"Experimental investigation of the hydrodynamic response of a fluvial confluence: a case study of the Chiaravagna River."

Nowadays, the attention regarding hydro logical risk increases exponentially. Genoa is a critical city in terms of flooding, which implies strong consequences in terms of money and human safety. A confluence between Chiaravagna River and Ruscarolo Creek insists in Genoa Sestri Ponente. More often in this zone, flooding events occurred involving the surrounding buildings. In the studied confluence, an instability phenomenon has been observed. In particular, the development of an unsteady transversal wave takes place. For this purpose, a physical model has been created in laboratory. Velocities have been acquired using two different calibrated devices to carry out a bi-dimensional measurement. The instruments used are a micro-propeller and an acoustic Doppler velocimeter. Three different hydrological conditions have been evaluated, one of them implies the addition of a septum in the middle of the confluence, which has the role of damping the oscillations. Successively, the acquired signals have been analysed in the frequency domain at various locations. Then, the first configuration has been studied to evaluate at which frequency the creation of the disturbance corresponds. Secondly, the relation between the disturbance generation and the discharge has been analysed. Finally, the effect of the central septum in damping the velocity and the free surface oscillation has been evaluated. The results show that the hydraulic instability is mainly generated by the Ruscarolo creek. Furthermore, it has been observed that there is a relation between the instability trigger and the discharge variation speed.