Author(s): Bernard Michel
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Abstract: There are many different mechanisms governing the accumulation of ice in a river depending on a combination of hydrodynamic and atmospheric conditions. We will review these mechanisms and present a general representation including each one. Recent field measurements in Canada will be discussed in relation to this overall picture. At freeze-up, ice accumulations are formed when slush and ice cakes feed an ice cover in a regular manner for a significant interval of time. The accumulation freezes on top which gives it a high resistance to the hydrodynamic thrust. At certain places, thick ice covers are formed by accumulations of this slush and cakes. At other places, the ice pieces accumulate underneath the solid ice cover to form underhanging dams. At break-up, ice jams are formed in a much different manner. The conditions of break-up of the solid ice sheet will be discussed in function of the resistance of the solid part of the cover. When small accumulations break through a retaining ice cover, the brokenup ice floes move in the river in a close-pack formation, so the feeding of the site of a downstream jam is quite sudden. During the time of packing of the floes in a jam, the outside thermal influence is small and the pack acts like an unconsolidated ice jam which is only a hydro-mechanical phenomenon.
Year: 1978