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As part of the Oil Sands Joint Monitoring Program, the present study aims to understand and quantify the erosional and sediment transport capacity of the Lower Athabasca River during the ice breakup period. Of special interest is the very steep reach above Fort McMurray, which is a potential natural source of polycyclic aromatic hydrocarbons. A two-year field program (2013–2014) has furnished unique data, reported in a companion paper, on the spatio-temporal water level variation during the breakup event. Herein, methodology is developed and applied for using the water level data sets to extract values of key hydrodynamic variables, which cannot be measured during breakup and ensuing ice runs. The results of the analysis indicated that flow velocity, discharge, and bed shear stress can exceed 4 m/s, 10,000 m 3 /s, and 100 Pa during the passage of sharp waves caused by releases of ice jams. According to past reports, the 2013 and 2014 breakup events, though dynamic, were not extreme. Yet, their severity exceeded by far the highest open-water flow values in the same reach over the period of record (2.5 m/s, 4440 m 3 /s and 35 Pa). Suspended sediment concentrations and loads during breakup were estimated via flow-based rating relationships developed from WSC sediment data. It was shown that concentrations could easily exceed 10 g/L, while a breakup event could supply a significant fraction of the total sediment load for the year and transport naturally occurring PAHs into the industrial oil sands reach. [ABSTRACT FROM AUTHOR]

Highly dynamic flow conditions that often occur during the river ice breakup can cause greatly increased in-stream sediment concentrations and loads, with significant impacts on aquatic ecology and the environment. Sharp waves accompanying the releases of ice jams cause transient but very high flow velocities and shear stresses. However, very limited quantitative information is available on how such ice jam-generated waves (or “javes” for short) influence the transport of suspended sediment even though their effects on it are visually apparent. Suspended sediment concentrations (SSCs), obtained during a 5-year study of ice and sediment processes in the Saint John River (NB), reveal occasional spikes in concentration, consisting of relatively brief upward excursions to nearly order-of-magnitude higher values. Such spikes are concurrent with javes and ice runs. Documented cases of sediment pulses during river ice breakup events in the Saint John River form a unique data set demonstrating temporal and spatial characteristics. Peak SSC values approach 1 g/L and approximately coincide with peak jave stages and surface ice concentrations. Pulse durations amount to several hours, and are shorter than those of the concomitant javes. Despite their brevity, pulses can deliver sediment loads that are significant fractions of the total load for the entire breakup event. Measurement of breakup sediment pulses is not feasible under existing monitoring programs. Instead, focused short-term studies could lead to development of predictive capability, linking pulse properties to hydro-climatic variables that drive the breakup event. A strong influence of river discharge has been detected, leading to projected increases in pulse sediment amounts under a changing climate. [ABSTRACT FROM AUTHOR]

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 numerous channels and lakes. Ice jams that may form during the spring breakup often result in flooding, thus replenishing delta lakes with essential water, sediment and nutrients. These processes are primarily driven by the flow of the lower Mackenzie River. The present study, carried out under the auspices of the International Polar Year, examines how the ice cover of the lower Mackenzie River can break up while still retaining a significant portion of its mechanical strength. This is the so-called mechanical breakup, a necessary condition for occurrence of ice jams farther downstream. In most rivers, mechanical breakup can simply result from the rising freshet flow, but this is doubtful for the Lower Mackenzie, owing to the low water surface slope and thick winter ice cover. Analysis of extensive measurements obtained during the 2008 breakup event indicates that mechanical breakup can primarily result from javes, the sharp waves generated upon ice-jam release, which are known to amplify hydrodynamic forces. Further confirmation is provided by archived hydrometric station data for the period 2000–2011. The present results on the conditions of breakup initiation are consistent with past findings while indicating a lower base temperature for the accumulation of “thawing” degree-days. This difference is shown to be linked to water–ice heat exchanges and radiative fluxes. Recommendations for future research include upstream extension of the study reach to include the range of influence of releasing ice jams, and physics-based modeling of the decreasing ice competence during the pre-breakup period. [Copyright &y& Elsevier]

Abstract: Ice-jam release waves, or javes for short, are highly dynamic events that occur in ice-forming rivers. They are known for serious ecological and socio-economic impacts, which are usually detrimental but on occasion beneficial, particularly with respect to ecosystem maintenance in the large freshwater deltas of northern Canada. Detailed water level data have been obtained during the passage of javes in the past 10years or so, but their study is hampered by lack of velocity and discharge measurements, owing to the presence of moving ice in the flow. A previously developed method to analytically compute such parameters, which is based on measured waveforms, has given encouraging results in several applications. Herein, this method is first subjected to comprehensive validation using numerical model output for a hypothetical jave in a prismatic channel. The analytical method is shown to perform adequately with respect to all hydrodynamic jave characteristics, such as celerity, velocity, discharge, and bed shear stress. Jave data from various rivers are then compiled in tabular form and it is shown via dimensional analysis that bulk predictions can be made in terms of jave height and rate of rise of the water level. Implications of the present findings to riverbed scour and to ecologically vital ice-jam flooding of flat rivers and deltas are explored and research challenges identified. [Copyright &y& Elsevier]