Modelling river-sea continuum: the case of the Danube Delta

Abstract. Understanding water transport and circulation in coastal seas and transitional environments is among the key topics of oceanographic and climate research, as well as recognizing the role of the land-sea interface. The Danube Delta represents a natural laboratory for river-sea hydrodynamic modelling due to its complex morphology and being subjected to several natural and anthropogenic stressors. In this work, we present the results of the SHYFEM finite element hydrodynamic model application to the whole river-sea continuum of the Danube Delta region. The model was run for several years to characterize: 1) the water discharge distribution among the river branches, 2) the general hydrodynamic characteristics of the coastal region of freshwater influence, 3) the transport time scale of the Razelm Sinoie Lagoon System, and 4) the processes driving the river-lagoon-sea interconnections. The unique numerical description of the transport and mixing in the different water bodies of the Delta (river branches, channels, lagoons and coastal sea) may be used to provide the scientific basis to assess the impact of human activities and to design efficient management choices. Indeed, we used the modelling framework to evaluate the effect of reconnection (restoration) measures in the Razelm Sinoie Lagoon System designed to improve hydrological connectivity.