Comparison of Nonlinear Reservoir and UH Algorithms for the Hydrological Modeling of a Real Urban Catchment with EPASWMM

This paper presents a comparative analysis of two hydrological models in the Storm Water Management Model (SWMM) software, namely, the non-linear reservoir (N-LR) and the unit hydrograph (UH), on the urban catchment of Cascina Scala, Pavia in Italy. The two models were applied for the simulation of the rainfall-runoff transformation in the 42 sub-catchments in Cascina Scala, while flow routing in the underground channels was simulated by means of the De Saint-Venant equations. A dataset of rainfall and runoff for 14 events from 2000 to 2003 was adopted for the calibration and validation of the models. The calibration was performed on 7 out of the 14 events by maximizing the fit of modeled-to-measured hydrographs in the final channel of the system. Prediction performance was assessed through different indices. Results from both models fit measured data well in terms of the total hydrograph. Whereas the time to peak was reliably predicted by both models, the N-LR was found to slightly outperform the UH in terms of total volume and peak flow prediction, though it requires a more detailed knowledge of the system for its implementation. Accordingly, the UH must be preferred in the case of a scarcity of data.