New insight into river flows and sediment transport under ice cover

The ice‐covered season plays an important role developing river channels. These earth surface processes and landforms are a new study from the University of Eastern Finland shows. The spatial variability of sediment transport and differences in depositional and erosional locations increase in ice‐covered conditions.

However, the greatest erosional forces locating in the shallow sections of the river. That’s in both open‐channel and ice‐covered conditions. Although, ice cover narrowed the flow area. The findings published in Earth Surface Processes and Landforms.

“In subarctic regions, the ice-covered flow season lasts up to eight months of the year. Most noteworthy, this is something that is taken into consideration. Especially when analysing sediment transport in rivers. Yet, this has very rarely been the case,” says Dr Eliisa Lotsari from the University of Eastern Finland.Researchers at the University of Eastern Finland and the University of Turku simulated the ice‐covered flow in a meandering subarctic river, the Pulmanki River, in northern Finland.

Using hydrodynamic 2D modelling, the researchers explored spatial variation in flow characteristics and the erosion and sedimentation potential of the ice‐covered flow compared to open‐channel conditions. Up until now, ice-covered flow and sediment transport conditions have mainly been studied in laboratory conditions. Moreover, earlier studies have mainly focused on major floods or open-channel conditions.“

Future changes in seasonal temperatures and in rivers’ ice conditions may impact on river morphology in colder climates, as there may be changes to river flows, sediment transport and river origins.

These may also have long-term ecological consequences for rivers’ vegetation and animal populations,” Lotsari says.The study found that ice cover influenced occurring and circulating flow structures. It also increased sizing of small circulating flow structures. Low flow speed in these “whirlpools” also enable sediment deposition. However, the critical thresholds for particle entrainment exceeded more often in open-channel conditions than in ice-covered ones.

The study funding by the Academy of Finland, Maj and Tor Nessling Foundation, and the British Society for Geomorphology.

Research article by:Eliisa Lotsari, Tiia Tarsa, Maria Kämäri, Petteri Aho, Elina Kasvi. Spatial variation of flow characteristics in a subarctic meandering river in ice-covered and open-channel conditions: A 2D hydrodynamic modelling approach. Earth Surface Processes and Landforms. 2019. https://doi.org/10.1002/esp.