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North side of Whistler Mountain slips after heavy rains

Other areas of greater concern during storm An area prone to small landslides on Whistler Mountain has slipped another half metre towards Fitzsimmons Creek after the recent heavy rains. The municipality is not alarmed by the movement.

Other areas of greater concern during storm

An area prone to small landslides on Whistler Mountain has slipped another half metre towards Fitzsimmons Creek after the recent heavy rains.

The municipality is not alarmed by the movement.

"(It) doesn’t surprise me at all," said Brian Barnett, general manager of public works and engineering at the municipality.

"I would have been a little nervous if it had moved several metres like it did years ago but (half a metre) would be what we’d expect."

The small chunk of sensitive Crown land, lying 2.5 kilometres upstream from the village, has been slipping down towards the creek for years. It raised serious concerns for Whistler when a heavy rainstorm in 1991 caused the land to drop more than three metres at once.

An independent geological engineer who has studied the area extensively was concerned when he heard about the latest movement.

"That is not good. As a matter of fact, that’s bad news," said Frank Baumann, an engineer based in Squamish.

Even small slips in the land could cause damage in Whistler he said particularly in the area near the day skiers’ parking lots and the bus loop.

"It doesn’t matter whether it’s slowly moving," he said.

"Any movement of a major failure like that is cause for major alarm."

Studies point to the area moving in small increments, about 100 millimetres a year, at a time. A major movement like the 3.3 metre drop in 1991 is likely to occur only once every 100 years.

"All the engineering studies we’ve done to date show it’s really quite stable," said Barnett.

"It’s not so sensitive that it’s considered to be a significant threat or hazard."

Ledcor, the power company proposing to build a small hydroelectric power project on Fitzsimmons Creek, has done its own independent studies, with Baumann’s help, about the risk of putting a small run-of-river project in the area.

Project Development Manager Derek Hutchinson said the company is taking into account a worst-case scenario where a big portion of the land would slide, forming a dam in the creek, with the water then filling behind the dam and eventually bursting.

"That has always been the risk," said Hutchinson.

"By doing some field measurements we’ve figured that in the absolute worst case we could get a 17 metre high dam and that could store 70,000 cubic metres of water.

"What is the real challenge in this is you’ve got this dam but you don’t know how quickly it will fail... but making certain prudent estimates we think that we would get a flood wave on the order of 750 to 1,000 cubic metres per second."

As a comparison, at the peak of the Oct. 17-19 storm the inflow into the Daisy Lake reservoir reached 700 cubic metres per second.

Breaking the dam, the water would barrel down Fitzsimmons Creek with a tremendous force, washing debris down with it too.

Hutchinson said Ledcor will design the powerhouse so that it would be elevated above the flood water level, plus a little bit of a safety margin. It will also be tucked into the side of the mountain, sheltered as much as possible.

"So it’s not like a bowling pin in a bowling alley if you will," he said.

This was Ledcor’s worst case scenario but it will not stop the company from moving ahead with the project. The power project is on hold for the time being as the site will overlap the bob-luge track for the 2010 Winter Olympic Games and details have yet to be worked out with Olympic organizers.

Certainly when the heavy rains hit on Oct. 17 Barnett said the landslide area was not top of his concerns.

"We were dealing with a number of things that appeared to be quite urgent at the time," he said.

With heavy rain warnings in effect for that weekend, the municipality had scheduled extra crews to work. They checked the culverts and drainage systems beforehand to ensure everything was in order.

No amount of preparation could have stopped the logs coming down 21 Mile Creek and jamming the culvert at Alta Lake Road at 8 p.m. on Friday night. Hours later there was a log jam near the top of 19 Mile Creek and on Saturday morning the dike on that same creek began to leak a little.

Excavating crews were hard at work throughout the night but there was no respite from the rain.

By 5 a.m. on Saturday things were really starting to become a concern and directing crews and staff from his cell phone at home, Barnett called an emergency operations centre meeting.

Fortunately things started to settle down on the rivers and creeks on Saturday morning and concern switched to the flooding at Tapley’s Farm and Adventures West. The sandbagging began and major disaster was averted throughout Whistler.

"There’s a lot of things that could have gone wrong easily," said Barnett, adding that the bridge on Highway 99 over the River of Golden Dreams was also a major concern and could have been lost.

"Whistler could have been in fact isolated, cut right down the middle."

Barnett credits the work of the site personnel who worked tirelessly throughout the weekend to clear Whistler’s waterways.

Days later Barnett flew over the landslip area to monitor the movements of the ground. He said the half metre slip means the land is "behaving normally."

Since the three-metre movement in 1991, the municipality has also taken steps to mitigate any danger in the area as outlined in the comprehensive study called the Golder Report.

That study painted an ominous picture of a massive wall of water and mud spilling into the village. Baumann said new studies show that will not happen but there is still a chance that the day skier parking lots and the bus loop are at risk.

The municipality has built diversion ditches on the edges of the landslip area to direct any water flowing down the mountain around the sensitive section.

"If you have a diversion ditch to divert the water away, it remains relatively dry compared to the rest of the water infiltrating soils in that area. Then it’s stable," said Barnett.

The Golder Report also recommended building a diversion channel parallel to the creek. This channel would carry water around any dam should the land slide into the creek. It has yet to be built. The municipality estimates a construction cost of around $1 million. Baumann maintains it would cost $250,000. But the question remains: who pays for it?

Since the Golder Report came out Whistler and the province have been in discussions about responsibility for the landslip area.

"While we realize that there is probably more work that could be done up at that site... there’s quite a big price tag for it," said Barnett.

"It’s not fair to burden the Whistler taxpayers with that cost because it’s somebody else’s property. So we’d much prefer the provincial government to move forward on any work that’s necessary."

Technically the province owns the land, Whistler-Blackcomb is the tenant, and the municipality is the most affected should anything happen.

The province does not have a budget right now to deal with the problem.

"To my knowledge it’s not funded through the flood protection systems fund," said Ron Henry, deputy inspector of dikes for the Ministry of Water, Land and Air Protection.

"Just because it’s on Crown land... there’s lots of Crown land that has unstable slopes."

Discussions are ongoing with the province.

Barnett said: "It’s just not considered to be a significant hazard so nobody is putting money against it because it’s not considered to be a problem."