Multiscale hydrodynamic modelling of the Danube Delta

Floodplains are a key component of deltaic systems, influencing hydrodynamics, ecosystem functioning, and local socioeconomic activities. Situated at the interface between the Danube River and the Black Sea, the Danube Delta forms a complex mosaic of channels, lakes, and floodplains. Despite its key role as a transition region—that filters nutrients, buffers floods, supports biodiversity, and sustains local livelihoods and economic activities—the Danube Delta remains understudied. In this thesis, we use the 2D version of the multiscale hydrodynamic model SLIM to evaluate the influence of floodplains on the hydrodynamics of the Danube Delta. We first examine the role of mesh configuration in such braided river–floodplain environments and propose hybrid curvilinear–unstructured meshes as the best compromise between accuracy and computational efficiency. We then present a first comprehensive, high-resolution, easily accessible bathymetric dataset for the three main branches of the Danube Delta, filling a key gap in available data for hydrodynamic modeling in the region. Finally, we demonstrate that including floodplains in deltaic hydrodynamic models improves hydrodynamic representation and offers alternative pathways for water flows. In the Danube Delta, we estimate that the proportion of the upstream discharge reaching the sea through routes other than the six main river mouths ranges from 10.0±4.1% (2024) to 10.8±4.8% (2021). This thesis highlights the essential
role of floodplains in deltaic environments and represents an important step toward a more realistic representation of the Danube–Black Sea continuum.