Erosion potential of dynamic ice breakup in Lower Athabasca River. Part II: Field data analysis and interpretation

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 m3/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 m3/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.