On a recent day after a rainstorm, several dozen fall-run Chinook salmon trying to migrate upstream in Auburn Ravine found their progress frustrated. Efforts to complete their long spawning run from the Pacific Ocean were halted by a small dam on the outskirts of Lincoln.
Known as Hemphill Dam, for decades it has blocked fish from accessing more than 5 miles of potential spawning habitat in Auburn Ravine, a creek that runs from the Sacramento River into the Sierra Nevada foothills beyond Auburn. Only in very high flows can salmon manage to jump over the dam and carry on.
“There’s so many salmon pooling up at the bottom of the dam, and there’s so little water in there, that the salmon are just in there swimming back and forth,” said Jack Sanchez, president of Save Auburn Ravine Salmon and Steelhead, a nonprofit group working to restore the creek. “It’s very frustrating because the salmon are here and we can’t get them over the dam.”
Fixing such impediments is considered crucial to the survival of Central Valley fall-run Chinook salmon, particularly as water temperatures warm due to climate change. The fish need better access to cold, high-elevation water cut off in prior decades by major water storage projects, like Folsom Dam on the American River.
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The Nevada Irrigation District, which owns Hemphill Dam, has been working with Sanchez’s group for several years on a plan to modify the dam for better fish passage.
Relatively simple fixes at small dams can open up many miles of habitat to wild-spawning salmon. These fish serve as an important buffer against the negative effects of hatchery salmon production. Studies have shown that salmon produced in hatcheries have less genetic diversity and are less able to withstand environmental strain such as drought, disease and low water flows.
“It’s been on my priority list for a number of years now,” Michael Healey, a fisheries biologist at the California Department of Fish and Wildlife, said of Hemphill Dam.
The Hemphill Dam, about 100 feet across and 6 feet high, was built in the 1920s and diverts water from the ravine into Hemphill Canal, which delivers irrigation water to rural properties in the Lincoln area.
The dam allows water to flow downstream into Auburn Ravine in a narrow band – only about a half-inch deep – across its entire width. This is too narrow for fish movement. Last year, the district spent $20,000 to install new stainless steel panels to shunt more water toward one side to create a deeper channel of water, in hopes this would create an easier path for fish.
This year, the district planned to spend an additional $50,000 to build a fish passage channel out of boulders downstream of the dam. Sanchez said the district waited too long to seek a required streambed-alteration permit from the Department of Fish and Wildlife, and the project didn’t get built in time for the salmon run.
Healey, at the Department of Fish and Wildlife, said the permit application was submitted to his agency on Nov. 3. By then, the salmon run was already underway. The permit is pending and may still be approved, he said. But such permits generally forbid working in streams when fish are present, which is likely to be the case for the rest of this year.
Remleh Scherzinger, general manager at Nevada Irrigation District, said his agency is “fully engaged” in trying to help salmon navigate the dam.
“We are aware that there is a fish passage concern there,” Scherzinger said. “It is not a barrier to passage, but it does pose a problem. We need to be good stewards, and we need to do the appropriate permitting. There are a lot of players to get to the table.”
In 2012, the district spent $1 million building a fish ladder at the Lincoln Gauging Station, a smaller structure downstream that also blocked fish movement. This was successful, allowing salmon to swim as far as Hemphill Dam under most flow conditions.
“I think that demonstrates our commitment to a solution,” Scherzinger said.
Yet other questions surround Hemphill Dam. The Placer County District Attorney’s Office is conducting an investigation into the dam, although officials won’t say why. Scherzinger said he was unaware of the investigation.
“Because the investigation is ongoing, it would be inappropriate to comment on any facts surrounding the investigation,” Assistant District Attorney Jeffrey Wilson told The Bee, via email.
Sanchez said it may be related to repairs made to Hemphill Dam in the 1980s, after a flooding event.
Scherzinger said the federal government approved the work and also provided grant funding.
“Those modifications were done under federal authority,” said Scherzinger, who did not work for the irrigation district at the time.
Adding some urgency to the situation, Healey last year completed a salmon survey in Auburn Ravine, which revealed a surprise. The survey found numerous juvenile winter- and spring-run Chinook salmon, both of which are endangered species, unlike the fall run. He suspects the endangered salmon were born in other streams and swam up Auburn Ravine from the Sacramento River, in search of safety and food, before completing their downstream migration to the ocean.
“It shows these smaller tributaries are probably providing some pretty good rearing habitat for some of these endangered fish,” Healey said. “And little is known about that.”
Call The Bee’s Matt Weiser at (916) 321-1264. Follow him on Twitter @matt_weiser.