Multiple inflow branches at supercritical-type vortex drop shaft

Vortex drop shafts serve to overcome important elevation differences in drainage systems. If well designed, they are performant in terms of energy dissipation and safety. However, the standard design requires well-defined approach flow conditions to ensure the reliability of the structure. In practice, these conditions are frequently ignored due to space restrictions and the fact that several inflow branches may arrive at various elevations with supercritical and/or subcritical flows. The literature provides preliminary concepts for such situations that were not adaptable to the case discussed herein. Nevertheless, in order to apply a standard vortex drop shaft, a novel concept was developed that comprises a junction chamber to merge the inflow branches followed by a very short and steep inlet channel. Extended physical model tests have proven its feasibility. The hydraulic aspects discussed herein allow, at least partially, the adoption of the presented concept in similar situations.