Coupling of Ultrasonic and Photometric Techniques for Synchronous Measurements of Unconfined Turbidity Currents

Abstract

By synchronizing data collection, such as photometric and ultrasonic Doppler profiling (UVP) measurement techniques, new insights can be obtained into environmental flows, such as highly dynamic turbidity currents. We introduce a combined experimental setup, which ultimately allows a time reduction in testing programmes, and discuss the measurement advances with the help of four surface conditions we tested for unconfined turbidity currents: (a) a smooth surface; (b) a smooth surface with an obstacle present; (c) a rough surface; and (d) a rough surface with an obstacle present. We show that data from both measurement techniques indicate that a rough surface reduces global current velocities and the magnitude of turbidity current phenomena, including Kelvin-Helmholtz instabilities and lobe-and-cleft formation. However, by coupling the techniques, photometric data give valuable insight into the spatial development of instabilities, such as the grouping of lobe and cleft formations. The presence of an obstacle causes local regions of an increased and decreased velocity, but does not affect the global current velocity. Additionally, the obstacle created three local intensity maxima upstream, dissipating to two maxima downstream, supporting the presence of local eddies. The study shows that the combination of UVP and photometry is an effective way forward for obtaining detailed qualitative and quantitative insights into turbulent flow characteristics and we highlight the potential for future research.

Velocity Structure of Density Currents Propagating over Rough Beds

“…The density-driven currents are known as the main agent for sediment transport in reservoirs; these can carry incoming suspended sediments and existing sediment deposits over the reservoir bed to the area near the dam. These currents decelerate as they approach the dam, and this can give rise to sedimentation [3]. Reservoir sedimentation is a worldwide issue hindering the sustainable use of reservoirs and sediment balance of impacted rivers [4].…”

“…Water 2021, 13, x FOR PEER REVIEW 2 of 16 the area near the dam. These currents decelerate as they approach the dam, and this can give rise to sedimentation [3]. Reservoir sedimentation is a worldwide issue hindering the sustainable use of reservoirs and sediment balance of impacted rivers [4].…”