Barrier beach modelling as a management tool

Abstract

Barrier beaches are one of the most dynamic and vulnerable coastal landforms found between open seas and closed/semi-closed enclosures like bays, marshlands or estuaries. Being a very narrow coastal feature, they are susceptible to frequent storm induced flooding and breaching. Further global sea level phenomena also a pose serious threat to their very existence. In this work, storm and sea level impacts on Trabucador barrier beach located in the Ebro Delta of southern Spain is studied using state of the art, open source XBeach numerical model. In the past, Trabucador barrier beach has undergone several breaching incidents during storm events which hinders economic activities for month and exposing the bay to direct wave action causing environmental concerns. Model calibration and validation was first carried out using goodness of fit approach by comparing modelled and observed breached islands. Further, feasibility of alternating embryonic dunes and classical shoreface nourishment approach as the protection measures to mitigate barrier breaching is explored in both current and sea level rise scenarios under different storms. Once sufficient model predictive ability is achieved through the calibration process, 45 different combinations of scenarios are modelled which is combination of 3 storms- Gloria, Filomena and Isaak, 4 water level conditions- Current, SLR of 0.27m, SLR of 0.57m and SLR of 0.75m, 4 beach states – No protection, Alternating dunes, Continuous dunes and Classical Nourishment. In addition, double storm Filomena and Isaak are studied in current water level conditions. Model results show, both alternating dunes and classical nourishment reduced breaching to a great extent with classical nourishment performing better. At higher water levels, the protection measures fail especially, classical nourishment scenario produced more breaching than the rest. At lower water levels, width of beach played a major role in reducing the breaching but at higher water levels beach elevated gained the significance.