## 3 Results
### Water Level versus Suspended Sediment Concentration  
In order to find a relationship between water level (changes) and turbidity, the relationship between the two parameters in the time series was sought. The recorded turbidity as a function of water level was given for the floods listed in Table 1.  
Several conclusions can be drawn based on the water level and sediment concentration time series, as well as the peak water level and sediment concentration. It is assumed that sediment concentration (similarly to discharge) peaks after the water level. It can be observed in the time series that the water level and sediment concentration do not always peak at the same time. Comparing the water levels and the sediment concentrations, it can be concluded that floods with approximately the same peak water level do not peak with the same sediment concentration. It can be also observed that peak values do not follow each other consistently: the peak water level of 400 cm had a peak concentration of 60 mg/L, but two weeks later the next flood peaked with a lower, 350 cm water level and a  
Figure 6: Turbidimeter turbidity versus probe turbidity relationship.  
higher, 100 mg/L sediment concentration. The examined floods also include ones where there has been no increase in concentration during the entire duration of the flood.  
Figure 7 shows the sediment concentration as a function of water level for three periods from Table 1. The three biggest floods peaked with water levels between 570 and 670 cm, but the peak sediment concentrations are not proportional to the peak water level, as they were between 50 and 230 mg/L. In addition, in the case of the two largest flood waves, a hysteresis of sediment concentrations (similar to discharge hysteresis) can be observed. The shape of the curves for each flood wave are different. The hysteresis curve of the 2020 February flood wave has the shape of an asymmetrical 8. The next flood wave, which occurred in June and July 2020, does not have an exact shape nor a significant rise in the suspended sediment concentration, while the flood wave of June and July 2021 has a shape of an open 8. The higher suspended sediment concentrations occurred at the falling limb in the case of these flood waves.  
According to [24], the main factors influencing sediment hysteresis in the case of this particular gauging station of the Danube River may be the magnitude and sequence of  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Period**} & **Peak Water Level** & **Peak Discharge** & **Peak Turbidity** \\  & **[cm]** & **[m\({}^{3}\)/s]** & **[NTU]** \\ \hline February 2020 & 639 & 4450 & 150 \\ \hline June-July 2020 & 574 & 4000 & 50 \\ \hline June-July 2020 & 483 & 3350 & 25 \\ \hline June-July 2020 & 400 & 2800 & 30 \\ \hline July–September 2021 & 668 & 4700 & 230 \\ \hline July–September 2021 & 540 & 3750 & 70 \\ \hline July-September 2021 & 496 & 3450 & 55 \\ \hline July-September 2021 & 397 & 2800 & 60 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Attributes of the analyzed flood waves [23].  
Figure 7: Suspended sediment concentration as a function of water level in the case of three flood waves, with the separation of rising and falling limbs, based on [23].  
events, PSD, and sediment source. As in the discussed analysis, these latter two factors were not investigated, and at the moment, no explanation is sought for the described hysteresis phenomena. However, sediment dynamics are complex, and the hysteresis patterns may be linked to many other factors as well.