Total Rainfall - November 11 to 16
This data layer, derived from the Global Precipitation Measurement Mission (GPM), shows the total rainfall that fell between November 11 through the 16th.
The data is created from satellites measuring microwave radiation, which is calibrated using ground-based weather stations. It is colorized across a range of 0 to 300+ millimeters.
The vast majority of the rain occurred between the 14th and 15th of November. Looking at the data, we see that rainfall from the storm was concentrated around the town of Hope; however, significant rainfall was experienced across much of southwest BC.
Road Damage Locations
We mapped locations of damage along major BC highways, shown here as red dots.
In total we found 36 locations of damage spread across 7 different highways.
The majority of damage we found on three highways: Highway 5 (Coquihalla Highway) between the towns of Hope and Merritt; Highway 8 (Nicola Highway) between Merritt and Spences Bridge; and Highway 1 (Trans-Canada Highway) between Spences Bridge and Lytton.
Burn scars from 2021 fires were nearby to many of the damaged locations along these highways.
Coquihalla Highway
Let us look first at the Coquihalla Highway. The road runs north-east from the town of Hope to the city of Kamloops where it intersects with the Trans-Canada Highway. It is one of three major routes linking Vancouver and the rest of Canada, and experiences the highest traffic of the three.
We mapped 13 locations of damage along the Coquihalla. Most of the damage occurred where the road crossed over or near rivers. Large sections of bridges were destroyed, and portions of the road were washed away. Landslides also covered the road in several locations.
Coquihalla Highway - River Basins
Damage on the Coquihalla was split between the Thompson and Fraser River basins. The divide between the basins occurs at the Coquihalla Summit.
South of the divide, the highway follows the Coquihalla River, which flows in a south-west direction, merging with the Fraser River near Hope.
North of the divide, the highway follows the Coldwater River, which flows north toward the city of Merritt.
We will explore the section of the highway north of the divide first.
Coquihalla Highway - Coquihalla Summit to Merritt
We mapped 5 damage locations along this section of the Coquihalla Highway. We also mapped damage in 2 other locations on secondary roads and bridges near the highway.
In all cases the damage occurred when the road either crossed over the Coldwater River or was nearby to it.
Most of the damage was in close proximity to the burn scar from the July Mountain Fire, which burned on both sides of the highway.
Rain falling on the water repellent fire-scarred soils would have had a higher tendency to run off into the Coldwater river rather than being absorbed. The increased volume of water flowing through the river would have increased its destructive power.
City of Merritt
The surging Coldwater River caused extensive flooding in the city of Merritt, and forced the evacuation of all 7000 of its residents.
Nicola Highway
The Coldwater River joins with the Nicola River at Merritt, and their combined waters flow north-west, joining the Thompson River near the community of Spences Bridge.
BC Highway 8, the Nicola Highway, follows closely to the course of the river and intersects with the Trans-Canada Highway (Highway 1) at the confluence between the Nicola and Thompson rivers.
We mapped damage in 13 locations along Highway 8. Entire sections of the highway were washed away, and several bridges across the river were also destroyed.
Nicola Highway
Most of the damage on Highway 8 occurred where the road passed close to the river, particularly near the outer bank along meanders, curves in the river path where strong erosion would be expected.
The scar from the 2021 Lytton Creek Fire was adjacent to the highway for much of its length.
While a lot of the damage may be due to flood waters from the Coldwater River alone, it is possible that rain running off from the fire scar contributed to the road damage, both directly through erosion, as well as by increasing the amount of water in the Nicola River.
Trans-Canada Highway
The Trans-Canada Highway (Highway 1) is a transcontinental highway, connecting all ten provinces in Canada. While this section of the highway is less heavily trafficked than the Coquihalla, east of Kamloops it is the main route through the province.
We mapped 5 road damage locations along the Trans-Canada between the communities of Spences Bridge and Hope.
4 of these occurred between Spences Bridge and Lytton, where the highway follows the Thompson River. The 5th location was south of Lytton, where the road follows the Fraser River.
Trans-Canada Highway
Unlike the damage along the Coquihalla and the Nicola highways, the damage along the Trans-Canada does not appear to be due to heavy river flow; instead, it appears to have been caused by runoff and landslides from the mountain slopes above the highway.
The mountains overlooking the 4 damage locations between Spences Bridge and Lytton were severely afflicted by scarring from the Lytton Creek Fire.
For the single location south of Lytton, the slopes above were scarred from the Mowhokam Creek Fire.
It seems likely that enhanced runoff and erosion from these burn scars contributed to the damage observed on this highway.
Other Road Damage Locations
So far we have looked at highways where recent fires may have contributed to the flood damage.
We did, however, map 11 damage locations which did not directly correspond with any 2021 wildfires.
The majority of these were in the south near the town of Hope. There were also 2 locations further north, near the town of Lillooet.
Road Damage Near Hope
The road damage locations around Hope were all within the Fraser River basin. Most were on the Coquihalla Highway, between Hope and the Coquihalla Summit.
Unlike the north section of the highway, we found no recent fire scars that could have enhanced the damage.
We mapped 6 locations along this section of the Coquihalla. The type of damage included bridge outages along with debris slides from the mountains overlooking the highway.
There were 3 damage locations not on the Coquihalla: one on the Crowsnest Highway (Highway 3) southeast of Hope, and two east of the city of Chilliwack.
High Slopes and Heavy Rains
The area surrounding Hope experienced the heaviest rainfall brought by the atmospheric river.
The large amount of rain in this region was likely enough to cause significant damage regardless of the presence of any recent wildfires.
Another potential factor was the steep mountain slopes in this area. Higher slopes increase the amount of runoff as well as the risk of erosion and landslides.
Road Damage Near Lillooet
We mapped two landslides near the town of Lillooet: one was located 30 kilometers to the southeast along Highway 12. The other was 36 kilometers to the southwest along Highway 99 near Duffey Lake.
As with the damage around Hope, we found no recent burn scars which could have contributed to the damage here. The McKay Creek fire occurred just north of Lillooet and likely enhanced runoff entering the Fraser River; however, as the damage at these locations was from landslides, it was not directly tied to damage from surging rivers.
Less Rain than Hope
Taking a look at the precipitation layer, we can see that this region received significantly less rain than the area around Hope.
The amount of rain directly uphill from the slide on Highway 12 (southeast of Lillooet) was around 50 mm according to the precipitation data. While still a large amount of rain, it was not close to the 300+ mm measured around Hope.
The Highway 99 slide experienced higher precipitation around 100 mm; still not at the same level as Hope, but nonetheless a large amount of rain.
BC Highway 12 - Between Lytton and Lillooet
Rock debris covered the highway at this location. The slide coincides with the location of a small stream catchment coming down from the mountain above.
Satellite Imagery
Examining high resolution satellite imagery of the area, there is evidence for previous slides at this location.
This suggests that there may be some other factors which make the slopes here particularly unstable and prone to landslides.
BC Highway 99 - Near Duffey Lake
This slide occurred on Highway 99 near Duffey Lake. Several vehicles were swept away by the slide, tragically leading to five fatalities.
This location is overlooked by steep mountain slopes. As previously discussed, steep terrain increases the risk of landslides.
This coupled with the 100+ mm of rainfall experienced in this area may have been enough to trigger the slide.
Satellite Imagery
Examining the satellite imagery reveals some recently logged clearcuts as well as older clearcuts immediately above the slide location.
While the exact date of this satellite image is unknown, we looked at known imagery from 2021 and the area appeared substantially similar.
There is a relationship between logging and increased landslide activity, so this also may have been a contributing factor.
