Long-term prediction of sediment transport and morphological behaviour in the coastal zone is becoming increasingly important, as a result of human interference and changing environment conditions. The research presented describes modelling concepts, which have been applied to a challenging coastal/estuarine environment in Cardigan Bay, mid-Wales, U.K. The TELEMAC
Modelling System has been applied to the Dyfi Estuary and neighbouring coastline to recreate the annual wave-current conditions and the resulting sediment fluxes and seabed evolution. 'Input reduction ' methods have been required to produce realistic schematisations of events in feasible computation times. A field campaign carried out in January-February 2006 provided data for
validation of the TELEMAC modules. To improve model accuracy refinements were implemented with regard to the parameterisation of the bed roughness, the advection-diffusion scheme for suspended sediment and also, the sand transport formulation itself. The success/failure and limitations of the morphodynamic modelling attempts, using SISYPHE, have been presented. A parameterisation of the results from the UWB 1DV sand transport 'research' model, for the conditions in the Dyfi Estuary, has been introduced as an alternative option to Bijker's (1992)
model, allowing SISYPHE to provide greater realism in the morphological predictions. The predicted sand transport patterns in the Dyfi Estuary, the case of present interest, have posed some interesting questions relating to the sediment budget of the system. Tidal currents in isolation give rise to net sand transport out of the estuary, which is enhanced by the presence of waves. The magnitude of the annual net transport appears to rely also on the frequency and intensity of wave events. In contrast, sea level rise led to a net inward sediment flux into the
estuary. Investigation into the flood-ebb dominance of the Dyfi has resulted in the development of a conditional parameter set delineating net import/export of sediment into/out of the estuary.
One practical objective of the present study was to investigate the possibility of a sustainable harbour pit, off the town of Aberdyfi located at the seaward limit of the Dyfi Estuary. This would greatly improve existing mooring facilities. The development of such a pit in a mobile area of channels and banks, combined with threats such as sea level rise and climate change, requires accurate prediction of transport rates and morphological change. Various pit scenarios have been tested with a view to minimising infill rates. Finally, consideration was given to the future impact of increased sea level and storminess in the Dyfi Estuary.