Water & Drought

Oroville Dam: Farmers blame sudden spillway shutoff for eroded riverbanks

For three generations, Phillip Filter’s family has tended orchards that grow on a shelf of floodplain above the Feather River.

Because the trees stand between the river and a major flood-protection levee, Filter’s family is no stranger to floods that sometimes spill over the river banks, inundate the orchards and then recede back into the channel below.

But Filter has never seen damage to the riverbanks like what happened last week after the state suddenly shut down flows from Oroville Dam’s badly damaged spillway upstream.

For miles along the channel, huge chunks of the river’s banks collapsed into the water, toppling wild cottonwood, oak and black walnut trees. Filter said neighboring farmers lost irrigation pumps into the river. Roots from some of Filter’s orchards are now dangerously close to the gaping wounds in the river bank.

“We have no protection now,” he said.

Last week, over the course of a few hours, state officials dialed back releases from the spillway from 50,000 cubic feet per second to zero in order to give heavy-equipment crews a chance to begin dredging out the massive piles of debris that formed below the fractured concrete chute. As the river went from raging floodwaters to languid flows more akin to summer in a matter of hours, thousands of fish, including some endangered and threatened Chinook salmon, became stranded in low spots between the levees. Teams of biologists spent last week in boats trying to rescue as many fish as they could find.

State officials said speed was important, but they did their best to protect fish and the levees that line the river. The fear was that cutting back flows too suddenly could cause levees to slump or sag if the earthen material wasn’t given time to firm up.

For the major flood-protection levees, the strategy appeared to work. No significant problems were reported along the miles of levees that protect communities such as Oroville, Marysville, Live Oak and Gridley from flooding.

Between those levees, the state isn’t conceding that it is to blame for the slumping riverbanks.

“I don’t think we can say for sure that’s why the riverbanks eroded,” said Lauren Bisnett, a spokeswoman for the Department of Water Resources, which operates Oroville Dam.

She said almost a year’s worth of water gushed through the channel over the past two months, and “it’s not unusual to see erosion under those conditions.”

Whatever the cause of the riverbank erosion, the state’s efforts to reduce flows from the spillway to remove debris appear to be paying off. As of Monday morning, crews had removed some 427,000 cubic yards of rocks and debris from below the spillway. That allowed for Oroville Dam’s power plant to switch back on Sunday.

The power plant is considered vital to the state’s efforts to operate the troubled dam through a wet spring.

When fully operational, the plant is the reservoir’s primary outlet outside of the flood season. The hope is the releases from the plant can accommodate spring runoff and allow for repairs on the battered spillway. An enormous gash was spotted in the structure Feb. 7, prompting a temporary shutdown of water releases as a major storm rolled in. Water eventually rolled over an adjacent emergency spillway. Officials ordered the two-day evacuation of 188,000 downstream residents when the emergency structure nearly failed.

Filter, the Live Oak farmer, said he appreciates the unprecedented and dangerous situation the state is in. But looking out Monday over the mangled river bank and the downed trees – some of them oaks nearly a century old – he said he wishes the state would have shut down water flows from the main spillway more gradually. He worries bigger chunks of the riverbank will collapse in the next round of storms, bringing down some of his valuable trees with them.

“That’s the risk you take (farming) between the levees,” he said. “But this isn’t normal.”

Ryan Sabalow: 916-321-1264, @ryansabalow

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