Effects of soil properties on erosion and breaching of natural coastal barriers under extreme storm surges

Natural coastal barriers (NCB), e.g., barrier islands and dunes, represent important defense features against storm surges and coastal flooding. Due to climate change, the probability of extreme storms has been increased. Consequently, NCB may suffer significant erosion, which increases their breaching probability. However, available numerical models for NCB breaching still predict locations and sizes of possible breaches with moderate accuracy. This observation highlights the need for a deeper understanding of the factors triggering the alongshore variable response of NCB to storm surges so that weak locations can be determined. This exploratory study offers a synthesis of evidence that alongshore varying soil permeability of unvegetated NCB may control the alongshore varying abiotic soil resistance to erosion and determine possible breaching locations. Following research, therefore, presents an extension to the XBeach model, now accounting for spatial variability of soil resistance through soil permeability. To numerically quantify soil permeability effects on wave-induced breaching, the extended XBeach has been applied to a synthetic case study of spatially varying soil resistance. Results revealed that longshore variability of soil resistance along the barrier is mainly triggered by spatially varying permeability. The results also guide toward enhancing the resilience of NCB against breaching through improving their soil properties.