Morphodynamic response on hydroclimatic conditions - A 50 year time-series of a northern river system

Abstract

In the rapidly warming sub-arctic areas, it is not known how the climate emergency driven changes in hydroclimatic conditions will affect the fluvio-morphological processes like bank erosion, sediment transport and meander migration, and especially their spatial-temporal mechanisms. At the moment, one big spring flood event is controlling the morphodynamics of the northern rivers, but the significance of this event is expected to decrease when the hydroclimatic conditions change and larger amount of the annual precipitation is expected as rainfall during autumn and winter months instead of snow. In this study, we utilize a 50 year hydroclimatic time-series together with 21 years of bank erosion and meander migration observations from two meander bends in Northern Finland. The aim of this study was to find the main controlling hydroclimatic factors for hydro-morphological processes, like meander migration and sediment transport, and analyse the changes and trends of these factors during the past 50 years. These observations were then used to forecast, how these processes will behave in the future under the changing hydroclimatic conditions in the rapidly warming high latitude areas. We used time-series of historical aerial imagery, geometric levelling data, sediment sampling and Terrestrial Laser Scanner to measure and analyse the bank erosion volume, sediment transport and bend migration in the past, present and future. A series of statistical analysis was then performed for the hydroclimatic time-series to recognise trends and to link the annual events with bend migration, erosion and transport volume. The results indicate how these unique northern river systems are responding to hydroclimatic changes and how the hydro-morphodynamics will be in the future. The results help adapting the river management, flood protection, mitigation strategies for extreme fluvial events in present and in the future at high latitudes.