Kamloops could flood like it’s 1999, according to the latest information city council heard this week as a foreboding thunderstorm raged outside.
The city’s utility services manager, Greg Wightman, detailed to council on May 31 the latest snowpack information, outlook and preparations for a delayed flood season this year.
“Take advantage of the next couple of weeks while we still have relatively low waters and get prepared for this because it’s going to be a bad year,” Wightman advised the public while addressing council.
Wightman said the BC River Forecast Centre is predicting a significant seasonal flood risk for the Thompson rivers, given a historically high snowpack — the runoff of which has been slow due to a cooler than normal spring and continued snow accumulation.
As of May 15, the North Thompson snow basin index is at 142 per cent of its seasonal average — the highest in seven years. The previous high was 114 per cent in 2017. Meanwhile the South Thompson is 113 per cent of normal, which is the second-highest in seven years.
Wightman said snowmelt this season is about four weeks behind schedule and river levels through Kamloops have yet to rise to levels typically seen in May. They are predicted to peak later than normal.
The North Thompson usually peaks on June 6. The South Thompson usually peaks on June 22. Where the rivers meet, just east of Overlanders Bridge, the peak is usually during the second week of June.
That peaking at the confluence this year is expected in early July, Wightman said.
The delayed rise increases the risk of flooding from extreme weather as this year’s spring runoff is pushed into June — historically the rainiest month of the year. In addition, long days of sun exposure that could melt the snowpack rapidly, Wightman explained.
“When that precipitation is falling on snow, it really accelerates the snowmelt, so you would like to see that snow gone by June,” Wightman said. “The predictions as they are right now … we’re looking at an event that could be similar to what we saw in 1999,” Wightman said.
In 1999, snowpack levels and weather combined to create a potentially dangerous situation for the Kamloops area. Forecasts predicted high water that could have approached 1972 levels.
That was not the case, but the water was high — peaking on June 24 at 344.7 metres above sea level, just shy of 1948 numbers and a half-metre short of 1972 measurements.
Preparations for the 1999 flood began in mid-May, with sandbag supplies delivered to low-lying areas. An earthen berm was also constructed along Schubert Drive and, in mid-June, storm drains were sealed to prevent potential backup.
Flooding could occur if the Thompsons’ peak flows are synchronized, there is about a week of above average temperatures or a severe rainstorm bringing more than 30 millimetres of rain, Wightman told council, noting sunny days in the low 20 C range would be preferable.
Wightman said the North and South Thompson are two of the most concerning rivers for the province this year and earlier this week discussed potential financial needs and resources Kamloops may need with Emergency Management BC and the Ministry of Forest, Lands and Natural Resources.
“They’re very comfortable giving us those resources, which they are trying to conserve for communities on the Fraser River,” Wightman said.
Ahead of this year’s flood season, the city now has two permanent dikes in place — one protecting the north end of McArthur Island and the other along the beach at Riverside Park, which is part of ongoing rehabilitation work. Both appear as elevated walking trails, but are designed to protect each park's infrastructure from a one-in-20 year flood event.
Wightman said the city continues to monitor river levels daily, is inspecting pump stations and distributing sandbags. He said the city would have already sealed off catch basins by this time of year, but the river levels are still too low.
Residents of waterfront properties should begin flood preparations now, he said, noting the city’s obligation is to first protect public infrastructure before addressing private properties.
“We can’t guarantee we’re going to be protecting homes. We’re going to protect infrastructure,” Wightman said, adding the municipality has sand and sandbags at various locations, which are listed on its website at kamloops.ca.
The immediate threats
Environment Canada issued a severe thunderstorm watch for the Kamloops area on June 3, with heavy rains, strong winds and hail possible.
The River Forecast Centre has issued many high streamflow advisories for various waterways in B.C. As always, people are advised to steer clear of riverbanks and edges of creeks during this time of the year.