Numerical Modelling Of Hydrodynamics,Sand Transport And Long-term Morphology In Liverpool Bay

Reconstructions in coastal areas will contribute to changes in hydrodynamics, sediment transport and shoreline evolutions. And these changes in return will affect local coastal enginnering. Sea level rise (SLR) is resulted from climate change and human activities. The expected results of SLR would be the inshore movement of the coastal processes with the increased water depth, which consequently increase the possibility of shoreline erosion and more frequent inundation. Thus the economy, environment and ecosystem in coastal areas would be significantly influenced. Researches into the potential effects of physical processes on coastal sediment transport and morphological changes are necessary for coastal authorities to consider a range of possible options for enviromental protection and coastal management.Liverpool Bay around North West England is chosen for detailed study using an open-source2D numerical model system, TELEMAC. The model system is modified in order to research in several aspects including:the interactions between tide and wave; effects of tide, wave and sea level rise on dynamics and sediment transport; combined effects of tides, waves and sea level rise on long-term morphological changes in Liverpool Bay.An improved numerical model is developed using TELEMAC-2D and SISYPHE to compute tidal flow and sediment transport. The source program in TELEMAC-2D is modified in order to input a variable water elevation induced by several tidal constituents on the boundary. Modifying the source program in SISYPHE allow to customize sediment sizes on each node. The result shows that tidal asymmetry results in onshore sediment transport in coastal areas.An efficient model considering both tide-wave interaction and wave stirring effect on sediment transport is introduced. Study in interactions between tides and waves shows that the tidal elevation and tidal current both have significant influences on wave propagation and wave breaking in shallow water areas. With the same direction of wave and flow, the wave surf and breaking would be significantly weakened, or it would be slightly enhanced with the opposite direction of wave and flow. Wave energy can be transferred into long-shore currents by radiation stress, thus further changes the near shore currents. In addition, waves will affect sand transport in shallow water areas where wave transformation and wave breaking largely happen. Coastal sediment transport can be significantly increased by wave stirring and flow, which is also the key mechanism for non-linear coastal sediment transport under combined effects of tides and waves.Simulations on the effect of combined wave and tide on sediment transport under a given50cm SLR are carried out. The overall impacts on the tidal range and flow speed are found to be small. Nevertheless, the wave surf and breaking zone would move onshore with the SLR, thus results in increased sediment transported into estuaries like Mersey.A numerical model considering combined effects of tides, waves and sea level rise on long-term morphology change is developed. To simplify the hydrodynamic conditions, an ’input-reduction’method is used to choose representative tide and waves. A changed ’Parallel online’ approach with different morphological factors is introduced to compute long-term morphology changes under several conditions in parallel, which largely improve model efficiency. The90-year morphological evolution is investigated and reveals that the most commonly occurring waves tend to bring sediment onshore and into the estuaries by eroding Outer Estuaries and channels, but storm-driving waves tend to erode Inner estuary. Moreover, SLR will change morphology in wave surf and breaking zone and result in further coastline erosion.