A 250 Ft. Wall of Water on the Trinity River Is Still a Big Threat
“If Oroville had overtopped, the surging water would’ve rapidly eroded the dam, ultimately unleashing a massive flood down the Feather and Sacramento Rivers.”
Trinity Dam has been a source of anxiety ever since Oroville Dam on the Feather River almost failed during the megastorms of 2017. Both are earth-fill dams, and both are vulnerable to overtopping.
“If Oroville had overtopped, the surging water would’ve rapidly eroded the dam, ultimately unleashing a massive flood down the Feather and Sacramento Rivers,” according to a press release from the California Water Network. “The same scenario applies to Trinity Dam, its downstream earth-fill sister structure, Lewiston Dam, the Trinity River, and the Lower Klamath River.”
“Trinity and Lewiston Dams actually pose a bigger threat than Oroville because they have such poor outlet structures,” said Tom Stokely, a Board Member of the California Water Impact NetFor a reservoir of Trinity’s size, said Stokely, “That’s completely inadequate – especially because a failure at Trinity would dump the water into Lewiston Reservoir, which would likewise fail, adding to the downstream flood.”
According to the U.S. Bureau of Reclamation, Stokely observed, “If Trinity and Lewiston Dams failed it would send a wall of water 250 feet high down the Trinity River and Lower Klamath River. You’d lose all the towns along the way – Lewiston, Douglas City, Junction City, Willow Creek, Requa – and all the homes and farms between them. Highway 299 would be destroyed. It would be a massive disaster.”
Stokely and other dam safety advocates first warned of the threat to the Trinity River’s dams during the spectacularly wet winter of 2017, when Oroville’s main and emergency spillways were eroded by exceptionally heavy rains and a high reservoir level.
“Unfortunately, nothing has been done to even evaluate possible remedies since then,” said Stokely. “Right now, Trinity Reservoir is more than 80% full, and we still have a lot of the winter left. We could see more atmospheric rivers, and we can expect continuing accumulating snowpack. With the reservoir this high, the nightmare scenario – a large snowpack followed by heavy warm rains that melt the snow, leading to an overtopped Trinity Dam – is possible.”
What’s making a bad situation worse, said Stokely, is the government response to the danger.
“By ‘government response,’ what we really mean is ‘no response,’” said Stokely. “Trinity County asked the Bureau of Reclamation [which controls Trinity and Lewiston dams] to provide the safety criteria the agency used to determine dam safety – how high the water in the reservoir must be before specific volumes of water are released, and so on. Reclamation refused to provide them. Also, Reclamation isn’t providing an early warning system, inundation maps and evacuation routes to the public for catastrophic dam failure.”
The threat to the Trinity system is likely to increase with ongoing climate change, said Stokely, citing a 2019 peer-reviewed study published in an earth sciences journal that concluded Trinity and Lewiston dams are particularly vulnerable to climate change-induced floods.
“And new research from the Scripps Institution of Oceanography recently concluded that atmospheric rivers are likely to play a more central role in California’s precipitation than El Nino and La Nina,” Stokely said. “What that means is reservoirs can rise dramatically from a single precipitation event. And if you have a nearly full Trinity Reservoir – as we do now –combined with multiple atmospheric rivers lined up one after the other – as we’ve seen in recent years – you end up with a very dangerous scenario.”
If the situation is bad now, continued Stokely, it’s only likely to worsen under President Trump, given his administration’s wholesale firing of government employees in essential public safety and science positions.
“The Clear Creek Tunnel that moves water from the Trinity River to the Sacramento River is down for repairs until April, further limiting water releases for dam safety,” said Stokely, “and right this very moment DOGE is gutting the National Oceanic and Atmospheric Administration, which tracks and provides critical hydrological and weather data. Similar cuts also are happening at Reclamation. We’re at a critical juncture – we need timely information, new operational plans and emergency notification for Trinity and Lewiston Dams that reflect climate change realities and public safety risk. Unfortunately, it seems highly unlikely any of that will happen.”
