Morphodynamics of the Dee estuary

The evolution of estuarine morphology is a process of dynamic equilibrium in the short-term (decades to centuries), while estuaries may be regarded as ephemeral in the long-term (millennia). Short-term processes of erosion and deposition are controlled by the estuarine hypsometry, tidal asymmetry, sediment supply and river flow. The Dee estuary, UK, is a macrotidal funnel-shaped estuary, known to have undergone significant infilling over the past two centuries. In macrotidal estuaries (such as the Dee), tidal asymmetry may be the main factor affecting morphological change (Dronkers, 1986; Wang et al., 2002). Tidal asymmetry is a result of higher order harmonic overtides (particularly the M4 constituent) which are generated by the effects of friction, convergence and continuity (Speer and Aubrey, 1985). While the estuary as a whole may be ebb- or flood-dominated, different processes dominate in the tidal banks and channels. The balance between these processes may determine whether the estuary acts as a net sediment source or sink.