Coastal communities around Greater Victoria are being encouraged to review their emergency plans as an unusual combination of ocean conditions raises concerns about flooding along parts of British Columbia’s coast. A Kelvin wave associated with El Niño is expected to push sea levels higher, adding to the potential risks when combined with seasonal king tides, winter storms and storm surges. So, what exactly is a Kelvin wave? Environment and Climate Change Canada research scientist Bill Merryfield explains that it is a pulse of elevated ocean water created by changes in Pacific trade winds. It travels across the ocean before reaching the B.C. coast, temporarily raising sea levels. While the increase may not be noticeable during an ordinary walk along the waterfront, even a relatively small rise can make a significant difference when several coastal hazards occur at the same time. Merryfield says the current El Niño event is exceptional. “We’re seeing an El Niño event that is unlike and stronger than any that has been experienced by anyone who is living today,” Merryfield said. El Niño is a naturally occurring climate pattern that develops when surface waters across the central and eastern equatorial Pacific become warmer than usual. The resulting changes in ocean temperatures can influence weather patterns around the world, including winter conditions in British Columbia. During two previous super El Niño events, Merryfield says average sea levels along the West Coast were elevated by approximately 30 centimetres during the winter months. That increase is relatively small compared with daily tidal fluctuations, which can exceed two metres. However, it becomes more significant when combined with exceptionally high tides or a powerful winter storm. “An extra 30 centimetres on top of that extra high tide could make a bit of a difference in locations that are sensitive to the highest tides,” Merryfield said. The risk becomes greater when a winter storm enters the picture. “Where you could really get into trouble is if you have a winter storm, which causes a further rise in sea level due to the storm surge. That could cause some coastal flooding regardless. But if you put another 30 centimetres on top of that, that’s enough to make a difference,” Merryfield said. Merryfield says El Niño can also influence marine ecosystems, bringing species normally found farther south into local waters while potentially delaying the spring plankton bloom that supports the marine food chain. Victoria preparing for a changing coastline The City of Victoria says preparing for coastal flooding is already an important part of its short and long-term infrastructure planning. Jas Paul, assistant director of infrastructure services with the city’s engineering department, says staff monitor weather forecasts and tide levels throughout the fall and winter, with crews ready to respond when conditions deteriorate. “Operationally, we’re monitoring weather conditions 24/7 in the fall and winter and we’re tracking forecasts and we’re looking at tide levels,” Paul said. Preparations can include clearing leaves from catch basins, inspecting infrastructure and coordinating staff across different city departments. But the work extends well beyond the immediate storm season. The city is modelling future climate scenarios, including an estimated one-metre increase in sea level elevations by 2110, while considering the combined effects of storm surges, heavy precipitation and atmospheric rivers. One example is the major stormwater outfall renewal project underway along Dallas Road near Ross Bay. The work involves replacing aging pipes and installing a valve. The system is intended to prevent seawater from backing up into the city’s stormwater network and flooding areas farther inland. “What we’re doing here is renewing the infrastructure, renewing the pipes. But we’re also installing a special valve that automatically closes when the sea level rise gets too high,” Paul said. The city is also benefiting from previous coastal protection work at Ross Bay. The area was historically vulnerable to storm surges, which caused flooding along the roadway and threatened Ross Bay Cemetery. The work involved bringing in large quantities of rock and other material to strengthen the natural shoreline and reduce the impact of incoming waves, helping protect the road and cemetery. Paul says the investment continues to provide protection today. What homeowners can do to prepare Paul says residents can also take steps to reduce the risk of flooding around their own properties. That includes keeping gutters clean and clearing leaves and debris from nearby catch basins. “It’s always a good idea to have a plumber inspect the drainage system, the pipes on their own property. It can easily resolve a lot of headaches during the storm season,” Paul said. What residents can expect Paul says people should use caution around exposed coastal areas during major storms. Along Dallas Road, the most noticeable impacts during severe weather can include road closures, restricted access to sidewalks and beaches, debris washing onto roadways and powerful waves sending spray over the shoreline. “It’s really exciting and fun to come watch those storms. But we encourage people to stay off the closed trails and sidewalks,” Paul said. The city is also working with neighbouring municipalities, including Saanich, Esquimalt and View Royal, on a study examining the potential impacts of future sea level rise along the Gorge. The study will help identify vulnerable properties and consider possible protective measures, including the effects of flooding and tides. Regional planning is also being informed by the Capital Regional District’s coastal flood inundation mapping project, completed with support from the federal and provincial National Disaster Mitigation Program. The project provides regional information about potential coastal flooding from storm events, rising sea levels and tsunamis. Its findings are intended to help emergency managers and planners identify vulnerable infrastructure, ecosystems, cultural sites and residential areas across southern Vancouver Island and the Southern Gulf Islands. Paul says the investment continues to provide protection today but acknowledges that more work will be needed as sea levels rise and coastal conditions change. Merryfield cautions that El Niño doesn’t necessarily predict the severity of individual storms, which can vary significantly from one winter to the next. Both he and Paul say understanding the risks and preparing ahead, from municipal infrastructure upgrades to protecting individual properties, will be increasingly important for coastal communities. With files from CTV News’ Brendan Strain
