Author(s): Nejc Bezak; Matjaz Mikos; Klaudija Lebar; Mojca Sraj

Linked Author(s): Nejc Bezak

Keywords: Design Discharge; Flood hydrograph; Peak discharge; Methodology; Uncertainty

Abstract: 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. Selection of suitable method(s) mostly depends on availability of measured discharge data. In case that discharge data is available one can apply the multivariate or univariate flood frequency analysis or set-up, calibrate and evaluate the rainfall-runoff model. In case that discharge data is not available, alternative methods should be applied taking into consideration regionalization concepts, empirical approaches, etc. Engineers that are dealing with the design of hydro-technical structures such as culverts, dams, 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 engineers often apply very simple empirical equations for the estimation of the design peak discharges and at the same time use very complex 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 catchments in Slovenia. The methodology will take into account state-of-the-art methods developed and applied throughout the globe and adopt them based on the characteristics of Slovenia (e.g., climate, topography). The methodology will make use of recently developed regional empirical curves (for Slovenia) for the peak discharge estimation including uncertainty. Additionally, the methodology for the design hydrograph estimation will be based on the application of copula functions that simultaneously consider peak discharge and hydrograph volume in case that measured discharge data is available. In case that discharge data is limited or not available, a methodology using the rainfall-runoff models will be presented. The main aim of this contribution is to present recent methodological development done in Slovenia and raise awareness among engineers about possible uncertainties related to the design peak discharge and hydrograph definition. We acknowledge the financial support from the Slovenian Research Agency (grant: V2-2137).

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221750

Year: 2022