Recent developments in numerical modelling of coastline evolution : Advanced development and evaluation of ShorelineS Coastline Model

Even though coasts including coastlines, beaches, and dunes will always tend to reach a dynamic equilibrium state, they are exposed to coastal erosion and coastal flooding as a result of sea level rise and the human interventions. As these problems worsen as the days pass, they have posed many challenges to get into details about understanding the causes of these issues. Many coastline models have been developed on that purpose; however, the limitations of those existing models haven’t provided the complete capability of keeping pace with this dramatic evolution of coastline and dunes. Accordingly, ShorelineS was developed as a new vision into overcoming the limitations of the existing coastline models based on simple principles based on the one-line theory (Pelnard-Considère, 1956). The model is unique in describing the coastline as chains of grid points that can move freely without any references in addition to the allowance of an arbitrary number of coast sections (e.g. islands or beaches near harbours). The model also can produce spits which can migrate and join other coast sections. This research aims at improving ShorelineS behaviour near shore-normal structures (e.g. groins) by enhancing the definition of the shore-normal structures in the model and introducing sand bypassing and transmission. Those developments complement each other as the new definition of the shore-normal structures has provided two coastline grid points exactly at the structure, which are the most accurate place where the bypassing lateral boundary can be applied. Two approaches regarding sand bypassing have been introduced in the model, and both have produced satisfactory results compared to the analytical solution. Moreover, this research aims also at enhancing the capabilities of ShorelineS to simulate the impact of short extreme storms on foredunes and dune foot evolution in long-term periods and extend that for complex real-world beach dune systems. That has been implemented by developing a dune foot evolution model based on simple principles along the lines of (Larson et al., 2016). Following the same description of the coastline, the dune foot is described as a free moving string of points. The foredunes are assumed to move horizontally along the beach berm width and represented in the dune foot movement which is triggered by cross-shore wave transport and the abelian transport. The interaction between the coastline and the dune foot described in the exchange of the sediment are taken into account and contributing to the coastline change. To validate ShorelineS after all developments, three real-world applications were selected to cover all the conducted developments and to ensure that the research objectives were successfully achieved with rational answers to the research questions. The first case that covers the bypassing and structures development is a groin field located in Egypt along the Mediterranean Sea, while the other two applications are located along the Dutch coast on the North Sea, where sand dunes can be found. All cases have produced satisfactory results; however, overcoming the listed research limitations will enhance the model behaviour, particularly in the simulation of the dune foot evolution