## 4 Discussion
### Near-Bank Suspended Sediment Concentration versus Suspended Sediment Yield  
Two regression lines were fitted for the simultaneous data of the near-bank suspended sediment concentration and the suspended sediment yield. The accuracy of the relationship between the near-bank suspended sediment concentration and the suspended sediment yield (R\({}^{2}\) = 0.85-0.90, Figure 9) is better than the suspended sediment yield rating curve based on the discharge either in the case of historical or new data (R\({}^{2}\) = 0.42-0.57, Figure 8).  
The breakpoint of the slope between the two regression lines will be more accurately marked by increasing the number of measurements. In the article [15] published in 2020, the authors defined the breakpoint between the regression lines at around 30 mg/L suspended sediment concentration for the Danube reach between Szodliget and Rackeve. There is a relatively long distance between these stations and Baja (130-190 km), the PSD of the transported sediment is rather different, and the difference between the breakpoints (breakpoint of Baja is at 80 mg/L) can also be caused by the different geometries of the two cross-sections.  
The results so far provide a good starting point; however, 11 measurements are not yet enough to establish reliable relationships covering all ranges. In the future, the measurements will continue in order to refine the relationships. After the establishment of an acceptable relationship which covers all the ranges, this integrated method will be compared with the sediment yield rating curve method by determining and comparing the annual and flood wave sediment regimes. Further tests will be carried out about the suitability of the selected gauging station (Baja), as during the measurements made so far, the water level of the Danube River did not exceed the point of overflowing the banks of the main riverbed (400 m wide), so the effects of the floodplain (7 km wide) on the sediment transport in the case of the integrated method could not yet be detected.  
Overall, the prospect of large-scale applications of proven suspended sediment surrogate technologies is a revolutionary concept in fluvial sediment monitoring technologies with important future benefits, providing for safer, more frequent and consistent, arguably more accurate, and ultimately less expensive fluvial sediment data collection [8], which underlines the importance of the presented research.  
Conceptualization, L.V; methodology, L.V.; formal analysis, L.V. and E.A.T.; resources, L.V. and E.A.T.; writing-original draft preparation: L.V. and E.A.T.; writing review and editing, L.V. and E.A.T.; visualization, L.V. and E.A.T.; supervision, L.V. and E.A.T. All authors have read and agreed to the published version of the manuscripts.  
This research was funded by General Directorate of Water Management, H-1253 Budapest (probe), Lower Danube Valley Water Directorate, H-6500 Baja (sediment samplings) and the University of Public Service, Faculty of Water Sciences, H-6500 Baja (sediment samplings). The station was designed by the General Directorate of Water Management and was built by the Lower Danube Valley Water Directorate and VITUKI HUNGARY Kft, H-1097 Budapest. Measurements of UPS FWS were carried out in frame of a research contract in the HOMER project and during higher education teaching of field measurement techniques. The funding from General Directorate of Water Management and Lower Danube Valley Water Directorate were institutional.