SACRAMENTO, Calif. – A U.S. Army Corps of Engineers program to improve salmon habitat by placing spawning gravel in the Yuba River is working, say researchers evaluating the program.
Biologists with the Pacific States Marine Fisheries Commission found in underwater surveys from September 2011 through January 2012 that Chinook salmon have created dozens of nests, or redds, with gravel the Corps placed in the river below Englebright Dam.
The gravel project is also intended to provide spawning habitat for Central Valley steelhead trout. Both species are listed as threatened by the National Marine Fisheries Service.
Completed in 1941 to trap sediment from upstream hydraulic mining, Englebright Dam also blocks gravel in the Sierra Nevada from traveling downstream to become spawning habitat. A biological opinion issued by the National Marine Fisheries Service in 2007 called for gravel placement as part of a broader plan to improve habitat near Englebright and Daguerre Point dams, both operated by the U.S. Army Corps of Engineers Sacramento District.
The district placed 500 tons of gravel in the river in 2007 as a pilot project, and finished placing another 5,000 tons in January 2011.
The program was designed by Dr. Gregory Pasternack, hydrology professor at the University of California - Davis.
“One of the effects of dams is to block the natural supply of gravel that would come out of the mountains,” Pasternack said. “So we then have to augment that and provide that material for [fish] below the dam.
“Once we identified that the section of the river immediately below Englebright Dam was the most important for helping the run that’s most at risk, the spring run of Chinook salmon, we had the reach that we wanted to focus on,” he said.
After an initial survey of the river canyon, Pasternack identified where in the river the gravel should be placed, and has been working to map where that gravel has moved to help determine where future injections would provide the most benefit.
Stitching together photos of the river canyon, his research team is creating a virtual 3-D model of the reach to better predict how water flow will move the gravel. Pasternack’s research and the model will guide placement of another 5,000 tons of gravel in the river later this year, as funding becomes available. The plan calls for a total of 15,000 tons.
Meanwhile, PSMFC biologists continue to study how fish are using the gravel. Snorkeling the river, they inventory redd locations with GPS coordinates, accurate to within half a centimeter. Though it’s early to make any judgments about the overall effectiveness of the program, PSMFC program manager Duane Massa said, “As far as we can tell, those gravels are being utilized by Chinook salmon.”
Englebright Dam manager, Doug Grothe, said he’s encouraged by the results.
“It’s really exciting to see this,” Grothe said. “The Corps of Engineers has historically been flood control, debris management, navigation programs.
“The Corps is now stepping into a phase of environmental stewardship. It’s very important to all of us,” Grothe said. “And it’s just a really neat thing to be able to help a species…maybe not be an endangered species anymore.”