Half of Fraser River dikes would overtop in repeat of 1894 flood

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In Could of 1894, fast snow soften triggered an enormous flood from the higher Fraser Valley to Richmond. Houses, barns and bridges have been swept away and railway tracks have been left twisted from the lethal flooding.

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The flood was the biggest on the Fraser River since settlers arrived. However as a result of the inhabitants was so low, the worth of property damages was not nice, maybe a half-million {dollars} by one estimate.

At present, an identical occasion would have a a lot completely different consequence.

A Postmedia evaluation of knowledge not too long ago supplied to Decrease Mainland municipalities reveals greater than half of the dikes alongside the decrease Fraser would overtop in a repeat of 1894, inundating houses and companies in cities and First Nation communities, and huge swaths of farmland.

The info supplied to Metro Vancouver and Fraser Valley municipalities — and to Postmedia at its request — used the newest dike crest survey data produced by the province in 2019 and 2020 and was utilized to 5 flood situations, starting from the 1894 flood, thought of a one-in-500-year occasion, to a one-in-20-year occasion.

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The info for 100 dikes was produced by the non-profit Fraser Basin Council, which helps co-ordinate a Decrease Mainland flood technique with municipalities, the province and Ottawa.

The brand new data is supposed to assist communities put together for spring high-water ranges on the Fraser, referred to as a freshet, and to affect longer-term plans to enhance flood resiliency as local weather change is anticipated to make flooding extra frequent and extreme.

“It’s one piece of the puzzle,” says the Fraser Basin Council’s director of water applications, Steve Litke, who introduced the knowledge to a latest assembly of the Metro Vancouver flood-resiliency activity drive.

“Clearly, the crest top of the dike is critical, a reasonably necessary a part of a dike functioning correctly relative to completely different flood occasions. … This does reveal deficiencies when it comes to top,” stated Litke.

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The newest data does include caveats.

The evaluation focuses on the spring freshet and doesn’t embody potential flooding from coastal storm surges or flooding from different rivers — and in consequence doesn’t embody all of the dikes alongside the decrease Fraser.

The Fraser Basin Council has cautioned native governments the knowledge ought to be checked on the bottom for measurement errors or conditions the place some characteristic reminiscent of adjoining excessive floor offers flood safety.

Litke stated he believes the most important limitation is the actual fact there are different ways in which dikes can fail earlier than overtopping, together with erosion and seepage. “So, that’s a further concern that isn’t mirrored in these outcomes,” he stated.

Postmedia used the knowledge to estimate how a lot of every dike would fail within the 5 flood situations, which additionally embody one-in-200, one-in-100 and one-in-50-year floods.

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That data was then used to calculate the share of all of the dikes the place not less than some part of dike was anticipated to overtop within the 5 flood situations.

Along with the greater than 50 per cent that will overtop in a flood just like the one in 1894, the Postmedia evaluation confirmed a bit of greater than one-third of the Fraser River dikes would overtop in a one-in-200-year flood, 20 per cent in a one-in-100-year flood, 16 per cent in a one-in-50-year flood and greater than 10 per cent in a one-in-20-year flood.

Postmedia additionally examined data on whether or not dikes met the province’s tips for a buffer between the high-water mark and the highest of dikes, referred to as freeboard. The rules name for a 0.6-metre buffer for the one-in-500-year flood.

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The info confirmed 83 per cent of dikes had some sections that didn’t meet this guideline.

Craig Hodge, a Coquitlam councillor and vice-chair of the Metro flood-resiliency activity drive, stated the newest dike crest-flood situation modelling helps help work on a Decrease Mainland flood technique and underscores the necessity for funding and the urgency to get began on dike enhancements.

In the course of the catastrophic flooding in November, though Coquitlam was not flooded, the neighborhood was affected, for instance, by minimize off transportation routes and fuel rationing. The lethal flooding within the Fraser Valley and B.C. Inside washed away houses, bridges and roads and resulted within the evacuation of 14,000 individuals.

“We simply must carry all people collectively. Actually there’s a transparent must co-ordinate flood administration methods,” stated Hodge. “Now, we all know we will’t wait.”

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Communities the place there are important parts of dikes that will overtop within the flood situations embody Maple Ridge, Mission, Delta and Nicomen Island within the Fraser Valley, which features a neighborhood of the Leq’á:mel First Nation.

Within the Metropolis of Maple Ridge, practically 90 per cent of the two.5-kilometre Albion dike would overtop within the one-in-500-year flood, with seven per cent of it overtopping in a one-in-20 12 months occasion. Virtually all the dike doesn’t meet the province’s freeboard guideline, in response to Postmedia’s evaluation.

Metropolis officers stated the Albion dike isn’t owned by town, nevertheless it has been finishing up work on the request of the province.

Metropolis spokesman Fred Armstrong stated town has the newest Fraser Basin Council figures and had carried out its personal surveys, which have helped affect town’s freshet flooding plan.

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“Within the occasion of potential inundation of the areas, town’s freshet flooding plan has an interim plan to put concrete blocks alongside the sting of the river to behave as a brief dike till such time as a everlasting dike can be accomplished,” stated Armstrong.

The town has stated it’s prepared to take possession of dikes within the metropolis however not till the province offers funding for upgrades to present requirements, which additionally should be a part of a complete plan alongside the Fraser River, famous Armstrong.

The Decrease Mainland flood technique was meant to set flood mitigation priorities, prices and a cost-sharing mannequin however is 4 years overdue. Hodge, the Metro flood-resiliency activity drive’s vice-chair, stated it’s nonetheless in all probability not less than one 12 months away.

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Work carried out earlier for that flood technique estimates an identical 1894 flood immediately would trigger about $23 billion in injury and lead to extreme financial fallout.

These newest flood situation figures underscore the numerous enterprise wanted to enhance flood safety on the decrease Fraser — and the struggles native governments and First Nations have to try this.

A latest Postmedia Information investigation discovered that municipalities don’t have the billions of {dollars} wanted to improve flood safety after the province downloaded duty to municipalities starting in 2003.

In Mission, evaluation confirmed 16 per cent of one among its dikes alongside the Fraser River, largely defending industrial property, would over high within the one-in-500 12 months flood, 10 per cent within the 200-year occasion and 6 per cent within the 100 12 months occasion.

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Greater than 20 per cent of the dike doesn’t meet the freeboard tips.

Metropolis of Mission spokeswoman Taryn Hubbard stated they acquired the Fraser Basin Council knowledge and have used it alongside different stories and research to affect their work and planning. A latest report on the state of Mission’s dike system discovered they’re “poor” with points reminiscent of being decrease than design flood ranges, and pumps not having sufficient capability.

Within the Fraser Valley, Nicomen Island’s dikes additionally face overtopping in flood occasions. About 90 per cent of the 35-kilometre dike system would overtop in a one-in-500 12 months occasion, in response to Postmedia’s evaluation. And not one of the dike meets the province’s 0.6 metre freeboard tips.

In March 2017, beneath the then-B.C. Liberal authorities, the province introduced $10.5 million to improve the Nicomen Island dikes.

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Though the dike is beneath the authority of a diking district with a volunteer board, the province supplied the cash to the Fraser Valley Regional District to manage on behalf of the diking district.

A number of the funding is anticipated for use to improve 5 pumping stations, whereas different funds could also be used to widen and lift a number of the dike system, stated Fraser Valley Regional District spokeswoman Angelique Crowther.

A 2015 report estimated the price to improve your entire Nicomen Island dike system to fashionable requirements can be $65 million.

In Delta, there are sections of its dike system within the Ladner space that have been discovered to overtop in numerous flood situations, in response to Postmedia’s evaluation.

Suman Shergill, supervisor of utilities and engineering for town, stated because of the neighborhood’s proximity to the ocean, its dikes are constructed to resist a 200-year winter coastal flood, which produces larger water ranges than a spring freshet.

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The town didn’t say whether or not it had acquired the newest dike crest-flood situation data from the Fraser Basin Council and had checked the figures on the bottom.

Following final 12 months’s lethal flooding that triggered billions of {dollars} in injury, B.C. municipalities and First Nations have been calling for the province and Ottawa to indicate extra management on flood safety.

The November flooding was brought on by an atmospheric river, a torrential downpour in a brief time period. That is completely different than a spring freshet but additionally anticipated to extend in frequency and severity due to local weather change.

B.C. authorities officers famous that they had funded the newest work of the Fraser Basin Council, saying the knowledge was supplied primarily for native governments to arrange for the freshet alongside the Fraser River.

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However Andrew Giles, supervisor of the River Forecast Centre and flood security for the province, stated the knowledge additionally helps longer-term planning by dike authorities by way of the 4 parts of emergency administration: preparedness, response, mitigation and restoration.

“This data additionally offers a basis for additional dialogue between the province and diking authorities towards flood danger discount,” stated Giles.

The federal authorities referred questions concerning the new dike data, and what it meant for its plans, to the province.

ghoekstra@postmedia.com

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