Design hyetograph or design storm definition is one of the most important parts of the design discharge determination in case of ungauged catchments. Design hyetograph duration and temporal rainfall distribution can have large impact on the peak discharge values and the shape of the runoff hydrograph. The influence of these two factors on the design runoff values is presented in the case study of the Glinščica River catchment that covers 16.85 km2 and it is located in central part of Slovenia, Europe. A combination of Huff and intensity-duration-frequency (IDF) curves is used to construct the design hyetograph for the presented case study. The duration of the design storm is determined by the catchment time of concentration. The results are compared to the Natural Resources Conservation Service (NRCS) curves and the so-called frequency storm method. The hydrological modeling result that was carried out using the hydrologic modeling system (HEC-HMS) software indicates that differences among different methods should not be neglected. For the 10-year return period, differences in the peak discharge values can be larger than 10%, while even larger differences can be expected for longer return periods. Some studies showed that these can be larger than 50%. Therefore, the guidelines on how to construct the design hyetograph are presented.
Part of the book: Engineering and Mathematical Topics in Rainfall
Extreme events such as floods can endanger human lives and cause large economic damage. The Savinja River catchment is one of the most frequently flooded areas in Slovenia, Europe. In order to evaluate the impact of the proposed flood mitigation measures on the flood safety in this catchment, the combined hydrological and hydraulic modelling approach was carried out. The hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV-light) was used to perform hydrological modelling. The hydraulic calculations were carried out using the HEC-RAS 5.0.3 model in order to simulate the combined one- and two-dimensional unsteady flow. Using the calibrated and validated hydrological and hydraulic models, the impact of the proposed measures was assessed in the light of the sustainable flood management. Additionally, with analyses of the historical data and past flood events, we were able to investigate the characteristics of the extreme floods in this area and also downstream at the confluence with the Sava River. Moreover, it was found that the backwater effect has an important role on the water level and flood safety along the river reach, which is often neglected in the aspect of flood management.
Part of the book: Achievements and Challenges of Integrated River Basin Management