Design hydrograph estimation in small and ungauged basins: a comparative assessment of event based (EBA4SUB) and continuous (COSMO4SUB) modelling approaches

Abstract

Aim of the study: Aim of the study is to provide a comparative assessment of event based (EBA4SUB) and continuous (COSMO4SUB) modelling approaches for rainfall-runoff modeling for small and ungauged basins, focusing on the influence of the Antecedent Moisture Condition (AMC) of the soil on the estimated design peak discharge. Material and methods: The event based approach is the EBA4SUB software. It consists in selecting a design rainfall event, in estimating the rainfall excess and in transforming it into the direct hydrograph. The continuous approach is the COSMO4SUB framework. It consists in generating a long synthetic rainfall time series at sub-daily resolution that feeds a continuous rainfall–runoff model. Then, a discharge time series is determined, providing the estimation of the runoff and the related peak discharge. Results and conclusions: Results show the critical role of antecedent moisture condition (AMC) and how subjective the event-based approach is for determining the design hydrograph and peak discharge. In the event-based approach, AMC is arbitrarily selected by the analyst, while in the continuous modelling it is automatically determined using the synthetic rainfall input. Our findings indicate that the event-based approach systematically leads to a considerable overestimation of floods if AMC III (wet soil) is assumed or to a slight underestimation of floods if AMC II (average condition for soil humidity) is selected.

Keywords

• rainfall-runoff modelling
• continuous modelling
• cosmo4sub
• eba4sub
• event-based approach