Porpoise System Deployment

Q & A with ‘Ike Wai’s Dr. Eric Attias on marine controlled-source electromagnetic (CSEM) imaging

By Maria Dumanlang

Estimated reading time: 7 mins

‘Ike Wai researcher Dr. Eric Attias recently conducted an offshore survey along the Kona coastline of Hawai‘i Island to better understand the Hualālai aquifer system. He speaks now about the role his work plays in the ‘Ike Wai project and how the novel application of this state-of-the-art technology has helped to increase the understanding of the aquifer system and its potential benefit to the community.

From left, Eric Attias and Jake Perez deploy the system

Q: What is your role in ‘Ike Wai?

A: “I’m in charge of marine geophysics. I’m trying to image the groundwater deposit beneath the seafloor that might exist…I’m trying to image it based on electromagnetic methods.”

Q: How long have you been with the project and what inspired you to join the team?

A: “I arrived [in] December 2017 … what inspired me is that [‘Ike Wai is] a large scale project that has a lot of components. It really has the ability to answer a major question while looking at [it in a] multidisciplinary way. I’m doing one part, but there are many other groups that are doing different parts. That’s why it’s interesting because you can get answers to what you’re seeing through other data sets and get a complete understanding of the [water] system as a whole.”

Q: How did the idea of doing the survey come up? It wasn’t part of the original plan of the project.

A: “Yes, it wasn’t … I came in with the ambition to extend the project to my field … It’s crucial for this project to look at the offshore environment because it’s an island, it’s a big part of the system as a whole. There is a huge discrepancy in the volume between what the recharge is, what they pump, and what the discharge is. Where does the other 30 to 40 percent of the other water go to?”

“In completely understanding the system, or to answer a question of this project – how the groundwater system of the Big Island works – there is no way to avoid looking at the offshore environment unless you want to give half the answer.”

Q: What has your work done to help answer some of the questions of the project?

A: “The work is in progress, but once I have solid results it will highlight a few things. First of all, the interconnectivity [of freshwater] between the land and the offshore environment. Second, it will show us, offshore, where we have deposits of groundwater located. Which means we get their location, their lateral and vertical distribution, and how deep they can extend. My system can image about 500 meters down below the seafloor.

“I can give you an example; let’s just say we have all this information … to give to the Board of Water Supply. Then they can say, ‘In terms of volumes, in this area offshore, we have 20 times more [fresh water] than [these other] ten wells that we are taking water from on land. So why don’t we just drill one well offshore and get the water over there.’ The benefit of that are two things; it’s passing the ecosystem, so you’re not interfering with the community, you donʻt have structures on land, and you don’t block water from getting to the fishponds and the things that [the residents] care about. Second, in terms of the energy [needed] to pump [freshwater] – pumping is very high, so it is a lot of energy to invest in order to pump water a few kilometers down. If you go to the offshore, you have hydrostatic pressure … [so it is easier to pump and] it could save [in] costs of energy of extracting water, and it [would] have minimum effect on the environment. This is what I see as the ideal outcome of my project.”

Q: The technology you used for the survey is state-of-the-art. Can you tell me a little about that?

 A: “The entire method that I’m using – it’s called controlled-source electromagnetic [imaging]. The idea of how to use it was [developed] back in the ‘60s by Exxon Mobile and big companies. The first time they actually built instruments and used [this method] was only 12 years ago for the…oil and gas industry. The people who built those first instruments was Scripps [Institute of Oceanography] -, I used their equipment for the survey. Southampton built the Deep Tow system, so the oil and gas industry can take [the system with a big marine] vessel, and the source and run it [down to] 50 meters above the seafloor to image places that are very deep. This is how it was for many years, and now there are big companies that use it industry-wide. Three years ago, Steve [Constable] at Scripps said ‘Let’s do the same system but for shallow water’… that particular system design, it’s unique – only Scripps has it. No other institution or industry has it. It’s been proven to work really well for gas hydrate detection in permafrost in Alaska. It’s never been used for groundwater.

“You have two novelties here, you have a very new system, in terms of worldwide, which is one-of-a-kind, and the second novelty is the capability of this system to detect deep submarine groundwater deposits. Hence, both the technology and its application are new.”

Q: You used a multi data approach for the survey, can you tell me about that?

A: The backbone or the core of the survey is the controlled-source electromagnetic (CSEM) data. This just gives me the sub-seafloor resistivity structure. When I designed the survey, I said … ‘I should add more layers of data on top that will give me more indication and validate my backbone data.’ I added a high-resolution multibeam system that shows in fine detail how the seafloor is changing. That helped me to model the CSEM data. If we see a region of interest and we see that there is very sharp typography there, we can relate those two.

We also collected data on the water column in terms of the intensity, [to see if] we might see some signatures in the water column that comes from the areas below the seafloor. [If I see some resistor, I look at the seafloor, if there is some resistivity. I look at if the water has changing values in salinity, in temperature. When you have fresh water, the salinity drops, the temperatures become lower, much colder and the sound velocity decreases – those are some indicators. I also have a magnetometer that can give me more structural information. The idea is, if I put a few layers of data it gives me more confidence on what my main results are. If they match – or it could contradict – then you’re looking at a few different angles of the same thing which can give you a better idea of what you’re seeing is real or not and what’s the extent of it.

CSEM Porpoise System

Q: What is the most important thing you would like people to know about the work that you’re doing?

A: “That resources don’t end on land. The general conception all over the world is that groundwater or aquifers, you can only [find] them over land. There is more and more evidence from all over the world that [they] have found large deposits [of freshwater] very far from the coastline. These could be valuable resources while there is so much scarcity in water.  It could be [pumped] with very little interference, it could be good for the environment, even better than doing the work on land. That could solve a lot of potential problems. Look at the ocean as another possibility.”

Q: Looking to the future, what else is coming up for you?

A: “In January, I was … offshore with the Lamont team [from] Columbia University, imaging subduction zones for thirty days, offshore of New Zealand. At the end of May/June I will do another month like that in Alaska with the same group. These are two projects that I’m collaborating on with them.”

“In terms of ‘Ike Wai now, there is a lot of work. I’m hoping that from the initial results, I could write a proposal to look at the further extent of the Hualālai system…that will look at the system much deeper. Now, we’re limited to 100 meters of water depth, because we towed the system on the surface. If I take a Deep Tow system, I could go to 2, 3, 4 kilometers down and see if the water really goes down to the shelf edge deeper.”

Learn more about Dr. Eric Attias and his work at the following links: