Characterization of sediment transport and storage in the upstream portion of the Fraser River (British Columbia, Canada)

Several techniques to determine the in-situ size, morphology, settling and storage characteristics of fine grained sediment have been used in the Fraser River at Prince George. The river was sampled both upstream and downstream of the effluent outflow of a major pulp mill (Northwood) to determine the role of this effluent in modifying the transport and storage of sediments, Both the natural suspended sediment load (upstream) and the effluent-sediment mix (downstream) were characterized by concentration, organic/inorganic ratios and image analysis to identify the presence and size of aggregates or flocs in the water column. Preliminary analysis of the data from the first eight months of 1997 indicates seasonal changes in flee size of the natural sediments but no significant difference between sites upstream and downstream of the effluent pipe. Buried gravel traps were used to quantify and characterize the amount of fine grained storage in the gravel bed during the post flooding period. Over short periods (four days) abundant fine grained (<63 mu m) material was collected. The modal size of the constituent particles in the size class below 150 mu m was 40-60 mu m This storage of silts and clays in the gravel bed is important in the context of both habitat quality and sediment associated contaminant transfers.