In Situ Size Distribution of Suspended Particles in the Fraser River

Abstract

Size distributions of suspended sediment particles under low flow conditions in the Fraser River were measured using a submersible laser instrument. By comparing the in situ size distribution measured using this instrument with the size distribution of primary particles (measured by collecting sediment samples and analyzing them for size distribution after dispersing the particles by ultrasonic vibration), it was concluded that suspended sediment particles in the Fraser River downstream of pulp mill effluent outfalls are transported as agglomerations of particles (flocs) rather than as individual particles. Flocculation of river sediments in estuaries has been investigated in earlier studies, which show that saltwater intrusion contributes to the flocculation mechanism. Freshwater flocculation, such as the one observed in the present study, also has been reported in the literature, and it is attributed to the presence of organic materials and other contaminants from industrial and sewage treatment plant effluents. This paper describes the details of the submersible laser instrument and its use in the Fraser River, British Columbia, Canada.