It’s a tough row to hoe for young salmon in the Pacific Northwest as they make their perilous journey from upriver to the ocean. Besides hungry birds and sea lions, the regions many hydroelectric dams and their swirling turbines produce manmade currents and other obstacles that make it challenging for the fish to navigate.
But now with the help of an artificial Senor Fish created by the Pacific Northwest National Laboratory (PNNL), existing larger dams and newer, smaller hydroelectric facilities can become more fish-friendly. By measuring, recording and analyzing the many physical stressors faced by the fish on their trek, dams can make adjustments to their facilities to ease at least a portion of the journey.
Renewable energy in the US accounts for around 7 percent of the country’s total power generation, with hydropower making up more than half of that figure. The majority of hydropower comes from large dams, most of which were built in the 1970s or earlier, and are soon to be relicensed. They’ll also be evaluated for ways to reduce their environmental impact, which includes improving the well-being of migrating fish. At the same time, there is increasing interest in constructing smaller dams, hydro facilities and pumped storage plants that generate 10 megawatts of power or less.
While it’s easy to assume spinning turbine blades represent the greatest danger to passing fish, the Sensor Fish research has shown a variety of potentially harmful forces on fish, including abrupt pressure changes in turbine chambers. As aging dams undergo upgrades and retrofits in the coming years, all of the collected data is helping with turbine redesigns that not only create less of a pressure change but increase power production.
The Sensor Fish is a small tubular-shaped device 3.5 inches (9 cm) in length and 1 inch (2.5 cm) in diameter, and weighing 1.5 ounces (42 g). And while no bird or sea lion will confuse it for an actual fish, the lithium-ion battery-powered device is the same size as an actual juvenile salmon. It’s also packed with sensors that measure the stressors fish experience such as pressure, acceleration, strain and turbulence.
The device is able to record around five minutes of data via flash memory, and reads 2,048 measurements per second. It can record up to 174 pounds (78 kg) per square inch of pressure and acceleration that is 200 times the earth’s gravity (200 g), as well as 2,000 degrees per second of rotational velocity and temperatures between -40 and +260 degrees F (-40 to 127º C). Its neutral buoyancy allows it to remain below the surface like a regular fish.
The Sensor Fish is an upgrade from an earlier version, which was originally developed in the late 1990s to improve the survival rate of salmon navigating dams along the Columbia River Basin. And while the earliest clear rubber version was fish-like in appearance, it came up short in capturing the full fish experience. The first generation of Sensor Fish was issued in 2004 with sensors, circuit board and rechargeable battery.
According to the project’s director and chief scientist, Z. Daniel Deng, the sensor fish was originally designed to read the effects of the Kaplan turbine, the most common type in the Columbia River Basin where most of the testing is done, particularly at the 100-foot-high Ice Harbor Dam. The pressure change within the turbine was found to be the equal of traveling from sea level to the top of Mount Everest in a flash.
The latest, second-gen Sensor Fish, will accommodate other turbines and hydraulic structures, including pumped storage. "The new version has better pressure, acceleration (accelerometers), and rotational velocity sensors (gyroscopes)," says Deng.
It also has a radio transmitter and automatic retrieval system that floats the device to the surface after a predetermined amount of time by dropping a pair of small weights. The cost of the device has dropped about 80 percent from its predecessor, and now costs $1,200 per Sensor Fish.
Next year will be a busy one for the Sensor Fish, tasked to evaluate three small hydro projects and a conventional dam in the US, irrigation structures in Australia, and a dam on the Mekong River in Southeast Asia. Deng and his staff currently build the Sensor Fish by hand in PNNL’s Bio-Acoustics & Flow Laboratory, with funding from the Electric Power Research Institute and the US Department of Energy’s Office of Energy Efficiency and Renewable Energy.
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