Hydraulic features of the dissipation chamber for vortex drop shafts

Drop structures are often necessary to connect shallow to deep sewers in steep areas. Vortex drop shafts were originally introduced by Drioli (1947) as an overflow structure for dams; actually these structures are widely used within sewer systems. Given the complexity of the flow features, the hydraulic behaviour of vortex shafts has been mostly studied experimentally. General design criteria have been issued, mainly for the intake structure and the vertical shaft. Few experimental data are available for the outlet structure, essentially referred to specific case studies. Preliminary experiments investigated various types of dissipation chambers, aiming to characterize the energy dissipation mechanism of the outlet structure. The present study presents further results of the experimental campaign conducted at the Hydraulics Laboratory of the University of Naples ‘Federico II’, mainly focusing on the optimum location of constriction elements to be placed within the outlet structure.