The Coquihalla, or Highway 5, was first built in the late 1980s as a shortcut between Hope and Kamloops. The four-lane highway offered a faster route not just for travelers, but also for goods moving to and from the Port of Vancouver.

In November 2021, an atmospheric river brought heavy rain, landslides and deadly flooding to B.C. The Coquihalla and Coldwater rivers, which follow Highway 5, became so swollen with water that they easily overwhelmed the roadway’s defences against weather damage.

The damage forced the B.C. government to close Highway 5 temporarily. A state of emergency in the province ended two months later, and on the same day the highway reopened to non-essential traffic at reduced capacity.

By that time, the province had spent roughly $50-million on temporary repairs. It has now embarked on an unusual collaborative approach to a permanent solution: it hired design and construction firms at the same time, to accelerate the work. The repairs are scheduled to be substantially complete by the end of this year.

This meant beginning repairs this past spring without a firm design or budget in hand. What is known is that the engineering standards that were considered to be the best when the highway was originally built proved insufficient in November. Climate change has made the weather less hospitable, and the Coquihalla needs to evolve accordingly.

It is estimated that the flow on the Coldwater River in November was a one-in-1,000-year event – but the storms tore out the monitoring equipment, so the data are incomplete. The flow along the Coquihalla River, meanwhile, is estimated to have been a one-in-500-year event.

The Globe and Mail visited and photographed five locations along the highway that exemplify the range of problems the repair effort will need to overcome.

Location 1: 79 KM to hwy end

In 2010, the province asked Engineers Canada to study the Coquihalla Highway for risks associated with climate change. They found that the highway was generally well engineered, but warned it was vulnerable to extreme rainfall events, including atmospheric rivers, which were then referred to as the Pineapple Express. The extreme rain in November proved their point.

Dr. Matthew Lato, a senior geotechnical engineer for BGC Engineering, identified this location on the side of Highway 5, south of Merritt, as one of the five biggest landslides detected along the corridor after the storms. This single slide dumped more than 60,000 cubic metres of debris into the Coldwater River.

Prior to the storm, every bridge along the corridor was routinely inspected. Kevin Weicker, the B.C. Ministry of Transportation and Infrastructure’s lead engineer for the Coquihalla emergency repairs, said those inspections gave no indication that the infrastructure was at risk.

Inspection reports, obtained through a freedom of information request, chart wear and tear from more than three decades of traffic. The highway’s bridges required constant routine maintenance that included tightening loose bolts and rails, filling potholes and injecting epoxy into cracks in concrete.

But the scale of slides like this one, and the way the river shifted in November – particularly at bends, where the force of the water was strongest – were well beyond the range of what the infrastructure was built to withstand.

Just south of the landslide is Brookmere bridge. It did not collapse in November, but did suffer from erosion, as shown in this photo from the Ministry. The abutment nearest the camera is hanging over the water, when it should be buried in the terrain like the one on the other side of the river.

Mr. Weicker noted that the geometry of the river played a large role in determining which bridges were left standing and which failed. Where the river curves next to the highway, water moved faster on the outsides of the bends, increasing the odds that the highway’s armour – piles of jagged rock known as riprap – would be eroded.

Location 2: 62 KM to hwy end

In this area, where the Coldwater River crisscrosses Highway 5, the tremendous force of flood water led to the collapse of the southbound Juliet bridge. The water also eroded the footing of the northbound Juliet bridge.

BGC created a 3D model in late November that shows that every outer bank of the river moved substantially during the floods. Here, there was a 50-metre lateral shift.

“We found a mess,” said Jennifer Fraser, the Ministry of Transportation and Infrastructure’s executive project director for highway repairs in B.C.’s Southern Interior.

The Juliet bridges were built to the standards that were in place in 1986, which meant their footings were set on top of platforms on the surface, rather than columns set deep into the ground. The riprap that protected the structures proved to be insufficient.

“That was the code when these bridges were constructed,” Ms. Fraser said. “It is a more vulnerable standard.”

The current standard requires the highway to be engineered to withstand a 1-in-200-year high-water event (that is, one that has a 0.5-per-cent chance of occurring in any given year). Climate change is altering what an unusually high stream flow looks like, Ms. Fraser said, and the province will need to update its measure of what counts as a 1-in-200 year event.

Repair crews raced to shore up the foundations of the northbound Juliet bridge with fresh riprap, and it is currently open to two-way traffic – making it one of the traffic pinch points on the route, which normally has two lanes in each direction.

Ms. Fraser expects the new design for Juliet will have different footings. And the new bridges might be longer than the old ones, so they can better accommodate river movement in the future.

The cost of the repair work won’t be known for some time. “We’re looking for innovative and creative solutions that reflect climate change as we know it today,” she said.

Location 3: 20 KM to hwy end

The Coquihalla River crisscrosses the lower section of Highway 5. Damage at this location resulted from two forces: erosion from the river below and a 12,000-cubic-metre debris flow from the mountainside above.

The debris flow came from a logging road just north of Coquihalla River Provincial Park. The province is now grappling with the impact of forest losses from logging and wildfires. “We often see associations between forestry activity and landslide activity,” said BGC’s Dr. Lato.

University of British Columbia forestry professor Younes Alila’s research calls for a shift in forest harvesting practices in flood-prone areas. He has argued that B.C. hasn’t used the right metrics to determine if forestry is influencing floods.

“Without treetops and root systems to absorb rain and slow snowmelt, cleared areas can act as water basins. On mountainsides, runoff has nowhere to go but down, spilling into and sometimes overwhelming low-lying areas,” he wrote in the spring edition of UBC’s forestry newsletter.

Mr. Weicker, from the Ministry of Transportation and Infrastructure, said his crews looked at the origins of the debris slides to determine if it was safe to begin emergency repairs after the floods.

They found no clear pattern. Some slides started in areas that had burned in wildfires, some in areas that had been cleared by logging and some in untouched forests.

Location 4: 3 KM to hwy end

All along the highway there are different types of infrastructure sharing the same route. Repairs near the community of Othello, in particular, called for collaboration with a wide cast of characters.

Alongside, amid and underneath the highway is a complex network of conduits: The Trans Mountain oil pipeline, an Enbridge natural gas pipeline and a telecom line.

Emil Anderson Construction was retained to do a portion of the emergency repair work. Colin Taylor, a vice-president at the company, recalled the initial post-storm scene: “The Enbridge pipe was in the median between the southbound and northbound lanes. It was very dramatic looking, because it was sort of floating on top of the water … We're like, wow, that doesn't look right.”

His job was to get a minimum of two lanes open, in a hurry. Repairs farther up the highway couldn’t start until this section was cleared.

But the Coquihalla River had shifted dramatically. Its centre had migrated by 250 metres and taken out the southbound lanes of the highway.

Elsewhere, four lanes of the highway were buried in mud from a debris torrent that came down from the slope above. It took Mr. Taylor and his colleagues almost a week just to assess the geohazards and ensure that their crews could safely begin work.

They used riprap to “retrain” the river to run in its old path. “It’s just brute force. We just had to move a bunch of material from where it is today back to where it used to be,” Mr. Taylor said.

They revived the dormant Nicolum Quarry, but they also concluded that a pillar of rock in the median between the north and southbound lanes at Othello would be a handy source of material. A series of blasts reduced the pillar to manageable chunks.

It was nice, hard rock – granodiorite, which is similar to granite. The pillar is now an impromptu quarry amid busy highway traffic. “It's very good rock and reasonably easy to get access to. Also, there were some sightlines that could be improved by taking some rock out,” Mr. Taylor said.

Crews were making progress in the aftermath of the first extreme rainstorm. “And then, two more atmospheric rivers showed up,” Mr. Taylor said. “We did a pretty good job, we were able to get a fair bit of rock … and almost nothing was wasted there.”

Location 5: 19 KM to hwy end

“At the Carolin bridge, most if not all of the previous week's work was just totally obliterated by the next two events, because we just weren't able to get enough rock in there soon enough to make a difference,” Mr. Taylor said.

In total, Emil Anderson Construction blasted roughly 115,000 cubic meters of material – 46 Olympic-sized swimming pools worth of rock, gravel and sand.

The residual pieces were used where smaller material was needed, such as the replacement roadbeds.

While the Trans Mountain pipeline through this corridor was shut down for three weeks, forcing gas rationing in B.C., the Enbridge line, which supplies natural gas from the Peace River region down to the Lower Mainland through a pair of pipelines, continued to operate at nearly full capacity.

That’s because the gas company had invested $1.5-billion in upgrades, in anticipation of a climate disaster. Those projects included a series of crossover assemblies linking the twin pipelines. The crossovers allowed this section of exposed pipeline to be shut down temporarily while gas was rerouted.

“Our natural gas system worked exactly as it should. In what’s been called a once-in-500-year weather event – which washed away roads, railways, and shut down other pipeline systems – we were able to continue to safely operate the West Coast system and provide people with the critical energy they rely on every day,” said Jesse Semko, a spokesperson for Enbridge.

This fall, contractors from Hope to Merritt are racing to complete the new and improved Coquihalla Highway. The target is to fully restore four-lane capacity before Christmas, but the scope and cost of the project are still evolving.

The market conditions are difficult: Inflation is driving up construction costs, and there is a skilled labour shortage in the province. “How are we going to get the people to do the work?” Ms. Fraser asked.

The federal and provincial governments have said they will “build back better.” The engineers have a lot of work ahead, Ms. Fraser said, to understand what that will look like on the ground.

Mr. Taylor said the long-term solution for the Coquihalla is still unclear. “We don't really know what to do in terms of design to make things bulletproof, or even what bulletproof would look like.” The Othello portion of the highway has a budget of $4.6-million for the permanent repairs, but costs for the rest of the corridor remain uncertain.

“We are still defining the project scope,” Ms. Taylor said “The whole approach to redesigning the Coquihalla is taking in new information about the climate we are designing into.”

Aerial photography by Melissa Tait

Additional aerial photography by Darryl Dyck/Canadian Press and Emil Anderson Construction

Editing by Steve Kupferman