Hydrodynamic properties of ice-jam release waves in the Mackenzie Delta, Canada

Ice breakup is a controlling factor in the hydrology of arctic Deltas, including the Mackenzie River Delta, which is characterized by numerous channels and lakes. Ice jams that form during dynamic spring breakup events often result in flooding, thus replenishing Delta lakes with essential water, sediment and nutrients. The present study, carried out under the auspices of the International Polar Year, aims to gather and analyze essential quantitative information for improving understanding of Delta ice processes and associated prediction capability. Recent work has shown that dynamic breakup in the flat Delta channels can only be triggered by javes, the sharp waves generated by ice jam releases, which amplify the hydrodynamic forces applied on, and can dislodge, the winter ice cover. First-ever measurements of javes in Delta channels are presented and their hydrodynamic properties quantified via the Rising Limb Analysis Method (RLAM), which enables calculation of the hydrodynamic properties of the measured waveforms. Typical leading edge and crest celerities were 10 and 5 m/s respectively, while a record value of 16.5 m/s was obtained on one occasion and linked to large local depths in Middle Channel. The hydrodynamic forces applied on the riverbed and the ice cover, resulting from various javes, are subdued in Delta channels relative to those in the lower Mackenzie River and in other, previously studied, rivers. This is primarily due to low water surface slope and points to a northward-decrease in the incidence of dynamic breakup and ice jams in Delta channels.