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River concentrations of suspended sediment and particulate contaminants, such as trace metals, increase sharply during ice breakup, with potentially detrimental ecological impacts that may be complicated by changing climatic conditions. To enhance the very limited knowledge on this issue, comprehensive data have been collected on the Saint John River (SJR). During breakup, the suspended sediment concentration (SSC) was found to rise gradually, crest, and decline, roughly in step with the runoff, but occasionally spiked to extremely high peaks. The latter ranged from 4.2 to 6.5 times the runoff-generated peak concentrations (RPCs), which ranged from 35 to 150 mg/L. Peak RPCs and individual-event sediment loads generally increased with flow discharge. The sediment spikes were invariably associated with waves resulting from releases of upstream ice jams and with the ensuing ice runs. Concentration–discharge graphs exhibited pronounced clockwise hysteresis, indicative of sediment supply constraints. This feature is more prominent in high-runoff events and typically associated with a lag of 1–3 days between peak concentration and peak discharge, which arrives later. Prediction of SSC via sediment-rating curves is hopeless, but such curves can be helpful in computing loads associated with individual events using a modified approach that terminates load computation 3 days after the arrival of peak discharge. The bulk of the sediment load is delivered on the rising limb of the hydrograph and is likely to be missed in routine sediment monitoring programs. Practical steps to capture this information are suggested. Increases in SJR spring flows during recent decades are projected to continue under a warming climate, resulting in considerable increases of SSCs and loads by the end of this century. [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: Since the late 1960s, a paucity of ice-jam flooding in the lower Peace River has resulted in prolonged dry periods and considerable reduction in the area covered by lakes and ponds that provide habitat for aquatic life in the Peace–Athabasca Delta region. To help identify the causes of this trend and assess future conditions under a changing climate, a field observation program was conducted during 1999–2003. Limited data were also obtained during a significant event in 2007. This program has furnished the first detailed documentation of ice processes in the lower Peace. Though focusing on the breakup period, relevant antecedent conditions were also documented. Freezeup often involves formation of thickened ice covers, which lead to high freezeup stages and potentially to enhanced growth of the solid-ice layer during the winter. Ice decay prior to breakup can be moderate to severe, and is manifested in saturation and candling. The type of observed breakup ranged from essential melt-out in 2000, to occasional jamming upstream of the delta reach in 2003, and to a moderate delta flood in 2007. The field observations and measurements, including the only ice jam profile that has been measured in the lower Peace, are shown to be consistent with current physical understanding of breakup and jamming processes. The main factors conducive to ice-jam flooding are identified and their relative importance is assessed using physically-based breakup criteria. Breakup patterns are shown to be strongly influenced by the very low slope of the river, which amplifies the importance of waves generated by ice jam releases. [Copyright &y& Elsevier]

Major ice jams forming in lower reaches of the Peace River during spring breakup have been identified as the main agents of flooding and replenishment of perched basins of the Peace–Athabasca Delta, one of the world's largest inland freshwater deltas that supports a dynamic and valuable ecosystem. The paucity of ice jamming in the lower Peace River following construction of the Bennett Dam and the potential impacts of climate change have raised concerns regarding habitat degradation. One of the factors controlling ice-jam formation is the thickness of the winter ice cover, which may decrease in the future as a result of climatic warming, known to be most pronounced in northern parts of the globe and during the winter season. Using downscaled daily output from six Global Climate Models under two Representative Concentration Pathway scenarios, ice thickness is calculated for the years 1950 to 2100. Comparisons of monthly model-generated air temperatures and winter snowfall to historical data at nearby Fort Chipewyan indicate satisfactory agreement in terms of both magnitude and variability. Future projections show that under the highest emission scenario, average thickness decreases by about 0.2 m between the 1980s and the 2050s; and by an additional 0.1 m by the 2080s. Projected probability distributions of ice thickness point to increased incidence of thermal breakup, potentially reducing the already-low chances of ice-jam flooding. At the same time, a need for enhanced ice thickness monitoring is identified, aiming to develop a database of annual thickness values at selected sites within the lower reach of Peace River. • Peace-Athabasca Delta is partly sustained by Peace River ice-jam flooding. • Ice cover thickness can be a limiting factor to ice-jam occurrence. • Downscaled daily temperature and precipitation from six CMIP5 GCMs examined. • Thinner ice covers projected for the 2050s and 2080s under two RCP scenarios. • Likely to result in reduced ice-jam flood frequency. [ABSTRACT FROM AUTHOR]