Flood Monitoring and Classification in Canadian Rivers Using SWOT Observations

Canada possesses one of the world's most extensive and diverse river networks, characterized by seasonal and regional variation in nival, glacial, and pluvial hydrological regimes and landscapes from lowland agricultural, to lakes and forests, to tundra and high mountains.  Long snow-covered winters and a large spring freshet characterize the hydrological regime of most of the country.  Monitoring river floods in this region faces significant challenges because of the sparse hydrometric gauging network, especially in northern Canada, and limited traditional remote sensing capabilities. The Surface Water and Ocean Topography (SWOT) satellite mission represents a transformative advance by providing all-weather, wide-swath measurements of water surface elevation (WSE) and water surface slope. This study presents a comprehensive framework to extract and classify river water wave dynamics across Canada using the SWOT_L2_RiverSP products. First, a quality-control protocol was established based on intrinsic orbital and geometric attributes. Evaluation of river width, cross-track distance, and WSE against observations from Water Survey of Canada hydrometric stations identified the river reaches where SWOT signals were most reliable. A novel Slope-WSE Phase Space method to classify river floods distinguished ice jam floods, confluence backwater effects, and freely propagating floods due to nival and pluvial mechanisms. The flood classification was then diagnosed using multi-source datasets, including ERA5 reanalysis precipitation/temperature and Landsat/Sentinel remote sensing imagery. SWOT successfully monitored floods, and the distinct hydraulic gradients of ice-jam induced backwater where water surface dynamics were previously unobservable by in-situ hydrometry. Even in the  narrow rivers (< 100 m), SWOT had good capability to measure the temporal propagation and hydraulic gradients of flood waves when compared with downstream hydrometric records. This research demonstrates the SWOT’s ability to monitor not just river water level dynamics, but also the underlying hydraulic processes of river systems under a wide range of cold regions processes on a continental scale, providing critical insights for observing and managing diverse flooding hazards.