Clear-cut logging of just 21 per cent of a B.C. watershed north of Kamloops caused an average flood size increase of 84 per cent, according to new peer-reviewed research at the University of British Columbia.
The Joe Ross Creek watershed is about 100 square kilometres, embedded in the Deadman River watershed, and has undergone increasing clear-cut logging over the years.
The average flood size in the Deadman River Creek watershed of 878 square kilometres, by contrast, increased 38 per cent from clear-cut logging, the study found. The team also studied a third control watershed that has undergone insignificant amounts of clear-cut logging.
“We need to be careful of blaming the flood risk and the increase in the flood risk that we have been experiencing in recent years just on climate change,” explained co-author and UBC hydrology professor Younes Alila.
“The power of the forest in reducing flood risk increases dramatically with the increase of the watershed size.”
According to Alila, he and first author Robbie Johnson, a post-graduate student, used a unique framework that allowed them to reach a causal conclusion about clear-cuts and flooding, rather than a correlational one.
That involved studying all of the factors that impact flood severity in a watershed, such as climate and topography, superimposing the watershed cut blocks, analyzing them over time with the frequency and severity of floods, “and plotting the magnitude versus the frequency with and without logging.”
The influence of clear-cut logging on floods depends not only on the area that is logged, but the physical characteristics of the watershed said Alila. With that study — two years in the making — now completed, he said he feels B.C.’s watersheds are at “very high risk already because of the default logging practices called the clear-cutting.”
In a statement, the Ministry of Forests said B.C. scientists and forestry workers “always consult significant amounts of data when determining where and when to encourage sustainable harvesting.”
“They review topographic maps, surface geology maps, and detailed terrain stability maps and consider all of these factors when developing their recommendations for silvicultural systems and harvest boundaries,” it added.
The ministry went on to say it is committed to developing and implementing alternatives to clear-cutting, and that any new research — including UBC’s paper — that could move the industry forward is welcome.
Clear-cut logging is a contentious practice in B.C., having contributed to protests, and at times, put environmentalists and some First Nations at odds with the province and logging companies.
Previous research has linked clear-cut logging to increased flood risk, but Alila said the UBC study is the first that examined large watersheds, as opposed to smaller ones or small headwater catchments. He hopes it lands in the hands of decision-makers, including First Nations, who can press for better forest management as B.C. undertakes its multi-year review of the Forest and Range Practices Act.
“We have been really giving lip service to the cumulative effect in the way we manage the forests.”
The Ministry of Forest’s website states that it is committed to “world-class sustainable forest management,” inspecting forestry activities for compliance with approved operational plans, and restricting the maximum allowable clear-cut size in various parts of the province.