Flood management of the Tevere River at Nazzano barrage, upstream Rome

This paper reports the results of a hydrodynamic study developed by an unsteady monodimensional numerical model, supporting the management of Tevere river floods in use by Enel at Nazzano barrage since the 1960s.
The model compares the effects of Enel operational criteria with the results obtained by applying the principles indicated by National Technical Services Guidelines in 1996, which don’t allow to anticipate the flooding event, except for those situations where specific models are studied in order to reduce the flooded areas.
Upstream Rome, along the Tevere river, 3 hydraulic Enel power plants are present, in sequence, run-on-river type, built in the decade 1950 – 1960: Ponte Felice about 100 km far from the city, Nazzano and then Castel Giubileo, just at the gates of Rome.
Since 1956, depending on the flow coming from the upstream power plant, at the intermediate Nazzano power plant, in the two hours before the passage of maximum discharge, the gates are gradually opened to reduce the upstream level by 2,50 m. Such operations are performed in order to avoid an increased frequency of flooding in upstream areas, where the freeboard is already small for the 10 years-return-time flood (280 m3/s).
The flood management operational scheme in use at Nazzano barrage is validated by the long managing period of the power plant during which, considering the most frequent floods, not higher than 1.500 m3/s, no significant problems have been noted either upstream in sections affected by the backflow, or downstream the plant .​