Author(s): Baldassare Bacchi; Giovanna Grossi; L. Pennesi; P. Potenza; Roberto Ranzi; Italeco
Keywords: Flood protection; Flood frequency analysis
Abstract: Eight floods observed at the Ponte Nuovo streamgauge station, draining an area of 4147 km² in the Upper Tevere riverbasin in central Italy, were simulated using a conceptual hydrological model with distributed parameters. Hourly hyetographs and hydrographs of the flood events were recorded at several raingauge and streamgauge stations to enable a realistic description of the rainfall field and the model verification in several nodes of the river network. For the flood routing, over the hillslopes and along the channel network, a kinematic wave model and a dynamical Muskingum-Cunge method were applied, respectively. For the net rainfall computation a modified version of the standard SCS-CN procedure was applied. In the application of this method it was observed, indeed, that the storm runoff volume was influenced by the precipitation measured in the 30 days prior to the flood event, instead of the 5 days, as recommended by the standard practice. As a consequence of this “experimental” result a WAPI30 index is computed to define the soil storage capacity parameter. As an alternative method to the distributed CN procedure a distributed runoff coefficient approach was also tested to compute the surface runoff production. This method results as being more ‘robust’ with respect to the inter-event variability of net- rainfall volumes and storm hyetographs than the non- linear SCS-CN. Some numerical experiments using synthetic hyetographs with a given return period and different spatial patterns suggest applying this method for flood prediction in the Upper Tevere basin.