In November, 2021, an ‘atmospheric river’ swept through southern BC delivering unprecedented rainfall levels. The rain volumes resulted in landslides and flooding that closed major roads and bridges for the region. In Maple Ridge we were fortunate that the storm abated before damage was done to the roads and bridges along the north and South Alouette rivers which would have blocked access into the Silver Valley neighbourhoods.
While these two rivers have independent rainfall catchment areas, their downstream floodplains can interconnect during rainfall events. As a reminder, both rivers are unconfined (without dykes) and flow rates are driven by local rainfall intensities. In some circumstances, BC Hydro can provide some flood attenuation for the South Alouette River, however this ability is dependent on rainfall intensity, available storage volume and the dam spillway capacity.
The City has exerted a lot of effort studying these two watercourses over the years culminating in the North Alouette and South Floodplain Analysis in 2016 and the completion of Integrated Stormwater Management Plans in 2021. Here is information specific to the flood risks associated with this part of our City.