Author(s): J. R. Harrington; J. P. O'Kane
Linked Author(s):
Keywords: River Rhone; Gulf of Lions; Stratification; Flocculation; Particle Modelling
Abstract: The behaviour of flocculating particles discharging as part of a river plume into an estuary is a complex process. The aim of this paper is to develop and apply a flocculation model to a stratified system to gain a greater understanding of the particle dynamics. The model has been applied to the mouth of the River Rhone which discharges to the Gulf of Lions in the North West Mediterranean Sea. This river/estuary system is characterised by a low tidal range with the formation of stratified waters consisting of a river plume overlying salt water. Existing information on river flows and suspended sediments within the system is summarised and river flow rate-suspended sediment concentration relationships are developed and presented. A numerical particle box flocculation model, called BOXFLOC, has been developed. It is more advanced and more widely applicable than previous models developed. It allows the use of fractal aggregates, includes particle flocculation and break-up effects and also can simulate particle settling, river, atmospheric and biological inputs. A two-box vertical model has been applied at the mouth of the River Rhone, the first such application to this type of river/estuary system. The model was successfully calibrated to available particle size distribution field data, using fractal particles. The model was run for different system conditions, in particular simulating the effects of different river inputs on the particle dynamics of the system. Model simulations show that the particle mass concentration is sensitive to changes in the river particle influx while the average particle size is not as sensitive. Model simulations also show that the effect of the stratified water system is to increase the particle flocculation effect, with this flocculation effect being further enhanced by the presence of larger, less dense flocs. Model results also suggest that the effect of a one day flood flow on the particle dynamics takes over two days to leave the surface box.
Year: 2003