Parametric flow hydrographs are used for design and management purposes in such fields as water management and aquatic engineering. They describe a theoretical hydrograph on the basis of such parameters as maximum flow, time to peak and surge duration. They are used to forecast flood risk and to evaluate the impact of land use on the run-off hydrograph. In Western Europe for many years methods have been used in which parametric hydrographs are determined on the basis of physical catchment descriptors (PCDs), which are divided into three groups describing the physical features of a catchment. These descriptors are used to derive formulae enabling the determination of parametric flow hydrographs for any computational cross-section. In this work, such formulae are derived for the catchment of the Raba river, using the principles of design hydrology applied in Western European countries. The parametric hydrograph is described using Baptista’s gamma density function. The input hydrograph was a nonparametric flow hydrograph determined by Archer’s method. For nine gauging stations located in the Raba catchment, physical catchment descriptors were obtained for two 30-year periods: 1961–1990 and 1983–2012. Based on the nonparametric flow hydrograph and the PCDs, two groups of formulae were derived to describe the parametric hydrograph. Analysis of agreement between the computed parametric flow hydrographs and the input hydrograph indicated a high quality of fit. It should be borne in mind that the presented formulae and analysis refer only to the Raba catchment. However, the results confirm the possibility of applying the presented methods to the determination of parametric flow hydrographs for any river cross-section.