Investigating water level change and water surface slope in one of the most energetic and dynamically complex regions in the St. Lawrence System.
The St. Lawrence Estuary is the only estuary in Canada advantageously located under SWOT fast-sampling orbit, which benefited from data at both high temporal and spatial resolution. This site is one of the most energetic and dynamically complex regions of the St. Lawrence System. With propagating tides reaching 7 m in range and with its unique geomorphology, characterized by large (>15-km wide) cross-sections and numerous islands, it presents significant spatiotemporal variability in surface conditions at all scales.
In addition, the fast-sampling orbit perpendicularly covered the Saguenay Fjord that discharges into the St. Lawrence. With up to 350-m high cliffs, the fjord allowed for the study of layover effects in some areas and for SWOT data validation in a standing tidal wave (low slope) environment. Both systems encompass a large range of water surface conditions within a finite geographical region and relatively short time scales. This represented a unique opportunity to participate actively in pre- and post-launch SWOT calibration/validation activities and enhance Canadian research and contribution to this mission.
Beginning March 2023 pressure transducers were deployed across the estuary to measure water level change and water surface slope within the estuary. In the same period, approximately 10 GNSS-R antenna arrays for water level, ice and wave measurements were deployed. 4 HF radars for surface waves and currents were mounted in strategic locations, along with wave buoys. In addition, LiDAR and AirSWOT airborne surveys were conducted during rising and falling tides in May 2023 (see Figure 1). Finally, Acoustic Doppler Current Profilers (fixed horizontal and boat-mounted) collected data for discharge measurements.
Estimating fluxes of water across the land-ocean-sea-continuum (LOAC) is critical to evaluate the export of carbon and nutrient to the ocean, the deposition of sediment along the shore and to assess the vulnerability of wetlands and ecosystems in the face of sea level rise, increased storm activity and freshwater diversion projects. It is also critical to improve hydrodynamic models in these regions to support navigation, hazard contingency plans and rescue efforts. While gauging of estuaries and channels is commonly used to manage coastal wetlands, availability of these in situ measurements is in decline globally. But even the most extensive gauge networks cannot capture overflows to and within the wetlands. Our experiment demonstrated the potential of SWOT as an alternative to expensive gauges networks to calibrate hydrodynamic models and retrieve seasonal freshwater discharge. These calibrate models and discharge estimates in estuaries and river deltas can be used to improve our understanding of the water and carbon cycles, thereby providing a powerful tool to monitor salinity gradients in these regions and their contribution to ocean carbon.
The St. Lawrence campaign was funded by NASA ROSES, CSA, Environment and Climate Change Canada, U. Laval, and UQAR.
Principal investigators: Pascal Matte (Environment and Climate Change Canada), Marc Simard (Jet Propulsion Laboratory, California Institute of Technology).
Contact point for the study site: Pascal Matte (pascal.matte@ec.gc.ca)
Publications:
Matte, P., Chartrand, X., Purnell, D., Simard, M., Christensen, A., Fortin-Legault, F., Morin, J., Côté-Nadeau, Y., Desrosiers, É., Ouellet, A. and Chavanne, C., 2026. A benchmark dataset of water levels and waves for SWOT validation in the St. Lawrence Estuary and Saguenay Fjord, Quebec, Canada. Earth System Science Data Discussions, 2026, pp.1-40. https://doi.org/10.5194/essd-2026-30