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Home » News/Events » The Journal » Vol. 14 Issue 1 » Setback Levees Mute the Damage of the Oroville Dam Failure Scare

Setback Levees Mute the Damage of the Oroville Dam Failure Scare

  • Michael Rogner, Sacramento ValleySenior Biologist
  • Julie Rentner, River Partners Board Director

Flooding following the Oroville spillway disaster at our Messick Lake Restoration Project

In February 2017, the nation focused its attention on a flooding disaster… record snowfall in the Sierra Nevada, record rainfall throughout California, and the Oroville Dam Spillway was failing. The 24-hour news cycle continued airing scary footage of a massive eroding hole in the concrete spillway, and graphics illustrating the way that the emergency spillway (which had never been used before) was eroding the land below and possibly compromising the dam itself. This is the tallest dam in America. Its reservoir supplies the California Aqueduct with irrigation water for the San Joaquin Valley and municipal water for millions of Southern Californians. And it provides flood control for hundreds of thousands of downstream residents. It is a big deal. When evacuations were ordered for 188,000 Californians, we knew this event was serious.

Feb. 2017 Oroville Dam main spillway damage. (Photo: DWR)

Large flow releases were required to save the dam, and those releases caused significant damages to the river corridor downstream. This is part of the untold story behind the near catastrophe at Oroville. Naturally, the focus of the news coverage was on the human element: the congested evacuation of the city of Oroville, the horrific damage which would have been unleashed on communities downstream of the dam if it failed. Now, months later, high flows have gone down and we can evaluate what actually happened on the Feather River during these floods.

Years ago, flood managers at the Three Rivers Levee Improvement Authority (TRLIA) and California’s Department of Water Resources conceived and undertook the Bear River and Feather River Levee Setback projects. Eight miles of the existing levees were knocked down and rebuilt further from the rivers. This allowed floodwaters to safely expand across the historic floodplain where there was no longer any expensive infrastructure or homes. That’s why setback levees are built – to control where floods do and don’t occur. Opening floodplains downstream of Marysville means that there is less floodwater in the river when it hits Sacramento. Instead the water sits on the expanded floodplains where it doesn’t do any damage, in fact it does some good.

Inside the levee setbacks, River Partners and the TRLIA planted nearly 1,000 acres of riparian forest. Riparian forest is one of the most endangered habitat types in California. As our climate continues to change, forested riparian corridors will provide migration pathways for wildlife retreating into the mountains from the hot valley floor. The trees and shrubs that make up these native forests evolved with regular regimes of drought and flood. Their growth and regeneration is actually stimulated by flooding. Following the emergency flow releases in February, the restoration project site remained flooded through the first week of August. Aside from the road which needed repair, there was little damage. Contrast that with flood fights elsewhere where people lose their homes and their livelihoods. It is clear that giving our rivers room to flow is a sustainable method of reducing the pricetag of floods.

Due to the flow releases from Oroville, landowners have filed lawsuits about the amount of erosion it caused. But on our projects, we don’t mind erosion. In fact, we like it. It’s a natural function of all rivers. That’s what they do. They meander. They move. Trees eroded into rivers become critical habitat for juvenile salmon. Gravel washed downstream becomes a place for salmon to lay their eggs. The finer sediments (dirt!) become the building blocks of future forests.

Still, there are areas where erosion is a problem – like when it structurally undermines dams and levees. At the setback levee area, River Partners planted an erosion buffer along the edge of the new levee to reduce erosion, and it worked! Levee segments up and downstream of the project that do not have trees and shrubs growing around them were hammered by water erosion to the tune of millions of dollars of needed repairs. At the setback levee area, that erosion didn’t happen and the needed repairs are minor. The trees and shrubs actually helped to hold the levee in place.

As of July, our flooded site had a happy riparian forest. Robins, grosbeaks, and lesser goldfinches nested in the vegetation above the floodwater. Otters and osprey hunted for fish washed in by the floods. And the fish hid in the vegetation we planted years ago. This is how riparian systems are supposed to work. And recreating them, especially with the use of setback levees, is not only great for wildlife, but is also the key to our future flood safety.

The above article originally appeared in the Fall 2017 issue of the River Partners Journal.