This project was carried out for the Northern River Basins Study (NRBS) to characterize the size distribution and the transport processes of suspended particles in the Athabasca River below the Weldwood Pulp Mill outfall at Hinton. The project consisted of two field surveys: one, during the winter of 1993 and the other during the fall of the same year. The reach sampled is between Entrance, which is eight kilometers upstream from Hinton, and Windfall, which is at a distance of 175 km downstream. The measurements consisted of flow field, size distribution of in-situ and dispersed particles and concentration of particles in the water column.
The data from the two surveys show that the pulp mill effluent has affected the physical transport characteristics of the ambient sediment. It promoted the flocculation of the incoming sediment particles and increased their deposition rates. During low river flow periods, when the ratio between the effluent discharge to flow discharge is the highest (about 4%), 74% of the incoming sediment deposited within 20 km from the outfall. During moderate flows (i.e., flows in the order of five times the winter flow) the deposition continued at a slower rate further downstream from the outfall.
The results point to a need for an improved sediment transport model that considers the flocculation mechanism of the incoming sediment in the presence of pulp mill effluent. Existing models such as the one in WASP-4 will not predict sediment deposition downstream from the Weldwood Pulp Mill outfall and therefore are not suitable for making realistic predictions of pulp mill impacts in the Athabasca River.