Development of topo-bathymetric continuum profiles for coastal barriers with global open-access data

Abstract

Coastal barriers are dynamic and vulnerable coastal environments exposed to storms and rising sea levels, requiring a thorough understanding of their physical and geomorphological characteristics. Despite this, high-resolution topo-bathymetric data are not openly available for most of the world’s coastal areas, preventing accurate estimation of the exposure to storms and associated risks. Global models of topography and bathymetry, derived from remote sensing techniques, are available worldwide as an open-source solution to characterise coastal morphology. However, their coarse resolution, limited vertical and horizontal accuracy, alongside inconsistencies in the transition from land to the shallow nearshore zone, make their use in coastal areas challenging, requiring careful evaluation. This study investigates the potential and limitations of four recent open-access satellite-derived topographic models (Copernicus GLO-30 DEM, AW3D30, TanDEM-X, Euro-Maps 3D) and three bathymetric models (GEBCO_2023, SRTM15+, ETOPO 2022) in five coastal barriers. It proposes a new approach to integrate global models to provide a consistent representation of the topo-bathymetric continuum profile in coastal areas characterised by a barrier morphology. Coastal barrier profiles, representative of natural sectors and characterized by morphological homogeneity, were derived by merging global topographic and bathymetric digital elevation models and implementing an equilibrium profile in the transition zone. The profiles obtained from the global models were compared with higher resolution local or regional topo-bathymetry. The global topographies tend to underestimate the dune top, with TanDEM-X giving the best results in terms of dune crest height and beach slope. The barrier continuum profiles that merged TanDEM-x and ETOPO 2022 global models were found to have the lowest error, with a vertical RMSE of 0.76 m. Based on integration of these remotely sensed models, it is possible to determine average representative coastal barrier profiles suitable for use in global to regional coastal studies or in data-poor areas, potentially serving as a cost-effective tool for preliminary coastal hazard assessments and early warning systems at wide spatial scales.