Offshore wind developer using sound waves to map seafloor off SLO County. Here’s a look
On a June afternoon, the scent of coffee and sea air mingled below deck aboard the Go Adventurer, a medium-sized ship tasked with carrying scientists and survey equipment to map a slice of the seafloor off San Luis Obispo County’s coast.
Golden State Wind is one of three corporations that holds a lease to build floating turbines in the 376-square-mile Morro Bay Wind Energy Area about 20 miles away from Cambria and San Simeon.
On July 1, Golden State Wind launched site surveys of its lease area — which is about 53 miles northwest of Morro Bay. The surveys are scheduled to end in late October.
Golden State Wind hired the international corporation Fugro to conduct the surveys, which use sound waves to map the seafloor, including locating sensitive habitats and shipwrecks and determining the consistency of the soil and the depth of the ocean floor. They will use the data to decide where to anchor floating platforms for the wind turbines and where to place cables that will carry electricity to land.
“The surveys are critical to developing environmental information about the seabed and below the seabed,” Golden State Wind CEO Tyler Studds said. “It’s going to help us identify critical resources and sensitive resources that will allow us to develop and operate the project in a manner that avoids any impacts on resources.”
Golden State Wind is checking for habitats, shipwrecks, seamounts — anything that could be harmed by construction, Studds said.
The surveys will prepare Golden State Wind to apply for three permits: the Benthic Habitat Assessment, which evaluates the habitat on the seafloor and in the sediment, the Marine Site Investigation Report and the Marine Archaeological Resources Assessment, Studds said.
The Go Adventurer, a 205-foot vessel, will return to Port Hueneme in Ventura County every 28 days to pick up a fresh crew and supplies. The ship will not dock in Morro Bay or Port San Luis, Studds said.
This is the first time the seafloor will be mapped so thoroughly, according to Tim Farrow, the regional director of Marine Geophysical Americas for Fugro.
The data could be used for Seabed 2030, a global initiative that aims to map the entire seafloor by 2030, he said.
Acoustic surveys to map the seafloor
Fugro will deploy a bright orange autonomous underwater vehicle to carry surveying equipment from the Go Adventurer to about 30 meters above the seabed, the Go Adventurer’s senior party chief Robert McDowell said.
The vehicle, built by Norway-based Kongsberg Maritime, will run surveys for about 24 hours at a time. After about 24 hours, the crew retrieves the vehicle from the water, swaps its batteries, then sends it back to the seabed, McDowell said.
The vehicle will dive between 140 meters and 1,450 meters below the Go Adventurer — though it is capable of plunging to a depth of 4,500 meters, he said.
Three types of equipment will be mounted to the vehicle: a multibeam echosounder, a side-scan sonar and a sub-bottom profiler.
The equipment emits pulses of sound that create images of the seafloor.
The multibeam echosounder will be mounted to the front of the autonomous underwater vehicle. Every half second, it shoots pulses of sound at the seafloor, which creates a 3D picture of the terrain.
“Is that a pipeline that we’re crossing? Cables, shipwrecks?” McDowell said. The multibeam echosounder answers those questions, he said.
Meanwhile, side-scan sonars mounted to two sides of the vehicle emit a fan of sound to detect the height of objects on the ocean floor.
Finally, the sub-bottom profiler will use pulses of sound, which sound like a “chirp,” to scan below the seafloor. This survey will gather information about sediment as deep as 40 meters below the seabed.
“Is it sand? Is it mud? Is it rock?” McDowell said. “They can interpret that based on the speed of sound as it penetrates the seafloor.”
Analysts aboard the Go Adventurer will receive and process real-time data collected by the survey equipment.
“When we collect the data, it’s in digital form. We bring it on board, they process it and they make a pretty picture,” McDowell said.
Studds added that Golden State Wind will not use more-powerful seismic airguns to survey the Morro Bay Wind Energy Area.
Seismic airguns penetrate 6 to 9 miles below the seabed for oil and gas exploration, while the sub-bottom profiler only sees 30 to 40 meters below the seabed, Studds said.
The equipment is permitted by the California State Lands Commission Low-Energy Offshore Geophysical Survey Permit Program, and it is routinely used by federal agencies and research institutions.
The sound is emitted at a pitch that doesn’t harm marine mammals, Studds said. In fact, most of the sound emitted is outside of the hearing range of fish and marine mammals, he said.
The multibeam echosounder will emit blasts of sound at between 200 to 400 kilohertz with a source level of 225 decibels underwater, Studds said. Meanwhile, the side-scan sonar shoots sound greater than 500 kilohertz with a source level of 205 decibels. Neither of these sound blasts can be heard by sea life, he said.
Fish and sea turtles hear sounds between 2 and 4 kHz, while larger marine mammals can hear up to 160 kHz, according to a June report by the California Coastal Commission.
Only the sub-bottom profiler will emit sounds between 1 and 10 kilohertz with a source level of 167 decibels, which can be heard by marine life, Studds said.
The impact of the sound is reduced if the sea life is more than 5 meters away from the source, the commission staff report said. The vessel is required to stay at least 100 meters away from marine mammals, which reduces the impact of the sound, Studds said.
To protect marine life, the Go Adventurer will limit its speed to 10 knots and remain at least 500 meters away from marine life.
Meanwhile, four trained species observers will travel on the vessel and take turns watching for marine life protected by the Endangered Species Act or Marine Mammal Protection Act, McDowell said.
During the day, two observers will scan the horizon with binoculars. At night, one will scan the ocean with infrared binoculars, while the other will monitor computers that show what is approaching the ship.
The observers have the authority to halt the ship or survey activities if they spot a protected species.
Additionally, staff aboard the ship communicate daily with fishermen by radio to notify them when and where surveys are being conducted, Studds said.
This story was originally published August 21, 2024 at 5:00 AM.
