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DESIGN HYDROGRAPH ESTIMATION IN SMALL AND UNGAUGED BASINS: A COMPARATIVE ASSESSMENT OF EVENT BASED (EBA4SUB) AND CONTINUOUS (COSMO4SUB) MODELING APPROACHES

Aim of the study Aim of the study is to provide a comparative assessment of event based (EBA4SUB) and continuous (COSMO4SUB) modeling 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, estimating the rainfall excess, and 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 modeling 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.