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Flood waters from the Fraser River surround a farm in Chilliwack, B.C. Thursday, June 28, 2012. Fraser Valley residents are bracing for a weekend of rising waters and potential flooding.

Jonathan Hayward/The Canadian Press

When Stephen Déry looks out at the Fraser River sweeping past Prince George and threatening to overflow its banks, he knows he is looking at something British Columbians could see a lot more of in the future.

"It is absolutely amazing. I've never seen the Fraser so high," said the professor at the University of Northern B.C., whose research indicates such high water events are becoming more common in the Fraser basin.

"Absolutely, we're going to see more events like this," he said Thursday in an interview from Prince George, which has been on flood alert for the past week.

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After analyzing 100 years of hydrological data collected at 139 Environment Canada river gauges scattered throughout the watershed, Prof. Déry and his colleagues have concluded the Fraser is increasingly experiencing extreme flows, largely because of climate change and a catastrophic pine beetle epidemic that has killed off much of the forest in the central province.

"The pattern we are seeing emerge is exactly what the model projections have been foreseeing," he said, referring to earlier theoretical research that predicted that in the future the Fraser would likely start to have one-in-100-year flood events every four to 10 years. "We may need to consider building higher dikes."

He said the data shows the Fraser and its extensive system of tributaries are not only having more high-water events, but more low-water events as well.

"Our main finding is that over time, the last three or four decades especially, what we're noting is greater year-to-year fluctuations," he said.

"When the flows are high they are really high, and when low they are really low, so we are flipping back and forth much more than we were in the past."

Prof. Déry said climate change is a major factor. "When we have warm dry years they are very hot and very dry and when you have cool years … they are very wet," he said.

And in wet years the loss of much of the pine forest to a beetle infestation in central B.C. is exacerbating conditions, he said.

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"The water … is not being picked up by the vegetation and instead runs off into the streams and creeks that feed the Fraser. And so we have a higher delivery of water because of the pine beetle kill," he said.

The low-water events are likely to get lower, he said, because glaciers in B.C. are rapidly retreating, which means less melt water will be flowing into tributaries in the summer.

Prof. Déry said the fluctuating water conditions could not only mean more flood threats, but smaller salmon runs too.

Jeff Grout, Fisheries and Oceans regional resource manager for salmon on the Fraser, said commercial fishing may have to be limited this year because of flood waters. He said the high water levels mean fish are battling stronger currents, and that can lead to exhaustion and death for fish.

Neil Peters, B.C.'s inspector of dikes, said it is not yet clear what the changing climatic conditions mean for the lower Fraser River in terms of flood threats.

He said climate change is expected to cause more rainfall in the spring, but it could also bring less snow during the winter, which could counterbalance the flood threat in the spring.

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This year a big snow pack, combined with heavy rainfall last weekend, pushed the Fraser to the highest level it has seen in 40 years.

Mr. Peters said the extensive diking system on the Fraser "did okay" under the circumstances, but he wouldn't like to see it tested by higher water levels, such as those that caused floods in 1972, 1948 and 1894.

Asked if the dikes as currently designed – to withstand a 100-year flood – are adequate, he replied: "Yes, for the event that we've had. I think it's a different question if we had an event that's closer to the [1894] design event or to 1948."

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