NOAA updates Unalaska Bay charts
The seafloor of Unalaska Bay is being mapped for the first time since 1935, and the technology's more thorough now, using electronic devices instead of a couple of people in a rowboat dropping a weighted rope to the bottom a hundred feet apart.
The National Oceanographic and Atmospheric Administration is conducting the hydrographic survey, using four 28-foot-long aluminum boats to map 38 square underwater miles, according to NOAA Lt. Bart Buesseler.
The new information aims to update nautical charts, in hopes of preventing another mishap like last summer's incident involving Shell's offshore oil support ship Fennica, which hit a high point underwater not identified on a chart between the Unalaska Airport and Hog Island. The old-school method of measuring depths always left gaps, missing high or low points in between the manual depth measurements.
Still, Buesseler said it wasn't like the boat operators had no warning at all, as the chart indicated shallow water with blue tint shading.
The survey's small boats arrived on the federal research ship Fairweather, for a job that should take nine people 20 days to finish. The 231-foot Ketchikan-based Fairweather is now off on another project, and will pick up the 28-footers when it returns.
Only two of the four small boats are in use at one time, while the other two remain in port, he said.
Buesseler gave a report on the project at last week's Aleutian Life Forum, a science conference at the Grand Aleutian Hotel which is also the hydrographers' local base of operations.
According to a statement from NOAA last year, the MSV Fennica, a Finnish multipurpose icebreaker, operating in support of Shell Oil Arctic drilling efforts, reported striking an obstruction in the vicinity of a charted shoal between Hog Island and Amaknak Island near Dutch Harbor, Alaska on July 3, 2015.?NOAA Ship Fairweather, while in Dutch Harbor for a scheduled port call, was contacted by a representative from the Alaska Marine Pilots to survey the area following the incident.
Preliminary data collected by NOAA Ship Fairweather shows that there are certain rocky areas shallower than five fathoms (30 feet), and one as shallow as 3.75 fathoms (22.5 feet).?These were not detected by the last survey of the area conducted in 1935.?No objects or obstructions such as anchors or debris were detected in the preliminary results.?NOAA has submitted a Dangers to Navigation Report to the USCG that identifies the shoal depths in the area.
Less than one percent of U.S. Arctic waters have been surveyed with modern survey methods.?Modern survey methods use vessel-mounted multibeam echo-sounders to measure ocean depths, and GPS for precise positioning, as the ship or boat moves along a planned track.?Many charts in the U.S. Arctic, including western Alaska and the Aleutians, still have depth information from pre-WWII surveys, which relied on hand lead lines or wire sounding machines for measuring depths, and sextants for positioning.?Other areas remain unsurveyed.
In anticipation of growing vessel traffic in the Arctic, NOAA is increasing its charting activities in the region to help ensure navigation safety. NOAA Ships Rainier and Fairweather are conducting a summer of hydrographic surveying projects in the U.S. Arctic along the western coast of Alaska, including Kotzebue Sound, Port Clarence, and Point Hope.?Reconnaissance bathymetry is also being collected along the main shipping route which extends from the Aleutians up through the Bering Strait as a joint effort with the USCG Cutter Healy.?NOAA will use these hydrographic surveys, which measure ocean depths and search for dangers to navigation, to update nautical charts for Alaska's waters.