Evolution and hydraulic resistance of anchor ice on gravel bed

This paper presents a laboratory study on anchor ice evolution and its hydraulic effect in channels with a gravel bed. The study revealed that anchor ice is initiated by frazil ice accumulation on bed gravel from half a gravel diameter below the crown level of the gravel. No in-situ ice growth within the frazil accumulation or downward growth towards the bed was observed. During the initial stage of growth anchor ice grew in the forms of tails, scales, or balls, depending on the flow velocity and Froude number. During the final stage of growth, when the gravel bed was covered by ice, the growth rate increased with the heat loss rate and Froude number, and inversely proportional to the flow depth. The overall hydraulic resistance of anchor ice was smaller for smaller bed gravel sizes and decreases with the increase in flow rate and flow depth. The rate of increase of the gross Manningʹs resistance coefficient decreases with the increase in Reynolds number. The bed/ice surface roughness first increases with anchor ice growth, then decreases to a minimum value after the initial stage of growth, when anchor ice grew out of the gravel bed.