Small-Scale Riverbank Erosion Experiments in Freezing and Thawing Conditions

Abstract

Climatic warming is projected to change the duration and intensity of frozen periods in polar regions, impacting hydrology and riverbank erosion. Herein we present a series of 125 laboratory flume experiments conducted in a novel cryolab morphology facility using a small-scale Friedkin channel. We assess the influence of discharge (flow velocity), water temperature, riverbank moisture content and temperature on riverbank erosion for varying air temperatures. The riverbank topography was quantified before and after each experiment and volumetric changes were calculated, using an array of images collected via a semi-automatic camera and structure from motion method. Videos were used to determine bank edge retreat during the experiments. Surface flow velocities were measured using particle tracking velocimetry method. An infrared thermal camera aided understanding the temperature variations across the riverbank. A non-linear relationship has been identified between volumetric erosion rate and air temperature, with the highest rates (at maximum up to 1.03 cm3/s) occurring at −5.2°C overnight air temperatures during highest tested discharge conditions. Erosion rates decrease when temperatures fall below or rise above −5.2°C, but increase again (at maximum up to 0.51 cm3/s) at +4.5°C. High moisture content slowed temperature propagation, caused by flowing water, through the riverbank. Erosion occurred as blocks in freezing conditions when the moisture content exceeded 18.9%, which further promoted thermo-erosional niche development, a phenomenon observed also in polar/arctic river systems. The non-linear dependency on air temperature highlights the importance of air temperature on erosion, with further implications for erosion with climate warming.