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City Light Dams and Safety

With the severe damage recently caused to the spillway feature of California’s Oroville dam, which forced 188,000 people to evacuate, we spoke with Chief Dam Safety Engineer Kim Pate, who shared insight on City Light dams, their structures and emergency protocols.

Can you explain what happened with Oroville?

The best way to get up to date information from Oroville is to refer to the California Department of Water Resources web site at California Governor Brown is providing updates and transparency to this incident and assessment.

How are City Light dams different/similar to Oroville?

Every dam is different. There are some generalities, but every dam is different in how they operate and how they’re constructed.

Most City of Seattle dams are concrete, except for South Fork Tolt which is an earthen embankment dam like Oroville, though the Tolt is about a third of the size and height. The issues with embankment dams are different than concrete which means we look at different information; not necessarily more or less significant, just different areas to watch.

Tolt also has a different type of spillway—a Morning Glory—which is a big round piece of concrete situated in the reservoir upstream of the dam and not on the face of the dam. When in service, the water pours in like a drain and comes through the concrete channel.

The other difference is that our dams don’t have anything like Oroville’s emergency spillway. We can’t rely on something like that, so we must keep a close eye which means our equipment is well-maintained. In fact, our Morning Glory spillway is going through a rehabilitation this summer just to improve the hydraulics of its lifting and lowering. It’s fine now, but it’s a step to ensure we’re increasing the reliability of our equipment.

We have numerous individual inspections at our projects, and in fact our City crew walks the project daily for a visual inspection.

What procedures does City Light have in place in case of a situation like this?

We have established a comprehensive Emergency Action Planning (EAP) process in concert with our regulators. This includes an annual process review and exercises to test the functionality of the program.

It’s important that people know that monitoring our dams is a daily routine. Our staff is constantly around these dams. If there’s any subtle changes—doesn’t have to be major—we’re actively looking from a civil, mechanical, electrical, operational point of view.

The important thing with an EAP is that it’s not just City staff who can activate it. If anyone sees something unusual they have the power to activate the EAP by contacting their emergency management agency, their local sheriff’s department or even their Mayor’s office. We also have annual meetings with the city of Carnation (located near Tolt) which is built around our emergency action plan. It’s a time where residents can ask us anything they want. We work closely with them. We even have an emergency siren that goes off once a month to check on it. The schools, the city halls, the whole region is very engaged in understanding our Tolt project.

For further information on City Light dams, consider a tour. Kim also suggests visiting FERC for up-to-date information about other projects and resources.