Physical Modelling Based Assessment of Some Influence Factors on Overflow Plume Behaviour
Type:
Presented during:
WODCON XX: "The Art of Dredging" - 2013, Brussels, Belgium
Authors:
Decrop B, Sas M, Ve Mulder T, Toorman E
Abstract: Dredging using Trailer Suction Hopper Dredgers (TSHD) with overflowing lean mixture can generate turbidity plumes in cases when fine sediment fractions are present in the pumped mixture. In view of the increased attention to environmental impacts of coastal and offshore dredging operations, research in this field is increasing. In this context the effect of turbidity generated by dredging activities plays an important role. The sediments brought in suspension can generate effects ranging from reduced light penetration in the water column over burial of sea bed ecosystems to dispersion of toxic materials attached to contaminated sediments. The dispersion of benthic material can have other impacts including siltation of still water bodies such as bays, docks or harbours. In the research programme of which this work is a part, laboratory experiments, numerical modelling and in situ measurements contribute to improving the knowledge on the behaviour of the near-field negatively buoyant fine sediment plume released from TSHD’s.
Based on scaled laboratory experiments, the effect of air bubbles and the presence of a schematised ship hull on the plume behaviour is assessed. This paper shows that both factors influence results in a significantly higher position of the plume compared to undisturbed cases and theoretical solutions of plumes in crossflow. Hence, simplified models for the prediction of the environmental impact of dredging plumes should incorporate these effects.
Keywords: Turbidity plumes, Trailer Suction Hopper Dredger, environmental impacts, suspended sediment, buoyant jets