What's Behind The Sumas Floods
- Vernon News Desk
- Dec 12, 2025
- 3 min read
Updated: Dec 16, 2025
Once again the relentless Nooksack River has surged north, flooding homes and farmlands on both sides of the U.S. – Canada border.
The Sumas Prairie near Abbotsford was once a shallow lake, naturally collecting rainwater, snowmelt, and runoff from the surrounding landscape.
The lake was drained more than a century ago through an extensive canal system designed to move water by gravity into the Fraser River. But that system has limits.
When the Fraser is already running high, floodgates close to prevent river water from entering the canal system. When that happens pumps are required to move water from the Sumas Canal past the gates into the Fraser.
If floodwaters from the Nooksack River in Washington spill north across the border at the same time, the entire system can be pushed beyond capacity, leading to widespread flooding on the prairie.
These floodwaters effect communities on both sides of the border. In Washington State, communities such as Everson and Sumas have seen roads, basements and agricultural fields submerged. In BC the Sumas Prairie and other parts of Abbotsford suffer the same fate.
Typical Behaviour of the Nooksack
The Nooksack River, entirely within Washington State, drains snowpack and rainfall from the slopes of Mount Baker and its tributaries. Under typical conditions it flows westward towards Bellingham Bay. However, during intense rainfall and elevated river flows, particularly in late autumn through early winter, water levels can rise rapidly. When the river exceeds its banks near Everson, much of the overflow follows low-lying topography north into the Sumas watershed within hours of overtopping.
In the early 1920s, the area was dramatically altered by the draining of Sumas Lake to create agricultural land.
Starting around 1920 and largely complete by 1924, the Chilliwack River was diverted, and the lake was emptied via the Sumas Drainage Canal into the Fraser River, creating the fertile flatland now known as Sumas Prairie.
To keep the former lakebed dry, a system of dikes, drainage channels (including the Sumas Canal), and the Barrowtown Pump Station were constructed. These works continuously remove water that naturally accumulates in the lowland area, channeling it into the Sumas River and ultimately to the Fraser River.
The Sumas Canal is a primary part of this drainage network, moving water from the Sumas Prairie into the Sumas River and helping regulate groundwater and surface flows.
What are the Causes of Flooding
Flooding in the Sumas Prairie occurs when one or more systems are overwhelmed:
Nooksack Overflow: When the Nooksack overtops its banks in Washington, water flows northward over the border, overwhelming the drainage capacity of the Sumas River and canals.
Pump Capacity Limits: The Barrowtown Pump Station and canal network have finite capacity; when inflows exceed what the pumps and channels can move, water spreads across the prairie.
Backwater Effects: High Fraser River levels can force floodboxes to close to prevent backflow, temporarily trapping water in the Sumas system.
Storm Intensity: Extreme rainfall events can overwhelm both river and drainage infrastructure.
Frequency of Floods Since Drainage
Since Sumas Lake was drained, major flood events have recurred with notable frequency. Significant historical floods include events tied to Fraser River freshets (e.g., 1894, 1948, 1972) and intense rainfall events such as November 1990 and November 2021, when Nooksack overflow caused widespread flooding in Sumas Prairie and Abbotsford.
Role of the Fraser River
While the Fraser River is a dominant flood risk in the Lower Mainland, its direct influence on Sumas Prairie flooding is usually secondary. High Fraser levels can impede drainage from the Sumas Canal and pump stations when floodboxes must close, exacerbating local flooding once water from the Nooksack or Sumas River arrives.
Flood control in this transboundary watershed raises challenging questions:
Engineering Upgrades: Strengthening dikes, expanding conveyance channels, and increasing pump capacity can reduce local risk but cannot eliminate it entirely.
Floodplain Management: Creating additional space for floodwaters (e.g., restoring natural floodplains) may absorb peak flows but requires land use changes and long-term planning.
Transboundary Collaboration: Because the Nooksack lies entirely within the U.S. but affects Canadian communities, unilateral action by one country is insufficient.
The Transboundary Flood Initiative, a collaborative framework involving Canadian and U.S. governments, First Nations and tribes, is explicitly aimed at shared flood risk reduction and ecosystem restoration.
Comments