Salmon cannons and dancing rods: the wild world of hydropower fish management

Posted: November 15, 2024

For a brief moment in the summer of 2019, a 90-second video of fish fired through a tube captivated the internet.^[1] The “salmon cannon” was invented by a company called Whooshh Innovations, and worked precisely as the name suggests: salmon were fed into a tube that swiftly sucked them up, sped them through and shot them out the other end.

What ended up a meme was rooted in dry practicality. As the promotional clip noted, moving fish between bodies of water has plenty of real-world applications. It could help aquaculture companies safely transport their farmed fish, or move wild animals to cooler waters during droughts. Or it could channel fish back to migratory routes disrupted by human infrastructure, such as hydroelectric dams.

This last solution is what Whooshh has honed in on since its heady days of online fame. It’s also where scores of other companies have tried to innovate in order to solve a problem that has long haunted hydro: what to do with all those fish?

How fish are managed at hydropower plants

Humans likely paid little heed to handling fish and their needs during the advent of modern hydropower in the late 1800s. Today, with environmental concerns front and center, utilities are constantly looking for ways to improve fish safety and manage a plethora of threats—from dams that disrupt spawning runs to the spinning turbines in run-of-river plants.

There are thousands of hydroelectric dams in the US alone (and tens of thousands more dams that provide flood control, water supply and irrigation).^[2] Historically, many of them have used fish ladders or elevators to help salmon and other migratory species travel upstream, sending them hopping through a network of small pools that essentially break the dam’s height into manageable chunks. 

When it comes to travel in the other direction, power companies often try to channel fish away from the turbines, which pose the highest risk of injury, and send them through specially constructed spillways or bypasses instead. 

The required engineering can get complex: at the McNary Dam, a nearly 1.5-mile long barrier across the Columbia River on the border between Oregon and Washington, fish encounter enormous submersible screens that divert them away from the plant’s powerhouse. Engineers at the plant spend a lot of time tending to the submerged electricals and keeping the screens clear of debris; once a year, the whole system has to be removed for repairs and maintenance.  

“Not to mention…during fish passage season, if something goes wrong with that screen, this turbine has to shut down. You can’t run them without it,” says Marty Ahmann, Chief of Maintenance at the dam.  

Improving fish management in hydropower 

When fish do get sucked through a turbine, it doesn’t need to spell their end. While blade strikes and the abrupt pressure changes in the powerhouse can be lethal,^[3] start-ups are now pioneering a range of gentler turbines—a development perhaps long overdue, considering that the most widely-used model was developed in 1849. 

One such company is Natel Energy, which designed a turbine with thicker blades, rounded edges and a forward slant to allow fish to pass safely downstream. The company says the unique shape of the turbine, which is meant for smaller distributed hydro plants, is informed by lab studies of blade strikes, computational modelling of fluid dynamics and extensive tests with various species.^[4][5]

The design also reduces installation costs because it eliminates the need for diverting screens. ‍And Natel claims the additional water flow that isn’t lost to bypass channels, for example, means up to 10% more power generation.

Elsewhere, scientists are also busy getting a better sense of how fish can safely navigate power plants. At the Pacific Northwest National Lab, researchers have developed a so-called  sensor fish—a small autonomous device similar in size and density to a yearling salmon smolt.  

The device is sent through and around dams in lieu of live fish to test physical stressors, measuring everything from acceleration and pressure to rotational velocity and orientation. 

When it comes to studying actual behavior in the wild, the lab’s scientists also tag fish with tiny sensors, for example to track their movements along a stream. For long-term studies, they’ve even designed piezoelectric devices—essentially fish-powered generators that use the animals’ movements to produce electricity and keep their tags running. 

Using foam rods to guide fish to safety

The small Swedish town of Älvkarleby has few claims to fame. That is, unless you’re a salmon. 

Here, utility Vattenfall runs a research laboratory that exerts an outsize influence on Northern Europe’s fish populations. One of the lab’s halls houses the Laxelerator—“lax” being Swedish for salmon—a test facility with two 24-meter pools where Vattenfall’s engineers and biologists recreate river environments to test fish behavior in flowing water. 

Their mission is to come up with new and better ways to safely coax salmon and other species past the company’s roughly 100 hydropower plants. In the pools, they use pumps to control the water speed and adjust the temperature to emulate seasonal conditions. 

One of the research team’s latest projects looked at ways to improve how fish are diverted away from turbines. Vattenfall found that grates or screens, like the ones used at McNary, lower generation capacity by slowing down the water. The company had also experimented with bubble curtains—rows of tiny air bubbles that act as a natural barrier—but wanted a solution that didn’t require energy to operate. 

“We found inspiration in seaweed, kelp, and came up with an idea—that long foam rods could share the same characteristic, moving and dancing in the current and so having a deterrent effect on the fish,” says Karolina Carlström, an engineer in Vattenfall’s R&D department.

When the company tested its method, it found that salmon smolts would indeed avoid swimming through the foam rods and would follow them instead. Since Vattenfall didn’t want to spread microplastics, it worked with Jowan Rostami, a doctoral student at KTH Royal Institute of Technology in Stockholm and founder of start-up Cellufy, to develop a version made of water-resistant, cellulose-based aerogel instead. They are now refining the material to make it stable in water: flexible enough to sway but buoyant enough to stay upright.

The evolution of the salmon cannon

Back at Whooshh, time hasn’t stood still either. Since its last viral moment, the company has evolved its salmon cannon into a fully automated system, capable of transporting thousands of fish a day up to 1,000 feet. 

Fundamentally, it still works the same way, using a small pressure differential to propel fish through misted tubes. But it also boasts sensors and cameras to count and identify each fish, recording its size and whether it is wild or hatched, tagged or injured.  

The data can be used by fisheries managers and researchers interested in analyzing population dynamics, migration patterns, behavior and health. Whooshh’s system can even sort the fish in real time, for example allowing only native ones to pass upstream while separating out invasive species. 

The platform has been used in a handful of situations, for example a demonstration project at Washington’s Chief Joseph Dam, a few hundred miles upstream of McNary on the Columbia River. Near the base of the dam, Whooshh installed a floating barge to sort hatchery-bred and wild-born populations of Chinook salmon during their annual run, when the fish swim back upstream to spawn. 

Despite the more sophisticated set-up, videos of the trial still provide the same, oddly satisfying sight that made the original cannon such a hit: seeing salmon slip into a tube and come surging safely out the other side. 

References:

^{[1] https://www.cnet.com/culture/internet/fish-tube-meme-is-all-the-internet-cares-about-now/
[2] https://www.energy.gov/eere/water/types-hydropower-plants
[3] https://conbio.onlinelibrary.wiley.com/doi/10.1111/cobi.13870
[4] https://cdn.prod.website-files.com/660c637d4bb1ef487b6ff473/660c637d4bb1ef487b6ff75e_Natel_DesignValidationFishSafeHydro_HD2023_edit.pdf
[5] https://www.natelenergy.com/fish-passage}