Exploring coastal bathymetry retrieval for ocean modeling: a case study from West Africa

Abstract Coastal risk assessment requires accurate coastal bathymetry, which is largely lacking in many regions of the world's coastal oceans. This is particularly true in Guinea-Bissau, where the tidal range is the highest of any country in West Africa, affecting several socio-economic sectors such as agriculture and urban development. Here we present a selection of coastal bathymetry datasets available for generally poorly sampled coastal regions. These include the global GEBCO product, digital nautical charts (CMAP), and depth retrieval from satellite wave detection (S2Shores). While GEBCO provides the right regional envelop of bathymetry, the coastal zone is plagued with random bumpiness at scales below 10 km. S2Shores can be used to correct these errors and instead reveal the presence of small scale channels, reminiscent of very high-resolution satellite color images. These structures are also confirmed by nautical charts, which show the channels to be deeper than that indicated by the satellite retrieval. In simulations with the hydro-sedimentary coastal ocean model CROCO, the tidal energy flux is better channeled towards the coast in the CMAP and S2shores cases, while GEBCO produces larger form drag and sediment bed response, acting as a bathymetric correction to minimize friction. This result highlights the potential of combining different approaches to estimate up-to-date coastal bathymetry in the most challenging areas.