How river restoration ebbs flood risk in Edmundston

At the start of summer 2023, in the northwestern New Brunswick district of Saint-Jacques, a sudden and intense rainstorm dumped a reported 150 millimetres of rain in an hour onto the small city of Edmundston. The resulting flash floods affected over 230 homes, triggered a landslide, shut down roads, destroyed culverts and caused damages totalling $20.5 million. 

Edmundston is located upstream in the Wolastoq (Saint John river) watershed, a complex maze of tributaries, lakes and marshlands that wind through several cities in New Brunswick. The 2023 flood was just one example of extreme weather events in the province in recent years. 

In fact, the Edmundston flood was relatively minimal compared to the province’s record-breaking spring 2018 freshet flood — the second of that year after a January rainstorm unloaded as much as 127 mm — which closed 140 bridges, culverts and roads, affected 12,000 properties and caused $75 million in damages.

A year later, the freshet — the worst of 2019’s three flooding events costing a collective $93.2 million — brought the river even higher, reaching 8.37 metres in Fredericton and affecting 15 communities, with more than 1,200 evacuees and the military called in to provide support.  

Why is this happening?

With the Wolastoq’s serpentine river systems winding across the watershed to the sea, New Brunswick has always experienced flooding, especially during spring thaw — just not like these.  

Climate change has made floods more intense and more frequent, leaving behind a swath of damaged homes, infrastructure and habitats from too-rapid snowmelt and ice jams, and increasing extreme rain events and coastal storm surges. A 2019 study estimated the volume of flooding in New Brunswick could increase 30 to 55 per cent by 2100.  

A warmer atmosphere also increases the temperature of bodies of water, affecting cold-water species already at risk like the Atlantic salmon, an endangered migratory fish battling huge declines from overfishing, pollution and blocked migration paths. Warmer water temperatures and warmer winters have also increased the spread of invasive species (e.g. zebra mussels, forest caterpillars) that outcompete native species and disturb ecosystems. 

Which brings us back to Edmundston, where Stéphanie Paradis-Léger and her team at INNOV, the applied research division of the Collège communanutaire du Nouveau-Brunswick, have been working to reduce flood risks and improve climate resilience.  

Paradis-Léger’s case study on the Rivière-à-la-Truite watershed evaluated and recommended specific nature-based solutions to mitigate flood risks in the area. This study identified the eroded Rue Demers channel, a 230-metre section of the Rivière-à-la-Truite, as a priority area for floodplain restoration because of high flood risk, increased river speed and visible signs of erosion on the riverbanks and bridge. 

With the financial support of WWF-Canada and Wawanesa Insurance through their Climate Champions program, INNOV and the city of Edmundston restructured this channel. They constructed a series of rock structures that control the channel’s elevation and slope.

This helps reduce riverbed erosion, prevent excessive deepening of the channel and help manage the transport of sediment in areas so they won’t create drainage or flooding problems. Eroding riverbanks were also reshaped to appropriate heights and native trees and shrubs were planted on floodplains to lessen flood impacts when it does happen.  

The team planted a diverse range of native species, like silver maple, trembling aspen, dogwood and elderberry, to provide habitats for local wildlife. Some were chosen for their tolerance to wet conditions and/or how quickly they develop root systems, which helps the soil absorb more water and manage erosion. 

These plants also increase the roughness of the soil’s surface which helps slow down the flow of water during floods. Trees that provide shade over rivers also help moderate water temperatures, greatly benefiting cold-water species.  

“The cool thing about nature-based solutions is that even though it takes a bit longer to stabilize, once it does, it can have an indefinite life cycle with reduced maintenance over the years,” said Paradis-Léger, emphasizing restoration’s long-game.  

“We’re hoping to see ripple effects with more initiatives like this put in place in the region to mitigate flood risk and erosion problems.”