Modelling headland sandbank processes

• Main Author: Jones, Oliver Peter
• Published: University College London (University of London) 2007
• Subjects: 551.457
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444560

This thesis describes an investigation into near-shore headland-associated sandbanks that used process-based modelling techniques. The modelling experiments involved tidal, wave, sediment transport and morphological modules. The motivation came from a need to understand the dynamics of near-shore headland sandbanks which are valuable resources of raw material, ecology and coastal protection. An idealised model of a coastal headland was first used in which the physical system was simplified in order to quantify the influence of individual variables on sandbank initiation and growth. This approach provided a number of useful insights into headland sandbank dynamics. Firstly, the relative impact of the Coriolis force was shown to be minor in comparison with parameters including the seabed slope, headland geometry and tidal forcing. It was shown that a causal relationship between sandbank initiation and headland eddies does not exist. For certain headland geometries, however, the model suggested that the eddies become important in the long term maintenance of the associated headland sandbanks. The initiation and potential growth mechanisms of a real near-shore sandbank in the central Bristol Channel have also been investigated. The results confirmed many of the ideas obtained from the idealised investigation and provided a number of new insights into the complex physical system in which the bank exists. The presence of a wave- induced mechanism was detected, capable of replenishing sandy material in the large coastal embayments and supplying the headland sandbanks of the central Bristol Channel. The work also suggested that the sandbank itself was initiated, and its position controlled, by large gradients in the tidal currents produced by the headland. Its further maintenance and development was shown to be the result of a self- sustaining feedback mechanism, detected in the surrounding flow field.