USE OF A FIELD-BASED WATER ELUTRIATION SYSTEM FOR MONITORING THE IN-SITU PARTICLE-SIZE CHARACTERISTICS OF FLUVIAL SUSPENDED SEDIMENT

There is increasing evidence that a substantial proportion of the suspended sediment load transported by many rivers is composed of composite rather than primary particles. In consequence, improved techniques for determining the in situ or effective particle size characteristics of the suspended sediment and the grain size of the primary particles making up the composite particles are required in order to obtain a better understanding of both the transport and fate of such material in fluvial systems and the geochemistry of suspended particulate material. This paper describes a field-based water elutriation apparatus which has been successfully employed to investigate the in situ particle size characteristics of suspended sediment transported by the River Exe in Devon, U.K. The reported procedure allows suspended sediment to be drawn directly from the river channel and hydraulically sorted, without disturbance, into five effective size classes. In addition to providing information on the effective grain size distribution, the approach also enables the absolute grain size composition of each effective size class to be determined.