Authors: Tuure Takala, Pauli Kolisoja, Nuutti Vuorimies, Erik van Rooijen & Eliisa Lotsari
Publication type: A1
Abstract
High-latitude rivers are undergoing rapid environmental change as climate warming alters seasonal freezing, hydrology and sed-iment dynamics. This study investigates the erosion susceptibility of riverbank sediments in meandering reaches of three north-ern rivers: Pulmanki (subarctic Finland), Sävar (subarctic Sweden) and Koita (boreal Finland), focusing on how geotechnicaland sedimentological properties and freeze–thaw processes influence erosion. Field sampling included grain size, bulk densityand moisture measurements, with selected samples analysed using triaxial tests. At Pulmanki, continuous SoilScout monitoringprovided high-resolution data on soil temperature, moisture and movement during freeze–thaw cycles, which were linked toseasonal bank erosion derived from aerial surveys. Additionally, observed Accumulated Freezing Degree Days (AFDDs) from2021–2024 were compared with mid-century climate projections (2040–2099) from four global climate models under three SSPemission scenarios. Fine-grained sediments dominated all sites, but differences in moisture content, grain size and soil structurestrongly influenced shear strength and erosion susceptibility. Sävar sediments were the most erosion-prone, whereas Pulmankisediments were denser and more resistant, and Koita exhibited pronounced local variability. Water content emerged as the pri-mary control on shear strength, while coarser grain sizes increased resistance. Integration of DEM of Difference (DoD) analy-ses and in situ monitoring demonstrated that erosion is continuous and spatially variable, with sediment movement occurringduring both spring thaw and autumn freezing. These findings highlight the key role of freeze–thaw processes in controllingthe timing and mechanisms of bank erosion in cold-region rivers. Climate projections indicate a substantial decline in AFDDunder high-emissions scenarios, suggesting shorter and milder winters. This is expected to alter freeze–thaw dynamics andextend periods during which riverbanks remain unfrozen and vulnerable to erosion, potentially increasing erosion frequency infine-grained, moisture-rich sediments. Collectively, the results show that erosion in seasonally frozen rivers is governed by thecombined effects of sediment properties, moisture conditions and freeze–thaw processes. The integrated approach, combininggeotechnical testing, in situ monitoring and climate projections, provides a transferable framework for assessing erosion risk incold-region river systems and supports improved riverbank management under a warming climate.