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Abstract: 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 5m/s respectively, while a record value of 16.5m/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. [Copyright &y& Elsevier]

Abstract: Ice breakup is a controlling factor in the hydrology of arctic deltas, including the Mackenzie River Delta, which is characterized by a flat front and numerous channels and lakes. Ice-jam flooding replenishes delta lakes with essential water, sediment and nutrients. The present study, carried out under the auspices of the International Polar Year, aims to gather essential quantitative information for improving understanding of delta ice processes and associated prediction capability. Comprehensive observations and measurements, which were carried out during the 2007 and 2008 breakups, are described along with relevant analysis and data interpretation. The spacing of pre-breakup transverse cracks in delta channels is similar to that of rivers, typically ranging from 2 to 5 ice cover widths. Ice jamming in the delta is driven by major ice runs originating in the Mackenzie River and stalling in the upper reaches of Middle Channel. The data collected during the mechanical breakup event of 2008 permitted crude, but first-ever, quantification of flow re-distribution resulting from the formation of a Middle Channel jam. This jam also generated jams in East Channel and smaller distributaries. Examination of threshold velocity for ice block submergence indicated that, with notable exceptions, the expected kind of jam in delta channels is a surface accumulation of ice blocks and plates. This prediction is in accord with observations and hydrometric data at the Inuvik and Aklavik gauges. The use of portable loggers to record water level variations at selected sites proved to be a robust and effective technique for obtaining key hydraulic data. [Copyright &y& Elsevier]

The spring flow of the Mackenzie River into its delta drives the breakup ice jamming and consequent flooding and replenishment of the thousands of lakes on the delta plain. Daily flows for related studies are presently furnished by Water Survey of Canada, based on the records of a hydrometric station located close to the delta entrance. The relative proximity of the Beaufort Sea affects the local water surface slope, amplifying uncertainties that are normally associated with under-ice flow estimates. It is shown that gauge-derived spring flows often do not agree with other evidence, such as past discharge measurements, flows at the next upstream gauge, and hydraulic computations for the 2008 event. This appears to result in inconsistencies between spring flow hydrograph and observed severity of ice breakup. Options for improving spring flow estimates are discussed and installation of an auxiliary water-level gauge near Point Separation is recommended as a practical choice. [ABSTRACT FROM AUTHOR]

A unique feature that has been detected in the course of past morphological studies of Mackenzie delta channels, and which is of particular concern to the design of pipeline crossings, is the frequent occurrence of very deep scour holes. A recent survey along East Channel revealed many additional holes, with maximum depths ranging from 13 to 37 m. Using the results of recent and past surveys, an inventory of known scour holes and associated morphological parameters is developed. Most holes occur near bends, and often next to recesses in the channel boundaries, known as scour bays. It is shown that presence of scour bays indicates deeper-than-expected holes while repeat surveys of three holes indicate stability. Previously postulated formative mechanisms of bay-associated holes are critically examined; scour under ice jams is eliminated while lake capture is considered likely. Practical implications of the present findings are discussed and research needs outlined. [ABSTRACT FROM AUTHOR]

The article discusses the study on the spatial and temporal patterns of break-up and ice-jam flooding in the Mackenzie Delta in Northwest territories. It states that the Mackenzie Delta provides habitat for a range of species but the current hydrology in the Delta lakes are dominated by cryospheric processes. It notes that the backwater levels and discharge at the Mackenzie Delta will determine the physical rationale of the resulting spatial and temporal patterns.