As more countries consider alternative, renewable sources for energy, the need for accurate methods to assess the impacts of these new technologies is growing.
Dr. Len Zedel is the associate dean of Science (graduate and research) and a professor in the Department of Physics and Physical Oceanography. He is investigating an alternative use for a popular tool for measuring water velocity to see if it can also be used to evaluate the effects of in-stream tidal turbines on fish in channels being used for power generation.
“The turbine is similar to a windmill, only underwater,” he said. “So, depending on the model, it can have big blades rotating around. If it is blocking the flow of water, or creating large pressure differences, what is that doing to the fish? How are they reacting to the presence of the turbine?”
Currently, Doppler profilers are already in use in many of these testing areas to measure the impact the currents will have on the turbines and how much force the structure will have to withstand. Profilers use Doppler sonar, where a pulse of sound is transmitted into the water and is scattered by items being carried along by the water. The frequency difference between the signal sent out and the returned signal can tell how fast the object is moving; in other words, the speed of the water.
However, when the signal is “contaminated” by a fish swimming through the acoustic beam at a different rate of speed, that data is often thrown out. Dr. Zedel is hoping to prove this information can actually be used to count the number of fish present and monitor fish behaviour, which usually requires other types of expensive fish-finding equipment.
“Doppler technology is the standard for measuring water velocity,” he said. “Any other technology just makes measurements at one location, while a Doppler profiler can profile hundreds of metres of water velocity from a single instrument. So, they’re already collecting this data; they’re just not using it for this purpose. But in terms of deployment flexibility, measurement opportunities and cost savings, using this data for water velocity and fish monitoring could provide a number of benefits.”
Dr. Zedel’s initial findings from data collected at a test site in Grand Passage, N.S., have been the subject of a couple of well-received papers and seem to show consistent repeatable behaviour in acoustic data which gives him confidence this method will work. Now he is looking to purchase the fish-finding equipment necessary to do more accurate testing for comparative purposes; to validate whether or not what he is counting as fish signals really are just that.
“If so, it provides a means to see if the fish are responding to the turbine,” he said. “If you put a Doppler profiler near the turbine and one 50 or 100 metres away from it, if all other things are equal you should see the same number of fish. But if you don’t, that could indicate there has been some kind of impact and from there you can go on to evaluate whether it’s a significant impact or not.
“The problem the industry has is that, even if it is unlikely there will be an impact, they still have to demonstrate that to the community. Or, if there is an impact, is it one that can be tolerated? Especially if the long term vision is to put in a lot of these turbines. Any impact will be magnified by the number of units in place.”
While these turbines have not been deployed in Canada on a large, commercial energy generating scale, there is an intention to deploy two 16-metre turbines in Nova Scotia’s Minas Passage later this year, the world’s first multi-megawatt array of interconnected tidal turbines. The province’s ambitious plans for tidal energy from this region will see the initial demonstration project grow from a combined output of 4MW into a 300MW commercial scale project in the Bay of Fundy.
Dr. Zedel has been in contact with Open Hydro, the group overseeing this project, and hopes to partner with them on data collection after the instruments go into the water. Turbines being installed in Scotland, Ireland and France may also provide opportunities for collaboration.
But he doesn’t expect to see such technologies coming to this province any time soon.
“In the Bay of Fundy, the tidal flow is five metres per second, or 10 knots,” he said. “So the water is deep and it’s just ripping along. For the most part, in Newfoundland and Labrador we just don’t have the tides, the current velocities that would make in-stream turbines attractive. There are a few areas in Northern Labrador, but they would have the further complication of ice to deal with.”