Analysis into water stream and fish passage by way of dams within the US suggests new choices for assembly power and environmental wants, writes Alexandra Freibott for the US Dept of Power and Pacific Northwest Laboratory.
Hydropower dams present dependable renewable power, however in addition they have a direct influence on the setting, particularly fish. Adjusting the quantity of water spilling over a dam might help fish efficiently navigate dams. However spilling extra water means much less water is out there to supply energy. Figuring out when and the way a lot water to spill to assist fish move safely by way of dams whereas assembly grid reliability wants are critically essential questions.
Research at Pacific Northwest National Laboratory (PNNL) highlights the advanced dynamics round spill and fish passage by way of dams, and finds that spill is just not all the time the most important consider profitable fish passage.
“We discovered that fish exercise, swimming capacity, and time of day all play a job in fish passage, usually extra so than spill ranges alone,” defined PNNL Earth scientist Ryan Harnish. “Our information present that when younger salmon and steelhead are much less energetic within the spring—like at evening or in cooler water temperatures—spilling extra water could make an enormous distinction in serving to extra fish keep away from passing by way of the powerhouse. However beneath different situations, larger spill ranges have little impact.”
That is beneficial info for decision-makers who’re tasked with balancing water wants for environmental well being and power demand. Understanding when excessive spill ranges greatest assist fish passage—and after they don’t—gives choices for balancing the tradeoffs related to hydropower technology and environmental impacts.
Monitoring fish by way of a dam in 3D
Spilling water might help fish swim efficiently over a dam as a substitute of instantly by way of the powerhouse—the a part of the dam that features the turbine. However the timing and quantity of water spilled impacts each fish passage and energy technology. To take a more in-depth take a look at how spill degree impacts fish passage, researchers wanted detailed monitoring info exhibiting when and the way fish handed by way of a dam.
The usual monitoring methodology within the Columbia River Basin is to tag particular person fish with passive built-in transponder (PIT) tags above the dam, that are detected as fish move by way of a selected a part of the dam referred to as the juvenile bypass system. Whereas very dependable, this strategy doesn’t present details about the varied different routes fish can journey by way of a dam—info wanted to find out how spill degree impacts fish passage. To get this info, quite a few research had been carried out between 2008 and 2018 utilizing a distinct methodology: acoustic telemetry.
The PNNL group analyzed the ten years of acoustic telemetry information, together with 3D info on fish habits, from a number of dams alongside the Snake and Columbia rivers. This allowed them to determine the route fish took by way of the dam and the exact time of their dam passage. Mixed with details about fish habits and survival together with dam operations, they evaluated what elements had been most probably to have an effect on fish passage by way of totally different routes and situations. They particularly checked out spring salmon and steelhead smolts—younger fish migrating towards the ocean—to see how spill ranges affected the variety of smolts passing instantly by way of the powerhouse. The variety of smolts passing by way of the powerhouse turned out to be associated to their exercise degree and swimming capacity, not simply spill.
“Excessive spill ranges which are supposed to scale back the variety of fish passing by way of the powerhouse within the spring are more likely to be only when fish are much less energetic or have diminished swimming capacity, resembling at evening, throughout excessive river flows, or in cooler water temperatures,” defined Harnish. “Excessive spill ranges weren’t the only most essential consider smolt passage throughout the board.”
These findings level to the necessity for extra research like this that may present complete details about precisely when and the way fish move by way of dams. That info might help decision-makers decide the way to greatest assist fish passage and meet power wants sooner or later.
In a press release supplied to PNNL, the Bonneville Energy Administration (BPA)—which markets energy from 31 federal dams throughout the Pacific Northwest—mentioned, “This publication is one other piece to the puzzle of understanding fish passage by way of the federal hydrosystem. It ought to present the area’s scientists and managers with extra info to contemplate when evaluating operations that meet the a number of functions of the Columbia River System.”
(Above) The a number of paths fish can take when passing by way of and round a dam. The powerhouse contains the generators and the juvenile bypass system proven on this illustration (picture credit score: Stephanie King, Pacific Northwest Nationwide Laboratory). CLICK IMAGE TO ENLARGE.
Balancing wants
Hydropower generates over half of the electrical energy in Oregon and Washington and is a key a part of a dependable electrical grid. Fish passage is important to assist regional fish populations, notably salmon, which maintain important environmental, financial, and cultural significance. Understanding when and the way a lot to spill—or not—is paramount to balancing these wants.
For instance, when river water ranges are low, most spill ranges are comparatively excessive. This excessive spill degree interprets to an enormous lower in energy technology—equal to powering half one million fewer houses. This research predicts that beneath these river situations, most spill ranges would assist fish passage by way of the powerhouse at evening, however would make little distinction through the day when power demand is usually larger. This detailed info provides important perception for decision-makers and dam operators in search of methods to satisfy each power and setting priorities.
“Evaluating power and setting tradeoffs is a problem that requires the very best accessible information to tell selections,” mentioned Alison Colotelo, PNNL Hydropower Program Lead. “Higher understanding of what impacts fish passage by way of dams and the position of spill is important to supporting fish populations and energy technology.”
This analysis was funded by BPA, as a part of a cost-share settlement to broaden upon analyses initially funded and initiated by the Division of Power’s Water Energy Applied sciences Workplace.
