EFFECT OF FUTURE STORM CLUSTERING ON BEACH/DUNE EVOLUTION AND COASTAL FLOODING

Abstract

Future storm impacts on dune evolution due to changing storm frequency were simulated in XBeach at an exemplary dune system, Formby Point, UK. Probabilistic approaches were used to establish the future storm clusters from 2015 to 2065 in three scenarios, using measured data in Liverpool Bay. Cross-shore profile simulations were carried out in two series: Recovery and Cluster. Recovery used the same initial profile assuming that the profile is fully recovered when the subsequent storm event occurs. Cluster used the modified profile from the previous storm event. Within a single event, the maximum erosion and accretion of the profile occurred under the Recovery conditions due to the presence of a pronounced nearshore ridge-runnel pattern that evolved during severe storm events. Only a few storm events impacted on the upper dune area resulting in a bed level change, which under the Cluster approach was more noticeable when compared with the Recovery approach. The inter-tidal area experienced erosion while the sub-tidal area showed accretion in both the Recovery and the Cluster approaches, and the agreement of bed level change was considerably higher than that in the upper dune area. Vulnerability of the upper dune area increases in the Cluster approach as the initial storm events flatten the nearshore ridge-runnel pattern, and then the severe storm events directly impact on the dune front. High dune elevation at Formby Point prevents lowering of the dune crest due to the storm cluster erosion and therefore it can still withstand against flooding. Spatial modelling of the dune system is required to gain more insights of erosion and flood prone areas along this coast.