Laboratory investigation of anchor ice evolution under steady and varying heat fluxes

Anchor ice formation, growth, and release in rivers impact flooding risk, sediment transport, and aquatic habitats in winter. The heat flux is known to significantly affect the growth of anchor ice, but there have been no studies on how the anchor ice growth rate is affected by variations in the heat flux. This study investigated anchor ice evolution under steady and varying heat flux conditions in the laboratory. Anchor ice images were captured using a high-resolution camera, and air and water temperatures measurements were collected. Four steady cases with constant heat flux and six varying heat flux cases, in which the heat flux was increased by either decreasing the air temperature or applying wind at three different times during a supercooling event, were examined. Results showed that anchor ice growth during steady heat flux cases experienced initial, transitional, and final growth stages in sequence. An additional heat change stage, which was defined as the time period of increased anchor ice growth following an increase in heat flux, always occurred prior to the final stage in varying heat flux cases. The anchor ice growth rate (i.e., the rate of change of anchor ice thickness) during the heat change stage was 150% and 80% larger on average compared to the transitional and final stages, respectively. The peak anchor ice growth rate reached an upper limit of ∼9 cm/h when the heat flux exceeded ∼300 W/m 2 , and the growth rate during the transitional and final stages increased approximately linearly with the heat flux.