When state water officials scaled back their mass dumping of water from the damaged Oroville Dam this week, they knew the riverbed below would dry up enough to allow the removal of vast piles of debris from the fractured main spillway.

But they apparently did not anticipate a side effect of their decision to stop feeding the gushing Feather River — a rapid drop in river level that, according to downstream landowners, caused miles of embankment to come crashing down.

With high water no longer propping up the shores, the still-wet soil crashed under its own weight, sometimes dragging in trees, rural roads and farmland, they said.

“The damage is catastrophic,” said Brad Foster, who has waterfront property in Marysville (Yuba County), about 25 miles south of Lake Oroville.

The farmer not only saw 25-foot bluffs collapse, but also lost irrigation lines to his almonds. “When the bank pulled in,” he said, “it pulled the pumps in with it. It busted the steel pipes.”

Officials at the state Department of Water Resources, which runs the dam, said Friday that they’re monitoring the river for erosion. But they declined to discuss the situation.

The department is already wrestling with the problem of endangered salmon becoming trapped in riverbed pools since the outflows at the dam were cut. The falling riverbanks, reported mainly in Sutter and Yuba counties, are just the latest outgrowth of the state being forced to quickly increase and decrease flows from the swollen reservoir since early February.

Back to Gallery Riverbanks collapse after Oroville Dam spillway shut off 13 1 of 13 Photo: Chris Kaufman, Special to The Chronicle 2 of 13 Photo: Chris Kaufman, Special to The Chronicle 3 of 13 Photo: Chris Kaufman, Special to The Chronicle 4 of 13 Photo: Santiago Mejia, The Chronicle 5 of 13 Photo: Santiago Mejia, The Chronicle 6 of 13 Photo: Santiago Mejia, The Chronicle 7 of 13 Photo: Chris Kaufman, Special to The Chronicle 8 of 13 Photo: Chris Kaufman, Special to The Chronicle 9 of 13 Photo: Chris Kaufman, Special to The Chronicle 10 of 13 Photo: Chris Kaufman, Special to The Chronicle 11 of 13 Photo: Chris Kaufman, Special to The Chronicle 12 of 13 Photo: Santiago Mejia, The Chronicle 13 of 13 Photo: Santiago Mejia, The Chronicle

























The crisis began last month when the main spillway, which moves water from the lake into the river below, inexplicably ruptured. Five days later, about 180,000 people had to evacuate when an emergency spillway was activated and then nearly failed, threatening to send a wall of water downstream.

The state has since brought down the lake level, using the damaged main spillway and taking advantage of a break in the wet weather. On Monday, dam operators reduced outflow on the main spillway from a robust 50,000 cubic feet per second to zero in a matter of hours. Just 2,500 cubic feet per second was left running from a small auxiliary outlet.

The farm communities around Yuba City, where much of the riverbank damage was done, saw the rapid drop in water the next day.

“Most of the time, they’ll give us three to five days, maybe even a week to lower the river,” said Phillip Filter, who’s been growing prunes, walnuts and peaches on waterfront property outside the town of Live Oak (Sutter County) for decades. “But what they did to this Feather River now is just ridiculous.”

He said he has nearly three quarters of a mile of bluffs along the river, and that most of it crumbled. Many of the trees and bushes that form a natural buffer between the water and his crops, sometimes spanning dozens of feet, fell into the now slowly running river.

With the vegetation gone, Filter worries his land is even more vulnerable to erosion once the water level bounces back.

“Our concern is that if it does come up again, it will get into our cropland,” he said.

His niece, Julie Filter, who lives nearby, lost a road on her orchard.

“Our tracks where we had driven have fallen off and are in the river,” she said.

State officials, in an email to The Chronicle, said the reduction in outflows from the dam was “managed in a way to reduce risk to levees.” The email said nothing about the riverbank, except that local government agencies were responsible for addressing any erosion because it was private property.

The eroded lands are within the Feather River’s floodplain. They’re generally located between the river and levees that are designed to allow flooding there, but not beyond. Owning land between the river and the levees comes with a certain amount of risk.

Yuba County’s emergency operations manager, Scott Bryan, who has surveyed the deterioration of the riverside, said he hasn’t seen anything like it.

“The landowners understand that the water will come up and do damage to their trees, but this is different,” he said. “This is actual loss of their land due to sloughing.

“I can’t tell you 100 percent it was because the Department of Water Resources allowed the water to drop too rapidly,” he said. “But it’s consistent with that.”

The quick draw-down of water also left chinook salmon and steelhead struggling to survive in isolated pools and puddles on the river’s edge. The fish, which migrate to the Pacific Ocean, were trapped as the main stem of the river swiftly shrunk.

Biologists and staff from the state Department of Fish and Wildlife and the Department of Water Resources have been mucking through the muddy shores in an extensive rescue effort that continued Friday.

Between Tuesday and Thursday, crews saved close to 1,900 trapped salmon and steelhead, including more than 1,700 juvenile fall-run chinook salmon, plus 1,500 to 2,000 fish of other species.

The state sent as many as 14 boats a day down the Feather River, each with four people equipped with high-resolution aerial photos to guide them to the isolated puddles and ponds, many 50 to 100 yards away from the river, hidden by thick mud and underbrush. They plan to carry on as long as they find fish, possibly through Saturday.

“Often they’re not accessible. It’s one thing to be looking at a map and one thing to be tromping through the mud,” said Andrew Hughan, a spokesman for Fish and Wildlife, who was on the scene.

Young salmon in the area had to be rescued weeks earlier when debris pouring into the river from the damaged spillway clouded up water in the Feather River Fish Hatchery 4½ miles downstream, endangering the lives of 8 million hatchlings. Those fish were too young to be released into the river, so the Department of Fish and Wildlife trucked most of them to another holding facility. Many were lost.

On Friday, state officials said lower water levels beneath the dam enabled crews to clear enough debris from the broken spillway to restart an idled hydroelectric power plant. Concrete debris in the river had caused water to pool near the facility, increasing pressure on the turbines and threatening to damage them.

The power plant also serves as a river outlet, which will provide dam operators another way to release water from the lake. The plant can release more than 14,000 cubic feet of water per second.

Kurtis Alexander and Tara Duggan are San Francisco Chronicle staff writers. Email: kalexander@sfchronicle.com, tduggan@sfchronicle.com Twitter: @kurtisalexander, @taraduggan