Designing various hydrotechnical structures, planning, water management etc. require the knowledge of the peak discharge values and hydrographs. If measurements (discharge and precipitation) are available we can determine basic hydrological concepts and properties with greater reliability. In cases when measurements are not available or measurement period is relatively short, we can use different hydrological models or simple empirical equations for previously mentioned purpose.
In this graduation thesis, a hydrological model using the HEC-HMS software was developed for the upper part of the Dravinja river basin (up to the Zreče water gauging station) and it was calibrated using measured discharge data. The software SAGA-GIS was used to determine the topographic characteristics of the basin. On the basis of the characteristics of the basin we determined the parameters of the the unit hydrograph (UH) methods. Clark UH method proved to be the most appropriate method for the investigated basin.
Using different distribution functions, the results of flood frequency analysis were calculated. For comparison with the hydrological model, the logarithmic normal distribution was chosen because it gave the best fit to the measured data. One of the main parameters of the hydrological model is the Curve Number (CN) coefficient, which describes the precipitation losses for the selected river basin. The selected Clark UH method contains time of concentration Tc and the accumulation coefficient R parameters. Thus, during the calibration process three runoff events of different magnitudes were chosen. The calibrated model parameters were additionally validated using three different runoff events. It turned out that on the basis of the calibrated and validated hydrological model, we obtained comparable results with previously calculated parameters using the theoretical equations. Using the intenstity-duration-frequency (IDF) and Huff curves, design precipitation events were determined for a 10-, 50-, 100-year return period. Applying the calibrated and validated model design discharge values were calculated and compared with the results of the flood frequency analysis. Design discharge values obtained using the design rainfall events are slightly larger than the design discharge values calculated using the flood frequency analysis approach.