Why Sumas Prairie remains vulnerable to a repeat of 2021
Sumas Prairie's dikes, pump stations, and other infrastructure remain unable to handle flooding from the Nooksack River
The last two years worth of dike fixes, dredging, and awareness-building may help mitigate damage on Sumas Prairie the next time the Nooksack floods.
But no one is pretending they are enough to avert another major disaster. Indeed, the scope of the challenge and the practical realities of planning and funding large flood management projects mean that the largest, most-consequential works required to protect the prairie may not be completed for years—or decades.
Yesterday, we looked at the reasons Sumas Prairie is more prepared for a Nooksack River flood than in 2021. Today, we examine the massive vulnerabilities that remain. Tomorrow, we’ll consider the implications of a changing climate and the political obstacles to safeguarding the prairie.
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Next week we will look at other places that were affected by 2021’s atmospheric rivers, including Hope, Clayburn Village, and the Fraser Canyon.
Currently, Abbotsford’s dikes protect the Sumas Prairie’s lake bed in the event of a one-in-35-year flood event—or a flood for which there is an expected 3% chance each year. But they’re not much better than that, which leaves them far below provincial standards, which aim for a one-in-200-year standard, factoring in climate change.
The 2021 flood was a one-in-100-year event, meaning it was large and relatively rare, but not unprecedented. The probabilities are such that even discounting the impacts of climate change, a child born in 2020 would be likely to also live through another such flood.
So if an identical flood struck again this year, the prairie’s dikes, highways, pump station, and other infrastructure would still be incredibly vulnerable.
The City of Abbotsford has planned and designed a series of changes to its flood protection infrastructure to try to accommodate Nooksack overflows with as little damage as possible.
Its proposed dike and pump system would funnel water north from the United States towards the Sumas Canal. As the water flowed toward Highway 1, it would enter a floodway zone that would carry it beneath the highway. That floodway area would carry the water toward a new Sumas River Pump Station.
The station would be a new piece of infrastructure designed to address a major design flaw of the current Sumas Prairie flood management system.
The system currently operates on the assumption that when water levels in the Sumas and Nooksack rivers are highest and most prone to flooding, the elevation of the Fraser River is significantly lower. Water flows downhill, via gravity, through a floodgate next to Barrowtown Pump Station. Those floodgates can be closed in spring, when the Fraser River rises to its highest levels—if the gates did not exist, the Fraser’s springtime height would cause the Sumas River to flow backwards.
Floodgates allow water to drain from Sumas Prairie into the Sumas Canal and Fraser River. But 2021 exposed their limitations when water in the Fraser is too high. 📷 Tyler Olsen
Usually the Fraser is low in November, when precipitation across much of its massive Interior watershed is either relatively limited, or falling as snow.
But in 2021, the atmospheric river dumped huge amounts of water across a huge swath of land surrounding Merritt. The same water that washed away bridges in the Nicola Valley and along the Coquihalla River flowed into the Fraser, causing it to rise far above its normal November levels. That had consequences in Abbotsford because the water flowing into the Sumas River couldn’t escape into the Fraser River, which was even higher. For four days, the Barrowtown floodgates had to remain closed. If they had been opened, water from the Fraser would have rushed into the prairie, further aggravating the flooding situation.
“Sumas Prairie is like a big bathtub,” Rob Isaac, Abbotsford’s head engineer said. “When the floodgates closed, the drain closes in the bathtub, and if the water continues to flow across the border, that storage in the bathtub just increases.”
It’s even more complicated than that because there are actually two bathtubs. One in the western part of the prairie, another in the former bed of Sumas Lake. The western section is drained through the Barrowtown floodgates. The eastern is considerably lower and all water must be pumped out by the Barrowtown station. Two years ago, the floodgates closed, the water level reached the edge of the dikes surrounding the Sumas lakebed. Once it started to overtop the dikes, water rushed into the lake bed—the larger, deeper bathtub. As the water rushed over the dikes, it began to erode them, speeding up the flooding of the Sumas lakebed.
Understanding the floodgates is critical because they remains in place and are the impetus for a proposed new Sumas River Pump Station. In the event that the Fraser’s level was higher than water levels in Sumas Canal, a proposed new pump station would allow for water in the western prairie to be pumped uphill, to a level at which it would then be allowed to flow into the Fraser and to sea.
The new pump station would work in tandem with new and improved dikes that would funnel water toward it. But a new station would be incredibly expensive and it remains to be seen if and when it may be built.
The City of Abbotsford has designed its preferred flood mitigation plan. But it comes with a massive estimated cost of $2.5 billion. That money, which would both build a new pump station, and a series of new dikes, would be roughly equivalent to Abbotsford’s spending over an entire decade. The city doesn’t have that money, meaning that the work will rely on the provincial and federal governments to decide that it’s necessary and a priority.
A plan without commitment
The province is working on a new flood plan for the entirety of British Columbia that will restructure how such projects are funded. The federal government is also re-evaluating how it prepares for and funds disaster mitigation endeavours.
The flood defences are just one part of the equation. Governments are still reckoning with how they might floodproof vital pieces of infrastructure. The most obvious and vulnerable is Highway 1, and plans for its widening have been overhauled in order to consider how it might be made more resistant to flooding. (The fact this aspect wasn’t a consideration before 2021, despite the highway’s flooding in 1990, is another reminder of how lessons from previous disasters can be forgotten.)
The price tag of the proposed Sumas Prairie improvements dwarfs the work that the two governments have funded thus far. In fact, it’s likely to be larger than all flooding protection works undertaken across the entirety Canada this year. The Federal Government’s entire National Disaster Mitigation Program, which allocates money across all of Canada to help communities prevent recurring flood risks, had just $20 million to allocate. Abbotsford’s project needs 100 times that sum—though if it proceeds, costs would likely be mostly shared between the provincial and federal governments. And Abbotsford is hardly the only city in British Columbia or Canada that is vulnerable to flooding and needs help.
If Abbotsford’s plans are to come to fruition, they’ll likely be completed incrementally, in stages over the course of decades. The pump station—perhaps the most-expensive single piece of infrastructure—is necessary to safeguard the prairie in cases of dual Nooksack and Fraser high water events. But it’s not the most urgent piece of infrastructure given the fact that not all Nooksack floods will coincide with such high water in the Fraser.
Raising and readjusting the dikes without the immediate addition of a new pump station would still make Sumas Prairie considerably safer during November rain events. Even new dikes, though, will cost a lot of money. When the City of Abbotsford last considered the cost of raising its insufficiently high dikes, the cost was pegged at more than $400 million.
The cost of the proposed solutions speak to the amount of work still necessary to significantly reduce the flood risk on Sumas Prairie. The fact that such work is considered necessary also means the prairie remains vulnerable today.
The Current asked the province how the province will make a decision to fund or not fund Abbotsford’s preferred flood management concept.
The province provided an emailed answer response that cited a n agreement signed last year with the cities of Chilliwack and Abbotsford and local First Nations that it said “will support the design of mitigation projects in the Sumas River watershed and timely delivery of watershed recovery programs that benefit people and the farming community and protect infrastructure.”
The province said its funding for projects will depend on federal government approvals that have yet to be received.
The high level of the Fraser River in 2021 made it impossible to drain water from Sumas Prairie for days. 📷 City of Abbotsford