By Jim Cooperman, Observer contributor
While the Shuswap is not as prone to landslides as the coast or the Kootenays, nonetheless this region does experience extreme instability far too often and the problems are likely intensifying.
A number of factors are behind the increase, including geography, climate change and forestry. Some areas are definitely more susceptible, including Sunnybrae where a mudslide recently destroyed two homes, and above Mara Lake, where concern about landslides has prompted the regional district to support a logging moratorium.
Much of the Shuswap consists of gentle-over-steep terrain, where there is greater potential for forestry practices to cause slope failures that can result in significant damage to the environment, as well as homes and property.
Typically, the problems occur when a forest is clearcut and roads, skid trails and drainage systems are built on relatively gentle slopes without proper consideration for the impacts on the steeper slopes below.
When tree cover is gone, more snow accumulates and water flow is greater, especially when heavy rain falls on snow.
When combined with poor road and trail drainage management, this water ends off where it does not belong and slides occur.
Since 1990, when there was a massive slide into the Anstey River, I have visited numerous slides throughout the region, all caused by irresponsible logging and road building practices. On May 17, 1995, the snow melted quickly on a south facing clearcut on the top of Angle Mountain after a heavy rainstorm. All of the melting water drained into a culvert on to a saturated hillside that gave way into Hudson Creek, causing a massive debris flow that swept through the Anglemont subdivision, then across the road to the lake, causing extensive damage.
In July 1997, our environmental organization responded immediately after the massive debris slide devastated Swansea Point. We brought CBC National TV reporter Terry Milewski there to witness the aftermath of the slide, as well as to see first hand what was blatantly obvious to viewers across Canada, that heavy rain was still flowing down the cutblock skid trails and channeling directly into a culvert to the hillside that gave way and initiated the destructive debris flow.
The immediate response from the government of the day was that the cause of the slide was due to the heavy rain and not logging.
Within a few days, our organization had hired the distinguished U.S. hydrologist, Al Isaacson, who arrived at the site to do an initial study of the catastrophe. His analysis showed how logging and road building had indeed caused the slide, which was finally confirmed many months later by government experts.
Now Tolko wants to log this hillside yet again, despite the obvious risks to the community below. In what is likely the most comprehensive guidebook on the topic, Managing Forested Watersheds for Hydrogeomorphic Risks on Fans, the authors provide a risk analysis matrix. When the consequences are high and the hazard is very high due to steep slopes and soil conditions, then the risk is deemed very high. The authors reach the conclusion that, “the prudent decision may be that development should not occur…” This is exactly the situation with the proposed cutblocks.
Sunnybrae has seen at least five slides in recent decades, including a massive rockfall in the winter of 1959 that deposited boulders into the lake and the boulder that crashed into a home in 1983, killing two people.
These rockfalls are natural as all mountains slowly erode, and rocks often break off when moisture seeps into cracks, which expand when the water freezes. As a result, a large ditch and berm was constructed to protect the Bastion Mobile Village from future rockfalls.
Directly above the latest Sunnybrae slide is a steep clearcut hillside and related road development. Although the experts are claiming this was a natural event due to saturated soils, after my recent visit I believe there is a good possibility that the logging development contributed by increasing the flow of water to Hardy Creek after heavy rains.
Since the property was first homesteaded 80 or more years ago, there have undoubtedly been previous heavy rains without a massive slide until this month, after the hillside above was logged a few years ago.
As climate change intensifies exponentially, there will be more extreme weather, including intense rainstorms that can cause yet more landslides.
Given the higher probability for future slides and this region’s topography and logging history, it would be wise to be better prepared and be more cautious with forest development.