Vortex dropshaft retrofitting: case of Naples city (Italy)

This work describes the main hydraulic features of vortex dropshafts along with some examples of their mis-designs and consequent malfunction. Laboratory experiments were conducted to test the hydraulic performance of subcritical vortex intakes using supercritical approach flow design basis. The purposes of these drop structures are to: (i) convey the storm runoff towards the sea through the existing sewer system located at lower elevations and (ii) by-pass insufficient sewers. The proper operation of these structures is crucial to prevent flooding and to guarantee the urban safety. This issue is particularly relevant for the sewer system of Naples (Italy), which is strongly constrained by its hilly landscape. Several drop structures were realized to connect the modern urban drainage system to the early sewer mains located at the sea level. This work intends to highlight practical issues to enhance the existing vortex dropshafts, with possible applications to other cases similar to the Neapolitan context.