Overview
The lower reaches of the Athabasca River between Fort McMurray and Embarrass Airport are characterized by complex geometry, including vegetated islands, alternating sand bars, and an unpredictable thalweg. This study used a two-dimensional Environmental Fluid Dynamics Code (EFDC) model to investigate flows and the transport of sediment and associated chemical constituents in this river reach.
Model Setup
The models were set up and validated using available observed data in the region before being used to estimate levels of cohesive sediment and a selected set of chemical constituents — polycyclic aromatic hydrocarbons (PAHs) and metals — within the river system. Different flow scenarios were considered.
Key Findings
The results show that a large proportion of the cohesive sediment deposited within the study domain originates from the main stem upstream inflow boundary, although the Ells River may also contribute substantially during peak flow events. The floodplain, back channels, and islands are the major areas of concern for deposition of sediment and associated chemical constituents. Adsorbed chemical constituents tend to be greater in the main channel water column, which carries higher total suspended sediments than the floodplain. The levels of chemical constituents leaving the river system depend strongly on the corresponding river bed concentration levels, with higher outflows accompanying increases in bed sediment concentration.