Mudslides likely result of high concentrated rainfall

You don’t want “a large number of vehicles parked and waiting near a mudslide”

This week saw mudslides between Cache Creek and Clinton. As a result, Highway 97 temporarily closed down to all traffic.

Last Tuesday’s mudslide happened just north of the intersection of Highway 97 and Loon Lake Road. The area has a very small watershed, meaning there’s no real possibility for the cause to be anything but a high concentration of rainfall, according to Dwayne Tannant, a UBC Okanagan School of Engineering professor.

“With a large convective storm cell, it is common to see small mudflows concentrated in the same area where the storm cell passes. This occurred a few years [ago] along Highway 99. Another well-documented example occurred at Stemwinder park a decade or so ago.”

After the Stemwinder mudflow in 2004, experts from the Ministry of Forests as well as two consultants wrote a paper titled The Stemwinder Creek Mud Flow, an unusual event?

They concluded that “the reoccurrence of a similar magnitude event in Stemwinder Creek is dependent on the likelihood of a similarly sized rainfall event. If global warming models that predict more extreme weather patterns are accurate, this must be considered in future landslide risk analysis.”

Tannant echoes that sentiment.

RELATED: Ranchers stood on their porch as mudslide surrounded them

With climate change, if there’s an increase in weather extremes, we can expect to be dealing with bigger, more intense convective storm cells and hence more mudflows, he says.

“With the recent rains, the ground will be more saturated and then if another storm cell comes along, the probability of triggering a mud or debris flow will be higher.”

That’s part of the reason it’s important to keep the area clear, says Tannant.

“When the B.C. Highways guys close a section of road after an event they are also controlling the exposure of people to another similar mudflow event recognizing that the probability for another one nearby is higher given that one has already occurred. So they are controlling risk in this manner – waiting for things to dry out a little. What you do not want to happen, is to have a large number of vehicles parked and waiting near a mudslide or rockfall in a hazard-prone area, because the risk for these folks ramps way up. This has happened in B.C. before and people have lost their lives waiting in an area with elevated rockfall and avalanche hazard.”

It is difficult to reduce the risk of an event such as a mudslide with mother nature controlling the weather, the forest fires, the geology, the steepness of the terrain and more, he says.

“We might be able to control or direct the path of a mudslide with things like deflection berms or ditches. We might be able to control the exposure to the hazard by placing infrastructure away from potential impact zones. And, we might be able to control the exposure of people to hazards by informing them of risky times to be on the road, etc.,” says Tannant. “Minimizing risk usually comes with a financial cost too. So there is always this tension between spending money and what risk is acceptable to society.”

For linear infrastructure, such as roads, power lines or pipelines, as well as other infrastructure, there may be few alternatives to exposing the infrastructure to the hazards.

RELATED: B.C. woman launched from pool by force of mudslide

The effect of fire on soil

Wildfires create water-repellent layers, University of Idaho Forestry Associate Extension Specialist Yvonne Barkley notes in After the Burn, Assessing and Managing Your Forest Land after a Wildfire.

“Water repellency is most often seen after moderate to severe fires, and often is more severe on dry, sandy soils and least severe on wet, fine textured soils. Generally, water repellency weakens with each rainfall and does not persist for longer than two to four years after a burn.”

“Fire further alters physical soil properties by destroying organic matter, which is essential for maintaining soil structure. The removal of organic matter can increase soil bulk density and decrease porosity, resulting in decreased infiltration and storage as well as increased runoff and erosion.”

Like us on Facebook and follow us on Twitter.

Just Posted

Summer festival success bursts through the smoke

Attendance was estimated at 3,000

100 Mile House community fundraises for ‘community-minded’ man in hospital

Will Love is recovering in Kamloops after his colon ruptured on Tuesday, July 31

Lawnmower races exceed expectations in 100 Mile House

‘I had no idea how fast some people could make a lawnmower go. I just was completely blown away.’

Some roads in Cariboo region closed due to evacuation orders

The Ministry of Transportation has provided a list of road closures in the Cariboo

83 active wildfires and 9 fires-of-note in Cariboo Fire Centre Aug. 15

Up-to-date information about wildfires, evacuation orders and alerts in the Cariboo Fire Centre.

‘Queen of Soul’ Aretha Franklin has died

Publicist Gwendolyn Quinn reports Franklin passed Thursday at 9:50 a.m. at her home in Detroit

Missing B.C. hiker, dog found safe after 3-day search

Cranbrook hiker had been missing since Sunday, August 12, near Jumbo Pass.

UPDATED: B.C. RCMP dismantle Kinder Morgan protest camp

RCMP say they will enforce a court injunction today and remove Trans Mountain pipeline protesters who have been camped outside a Kinder Morgan terminal in Burnaby.

Italy says death toll will mount in Genoa bridge collapse

Authorities worried about the stability of remaining large sections of a partially collapsed bridge evacuated about 630 people from nearby apartments.

Former CIA Director: Trump worked with Russians and now he’s desperate

In an opinion piece in The New York Times, John Brennan cites press reports and Trump’s own goading of Russia during the campaign to find Democrat Hillary Clinton’s missing emails.

Church sex scandal: Abuse victims want a full reckoning

Since the crisis exploded in Boston in 2002, dioceses around the country have dealt with similar revelations of widespread sexual abuse.

Baloney Meter: is flow of asylum seekers at Canada-U.S. border a ‘crisis’?

“I think any time you have a government that allows 30,000 people over the course of a short period of time to come into Canada illegally, the impact that that has, that is a crisis,” said Conservative Leader Andrew Scheer.

Altidore nets 3 as Toronto drubs Whitecaps 5-2

Vancouver falls 7-4 on aggregate in Canadian Championship final

Ottawa intervenes to get B.C. ball player, 13, to Little League World Series

Before immigration issue was resolved, Dio Gama was out practicing the game he loves Wednesday

Most Read