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

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In Could of 1894, speedy snow soften triggered a large 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 most important 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 this time, an analogous occasion would have a a lot completely different end result.

A Postmedia evaluation of data just lately offered to Decrease Mainland municipalities reveals greater than half of the dikes alongside the decrease Fraser would overtop in a repeat of 1894, inundating properties and companies in cities and First Nation communities, and huge swaths of farmland.

The info offered to Metro Vancouver and Fraser Valley municipalities — and to Postmedia at its request — used the newest dike crest survey info 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 info 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 data to a latest assembly of the Metro Vancouver flood-resiliency job pressure.

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

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The newest info does include caveats.

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

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

Litke stated he believes the largest limitation is the very 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 data to estimate how a lot of every dike would fail within the 5 flood situations, which additionally embrace one-in-200, one-in-100 and one-in-50-year floods.

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That info was then used to calculate the share of all of the dikes the place at the least some part of dike was anticipated to overtop within the 5 flood situations.

Along with the greater than 50 per cent that may overtop in a flood much like the one in 1894, the Postmedia evaluation confirmed a piece 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 info 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 job pressure, stated the newest dike crest-flood state of affairs 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.

Through the catastrophic flooding in November, regardless that Coquitlam was not flooded, the neighborhood was affected, for instance, by reduce off transportation routes and gasoline rationing. The lethal flooding within the Fraser Valley and B.C. Inside washed away properties, bridges and roads and resulted within the evacuation of 14,000 folks.

“We simply need to convey all people collectively. Definitely there’s a transparent must co-ordinate flood administration methods,” stated Hodge. “Now, we all know we are able to’t wait.”

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Communities the place there are vital parts of dikes that may overtop within the flood situations embrace 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, almost 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 the entire dike doesn’t meet the province’s freeboard guideline, in line with Postmedia’s evaluation.

Metropolis officers stated the Albion dike shouldn’t be owned by town, however 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 job pressure’s vice-chair, stated it’s nonetheless in all probability at the least one 12 months away.

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Work carried out earlier for that flood technique estimates an analogous 1894 flood in the present day would trigger about $23 billion in harm and lead to extreme financial fallout.

These newest flood state of affairs 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 in every of 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 obtained the Fraser Basin Council information and have used it alongside different studies 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 comparable to 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 line with Postmedia’s evaluation. And not one of the dike meets the province’s 0.6 metre freeboard tips.

In March 2017, below 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 below the authority of a diking district with a volunteer board, the province offered the cash to the Fraser Valley Regional District to manage on behalf of the diking district.

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

A 2015 report estimated the fee to improve your entire Nicomen Island dike system to trendy 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 varied flood situations, in line with Postmedia’s evaluation.

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

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The town didn’t say whether or not it had obtained the newest dike crest-flood state of affairs info from the Fraser Basin Council and had checked the figures on the bottom.

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

The November flooding was attributable to 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 they’d funded the newest work of the Fraser Basin Council, saying the data was offered primarily for native governments to organize 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 data additionally helps longer-term planning by dike authorities via the 4 components of emergency administration: preparedness, response, mitigation and restoration.

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

The federal authorities referred questions in regards to the new dike info, and what it meant for its plans, to the province.

ghoekstra@postmedia.com

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