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Flow dynamics and internal velocities of experimental two-dimensional lofting density currents

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In an experimental set-up, lofting density currents marked by potassium permanganate for better visual enhancement were released in a tank. Their proceeding was recorded by video cameras and analyzed using a videocassette recorder with an automated editing control unit. Mean flow velocities of the flows were measured at different heights using ultrasonic doppler velocity profiling (UDVP). The lofting process occurred in five different stages: slumping, underflow density current, lofting, interflow plume and overflow hypopycnal plume. It was observed that during the underflow stage individual plumes began to rise off the rear parts of the lofting density current and ascended to the surface before the front part of the underflow started to loft. The current head showed its highest velocity in the interflow plume. The values of the mean turbulent velocity, u', of the experimental density current were highest near the bed, which was attributed to the entrainment of the ambient fluid. The lowest u' above the bed were due to the calm layer of the ambient fluid. The profiles of u' within the turbidity current and in the interflow plume showed a decrease in u' with distance from the lock gate. When the ambient fluid began to flow upstream this was reversed suggesting that the head of the intruding ambient fluid may have experienced more mixing instabilities than in the body. As a result, the head might possess sufficient energy to erode or suspend some of the recently deposited sediment.
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Keywords: HYPOPYCNAL; INTERFLOW; LOFTING; PLUME; TURBIDITY CURRENTS; TURBULENT VELOCITIES; UNDERFLOW

Document Type: Research Article

Publication date: 2008-10-01

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