Impacts of sea level rise on morphodynamics in Liverpool Bay

Abstract

In order to understand the influence of sea level rise (SLR) on the tide, waves and sediment transport on a regional scale, and more importantly the implication of such changes on coastal engineering practice, three estuaries in north-west England, Mersey, Dee and Ribble, were chosen for detailed study using a numerical morphological model system, Telemac. The numerical model was calibrated against available field measurements on both hydrodynamics and sediment transport. Simulations were first carried out for a given 0·5 m SLR condition. The overall impact of the SLR on tidal range and flow current speed was found to be small. It is clear that the surf zone is shifted inshore due to the increased water depth. Moreover, changes to the sediment transport within each estuary are complex due to specific interplays between hydrodynamics and tidal flats. Finally, a modified ‘parallel online’ approach with variable morphological factors was employed for a 90-year simulation with constant SLR rate, together with an ‘input-reduction’ method. The overall morphological evolution under a constant SLR rate was investigated, which clearly suggests that the most commonly occurring waves tend to bring sediment onshore and into estuaries by eroding outer estuaries and channels, but storm-driving waves tend to erode inner estuaries.