What's Behind The Sumas Floods
- ExNews.net
- 17 hours ago
- 4 min read
Once again the relentless Nooksack River has surged north, flooding homes and farmlands on both sides of the U.S. – Canada border.
In Washington State, communities such as Everson and Sumas have seen roads, basements and agricultural fields submerged as the Nooksack overtops its banks. Across the boundary, in British Columbia’s Fraser Valley, Sumas Prairie and parts of Abbotsford are under evacuation orders, with highways closed and farmland inundated as officials scramble to protect lives and critical infrastructure.
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.
Historically, local weather patterns such as intense Pacific storm systems (sometimes termed atmospheric rivers by meteorologists) bring heavy rains that saturate soils and drive the Nooksack above flood stage. While some scientists and agencies link these intense rain events to a warming climate, noting shifts from snow to rain and increases in winter flood risk, definitive attribution in any one event requires careful hydrologic and climate analysis beyond simple labels.
Sumas Prairie Before European Settlement
Before Europeans arrived, what is now known as the Sumas Prairie was dominated by Sumas Lake, a shallow freshwater lake surrounded by extensive wetlands. The lake’s ecosystem supported salmon, waterfowl and other wildlife, and was integral to the Semá:th (Sumas First Nation) people’s way of life, providing food and cultural connections to the land.
Draining the Lake and Keeping it Dry
In the early 1920s, colonial and provincial authorities dramatically altered the landscape by draining 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 Goes Wrong - 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.
Atmospheric Rivers and Flooding
“Atmospheric river” is a meteorological term referring to narrow corridors of concentrated moisture transport in the atmosphere — not a legal or climatological classification of climate change itself. These phenomena are associated with heavy precipitation and flooding across the Pacific Northwest, including in 2021 and 2025, but attributing them solely to global warming oversimplifies a complex climate and weather system that scientists continue to study.
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.
What Exactly Does the Sumas Canal Do?
The Sumas Canal is part of the engineered drainage system that moves water from the low-lying Sumas Prairie toward the Sumas River and Fraser River. It works in concert with dikes and pumps to lower the former lakebed and keep farmland and communities dry under normal conditions. However, the system’s capacity is limited; during major overflow or when downstream rivers are high, the canal alone cannot prevent inundation.
Flood Control: Possibilities and Limitations
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.
Cost and Shared Action
Comprehensive flood mitigation, including infrastructure upgrades, habitat restoration, and planning. would be costly. While specific dollar figures vary by project scope, municipal and provincial funding allocations (e.g., millions for canal and dike improvements) reflect significant investment even for relatively small segments of the challenge. Large-scale transboundary projects could run into the hundreds of millions or billions over decades, depending on design standards, climate projections and shared funding agreements.
Conclusion: Control or Coexistence
Full control of flooding in the Nooksack–Sumas–Fraser system may be neither feasible nor cost-effective.
Instead, reducing risk will require a combination of infrastructure improvements, land-use planning, and coordinated action between the United States, Canada and Indigenous partners, because floodwaters and weather do not respect political borders.