Riverbank Erosion Susceptibility Under Varying Sedimentological and Freeze–Thaw Conditions in Cold Climate Regions
Abstract
High‐latitude rivers are undergoing rapid environmental change as climate warming alters seasonal freezing, hydrology and sediment dynamics. This study investigates the erosion susceptibility of riverbank sediments in meandering reaches of three northern rivers: Pulmanki (subarctic Finland), Sävar (subarctic Sweden) and Koita (boreal Finland), focusing on how geotechnical and sedimentological properties and freeze–thaw processes influence erosion. Field sampling included grain size, bulk density and moisture measurements, with selected samples analysed using triaxial tests. At Pulmanki, continuous SoilScout monitoring provided high‐resolution data on soil temperature, moisture and movement during freeze–thaw cycles, which were linked to seasonal bank erosion derived from aerial surveys. Additionally, observed Accumulated Freezing Degree Days (AFDDs) from 2021–2024 were compared with mid‐century climate projections (2040–2099) from four global climate models under three SSP emission scenarios. Fine‐grained sediments dominated all sites, but differences in moisture content, grain size and soil structure strongly influenced shear strength and erosion susceptibility. Sävar sediments were the most erosion‐prone, whereas Pulmanki sediments were denser and more resistant, and Koita exhibited pronounced local variability. Water content emerged as the primary control on shear strength, while coarser grain sizes increased resistance. Integration of DEM of Difference (DoD) analyses and in situ monitoring demonstrated that erosion is continuous and spatially variable, with sediment movement occurring during both spring thaw and autumn freezing. These findings highlight the key role of freeze–thaw processes in controlling the timing and mechanisms of bank erosion in cold‐region rivers. Climate projections indicate a substantial decline in AFDD under high‐emissions scenarios, suggesting shorter and milder winters. This is expected to alter freeze–thaw dynamics and extend periods during which riverbanks remain unfrozen and vulnerable to erosion, potentially increasing erosion frequency in fine‐grained, moisture‐rich sediments. Collectively, the results show that erosion in seasonally frozen rivers is governed by the combined effects of sediment properties, moisture conditions and freeze–thaw processes. The integrated approach, combining geotechnical testing, in situ monitoring and climate projections, provides a transferable framework for assessing erosion risk in cold‐region river systems and supports improved riverbank management under a warming climate.