Analysis into water move and fish passage by means of dams within the US suggests new choices for assembly power and environmental wants, writes Alexandra Freibott for the US Dept of Vitality and Pacific Northwest Laboratory.

Hydropower dams present dependable renewable power, however in addition they have a direct affect on the atmosphere, particularly fish. Adjusting the quantity of water spilling over a dam will help fish efficiently navigate dams. However spilling extra water means much less water is offered to provide energy. Figuring out when and the way a lot water to spill to assist fish go safely by means of dams whereas assembly grid reliability wants are critically essential questions.

Analysis at Pacific Northwest Nationwide Laboratory (PNNL) highlights the advanced dynamics round spill and fish passage by means of dams, and finds that spill is just not all the time the largest think about profitable fish passage.

“We discovered that fish exercise, swimming means, 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 a giant distinction in serving to extra fish keep away from passing by means of the powerhouse. However below different situations, larger spill ranges have little impact.”

That is priceless 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 once they don’t—offers choices for balancing the tradeoffs related to hydropower era and environmental impacts.

Monitoring fish by means of a dam in 3D
Spilling water will help fish swim efficiently over a dam as an alternative of immediately by means 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 era. To take a more in-depth have a look at how spill stage impacts fish passage, researchers wanted detailed monitoring info displaying when and the way fish handed by means of a dam.

The usual monitoring technique 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 go by means of a selected a part of the dam known as the juvenile bypass system. Whereas very dependable, this strategy doesn’t present details about the varied different routes fish can journey by means of a dam—info wanted to find out how spill stage impacts fish passage. To get this info, quite a few research have been performed between 2008 and 2018 utilizing a unique technique: acoustic telemetry.

The PNNL workforce analyzed the ten years of acoustic telemetry information, together with 3D info on fish conduct, from a number of dams alongside the Snake and Columbia rivers. This allowed them to establish the route fish took by means of the dam and the exact time of their dam passage. Mixed with details about fish conduct and survival together with dam operations, they evaluated what components have been almost certainly to have an effect on fish passage by means of completely 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 immediately by means of the powerhouse. The variety of smolts passing by means of the powerhouse turned out to be associated to their exercise stage and swimming means, not simply spill.

“Excessive spill ranges which might be meant to scale back the variety of fish passing by means of the powerhouse within the spring are prone to be only when fish are much less energetic or have diminished swimming means, similar to at evening, throughout excessive river flows, or in cooler water temperatures,” defined Harnish. “Excessive spill ranges weren’t the one most essential think about 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 go by means of dams. That info will help decision-makers decide easy methods 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 means 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 means 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 stage interprets to a giant lower in energy era—equal to powering half 1,000,000 fewer houses. This research predicts that below these river situations, most spill ranges would assist fish passage by means of the powerhouse at evening, however would make little distinction in the course of the day when power demand is often larger. This detailed info provides vital perception for decision-makers and dam operators searching for methods to satisfy each power and atmosphere priorities.

“Evaluating power and atmosphere tradeoffs is a problem that requires the perfect accessible information to tell selections,” mentioned Alison Colotelo, PNNL Hydropower Program Lead. “Higher understanding of what impacts fish passage by means of dams and the position of spill is vital to supporting fish populations and energy era.”

This analysis was funded by BPA, as a part of a cost-share settlement to increase upon analyses initially funded and initiated by the Division of Vitality’s Water Energy Applied sciences Workplace.