A conceptual model of river ice breakup

Abstract

A conceptual model of ice breakup is formulated and used to analyze and compare data from four river gauge sites. Emphasis is on the development of generalized short-term forecasting methods, which to date have been site specific. The features to be forecast are the onset and flooding potential of breakup. These are related to the water surface width available for passage of the large sheets of ice that form by transverse cracking of the ice cover. Thus it is possible to study the effects of parameters such as ice cover dimensions and channel geometry. Owing to a lack of pertinent data, other parameters such as ice mechanical properties and flow characteristics are only considered indirectly. The mechanism of transverse cracking is examined in the light of recent field observations. Bending on planes parallel to the water surface, caused by stream curvature, could account for the observed crack spacing but more data are needed for positive conclusions. The present model does not apply in cases of “overmature” breakup, proximity of stage controls, and river planforms different from the single meandering channel type. Key words: breakup, cracks, field data, forecasting, gauge records, ice, ice clearing, ice sheets, model, onset, river ice, rivers.