Just ahead of spring rains, Seattle City Light and Puget Sound Energy met Federal Emergency Regulatory Commission licensing requirements to hold dam safety exercises by conducting exercises in March that simulated responses to a 100-year flood event and an earthquake in Washington.
Skagit County Public Works said the simulation involved a dam failure occurring at Diablo Dam about four days after a magnitude 5.8 earthquake. The flood event affected the Skagit River, causing a failure at PSE’s West Pass Dike, which is located southwest of Diablo Dam near Concrete.
Seattle City Light owns Diablo Dam, which is part of the 129-MW Diablo hydroelectric project on the upper Skagit River in Whatcom County. Diablo Dam is a 396-foot-tall concrete arch-gravity dam that impounds Diablo Lake. It is part of the Skagit River Hydroelectric Project that supplies energy to Seattle.
PSE owns West Pass Dike, a 115-foot-high earth and rockfill saddle dam near the right abutment of Upper Baker Dam, which PSE also owns. Upper Baker Dam, part of the 91-MW Upper Baker hydropower project, is a 297-foot-high, high-hazard concrete gravity dam that impounds a 285,500-acre-foot reservoir, also in Whatcom County.
Flooding from dam failures could affect several Skagit County communities: Burlington, Mount Vernon, Conway, Bow, Edison and La Conner.
“We’re testing out what needs to be done in an emergency of this magnitude,” said Akiko Oda, PSE spokeswoman. Knowing such information is important for emergency responders to determine where residents should be directed to evacuate.