Researchers concerned about impacts of B.C. flooding on local ecosystems

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The Fraser Valley, Merritt, and northern areas of Vancouver Island faced an atmospheric river that washed away roads, bridges, homes, and farms. Some regions are under a second flood warning this week as another atmospheric river approaches recovering areas. 

Large amounts of rainfall can be due to low pressure in the atmosphere, resulting in storm surges. But larger rainstorms in the fall and winter months result from atmospheric rivers, long bands of moisture that carry precipitation from tropical regions. And as the atmosphere warms, the more water it can hold. 

The atmospheric river that hit southern British Columbia on Nov. 14 and 15, dumping large amounts of rain across the region which resulted in widespread flooding and several mudslides. The last major flooding event in the Fraser Valley was in 1948 when the Fraser River flooded due to rapid snow melting in the spring season. 

“This is a really unusual flood. My impression is that it was bigger than a one in 200 years kind of event,” says Kai Chan, a University of British Columbia professor at the institute for resources, environment and sustainability. 

“Normally, the Fraser River flood levels are associated with snow melts in the interior and usually reach their peak around mid to late June. The peak on Nov. 15 went from low flow right up to higher than the springtime levels overnight,” says John Richardson, a UBC professor in the department of forest and conservation sciences.

Richardson says when the soil gets saturated, it becomes mud-like and breaks down easier than if it was dry. 

“A lot of our areas near water are diked, and that’s to protect human infrastructure. But that means when the water level rises, there’s nowhere for it to go or for the critters to go, like the fishes and vertebrates,” he says. 

A floodplain is a flat area of land next to a river or stream that is prone to flooding. In historical times, Richardson says the animals and organisms moved into the floodplain where the water flow was lower, but those plains are now used for human infrastructure.

“In some ways, it’s not surprising we have floods if you look at where and what we build in floodplain areas,” Richardson says.

Chan says logging has made some areas more prone to mudslides. A 2021 report by Sierra Club BC found that governments “can mitigate climate-related disasters like flooding, fires and heatwaves by swiftly reforming B.C.’s forestry practices.” 

“It means we lost a bunch of trees, a lot of animals drowned. And the mudslides are local disturbances for many organisms in those particular areas,” Chan says. 

The amount of water and the force pushing it can rearrange the habitats marine life rely on. 

“[The water] will have scoured up the bottom of a lot of streams … moving cobbles and rocks around. It’s possible that killed a lot of invertebrates, a lot of fish,” Richardson says, adding that salmon are particularly vulnerable this time of year, as they respawn in late summer and early fall. Because of this, they are at risk from being affected by the gravel that has been washed into the river.

The muddy water is a concern, Richardson says, due to increased turbidity. 

Turbidity is the degree to which water loses its transparency due to suspended particles, and water with higher turbidity blocks sunlight from travelling through water, which can be harmful to marine plants and wildlife. Clouds of sediment can also block the gills of fish, which can cause them to suffocate over time.

“Turbidity settles on everything at the bottom … it fills in spaces and can suffocate salmon eggs and invertebrates,” says Richardson.

A larger source of ecological impact is the release of toxic chemicals from houses, businesses, factories, and farms due to flooding. 

“Every farm likely has a gas tank, manure, fertilizer, and pesticides. All of that combined with the dead critters out there is going to cause water pollution problems in many areas,” Richardson says. 

Those chemicals can get into soils and don’t move quickly, resulting in contaminated groundwater that gets into streams. 

“[The chemicals] might be toxic to organisms even at fairly low concentrations when you get such a mixture of it,” he says. 

In addition to the collected chemicals from houses and farms, sewer systems are also vulnerable to flooding. In older parts of the region like Vancouver, Burnaby, and New Westminster, stormwater goes into combined sewers that carry sewage from homes and other buildings.

A sewer overflow can occur when heavy rainfall overloads the sewer system, or when there is damage to pipes, a power outage, or equipment malfunction. Wastewater is released into the environment instead of being processed at a wastewater treatment plant. This includes discharges from sanitary and combined sewers and wastewater treatment plants, reads the Metro Vancouver webpage.

In Metro Vancouver, the Iona Island and Lion’s Gate wastewater treatment plants provide primary treatment, which involves the use of “various mechanical processes to remove materials that settle or float” and “removes 50 to 60 per cent of the total suspended solids,” reads Metro Vancouver’s webpage.

The Lulu Island, Annacis Island, and Northwest Langley wastewater treatment plants provide secondary water treatment in Metro Vancouver, using bacteria to remove organic materials that have been dissolved in the water.

“The problem is that [where] we have that combination of combined sewer overflow and we have a lot of runoff happening, it all comes together on a street and in the sewage, and then a lot of that untreated sewage makes its way into the Salish Sea, or better known as the Georgia Strait,” Chan says. 

“If the chemicals make their way into the food chain that can be terrible for larger species and ecosystems, like the orcas…. Even for bears and wolves.” 

Unfortunately, we won’t know for sure the impacts of recent flooding events on our local environments until the spring. 

“This is a tough time of year for organisms to recover from. [Some] were just going into dormancy, and a lot of them weren’t ready for a big storm. The ones that have gone into dormancy in a place that gets flooded, they’re gone. It’s hard to know what that impact will be,” Richardson says. 

“If the water can’t spill out, and the fish and other critters have nowhere to go, there’s going to be losses. We need to think about bigger solutions when doing billions of dollars on rebuilding, and this gives governments an opportunity to think about it differently.” 

He suggests adapting our infrastructure, like pushing the dikes back to give the rivers room to expand, reducing the chances and challenges of flooding in those areas. Other solutions include relocating housing, farms and businesses, and investing in buildings and chemical storage that are more resistant to flood damage.

Chan says that extreme weather events are not one-offs anymore, which means that preparing for them is becoming increasingly important.

“It might have been once in 200 years looking backwards, but it’s not going to be 200 years looking forwards thanks to climate change,” Chan says.