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The Oroville DamAs many of you know, the big news on Tuesday was that the spillway on Oroville Dam had developed a large crater from water eroding away the Oroville Spillway structure.  Based on the large hole, DWR stopped all flows down the Spillway to evaluate the damage.  Water users downstream started to get nervous as Oroville was rising quickly, and folks feared that water could come over the emergency spillway, which would be uncontrolled.

So this might be time to back-up and offer some context.  Oroville is on the Feather River and holds about 3.5 million acre-feet.  It was about 80% full when this happened, and the operators were releasing about 70,000 cfs to make room for the storm that was on its way in.  Inflow into Oroville has exceeded 200,00 cfs in the past, and the levees downstream have historically started to be stressed at flows approaching the 100-year event, or about 150,000 cfs.  Thus, the strategy was to release enough water to make room to hold back the peak of the latest storm.  In other words, the reservoir was to function as intended.

As further context, we have also learned that both the Spillway and the emergency spillway are supposed to have been constructed on native bedrock, to ensure that erosion in a case like this could not travel back to the dam itself.  As you may also know, the dam is the tallest dam in North America and is an earthen dam.  Click here to view an image of the dam and the Spillway.  In this image you can see the Spillway running from the top to the bottom of the picture with the gates at the top.  If you look to the left of the gates you can see a concrete weir that runs for approximately 1700 feet.  That weir is the top of the emergency spillway.  It is a passive structure that kicks in only when water rises in the reservoir above the top of the weir, and then water runs down the hillside and connects back up with the river.

By Wednesday afternoon DWR had elected to run two tests of releasing 20,000 cfs through the Spillway to see what happened to the Spillway.  As you might expect, doing so resulted in additional erosion.  But the pictures after that test show significant additional erosion with huge sections of the Spillway gone.  Click here for the photo.  DWR then elected to increase the flows down the Spillway to 35,000 cfs, we believe to reduce the likelihood that water would have to flow over the emergency spillway during the incoming storm event.  As of late Wednesday DWR was also releasing approximately 13,000 cfs through the powerplant.

Unfortunately, on Thursday we learned that water could no longer be released through the powerplant.  Apparently the power lines served by the powerplant run across the Spillway and there was a risk that the erosion from the failing Spillway could erode the foundation of the towers supporting the power lines.  (If you look back at that last picture you can see the powerline towers just uphill of the erosion.)  As a result, by late Thursday DWR was releasing approximately 35,000 from the reservoir, with all water running through the Spillway.  We have also learned that inflow into Oroville is higher than anticipated, and as of Thursday afternoon was running at 185,000 cfs.  At that hour the reservoir was at 884.6 feet and rising at about a foot an hour.  The emergency spillway is set close to 901 feet. (Go here for the latest data on inflow and outflow.)

As of Thursday afternoon DWR had shared that it believes that no water will spill over the emergency spillway, although it is not clear to us that DWR has yet updated its modeling.  DWR had earlier shared that the peak of the storm would be Saturday and that it looked like no water would spill.  More recent data (higher inflow and reduced releases as a result of the powerhouse being shut down) suggests that water could start spilling on Friday evening.  However, DWR currently concludes that even if water were to spill from the emergency spillway, the flow would be lower than the design flow for the urban levees downstream for the storms forecasted for the next five days.

While there are lots of sources of information on this event, we hope to be able to share a collection of data and insights that bring it all together and make it all make sense.  Please check back for updates over the next few days.

Photo of Scott L. Shapiro Scott L. Shapiro

Scott Shapiro is known for his expertise in flood protection improvement projects throughout California’s Central Valley. He is helping clients with more than a billion dollars in projects in California’s Central Valley and issues involving the Federal Emergency Management Agency (FEMA) and the…

Scott Shapiro is known for his expertise in flood protection improvement projects throughout California’s Central Valley. He is helping clients with more than a billion dollars in projects in California’s Central Valley and issues involving the Federal Emergency Management Agency (FEMA) and the U.S. Army Corps of Engineers (USACE) throughout the Western United States.

With a special focus on massive flood protection improvement projects, Scott advises clients through regulatory, contractual, financing, and legislative challenges. Acting as general or special counsel, he regularly interacts with senior management at USACE (Headquarters, South Pacific Division, and Sacramento District), the California Department of Water Resources, and the Central Valley Flood Protection Board. He was named to the National Section 408 Task Force and has been invited to give testimony to the National Academies. Scott was instrumental in helping the first regional flood improvement agency that took a basin threatened by flood risk from less than 30-year level of protection to a level of protection approaching 200-year.

Having worked with FEMA on issues of floodplain mapping and levee accreditation for many years, Scott has developed collaborative environments in which he fosters win-win solutions for his clients. He is also currently serving as the lead counsel on a flood insurance rate map (FIRM) appeal and has drafted Federal legislation to modify the National Flood Insurance Program (NFIP) several times.

Scott is known throughout the region for his extensive litigation experience focusing on cases arising from levee failures. He has litigated levee failures resulting from underseepage, failed encroachments, and rodent burrows as well as briefing levee overtopping cases at the appellate level. Scott is one of the few attorneys with experience litigating flood cases on behalf of plaintiffs as well as defendant government entities.

Photo of Andrea P. Clark Andrea P. Clark

Andrea Clark specializes in water rights and flood control, serving as general counsel to a variety of public agencies from local reclamation districts and water districts to regional joint powers authorities.

Public agencies in the water and flood control fields rely on Andrea…

Andrea Clark specializes in water rights and flood control, serving as general counsel to a variety of public agencies from local reclamation districts and water districts to regional joint powers authorities.

Public agencies in the water and flood control fields rely on Andrea for her ability to explain in understandable terms the wide range of issues impacting them, including basic transparency laws (Brown Act and Public Records Act), public bidding and contracting, bond financing, the unique nature of joint powers authorities, and elections. She also regularly counsels clients on water transfers, Proposition 218 compliance, the California Environmental Quality Act, the National Environmental Policy Act, and financing strategies for major capital improvement projects.

With a special expertise in flood control and floodplain management, Andrea is regularly asked to speak on topics ranging from flood insurance to climate change and the future of flood control policy in California. Through her representation of clients in state flood policy and speaking engagements, she has forged strong relationships with key members of the flood control community in California.

Andrea also counsels private clients, including landowners and mutual water companies, on water supply matters, including proceedings before the State Water Resources Control Board, water rights determinations, and contractual disputes with Federal agencies.