# Evaluation of Different Simulation Methods for Analyzing Flood Scenarios in the Danube Delta
## 2 Study Area and Data
### Data  
Most of the time, floods occur as a result of high-water levels that are characterized by reaching a maximum point in terms of flow value. Thus, the available hydrological data for 51 years, between 1965 and 2015, were studied. Thus, Figure 2 presents the variation of the average annual flows at the Danube Delta entrance point, distributed by years, throughout the analysis period. The average flows of the Danube were then calculated at intervals of 5, 6, and 10 years, respectively, both at the delta entry point and on the three main branches (1965-1970, 1971-1980, 1981-1990, 1991-2000, 2001-2010, 2011-2015) (Table 1). From the analysis of this data, it could be concluded that the most probable value of the average flow over the entire analysis period at the entry point into the delta is between the approximate limits of 6700-6750 m\({}^{3}\)/s. The data analysis also shows that the maximum annual peak flow was recorded in 2010, a value of 16,600 m\({}^{3}\)/s, followed by 1970. This can be explained by taking into account variations in average annual flows over time. The flow that entered from the branches of the Danube into the main units of the delta in the period 1965-2015 was reduced. This reduction was caused by the alluvial clogging of some canal sleepers and the closure of others that generated clogging in the adjacent spaces [34]. From the longer \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Period**} & \multicolumn{6}{c}{**The Watercourse**} \\ \cline{2-9}  & \multicolumn{2}{c}{**Danube Entry**} & \multicolumn{2}{c}{**Sulina Branch**} & \multicolumn{2}{c}{**Sfantu Gheorghe Branch**} & \multicolumn{2}{c}{**Chilia Branch**} \\ \cline{2-9}  & **Q * (m\({}^{3}\)/s)** & \% & **Q (m\({}^{3}\)/s)** & \% & **Q (m\({}^{3}\)/s)** & \% & **Q (m\({}^{3}\)/s)** & \% \\ \hline
1965–1970 & 7683 & 100 & 1301 & 16.93 & 1522 & 19.81 & 4674 & 60.84 \\
1971–1980 & 6892 & 100 & 1289 & 18.70 & 1510 & 21.91 & 4076 & 59.14 \\
1981–1990 & 6209 & 100 & 1235 & 19.89 & 1399 & 22.53 & 3606 & 58.08 \\
1991–2000 & 6240 & 100 & 1253 & 20.08 & 1583 & 25.37 & 3390 & 54.33 \\
2001–2010 & 7005 & 100 & 1407 & 20.09 & 1572 & 22.44 & 4379 & 62.51 \\
2011–2015 & 6250 & 100 & 1255 & 20.08 & 1586 & 25.38 & 3396 & 54.34 \\ \hline \hline \end{tabular} \({}^{*}\)Q—river discharge.  
\end{table} 
Table 1: Average flows of the Danube at intervals of 5, 6, and 10 years, respectively, at the entrance to the Delta and on the three main branches (between 1965–2015). Figure 2: Variation of the average annual flows at the entrance to the Danube Delta, between 1965 and 2015.  
data series, starting with 1996, it was found that the years in which average annual flows of less than 6000 m\({}^{3}\)/s were recorded were the years 2003, 2007, 2008, 2011, and 2012, and average annual flows of more than 8000 m\({}^{3}\)/s were recorded in the years 2005, 2006, and 2010. River flooding usually occurs during the high-water phase [35]. The high-water levels of the 2005, 2006, and 2010 floods were imposed by the restriction of the freedom space of the lower Danube by damming the meadow, combined with significant rainfall. In addition, in July 2010, large-scale floods occurred in the Danube Delta as a result of a strong river flooding on the Danube. This phenomenon caused the almost complete flooding of settlements protected with local works or those simply unprotected, but also the rupture of some dams that had been dimensioned according to a class of greater importance (such as hydro-technical works). At the same time, the fact that there was an accumulation of water coming almost simultaneously from the flood in the whole delta, combined with the fact that the discharge to the sea was cumbersome, led to prolonged periods of water pressure on the protective dams. The year 2010 represented the reference year for the present study, considering the floods that took place in the Danube Delta. Figure 3 shows the monthly situation of water levels for 2010 and 2003.