From The Bristol Bay Times by
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 Oceanic 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 as though 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 Royal Dutch
Shell's Arctic oil exploration efforts, reported striking an obstruction
in the vicinity of a charted shoal between Hog Island and Amaknak
Island near Dutch Harbor 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 the 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 U.S. Coast Guard that
identifies the shoal depths in the area.
Less than 1 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.
ASV Global and TerraSond have completed a 5172 nautical mile hydrographic survey in the Bering Sea, off Alaska.
TerraSond used the C-Worker 5 Autonomous Surface Vehicle (ASV) alongside its Q105 survey vessel for a duration of 36 days.
TerraSond used the C-Worker 5 Autonomous Surface Vehicle (ASV) alongside its Q105 survey vessel for a duration of 36 days.
The C-Worker 5 completed 2275 nautical miles of survey lines operating as a force multiplier, running parallel survey lines to the Q105.
Both vessels ran multibeam sonars and simultaneously towed side scan sonars.
This 2016 deployment was a follow on from a proof of concept operation carried out between TerraSond and ASV Global in August 2015 during which an ASV platform became the first autonomous surface vessel to update the US nautical charts for NOAA.
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.
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