Flood control of the Bisagno river and of the Fereggiano, Rovare and Noce streams (Italy)

Studies conducted by the River Basin Authority, developed within the Basin Master Plan, underlined the risk of flooding of Genoa by the Bisagno river and the Fereggiano, Rovare and Noce streams. Such risk derives from the strong difference between the capacity of the river itself and the peak discharge with a return period of 200 years.

The project foresees a series of works due to reduce the risk of flood of huge urban areas. In particular, these works include: 

• Improvement of the hydraulic section located in the mouth reach, interested by a multiple barrel box culvert;
• realization of a river diversion to reduce the peak discharges flowing in the original riverbed.

The project of the river diversion includes, for the Bisagno river, the following works: 

• a river barrage equipped with n. 3 radial gates;
• a tunnel, with a horseshoe section with 9.5 m diameter, able to carry to the Tyrrhenium sea a portion of the flood discharges derived by a lateral weir; the total length of the tunnel is 6,650 m;
• three smaller diversion structures on the streams Fereggiano, Rovare and Noce, connected to the main tunnel through three tunnels 300 m length;
• a sea outfall structure of the main tunnel;
• two service tunnels.

To verify the hydraulic behaviour of the main structures, a series of tests have been performed on n. 6 physical model with regards:

• diversion structures at the Bisagno river and at the Fereggiano, Rovare and Noce streams;
• tunnel confluence between the main tunnel and the tunnel coming from the Fereggiano stream;
• sea outfall structure.

The physical model tests allowed the evaluation of: 

• the behaviour of the barrage, of the radial gates and of the lateral weir at the Bisagno barrage; 
• the wave field in front of the outfall structure and the jet stream dissipation;
• the stability of the rock revetment at the outfall structure;
• the hydraulic confluence between the main tunnel and the tunnel coming from the Fereggiano stream;
• the hydraulic behaviour of the diversion structures (vortex shafts) located at the Fereggiano, Rovare and Noce streams.