The evaluation of the design flood hydrographs determined with the Hydroproject method in the gauged catchments

In Poland there are several methods used for determination of the design flood hydrographs. Among the others, the method developed by Hydroprojekt is used. According to the authors’ knowledge, this method has not been published yet. The method assumes that the design flood hydrographs are to be determined based on the real registered floods in a given gauged cross-section. The method uses the random number generator from the range of (-0.1, 0.2) independently for time instants of the hydrograph rising and falling limbs. This enables that the hydrographs have different time courses at different peak discharges. The study analyses the results received from this method in comparison to the Cracow method, assuming that the model hydrograph is the rainfall hydrograph, unimodal with the biggest registered discharge. The Cracow Method is chosen as the most objective one because of the calculation procedures which enable to determine the average time course based on 8 biggest flood hydrographs, and this method enables to determine the design flood hydrograph volume during its construction based on the linear correlation. The comparative analyses were conducted for the reduced volume, i.e., flood volume at the discharges bigger than the peak discharge with given exceedance probability, Q50%. The comparison of rising times for the hydrographs determined with both methods was done as well. The comparisons were done for 11 gauged cross-sections located in the area of the Upper Vistula catchment and they included the rivers of different nature: mountainous, sub-mountainous, upland and lowland. The analyses were unsuccessful for the Hydroprojekt method. Similar to other methods where the base for the design flood hydrograph determination is one flood hydrograph, both the flood volume and the rising time in most cases are different from the average conditions determined with the Cracow method. When using a model hydrograph with the highest recorded peak discharge, the Hydroprojekt method does not perform well and rather should not be used