ABSTRACT
Anchor ice commonly occurs on riverbeds during frigid, open-water conditions. A prominent effect of anchor ice is extensive rafting-transport of bed sediment that often disrupts the coarse-sediment armor layers formed on riverbed surfaces. This paper presents observations and data regarding bed-sediment transport by anchor-ice rafting and briefly explains how thermal fluxes affect bed-sediment transport in rivers. Released anchor ice provides buoyancy to entrain sediment into the water column, whereupon currents move the ice-and-sediment masses downstream. Drifting anchor ice can transport (ice raft) bed sediment over downstream distances comparable to distances associated with open-water, bedload transport. Additionally, anchor ice rafting can influence channel morphology: e.g. in concert with ice-related floods, anchor ice can transport gravel and cobbles out onto a floodplain; and, through selective deposition of coarse particles in depositional areas, anchor-ice rafting can reinforce the development of certain channel morphologies.
