Author(s): S. Beltaos; J. Wong

Linked Author(s):

Keywords: No Keywords

Abstract: Experience suggests that ice jams are often grounded, usually near their downstream end or "toe". Whether and to what extent a jam grounds are important questions in assessing flooding potential, stability and release but little is known about grounded jams. Seepage through accumulations of ice blocks was studied in the laboratory and found to vary in proportion to the square root of the water surface slope. The coefficient implied in this relationship depends on ice floe characteristics and orientation. Tests with plastic blocks revealed two grounding mechanisms. The first consists of submergence and piling up of blocks that are too large to advance past an obstacle. Grounding persists until the upstream water level rises to that of incipient submergence. This level may govern flooding potential in relatively flat and narrow streams. The second mechanism of grounding occurs when a moving, thick, ice accumulation encounters competent ice cover and wedges between it and the channel bed. In the present tests, such accumulations were produced by the collapse and "snowballing" of surface jams. A third grounding mechanism was identified by theoretical analysis based on the internal collapse concept and applied to the downstream transition of the jam. In all three cases, the length of grounding was short, amounting to a few block widths or flow depths.

DOI:

Year: 1986