Author(s): Ismail Albayrak
Linked Author(s): Ismail Albayrak
Keywords: Vortex tube; Sediment connectivity; Bed-load transport; Bed-load diversion;
Abstract: Impaired sediment connectivity in river systems due to transversal hydraulic structures is a primary cause of channel narrowing and down-cutting, as well as reduced morphodynamic variability. Among various restoration measures, the vortex tube is a structural measure to re-establish bed-load conveyance during flood events at low-head hydraulic structures. Bed-load particles are entrained through a slit in the tube soffit and sluiced from an upper channel to a lower parallel channel. This paper presents and compares the results of two laboratory model studies on the optimal design of vortex tubes for run-of-river hydropower plants. Although the two case study hydropower plants are situated within 1.5 km distance along the same river, differences in boundary conditions considerably reduce the suitability of one of the plants for the effective operation of a vortex tube. The test results show that the energy head difference between the two channels is a decisive hydraulic boundary condition and should be larger than approx. 1 m at all times. The dimensions of the vortex tube should be adapted to the grain sizes of the transported bed-load. If the vortex tube does not span the entire channel width, an open tube end is recommended to increase its zone of influence. A diversion efficiency of 94% was determined for the optimal design. The present findings demonstrate that vortex tubes may be an appropriate structural measure to re-establish sediment continuity at hydraulic structures, primarily where the upstream and downstream channels are located in close proximity.