 100-foot cuts. The rest of the project, along the existing berths, has 11 cuts, but not all are dredged, because the bottom begins to drop off on the outer cuts.
The placement area is a half mile to three-quarters of a mile from the dredging area, and is 5,000 feet long by 1,000 feet wide and about 120 feet deep. Richardson explained that they open the hopper at the upstream end of the placement area and let the material fall out for the currents to carry downstream.
Soon after the crew change, Griffin raised the dragarms and signaled boat captain Mike Benton to head for the placement site, where the visitors got a good view of the water disappearing, followed by the fine mud sliding down the sides and out of sight. In 10 minutes, they had returned to the cut and were dredging again.
The Anchorage dredging season runs until October 31, at which time, the Westport will go back to Seattle to work until until time to return to Alaska for the beginning of the 2013 dredging season in June.