Seismic hazard at Jordan River
Study shows Vancouver Island dam has highest seismic hazard in BC Hydro's system
On December 5, 2014 BC Hydro released the results of a six-year, peer-reviewed, seismic hazard study of all regions in B.C. where our 79 dams are located. The study revealed that the expected ground motion at Jordan River in an extreme earthquake event — an 8 to 9 magnitude earthquake — is much greater than previously thought due to its proximity (about 40 kilometres) to the Cascadia subduction zone.
- Dam Safety at BC Hydro booklet [PDF, 10.7 MB]
- FAQ: Questions & Answers from public meeting at Jordan River
Located on the west coast of southern Vancouver Island, the Jordan River system is at the highest seismic hazard within BC Hydro's system. It's three times higher than that of the Lower Mainland, and about double the ground motion hazard of the Campbell River system. This is a very significant change in our understanding of the seismic hazard.
As Vancouver Island is a known seismically active region of the province, BC Hydro had already taken steps to upgrade the Jordan River Diversion Dam, most recently in the early 1990s. As a result, the dam is now one of the more robust dams in B.C.
Technical challenges thwart effective upgrades or replacement of dam
This new study shows that further upgrades or replacement of the dam would be needed to meet guidelines for the required higher level of seismic stability.
BC Hydro is not confident that such upgrades would be technically feasible for the Jordan River Dam. A second upstream dam, the Elliot Dam, would also require upgrades, but these are considered feasible due to the dam’s design features.
However, BC Hydro is not aware of any dams in the world that are built to withstand the ground motions expected in the Jordan River system as the result of a massive subduction zone earthquake.
Other options: Lowering water level or decommissioning of dam
BC Hydro also explored the possibility of lowering the reservoir behind the dams, concluding that this would significantly reduce the ability to produce power and require the construction of more transmission lines to serve southern Vancouver Island, at an estimated cost of $100 million to $200 million.
The option to decommission the dams was also reviewed, but would be highly costly, and would create a gap in our supply that would need to be filled through another source of energy. BC Hydro’s concerns include:
- Energy sources such as wind and run-of-river provide intermittent power that will be inadequate to meet peak-use demand.
- A natural gas generation option would be limited by pipeline and storage constraints, high costs, and siting and permitting challenges.
- Removal of the dams would put residents, campers and business operations downstream at much higher flood risks.
The safest course of action
The highest risk is to permanent residents or others who may be staying overnight downstream from the Jordan River Dam in a home or in a campground. They would have less ability to respond quickly to a major event.
BC Hydro is working with the Capital Regional District to improve emergency preparedness and awareness of seismic risks, including the potential to restrict future residential development and overnight camping. BC Hydro will also support the Capital Regional District should it wish to explore the potential of installing a warning siren.
Jordan River earthquake evacuation map [PDF, 934K]
We are also in communication with First Nations representatives to discuss this plan and to better understand their interests.
BC Hydro does not believe that restrictions on day-use activities are needed, given the available response time to evacuate the area. Surfing, hiking or logging activities, for example, should continue as before.
Residents living in Jordan River but outside of the evacuation area will not be affected by any release of water from the dams. But they need to understand the elevated seismic risks for this region of Vancouver Island, and make plans for their safety in a seismic or tsunami event.
BC Hydro offer to purchase nine homes
BC Hydro has offered to purchase the nine residences in the evacuation zone. Our goal is to work with each property owner over the coming weeks, and to continue our discussions with all affected residents and other parties in the area to get a full understanding of the situation and to explore other potential solutions.
We appreciate this is very challenging for homeowners, and BC Hydro will do everything it can to be sensitive to their needs. We recognize that homeowners need time to consider all information.
About the Jordan River system
The Jordan River system comprises the Bear Creek, Elliott and Jordan River Diversion dams, including a generating station. This system represents approximately one-third of BC Hydro generating capacity on Vancouver Island.
BC Hydro's generating capacity on Vancouver Island can only meet about 20 percent of the Island's total demand. About 80 per cent of the electricity to power the Island comes from the mainland through underwater cables.
The Jordan River system, which primarily serves greater Victoria, provides about 10 per cent of the electrical supply for Vancouver Island. However, the generating station does not run continuously, but only as needed to meet the peak-use times, when demand for electricity is very high.
Power from Jordan River also helps to support the Vancouver Island grid when there are outages in our transmission system.