# Evaluation of Different Simulation Methods for Analyzing Flood Scenarios in the Danube Delta
## 3 Materials and Methods  
The present study comprises the analysis of two scenarios where ruptures occur in the settlements' dykes in conditions of maximum levels on the Danube. The difference between these two scenarios is how long the breach remains open in the dyke. Thus, the first scenario of flood analysis was applied to the settlements by modeling a real scenario with the occurrence of a 20 m opening (breach) in the dyke, remaining present for 24 h at the maximum water levels of the Danube. The second scenario of flood analysis was applied to the settlements through a Geographic Information Systems (GIS) analysis (static from a hydraulic point of view), consisting of superimposing the information corresponding to the maximum water level over the digital terrain model. It corresponds to the most unfavorable scenario, namely the breach/breaches remaining present in the dyke at the same time as the maximum water levels of the Danube for a longer period (more than one day). For the analysis of the dam breaching scenarios, two methods were used: the dynamic method for the first scenario, and the static method for the second scenario. The steps followed are summarized in a process diagram (Figure 4). According to the figure above, the diagram of the applied process involves a continuous, interactive, and dynamic process. These stages do not form a linear process but move sequentially from one step to another and vary depending on the results of each stage. It is clear from the scheme that the input data are very important in flood scenario analysis. The data collection process begins with a regional assessment, an exploratory phase, or even an investigation, which provide input for the proposed diagram [36]. Following the data collection, in the first phase the raw data are obtained (in this case, the hydrological data, water flows and water levels, and topo-bathymetric data, transverse profiles, topographic maps, the digital terrain model, ortho photomaps, satellite images, etc. ), representing the primary data that require elementary processing for further use [37]. The data are obtained from external sources, such as administrative flow data, existing studies and research, maps, photographs, or internal sources (collected during the study using an appropriate methodology). The accuracy of the results of the analysis depends on the accuracy of the raw data [38]. As shown in Figure 4, the proposed methodology combines two methods of analysis. In the approach of each method, we need input data, such as the digital terrain model, hydrological data, topo-bathymetric data, and topo-geographic data for the Danube Delta area. Figure 4: Diagram indicating the methodology considered in the present work, and which describes the main steps. The basic element that the two methods are applied to is the digital terrain model (DTM). The DTM has the role of rendering the terrain configuration continuously from a spatial point of view, and can be manipulated by computer programs. Today, light detection and ranging (LIDAR) technology is known as an important source of geospatial information. The benefits of this technology are particularly valuable in a wide range of scientific and professional fields, such as land monitoring, hydraulic modeling of rivers/streams, and more [39; 40]. The data from the DTM used in this study (Figure 2) shows the terrain with a high degree of accuracy, for both axis direction: horizontally, 0.5 m \(\times\) 0.5 m, and vertically, 0.05 m. The accuracy is more important than resolution in hydraulic and hydrological modeling research and GIS analysis. The data files contain spatial terrain height data in a digital format, usually in a rectangular grid. As the study area considered overlaps with an extremely large space, the DTM had to cover the entire area of the Danube Delta itself, in order to have good data processing for the hydraulic modeling and the GIS processing.