Experimental investigation of turbidity currents triggered by an upstream water jet

Abstract:

Turbidity currents can be triggered in the environment by means of different natural mechanisms and processes, such as a sediment-laden open channel flow entering a water body. The high capacity of those flows to transport sediment in water reservoirs, lakes, coastal areas, and the deep sea have led to a large amount of literature on experimental research using the lock-exchange or continuously-feeding setups to reproduce them under controlled situations.

Alternatively, turbidity currents can also be intentionally triggered, as in the case of water injection dredging. After triggering a turbidity current with the water injection technique, the flow will propagate by means of natural processes. Hence, accurately predicting its development at the desired site, which depends on the boundary (triggered by the water jet) and initial conditions, is crucial for the successful application of the technique. An efficient and sustainable use of this technique also requires an understanding of how those conditions influence momentum, mass, and turbulent transport processes over the downstream topography.

To partially address these questions, a novel experiment has been developed at the Fluid Mechanics Laboratory of the Delft University of Technology in a 4 m long, 2 m high and 22 cm width flume. A 3D - printed diffusing device with adjustable angle was designed to define the initial 2D flow conditions of the impinging jet on the light weight sediment mobile bed, which is built with a constant slope. A set of preliminary experiments are herein presented and discussed, with the aim of defining the conditions under which turbidity currents will be triggered in the idealized experimental setup.

It is expected that the outputs of this research will contribute to more sustainable management of sedimentation issues, benefiting river basins’ water resources management and ecosystems.

Acknowledgments: This research is funded by CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior), a Foundation within the Ministry of Education in Brazil.