John Hart Dam muscles up for a major earthquake
Why and how we're strengthening an 80-year-old dam on the Campbell River
Grizzlies stuff themselves with berries and salmon in the lead-up to the hibernation they know is coming. Olympians train for their big day in the spotlight with a set date (and often a set hour) very much in mind.
But how do you plan to fortify dams for an earthquake that could happen today, in 20 years, or several centuries from now? The march of geologic time is achingly slow… until it isn't.
You can't predict when the earthquake will happen. While the last magnitude 8-plus earthquake in B.C. was off the coast of Vancouver Island on January 26, 1700, there's no way of knowing when the next will occur. All you can do is figure out the risks to dams that a major earthquake poses in one of the planet's most rambunctious seismic zones – the so-called "ring of fire" around the edges of the Pacific Ocean – then upgrade the dams at greatest risk.
One of the dams we're focusing on is the nearly 80-year-old John Hart Dam, the biggest of three dams on the Campbell River. It's located just a six-minute drive upstream from the town of Campbell River and also supplies drinking water to the town and spawning habitat for fish in an area known as the Salmon Capital of the World.
"A major earthquake occurs about every 500 years on average, and the range is between 300 and 800 years between events," says our senior stakeholder engagement advisor Stephen Watson. "We're now into that range, so we're doing the work so that the John Hart dam can withstand that severe shaking while continuing to safely continue to pass water downstream."
Over the past 10 years, we've replaced the downstream generating station at John Hart to meet seismic standards, maintain reliability, and protect fish habitat, and we're now in the process of completing the rebuild of the dam itself. Once completed, the dam will be able to withstand a 1-in-10,000 year event, a severe earthquake of magnitude 9.0 or stronger.
Started in 2023, the six-year John Hart Seismic Upgrade Project is part of our recently announced $36 billion, 10-Year Capital Plan to sustain and upgrade existing assets including B.C.'s valuable network of dams, transmission lines, and substations.
We lean on tech and a whole lot of rock to brace for The Big One
Originally built in 1947, the John Hart dam was designed with seismic considerations based on what information we had at the time. We now we have a much better understanding of the risks posed by earthquakes in what’s known as the Cascadia Subduction Zone.
Today's upgrades – mainly through "widening" of the dam base through the addition of upstream and downstream berms, and insertion of an additional water seepage barrier in the dam itself – are designed to bolster the ability of the dam to withstand the severe shaking of a quake.
The project will also include permanent flood and flow upgrades, notably a new overflow spillway below the road deck on the top of the dam and the replacement of three spillway gates and related works, such as the hoist system, so that the dam can safely and more reliably pass water downstream after an earthquake.
In his more than three decades with BC Hydro, Watson has seen a lot of impressive projects, including the construction of a massive new underground power station at John Hart. But he says he’s never seen anything quite like the process to insert a new water seepage barrier into the heart of the existing earthfill dam.
Completed this past spring, the new concrete wall is a metre wide, up to 37 metres deep, and over 100 metres long, and is designed to retain water within the John Hart Reservoir. It acts as a back-up wall to the existing wall within the dam.
"Observing this upgrade project and the unique equipment used was fascinating," Watson told the Campbell River Mirror in May. "Essentially, they completed concrete panels by excavating downward through the earthfill dam to the bedrock below, and as they excavated, the material removed was replaced with clay bentonite mix so the integrity of the excavation was maintained. Once the excavation was complete, a pipe was lowered down through the clay bentonite to the bottom, and then concrete pumped in pushed the clay bentonite out, leaving a nice concrete panel.
"This process was replicated over a hundred times, and the panels now provide one cohesive wall."
The addition of the massive earthfill berms, especially the one upstream of John Hart's middle earthfill dam, has been no less impressive. Massive amounts of organic material at the dam's base, including organic material such as stumps and other debris, are being removed by a dredge on a barge, then replaced with compacted rock. It's estimated that the combined amount of material being moved in and out of the reservoir for the berm work adds up to more than 750,000 cubic metres.
All that work on the upstream berm stirs up and muddies the water. To protect the reservoir's water quality for domestic water use and for fish, the impacted area is cordoned off by double silt curtains, anchored to the bottom of the reservoir by chains.
When completed, new and/or upgraded spillway gates on all three dams in the system will allow improved flow regulation in the event of a major earthquake.
"After a major earthquake, we'd need to lower the reservoir level upstream of Strathcona dam," says Watson. "Strathcona, Ladore and John Hart will all have their spillway gates upgraded so that we can safely pass water out of the system downstream."
Smaller earthquakes act as constant reminders to Campbell River residents
Each year, about 400 earthquakes are detected in the region stretching from Seattle to the north end of Vancouver Island, and about a dozen are felt by the area's residents. In July, a 5.7 magnitude quake off the Pacific Coast was part of a cluster of nine earthquakes – all of a magnitude of 4 or greater – in the region.
We work with the City of Campbell River and the Strathcona Regional District on earthquake awareness, and the city runs a role-playing earthquake evacuation exercise as part of the B.C. Great Shakeout earthquake drill, which occurs again on October 17, 2024.
"Basically, the warning is that if an earthquake is strong enough to knock you down, you need to get to higher ground if you're in the evacuation area downstream from the dam," says Watson. "In a worst-case scenario, water could arrive in an hour. That's why we're constantly working on the reliability of our dams, public safety, and the protection of the community downstream."
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