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Study puts FV flooding costs at $1 billion [Peter Mitham]

APRIL 2017 | MISSION – John Kerkhoven farms 350 acres at Deroche on Nicomen Island where he milks 100 cattle and runs a 60,000-square-foot cut-flower operation.

Kerkhoven also chairs the Nicomen Island Improvement District which oversees drainage and 35 kilometres of diking that protects residents from the Fraser River freshet each spring. The dikes are considered the most vulnerable in the region, being about a metre below the current standard, but Kerkhoven says they’ve served the community well.

“Our dikes have withstood many fairly high freshets, up to about almost 23 feet at the Mission gauge,” he says. “Even in 1948, our present-day dikes would have been challenged but it’s really only the flood of record, which is from 1894, that would have overtopped our dike.”

Water levels at Mission hit 26 feet in 1894 while in 1948 water levels reached 23.5 feet. The largest freshet of the past decade was 2007 when water at the Mission gauge hit 18 feet.

This year, with a near-normal snowpack set to melt into the lower Fraser River, Kerkhoven isn’t worried. Weather forecasters are calling for a cool spring in the run-up to summer and snowpacks further up the river are well below normal. However, he knows it’s not just the size of the snowpack but the speed of the melt that determines flood risk.

“You have to have a combination of warm temperatures, precipitation and a significant snow melt, and that’s really very difficult to predict because there have been years when there’s been enormous snowpacks and we haven’t had particularly high water,” he explains. “[Yet] if you look at the history of 1948, the total volume of water may not have been all that great but it came in an incredibly short period.”

Other freshets deliver a steady volume of water that keeps the river flowing at 18 to 20 feet for several weeks, keeping the ground moist as water seeps up through the porous soils.

“Those are actually a little bit more obnoxious, not because it might be detrimental or threaten our dikes, but we have to tolerate the seepage for a much longer period of time,” Kerkhoven says.

While most people think the biggest threat to a dike is an overflow of water, the sheer volume of water borne by a sustained freshet can force water through the soil to the point that it undermines the dike. This worries Kerkhoven more than a breach from above.

“I think the much more likely scenario is that you get pressure, you get piping, so you get the moving of aggregate – sand boils. And if you got a significant sand boil, your dike would actually fall,” he says.

Key infrastructure

A new study the Fraser Valley Regional District (FVRD) commissioned in partnership with the BC Agriculture and Food Climate Action Initiative estimates that Chilliwack would bear the brunt of damages in the event local diking systems fail – more than $363 million in direct farmgate losses, or 43.5% of the aggregate cost to the region’s producers.

BC is home to more than 200 dikes totalling 1,100 kilometres. The Lower Mainland alone is home to 600 kilometres of diking, infrastructure worth billions of dollars. It’s an investment that delivers good value: according to the Fraser Basin Council, a catastrophic flood would do $32 billion worth of damage across the Lower Mainland.

Based on four flood scenarios, the latest study estimates damages to the agriculture sector in the Fraser Valley Regional District (the area between Abbotsford and Hope) at $1.1 billion in the worst-case scenario.

The study examines the effect of a recurrence of the 1894 flood in which local dikes fail; a flood where flows are 17% greater than in 1894, also resulting in dike failures; a less powerful flood in which only weaker dikes fail; and a flood in which only the Matsqui dike fails.

The fact that a flood of the magnitude of 1894 hasn’t repeated itself is often attributed to the diking systems that protects the Fraser Valley, whose farmers enjoy annual farmgate sales of $1.1 billion – approximately 38% of the provincial total. Agri-businesses in the region have additional sales of $844 million, contributing to an economic impact the report estimates at $3.1 billion.

It could all wash away if the dikes fail.

“A disastrous flood of record that hits Chilliwack is going to impact the Fraser Valley, it’s going to impact British Columbia, and it’s going to have an impact nationally,” says FVRD chair Jason Lum, a Chilliwack councillor.

Many dikes along the Fraser River don’t measure up, according to a recent assessment the BC Ministry of Forests, Lands and Natural Resource Operations conducted, with the Nicomen Island system among the most vulnerable in the region.

A report the Fraser Basin Council issued last year identified an urgent need for improved flood defences.

“Significant funds are needed to rehabilitate existing dikes to meet current provincial standards. Upgrades would reduce the likelihood of multiple dike failures during a recurrence of the Fraser River flood of record or a large coastal storm surge,” the report said.

Nothing new

Yet concern regarding dike failures, like concern about earthquakes, isn’t new.

A report the Fraser Basin Council issued in 2006 garnered extensive media attention. The following year, the province allocated $15.5 million to flood mitigation measures, primarily in the Lower Mainland.

All told, the province has committed $182.7 million to flood mitigation projects around the province over the past decade, including $60 million on March 15 that included $10.5 million for Nicomen Island. However, it falls short of the hundreds of millions needed to maintain diking in the Lower Mainland.

Lum says the FVRD has spent millions on dike maintenance since Ottawa downloaded the job onto local government in the 1990s. It’s an arrangement that can’t go on.

“The investments required far exceed the capacity on the local tax base. We have one way to raise money and that’s property taxes,” he says. “While the FVRD and the municipalities have all taken active roles around pro-active flood mitigation measures, the investments required from the provincial and federal governments are going to be significant.”

The new study gives municipalities the information they’ll need to advocate for themselves, says Alison Stewart, strategic planning manager with the FVRD. While the FVRD doesn’t help farmers prepare for flooding or to mitigate the risks a flood event presents, she says the report provides information that can help them watch out for themselves.

“It’s a fairly broad-reaching study, and looking at what can be done to mitigate the risk,” she says. “It goes from a very high level down to how farms can flood-proof.”

Over on Nicomen Island, Kerkhoven commissioned an engineer’s report on the state of local diking in 2015 and last year convened a meeting to discuss flood responses. Still, improving the state of the dike will require cash – approximately $2 million per kilometer.

“We apply often, or whenever there’s an offer of infrastructure money – usually from both levels of government, provincial and federal,” he says. “[But] because we don’t have a railroad that could be of national or international importance, we don’t have any natural gas lines, we don’t have any major highways running through … and we have less than 10,000 residents, we are not at the top of the list for getting infrastructure upgrades.”

Kerkhoven understands that money’s tight and that choices have to be made. Richmond has just as much dike as Nicomen Island but it also has the airport and other valuable infrastructure. Yet the floodwaters won’t discriminate as they roll west to the sea.

It leaves him philosophical.

“We as residents and farmers on Nicomen Island have to reconcile the fact that everything other than the big one, we’ll do our best to survive,” he says. “We kind of have to live with that.”

Vol.103 Issue 4
APRIL 2017

CLBC April 2017 cover CLBC April 2017