Morphodynamic behaviour of a nearshore sandbank system: The Great Yarmouth Sandbanks, U.K.

Offshore sandbanks provide a major source of sediment and may have a significant impact on the evolution of the nearby shoreline. The prediction of sandbank evolution is extremely important for coastal engineers and managers. However, it is evident from the existing literature that additional investigations into the evolution of offshore sandbanks are needed. The present paper describes qualitative and quantitative investigations of the evolution of the Great Yarmouth sandbanks. A depth-integrated tidal model has been used to calculate the residual currents arising from the sequence of sandbank configurations observed from historic charts over a 150 year period. Tidal simulations were performed with a nested model covering the Southern North Sea and Great Yarmouth zone (east coast of the UK). Simulations were carried out for a period corresponding to several spring-neap cycles to calculate residual currents and were compared directly with field measurements. Model calibration and validation was performed against published tidal elevation charts based on many observations, tidal predictions and field measurements. These detailed comparisons have been used to determine the errors in the model predictions. Overall, the performance of the model is considered good. The model output has been analysed to investigate qualitative links between the sandbank configuration and the residual flow statistics. The results demonstrate that the long-term changes in sandbank morphology can be explained from the pattern of tidal residual currents.