# Evaluation of Different Simulation Methods for Analyzing Flood Scenarios in the Danube Delta
## 2 Study Area and Data  
### Study Area  
The Danube Delta is located in the eastern extremity of Romania and covers 2.5% of the country's area. The Danube Delta, including the peripheral lake areas, extends North to 45\({}^{\circ}\)27\({}^{\prime}\) northern latitude (Chilia branch, 43 km), South to 44\({}^{\circ}\)20\({}^{\prime}\) (Cape Midia), West to 28\({}^{\circ}\)10\({}^{\prime}\) E (Cat's Bend) and East to 29\({}^{\circ}\)42\({}^{\prime}\) E (Sulina) [27]. The Danube Delta is a complex environment, governed by the interactions between the Danube River and the Black Sea [28]. Ecosystem services, provided by the Danube Delta, are very diverse, due to the heterogeneity and high dynamism of ecological systems in the area [29]. As a result of the decrease of the floodplains in the Danube Delta area, the nutrient retention capacity has decreased, so the Danube waters are affected by strong eutrophication. These phenomena affect trophic cycles, leading to a decrease in biological diversity through the disappearance of some species, many of which have high landscape and even economic value [30]. The Delta area requires major investment and the development of quality studies on the modeling of flood phenomena. The transformation of wetlands into terrestrial ecosystems and the modification of ecosystem structures have decreased the capacities of floodable surfaces, as well as ecological, economic, recreational, aesthetic, and educational capacities. In the present study, the settlements located along one of the three main branches of the Danube (the Sulina branch with a length of approximately 71 km), which partly ensure the water flow to the Black Sea, were taken into account (Figure 1). The settlements analyzed were Partizani, Ilgani de Sus, Vulturu, Maliuc, Gorgova, Mila 23, and Crisanand Sulina. These localities are vulnerable to the high-water level of the Danube. These waters, entering the delta, reach the sea following several flow paths; the Chilia branch, followed by the branches of the secondary Chilia delta and the Tulcea branch, splitting onwards into the Sulina and Sfantu Gheorghe branches. Between the main water flow routes through the Danube Delta and the interior of the delta, and between these routes and the areas outside the delta, as well as between the delta and the sea and inside the delta, there are several connecting routes for water circulation, which play a particular role in the hydrological regime of the delta [31]. Through these routes, a natural accumulation reservoir role is played by the interior of the delta and by some outer areas, and secondary routes of water flow to the sea appear. The regime of this natural reservoir is determined by the flow of the Danube at the starting point of the Delta [32]. A major flood event in the Danube Delta was identified in July 2010 and examined in the present study. Major floods were generated by the appearance of significant water flow on the Danube. The flow resulting from the river flooding was of 16,600 m\({}^{3}\)/s, as opposed to the 6658 m\({}^{3}\)/s mean flow (between 1965-2015), registered at the Tulcea-port hydrometric station. The maximum level of the flood was recorded on 6 July 2010 as 4.95 m, measured for the Black Sea Sulina system, opposed to the  
Figure 1: Geographical locations of the settlements along the Sulina branch considered for this study, (**a**) the study area superimposed on the topographic map; (**b**) the geographical position of the settlements superimposed on the ortho-photomaps of the Danube Delta (the green dots are the settlements located along the Sulina branch) and the patch on which topo-bathymetric measurements were performed (S1, S2 describe the cross sections measured in the first part of the river, and S3 describes the cross section measured in the river’s second part); (**c**) the study area superimposed on the digital terrain model. 2.50 m mean level.