Fall 2016


Researching Dams’ Effect on Eel River Salmon

SNAKING ALONG CALIFORNIA’S NORTH COAST is the Eel River, the state’s third-largest watershed, which, along with its tributaries, covers 3,684 square miles and crosses five counties.

Along the upper part of the river sits the controversial Potter Valley Project, a massive power-generating facility that consists of two dams and a tunnel that divert water to the Potter Valley in the Russian River watershed.

Advocacy groups and others say the dams have had a serious impact on the river’s salmon populations and have called for the dams to be removed.

Now, as the government prepares to consider relicensing the project, Environmental Science & Management Professors Alison O’Dowd and William Trush, along with several HSU students, are working to get a better understanding of how the dams affect the salmon.

SALMON ARE NOT ONLY a charismatic species but they’re indicative of watershed health. So if the salmon aren’t doing well then the amphibians, invertebrates, and other aquatic organisms probably aren’t doing well either,” says O’Dowd.

The plummeting population of Eel River salmonids paints a grim picture. Before 1900, there were an estimated 500,000 salmonids (70,000 coho and 175,000 Chinook salmon, and 255,000 steelhead), according to the National Marine Fisheries Service.

Today, there are an average of 15,000 salmonids returning each year—a 97 percent drop in population that environmentalists have partially attributed to the PG&E-owned Potter Valley Project. The project began in 1908 with the completion of the Cape Horn Dam. Scott Dam was completed in 1922 and that year, the Federal Energy Regulatory Commission granted the project a 50-year license.

Over the next decade, the Commission will review licenses for about 150 dams, including Scott Dam, which is set to expire in 2022.

IN THE MEANTIME, local environmental advocacy group Friends of the Eel River, which has been fighting for the removal of the dams for the last 20 years, looked to O’Dowd and Trush to study blockwater releases. Blockwater is a set volume of water (e.g. 2,500 acre-feet) released from dams as a single pulse or as multiple pulses.

The impetus for their research, conducted through the HSU’s River Institute, was the plight of fish that lingered between the two dams. Under natural conditions, rising water temperatures and lower flows are Mother Nature’s signals for juvenile salmon to begin migrating out to the ocean.

However, fish rearing in the artificially cool and consistently flowing waters between the dams lingered into the summer months so that by the time the fish left and made their way downstream to the lower dam, they swam in water that was much warmer and potentially lethal, and with lower flow conditions.

O’Dowd and Trush hope to explore pre-dam flow conditions in the main stem of the river to help guide management of blockwater releases and inform the dam relicensing process. “That’s why we’re doing the science,” says O’Dowd, “to see how we can best help the recovery of these threatened fish species.”

To flush the fish downstream and help their outmigration, blockwater dam releases were conducted in 2012, 2014, 2015, and 2016. The most recent water release in May was based on recommendations from O’Dowd and Trush, along with input from various agencies and nongovernmental organizations.