Dropshaft cascades in urban drainage systems.

Dropshaft cascades are typical elements of sewer systems in steep urban catchment basins. The design of a dropshaft cascade, which is generally addressed as an optimization problem, also needs to consider the subsequent effects induced on the flow by the different elements of the cascade. Experimental research has been performed at the hydraulic engineering laboratory of the University of Cassino and Southern Lazio in order to investigate the basic flow patterns in a dropshaft cascade, with particular reference to energy dissipation and air entrainment. This research has shown that, regarding these aspects, a dropshaft cascade proved to be a more efficient solution of the single drop manhole with the same total drop height.