A coupled approach for planning in vulnerable coastal landscapes

Abstract

One of the most problematic steps in planning and management of vulnerable coastal systems under high level of uncertainties is anticipating potential design scenarios where multiple spatial scales interact. The mutual interference between beach morphodynamics and infrastructural needs of the wide territory poses several questions to urban planners and architects. In this study we assess the ability of the proposed coupled approach of MIKE 21 Spectral Wave and XBeach to significantly improve our understanding of vulnerable barrier beaches in urbanized areas, and hence to contribute to improved system design and management. Specifically, to improve the result accuracy and the time-computational efficiency of the proposed coupled approach, an additional module was developed. Located in the West Metropolitan Area of Cagliari city (Sardinia, IT), the barrier beach of La Playa is an important evacuation route that has experienced a coastal squeeze process under the increase in magnitude and frequency of sea storms. From an extensive beach survey, the “whole model composition” supports the selection of the territorial scale as the reference for defining a potential design scenario at the local scale in La Playa beach. While ordinary (10-year return time) storms create a nearshore sand berm with a protective function for the barrier beach and evacuation route against future storms, extreme (140-year return time) storms significantly erode the beach with a shoreline moving approximately 15 m landward and an overwash of Qcrest >20 l/m/s. Acting as a rigid impermeable obstacle against landward barrier migration, the evacuation route is destroyed. Urban planners and architects should consider the downgrade of the evacuation route as a part of a design potential scenario capable of minimizing the territorial vulnerability and reducing the local vulnerability. Rebuilt with environment-friendly functional road materials, this design scenario can also define a new flexible landward limit of the barrier beach and restore an eventual migration.