The impact of grain orientation and pebble surface roughness on the bond strength of simulated anchor ice

• Pebble depth of imprisonment in ice significantly increases the bonding strength with ice.
• Pebble surface area does not significantly increase the bonding strength with ice.
• Higher pebble roughness increases the bond strength with ice.
• Paint modifies the bonding strength between pebbles and ice.
• The presence of warm hyporheic flows may limit anchor ice formation and/or accelerate its melting.

Recent studies suggest that sediment transport caused by the release of anchor ice can have a significant influence on the annual sediment transport budget of a river. Our study examines the potential influence of different parameters on the strength of the bond between the ice and the surface of the pebbles. The main variables investigated are the roughness and orientation of aggregates, and the effect of hyporheic exchange under the anchor ice layer. Two experiments were conducted in the laboratory. The goal of the first experiment was to evaluate the influence of the size and roughness of the aggregates, while the second evaluated the influence of the size and roughness of the aggregates, as well as the effect of hyporheic flows. The results show that the depth of imprisonment of a pebble has a much greater influence on the strength of the ice–pebble bond than the surface area. It was also observed that surface roughness has a significant impact on this bond. Furthermore, the results suggest that hyporheic flows under the anchor ice layer likely weaken the strength of the ice–pebble link, promoting the release of the anchor ice. The use of oil-based paint was found to increase the strength of the ice–pebble bond. It should be noted that paint is commonly used as a method for identifying and tracking sediment movement and we suggest that its use could affect the results of sediment transport experiments involving anchor ice.