Dam Failure Case Study: Oroville Dam (California, 2017)

The Oroville Dam spillway incident was caused by a long-term systemic failure to recognize and address inherent spillway design and construction weaknesses, poor foundation bedrock quality, and deteriorated service spillway chute conditions. This systemic failure involved practices of the owner, its Federal and state regulators, its consultants, and the United States dam safety industry, and therefore the incident cannot reasonably be “blamed” mainly on any one individual, group, or organization.

During service spillway operation on February 7, 2017, water injection through both cracks and joints in the chute slab, and associated transmission of stagnation pressure under the slab, resulted in uplift forces beneath the slab that exceeded the uplift capacity and structural strength of the slab, at a location along the steep section of the chute. The uplifted slab section exposed the underlying poor quality foundation rock at that location to unexpected severe erosion, resulting in removal of additional slab sections and more foundation erosion.

Responding to the damage to the service spillway chute necessitated difficult risk tradeoffs while Lake Oroville continued to rise. The resulting decisions, made in the face of substantial uncertainties and differences of opinions, allowed the reservoir level to rise above the emergency spillway weir crest for the first time in the project’s history, leading to severe and rapid erosion and headcutting downstream of the weir and, ultimately, an evacuation order for about 188,000 people.