Turbidity maxima in four macrotidal estuaries

Hydrodynamic and fine sediment transport characteristics of four major macrotidal Northern European estuaries are compared. The four estuaries (Weser, Seine, Scheldt, Humber) are amongst those key to navigation and shipping in that they are home to several major European ports (e.g. Hull, Antwerp, Le Havre). In particular, the characteristics and behaviour of the estuarine turbidity maximum are described for each system. While this is a complex topic that continues to benefit from ongoing research, some similarities exist between the estuaries in terms of the response of the turbidity maximum to changes in tidal range (during the neap–spring–neap cycle) and fresh water flow (due to seasonal variations in rainfall in the catchments). The hydrodynamics of the four estuaries are very similar, and are characterised by faster, shorter flood tide currents compared with longer, slower ebb tides. Under low fresh water flow conditions, the turbidity maximum is in each case moved upstream, while high fresh water flow conditions cause a net seaward movement of the turbidity maximum. While in general the concentrations of suspended sediment within turbidity maxima are no more than a few hundred milligrams per litre, the particular topography of the Humber estuary system leads to concentrations considerably higher than this.

► Similarities in turbidity maxima (TM) of four major European macrotidal estuaries.
► Funnelling of the tidal wave causes faster currents during the shorter flood tide.
► The flood tide suspends and transports a large amount of sediment landwards.
► Higher fresh water flow during winter months moves the TM seawards.