Many dams have fish ladders that help the fish safely make their journey upstream. But getting downstream is a whole different story. Hydroelectric dams, in particular, present a huge challenge. Between strong currents, rapidly changing water pressure, and huge turbines, the young fish can get stunned, injured, or killed. Although there are various methods in place to keep the fish away from the turbines, many still end up going through the the engines.
As many hydroelectric dams built during and before the 1970s are currently due for relicensing, their environmental impact is being assessed. And one of the key indicators of a dam’s environmental impact is how well fish fare when they encounter one. Collecting precise data was nearly impossible until the invention of a nifty device.
The Department of Energy’s Pacific Northwest National Laboratory began developing the Sensor Fish in the late 1990s to improve fish survival at hydroelectric dams along the Pacific Northwest’s Columbia River Basin. The earliest design featured basic circuitry, sensors, and two AA batteries encased in a six-inch-long, fish-shaped piece of clear rubber. Though the appearance was fish-like, the design didn’t fully capture the experience of real juvenile salmon swimming through dams.
So PNNL staff went back to the drawing board in 2004 and devised a new Sensor Fish, which featured a hollow tube of clear, durable plastic that was stuffed with various sensors, a circuit board, and a miniature rechargeable battery. It was specifically designed to evaluate dams equipped with a common type of turbine along the Columbia River, the Kaplan turbine. Using the redesigned Sensor Fish, researchers discovered that the pressure change as the fish move through Kaplan-turbine-equipped dams is akin to traveling from sea level to the top of Mount Everest in blink of an eye.
That knowledge is helping engineers redesign the turbines so they create less severe pressure changes while maintaining or even improving power production. Many of America’s aging hydroelectric dams will be undergoing retrofits in coming years that will include newly designed turbines.
A new generation of Sensor Fish
To collect even more precise data in a wider range of hydroelectric dams, the design team came up with a new version of the device, which can be used in different kinds of hydro facilities, including unconventional, smaller hydropower plants and conventional dams with either Kaplan or Francis dam turbines.
The new Sensor Fish measures forces more precisely than the earlier model, and is significantly cheaper to produce (the newest devices cost $1,200 each, 20% of cost of the earlier versions). Other features have also been added, including sensors for temperature and orientation, a radio transmitter, and an automatic retrieval system that floats the device to the surface after a predetermined amount of time. Here are the details:
“Approximately smolt-sized, the Sensor Fish is a polycarbonate cylinder containing triaxial accelerometers, a pressure gauge, and rate gyros that measure angular rotation. It is reusable and contains modules that charge its internal battery, program the sensor settings, acquire data, and convert analog signal to digital form. The acquired data, collected at a 2,000 Hz sampling frequency over a recording time of up to approximately 4 minutes, are stored on an internal memory card and transferred to computers via a wireless infrared link using an external infrared link modem.”
“The earlier Sensor Fish design helped us understand how intense pressure changes can harm fish as they pass through dam turbines,” said lead Sensor Fish developer Daniel Deng, a chief scientist at the Pacific Northwest National Laboratory. “And the newly improved Sensor Fish will allow us to more accurately measure the forces that fish feel as they pass by turbines and other structures in both conventional dams and other hydro power facilities. As we’re increasingly turning to renewable energy, these measurements can help further reduce the environmental impact of hydropower.”