Physical controls on the dynamics of inlet sandbar systems
Knowledge of the physical processes acting at inlet systems and their interaction with sediments and sediment bodies is important to the understanding of such environments. The objectives of this study are to identify and assess the relative importance of the controlling processes across the complex sandbar system at the Teign inlet (Teignmouth, UK) through the combined application of a numerical model, field data and Argus video images. This allows the determination of the regions dominated by wave processes or by tidal processes and definition of the variability of these regions under different wave, tide and river-discharge conditions. Modelling experiments carried out for one stage of the evolution of the system show that the interaction between tidal motion and waves generates complex circulation patterns that drive the local sediment transport and sandbar dynamics, producing a cyclic morphological behaviour of the sandbars that form the ebb-tidal delta. The relative importance of each physical process on the sediment transport and consequent morphodynamics varies across the region. The main inlet channel is dominated by tidal action that directs the sediment transport as a consequence of the varying tidal flow asymmetry, resulting in net offshore transport. Sediment transport over the shoals and secondary channels at both sides of the main channel is dominated by wave-related processes, displacing sediment in the onshore direction. The interaction between waves and tide-generated currents controls the transport over the submerged sandbar that defines the channel’s seaward extend. High river discharge events are also proven to be important in this region, as they can change sediment-transport patterns across the area.
KeywordsEbb-tidal delta dynamics Sediment transport Teignmouth MIKE21
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The data used in the model calibration were collected by the partners of the EC COAST3D (MAS3-CT97–0086) project and by the UK Met Office (wind data). Offshore boundary conditions for the modelled period was kindly provided by Dr Dirk-Jan Walstra (WL|DELFT). The authors are also grateful to the Danish Hydraulic Institute (Dr. Pierre Regnier and Dr. Hans J. Vested) for the opportunity to use the MIKE21 modelling system in this study through the collaboration in the EC SWAMIEE (FMRX-CT97–0111) project. The Argus video monitoring programme was established by Prof. Rob Holman (Oregon State University). Installation of the Teignmouth Argus system was funded by the ONR NICOP project Intermediate Scale Coastal Behaviour (Award no. N00014–97–1-0792) and is currently maintained by the EC CoastView project (EVK3-CT-2001–0054). We also thank the reviewers for their constructive comments that improved the manuscript. E.S. is funded by CNPq – Brazil (Ref. no. 200784/98–6).