An integrated high-resolution bathymetric model for the Danube Delta system

Acting as a buffer between the Danube and the Black Sea, the Danube Delta plays an important role in regulating the hydro-biochemical flows of this land-sea continuum. Despite its importance, very few studies have focused on the impact of the Danube Delta on the different fluxes between the Danube and the Black Sea. One of the first step to characterize this land-sea continuum is to describe the bathymetry of the Delta. However, there is no complete, easily accessible bathymetric data on all three branches of the Delta to support hydrodynamic, biogeochemical or ecological studies. In this study, we aim to fill this gap by combining 4 different datasets, three in the river and one for the riverbanks, each varying in density and spatial distribution, to create a high-resolution bathymetry dataset. The bathymetric data was interpolated on a hybrid curvilinear-unstructured mesh with an anisotropic Inverse Distance Weighting (IDW) interpolation method. The resulting product offers resolutions ranging from 2 m in a connection zone to 100 m in one of the straight unidirectional channel. Cross validation of the dataset underlined the importance of the data source spatial pattern, with average Root Mean Square Error (RRMSE) of 0.55 %, 6.3 % and 27.6 %, for river segments covered by the densest to the coarsest dataset. These error rates are comparable to those observed in bathymetry interpolation in rivers with similar source datasets. The bathymetry presented in this study is the first unique, high-resolution, comprehensive and easily accessible bathymetric model covering all three branches of the Danube Delta. It will serve as an input in a hydrodynamic model of the Danube Delta, with the aim of better understanding the role of the Delta in the land-sea continuum between the Danube and the Black Sea. The dataset is available at https://doi.org/10.5281/zenodo.14055741 (Alaerts et al., 2024).