Design peak discharge and hydrograph estimation are one of the most frequently needed tasks in engineering hydrology. Therefore, numerous options and methods are available, from most simple empirical equations or more sophisticated flood frequency analysis to very complex rainfall-runoff models including stochastic rainfall generators. Engineers that are dealing with river engineering and the design of hydro-technical structures such as culverts, dams, and levees or preparation of flood risk maps are often applying relatively simple methods that do not account for the uncertainty related to the design peak discharge and hydrograph calculation. Moreover, in some cases not all available discharge data is used for the engineering design. Non-optimal selection of the methodological steps can lead to over- or under-estimation of the design peak discharge, hydrograph volume and duration. This can lead to higher costs of construction or questionable safety of the designed and constructed hydro-technical structures. Thus, a robust state-of-the-art methodology is needed to guide engineers in the process of the design peak discharge or hydrograph estimation. Such methodology is still lacking in Slovenia (central Europe) where river engineers often apply very simple empirical equations for the estimation of the design peak discharges without any consideration of uncertainty, especially in case of small torrential watersheds. At the same time, they use very complex 2D hydraulic models for flood simulations or design. This contribution will present recent developments in relation to the definition of the methodology for the design peak discharge and hydrograph calculation in case of gauged and ungauged watersheds in Slovenia.