Mudslide odds one in 500

Fairmont “debris flow” created by a perfect storm of events not likely to happen again within the next 500 years.

The aftermath from last July’s mudslide on Mountainside Golf Course in Fairmont.

The aftermath from last July’s mudslide on Mountainside Golf Course in Fairmont.

The mudslide that hit Fairmont Hot Springs last July was a once in 500 years event.

The finding was made in a technical report set to be accepted by the Regional District of East Kootenay (RDEK) board of directors on Friday, February 1.

The Fairmont Creek risk assessment found that the July 15, 2012 mudslide was not caused by a temporary dam near the creek’s headwaters, as emergency responders believed at the time.

In fact, the mudslide’s cause was cumulative, attributed to heavy rain falling on a higher than normal snowpack.

“Rather than any single trigger factor, the 2012 debris flow is judged to have initiated by progressive destabilization of abundant bedload in the mainstem channel by a locally-intensive convective rainstorm at a time when soils were already saturated from an unusually wet spring,” reads the report.

“I was surprised that the report noted the event was a 500 year event, while at the same time it mentioned other minor slide events that have occurred within the past 50 years. That was news to me,” said Area F board director Wendy Booth.

Fairmont Creek flows for seven kilometres from the peak of Fairmont Mountain, at an elevation of 2,600 metres, to the Columbia River, at an elevation of 820 metres. At its headwaters, the creek runs through steep, bedrock-controlled channels. Downstream, it transitions to a lower gradient channel before flowing through Marble Canyon.

Leading up to the July mudslide, snow pillow stations nearby reported a winter snow pack up to 170 per cent above normal. Then, starting in mid-May, there was a rapid snow melt. Finally, in the days before July 15, a localized storm cell brought between 20 and 26.4 millimetres of rain.

All of these factors led to the dangerous mudslide that tour through Fairmont at 4:15 p.m. on Sunday, July 15, 2012. An estimated 65,000 cubic metres of debris came down the creek at speeds up to 22 kilometres an hour.

It buried the hot springs source wells under seven metres of debris, washed out the RV park access road, severely damaged a foot bridge to the RV park, filled Marble Canyon with several metres of rock and debris, washed away a walking trail, and inundated several homes with mud, rock and debris. More than 350 people were temporarily evacuated.

The water source for Fairmont Hot Springs Resort and Mountainside Golf Course was lost, forcing the resort to close for three weeks during peak season, leading to a $1.5 million loss of revenue. Seven holes of the golf course were affected.

However, geologists predict such an event is only likely to happen once every 500 years, with only a 10 per cent chance it will happen again in the next 50 years.

Still, smaller, hazardous debris flows are likely to happen every 25 years, the report finds.

“With predicted climate change effects on precipitation, the increased frequency of storm events, and the potential for increased runoff due to wildfire, there is a corresponding increase in the potential for debris flow,” reads the report.

At risk from future debris flows are: 16 multi-family dwellings and 88 single-family dwelling; approximately 350 people; Mountainside Golf Course; a Community Recreation Centre; Fairmont Fire Hall; the only access to the RV Park; and Highway 93/95.

The report makes 12 recommendations in five phases to protect those assets from future slides. Phase 1 includes: restoring the channel and riprap dyke through Marble Canyon (work already underway); reconstructing the channel through the golf course; maintaining the golf course pond as a flood control structure; and inspecting drainage structures between the golf course and the creek’s outflow into the Columbia River. Phase 2 focuses on work upstream of Marble Canyon, including: widening the creek’s channel upstream of the resort; building a bridge over the access road to the RV Park; increasing the channel capacity through Marble Canyon and installing a refuge area on the walking trail; and constructing a debris flow barrier system in the canyon. Phase 3 is to complete a watershed management plan; phase 4 is to conduct five-year inspections along the length of the creek; and phase five is to install a rainfall gauge at the resort. In total, the recommended mitigation measures would cost $2.5 million.

Prepared by Clarke Geoscience and Golder Associates, both of Kelowna, the Fairmont Creek Debris Flow Hazard and Risk Assessment was commissioned by the RDEK in September and completed this month. It was funded by the Provincial Emergency Program with technical review by the Water Stewardship Division of the Ministry of Forests, Lands and Natural Resource Operations.

The board will discuss the report at its January 31 and February 1 meetings. Staff is recommending the board present the results of the assessment to the Fairmont community and consider it for future funding opportunities.

“The report mentions various things that can and should be done,” said Wendy Booth. “In order to complete all the recommendations in the report, it is about a $2 million price tag. I currently don’t know where that funding is going to come from, however I intend to do my best to secure the funding. Fingers crossed.”