Abstract's details
Stream direction reversals in Baltic rivers derived from SWOT water level observations
Event: 2025 SWOT Science Team Meeting
Session: Deltas, Estuaries and Coasts
Presentation type: Poster
Using Surface Water and Ocean Topography (SWOT) measurements, we investigated water surface elevation differences between the Baltic Sea near river mouths and upstream locations to identify instances where sea levels were significantly higher than inland waters. These directional reversal events have until now been poorly characterized in the Baltic, due to limited observational data of water levels and river flow directions. The recent launch of SWOT enables new ways to interpret river flow direction. By analyzing SWOT data, we explore how coastal riverine processes influence inland water transport and ecosystems, challenging assumptions of coastal boundary extents in the Baltic.
To investigate inland water dynamics near the Baltic Sea, we analyzed river profiles in 41 of the largest rivers draining into the Baltic Sea wider than 100 m. Each river was subsetted based on its width according to the SWOT river database. For each of the selected rivers, Level-2 pixel-cloud data were extracted for the period between September 1, 2023, and April 1, 2025. The data were filtered to ensure that no errors were flagged in the quality flags, indicating good data quality. Additionally, an interquartile range filter was applied to remove outliers in the datasets. After filtering, valid data points were projected onto the corresponding river centerlines to determine their upstream distance from the river mouth. We then compared sea level elevations of the Baltic Sea near the river mouth with inland river water levels to identify instances when coastal water levels exceed water levels further upstream, indicating bilateral flow.
Our analysis reveals upstream flow reversal events, suggesting the inland movement of water from the coastal zones, in 70 percent of the analyzed rivers. These flow anomalies challenge the conventional assumption of unidirectional river flow in Baltic rivers and indicate that coastal influences may extend far beyond traditional estuarine boundaries.
Since the Baltic Sea experiences little to no effect from tidal events, the observed directional changes are plausibly an effect of periods of elevated atmospheric pressure, increasing sea levels and wind speeds. Our findings raise important questions about the potential permeability of coastal boundaries and their influence on freshwater systems, with implications for nutrient transport, habitat integrity, and the management of ecosystems affected by the Baltic Sea.
Back to the list of abstractTo investigate inland water dynamics near the Baltic Sea, we analyzed river profiles in 41 of the largest rivers draining into the Baltic Sea wider than 100 m. Each river was subsetted based on its width according to the SWOT river database. For each of the selected rivers, Level-2 pixel-cloud data were extracted for the period between September 1, 2023, and April 1, 2025. The data were filtered to ensure that no errors were flagged in the quality flags, indicating good data quality. Additionally, an interquartile range filter was applied to remove outliers in the datasets. After filtering, valid data points were projected onto the corresponding river centerlines to determine their upstream distance from the river mouth. We then compared sea level elevations of the Baltic Sea near the river mouth with inland river water levels to identify instances when coastal water levels exceed water levels further upstream, indicating bilateral flow.
Our analysis reveals upstream flow reversal events, suggesting the inland movement of water from the coastal zones, in 70 percent of the analyzed rivers. These flow anomalies challenge the conventional assumption of unidirectional river flow in Baltic rivers and indicate that coastal influences may extend far beyond traditional estuarine boundaries.
Since the Baltic Sea experiences little to no effect from tidal events, the observed directional changes are plausibly an effect of periods of elevated atmospheric pressure, increasing sea levels and wind speeds. Our findings raise important questions about the potential permeability of coastal boundaries and their influence on freshwater systems, with implications for nutrient transport, habitat integrity, and the management of ecosystems affected by the Baltic Sea.