Spillway failure is third serious incident at Oroville-Thermalito complex

The failure of the lower part of the Oroville main spillway is the third serious incident at the Oroville-Thermalito complex. The causes of the incidents were all related to conditions previously noticed as safety violations by the Federal Energy Regulatory Commission’s Division of Dam Safety and Inspections.   The three incidents indicate serious maintenance issues at the Oroville facilities.

In 2007, a site inspection by John Onderdonk, chief of FERC’s San Francisco Regional Office of Dam Safety and Inspections, found three safety violations related to the later incidents. These were the items in Onderdonk’s letter to DWR:


  1. The bolts and nuts that secure the river valves to the pipe flanges were observed to be rusty. This item was also on the 2006 follow-up letter and your plan and schedule calls for the repair to be finished by November 2, 2007. […]

8. Small areas of spalling damage of the concrete on the floor of the spillway were noted during the inspection. By December 3, 2007, please provide a plan and schedule to repair areas on the spillway where the concrete has been damaged.

9. During the inspection, Mr. Onderdonk inquired when the last time that the spillway drainage system has been cleaned out and he was informed that it has been many years. There are a series of vertical clean outs located on each side of the service spillway. By December 3, 2007, please provide a plan and schedule to clean out the spillway drains.


  1. A five-gallon container of oil was found on the floor in the powerplant. By December 3, 2007, please provide a plan and schedule to remove the oil container or provide secondary containment for the container.  […]

These safety violations presaged 3 serious incidents:

  1. In 2010, five workers were injured in the river tunnels when a 6′ tall, 10′ wide steel panel with rusted bolts flew off during a test.
  2. In 2012, a fire destroyed the Thermalito Power Plant, caused by a relay short-circuit and an unknown source of fuel.
  3. In 2017, the main spillway developed a large crater.

Details of Incidents

  1. Rusty bolts in river tunnels

In July 2009, during a test of the river tunnels, a large steel panel flew off during a test in the river tunnels injuring five workers, one seriously.  As reported by Toni Scott in the Chico Enterprise-Record, the cause was corroded bolts:

Shortly after the valves were opened, a 6-foot-tall, 10-foot-wide steel panel near the employees collapsed, sending flying debris toward the workers and creating a vacuum-like force that pulled them toward a tunnel carrying water out of the dam.

The investigation also found that DWR failed to properly maintain the collapsed steel panel, finding that the bolts securing the non-structural panel to the wall were corroded and that the panel “was never inspected for integrity or safety for over 40 years.”

A foam sealant had been placed where the bolts had corroded, “indicat(ing) knowledge of corrosion and failure of the bolts and the seal of the door,” the report reads.

2. Five gallon container of oil on floor of powerplant

In 2012, the Thermalito Pumping Plant has a major fire. According to a presentation by DWR’s staff to an engineering conference, the fire cost an estimated $90 million in cleanup and $75 million in repairs.


The results of the forensic investigation of the cause of the fire were reported in Hydroworld.com. The investigation determined that a short-circuit in a relay was responsible, but lab controlled experiments were unable to recreate the ignition. The relay engineers said there were two possible additional causes:

  • An unknown source of fuel was available that could be and was ignited; and
  • The actual circuit No. 19 fault produced far more thermal energy than was generated during testing.

Forensic expert Mark Schafer, of Electro-Mechanical Recertifiers, also identified other contributing factors, including: aged cables, mixed voltages and over-stacked cables in the cable trays, a lack of fire stops between elevations, an inoperable dry chemical fire extinguisher cart, and combustible materials such as plant schematics and additional historical items printed on large paper sheets stored within the plant.

Two months before the fire, Mark Cowin, the Director of the Department of Water Resources had told the Metropolitan Water District Board that DWR no longer had the appropriate financial resources to operate and maintain the aging SWP facilities.

According to the State Water Project financial statements, the life of the equipment in the State Water Project power plants and pumping plants is 30-50 years.  The Thermalito pumping plant will be 50 years old in 2019.

lifetime table

3. Spalling damage to spillway chute and drains not cleaned out

FERC’s San Francisco office of Dam Safety and Inspections had to remind the Department of Water Resources in August 2008 that the repairs for the main spillway chute were needed.

An investigation by DWR in 2008 of the main spillway chute showed that the concrete surface had more extensive damage than just the “small areas of spalling” noticed by John Onderdonk in 2007.  The bid summary in 2009 shows that the main spillway chute needed 10,000 linear feet of sawcutting one inch deep, and 83 cubic yards of void repair. The chute also needed 3,900 linear feet of major crack repair, as well as 23,700 linear feet of contraction joint repair.

Although the letter from FERC requested Department of Water Resources to submit a followup report on the main spillway chute repair, California Water Research could not locate any report about the repair in DWR’s public FERC filings.  As previously reported by California Water Research, the Bureau of Reclamation’s Guide to Concrete Repair recommends investigation of the causes of cracks in concrete hydraulic structures.

This post was updated on April 10, 2015 to include information about the expected lifetime of facilities.

2 thoughts on “Spillway failure is third serious incident at Oroville-Thermalito complex

  1. This makes me mad , that with all them knowing this, did not say one thing about it. Also, what I’ve heard by a reputable source, the reason it’s taking so long to repair the spillway is fact that they have too much gold ,to bury it back up. So what is really going on.

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