A new study from the University of Eastern Finland shows the winter season plays an important role in the development of river channels. The spatial variability of sediment transport and differences in depositional and erosional locations increase in ice‐covered conditions, according to the University.
The greatest erosional forces are located in the shallow sections of the river in both open‐channel and ice‐covered conditions. However, the ice cover has narrowed the flow area.
“In subarctic regions, the ice-covered flow season lasts up to eight months of the year, and this is something that should be taken into consideration when analyzing sediment transport in rivers. Yet, this has very rarely been the case,” said Dr. Eliisa Lotsari from the University of Eastern Finland.
In the study, 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 modeling, the researchers explored spatial variation in flow characteristics and the erosion and sedimentation potential of the ice‐covered flow compared to open‐channel conditions. Ice-covered flow and sediment transport conditions have mainly been studied in laboratory conditions until recently. According to the University of Eastern Finland, previous studies have mainly focused on major floods or open-channel conditions.
“Future changes in seasonal temperatures and in rivers’ ice conditions may have a significant 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 said.
The study also found that ice cover influenced the occurrence of recirculating flow structures. According to the University, it increased the density of small recirculating flow structures. Low flow velocity in these “whirlpools” also enable sediment deposition. However, the critical thresholds for particle entrainment are exceeded more often in open-channel conditions than in ice-covered ones.