Report: Design, construction and maintenance of Oroville Dam are flawed
April 18, 2017
• UC Berkeley report details problems
• “The origins of the gated spillway failures are deeply rooted”
As work starts on a quarter of a billion dollars worth of repairs to Oroville Dam’s spillways, a new report from the Center for Catastrophic Risk Management at the University of California, Berkeley, says the dam’s design, construction and maintenance are flawed.
The state Department of Water Resources has refused to release details of the bids to repair the spillways, claiming it’s an issue of national security, but UC Berkeley engineering professor R. G. Bea, founder of the Center for Catastrophic Risk Management, has examined current publically available photographic and written documentation about the dam’s gated spillways to ascertain what he calls the “root causes” of February’s spillway failures.
“The origins of the gated spillway failures are deeply rooted in pervasive design defects and flaws developed by the California Department of Water Resources,” he writes.
Design defects and flaws
1. Spillway base slabs of insufficient thickness for the design hydraulic conditions: 4 to 6 inches thick at minimum points;
2. Spillway base slabs not joined with “continuous” steel reinforcement to prevent lateral and vertical separations;
3. Spillway base slabs designed without effective water stop barriers embedded in both sides of joints to prevent water intrusion under the base slabs;
4. Spillway base slabs not designed with two layers of continuous steel reinforcement (top and bottom) to provide sufficient flexural strength required for operating conditions; and
5. Spillway base slabs designed with ineffective ‘ground’ anchors to prevent significant lateral and vertical movements.
Construction Defects and Flaws
The design defects and flaws were propagated by DWR during construction of the spillway, he writes. These construction defects and flaws included the following:
1. Failure to excavate the native soils and incompetent rock overlying the competent rock foundation assumed as a basic condition during the spillway design phase, and fill the voids with concrete, and
2. Failure to prevent spreading gravel used as part of the under-slab drainage systems and ‘native’ soils to form extensive 'blankets' of permeable materials in which water could collect and erode.
Maintenance Defects and Flaws
“The design and construction defects and flaws were propagated by DWR during maintenance of the spillway. These maintenance defects and flaws included the following,” he writes.
1. Repeated ineffective repairs made to cracks and joint displacements to prevent water stagnation and cavitation pressure intrusion under the base slabs with subsequent erosion of the spillway subgrade; and
2. Allowing large trees to grow adjacent to the spillway walls whose roots could intrude below the base slabs and into the subgrade drainage pipes resulting in reduced flow and plugging of the drainage pipes.
Mr. Bea says that by the time of the February spillway releases, the gated spillway had become heavily undermined and the subgrade eroded by previous flood releases. “The first spillway release completed the undermining of the spillway slabs, allowing water cavitation and stagnation pressures to lift the ‘weak’ slabs and break them into pieces,” he says.
“After the almost catastrophic water release over the un-surfaced Auxiliary Spillway, the subsequent water releases down the gated spillway propagated the initial spillway breach until spillway releases ceased,” Mr. Bea says.
“A key question that can not be answered at this time is: ‘why did DWR and the responsible state and federal regulatory agencies (California Water Commission, Federal Energy Regulatory
Commission) allow these root causes to develop and persist during the almost 50 year life of the gated spillway,’” he says.
Mr. Bea says even if the Oroville Dam was designed and built to the standards of the time, today’s standards are tougher and it doesn’t meet them.
He also says the gated spillway failed in February during discharges that were much less than the design conditions.
He says his experiences with investigations of failures of the New Orleans hurricane flood protection system during Hurricanes Katrina and Rita “leads to a conclusion that it is likely that the wrong standards and guidelines are being used to requalify many critical infrastructure systems for continued service.”