Dam Failure Case Study: Hawkins Dam (Washington, 2014)

DamFailures.Org is an ASDSO project that provides individual dam failure case studies and lessons learned as a resource for dam safety engineers, dam operators, owners, regulators, managers, academia and students to help prevent future incidents.

On Thursday, August 21, 2014, the fire-swept Benson Creek watershed received from 0.4 to 0.9 inches of rain in one hour - about a 5-year event. There were high runoff flows and numerous mudslides throughout the watershed. As a result of this flooding, Hawkins Dam failed through headward erosion in its emergency spillway. Subsequent analyses showed that due to the fire, the soils of the watershed had greatly reduced infiltration parameters (hydrophobic soils), resulting in post-fire runoff flows on the order of 7 to 8 times the estimated pre-fire flows for the same rainfall event. It was estimated that the post-fire runoff flows from the August 21 5-year storm exceed the estimated pre-fire runoff flows from a 1,000-year storm event.