Quantification of uncertainties in shoreline response to the representation of offshore wave conditions

Dissanayake, Pushpa; Brown, Jennifer M. ORCID: https://orcid.org/0000-0002-3894-4651; Saulter, Andy; Reeve, Dominic E; Karunarathna, Harshinie. 2019 Quantification of uncertainties in shoreline response to the representation of offshore wave conditions. Southampton, National Oceanography Centre, 29pp. (National Oceanography Centre Internal Document, No. 20)

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Abstract/Summary

This paper presents the results of a sensitivity study investigating beach/dune response to offshore wave boundary forcing. The modelling study was based on the convex-shape Sefton coast, UK which has a complex nearshore morphology with ridge-runnel patterns and foreshore frontal dunes. Simulations were performed using a cascade of nested grids to transform offshore waves up to a high resolution nearshore XBeach model of the Sefton coast in which the beach/dune response was modelled. Two storm events representing low and high severity were simulated using uniform and varying wave boundary conditions at the offshore model boundary for both cases. The uniform boundary always resulted in higher storm waves in the XBeach domain. There were differences along the coast based on the coastline orientation and the local morphology, indicating different localised sensitivities to the wave boundary type. Bed level change within the tidal regions (sub-, inter- and supra-tidal) indicated landward decrease of the wave boundary effect. Volume change within the sub-tidal area showed the highest sensitivity to the space varying wave boundary forcing. Applying a uniform wave boundary for the XBeach domain exacerbated the wave impacts in the model domain. Our study suggests that application of a spatially varying wave boundary condition for the XBeach domain was able to correctly capture sediment transport and hence the beach/dune response of Sefton coast.