Experiments on gravity currents propagating down slopes. Part 1. The release of a fixed volume of heavy fluid from an enclosed lock into an open channel

Gravity currents formed by the release of heavy fluid from an enclosed lock on a sloping open channel were investigated experimentally. The experiments were conducted in a channel that had a running length of 13 lock depths, and could be inclined to a maximum angle of 17°. The release of heavy dyed salt solution from a lock with an aspect ratio (height to length) of 0.5, was examined using video images to determine the front velocity, and a particle-tracking technique was used to measure the two-dimensional velocity field in a vertical slice through the centre of the evolving current. The gravity current head velocity increased with time and downstream distance to a maximum at approximately 10 lock depths from the front of the lock. Flow visualization and the velocity measurements have shown that during the acceleration phase the head was being fed by a following current that increased its buoyancy as it propagated downstream. A modified version of the theory of P. Beghin, E. J. Hopfinger and R. E. Britter (J. Fluid Mech. vol. 107, 1981, p. 407) in which the measured increase in buoyancy was used, instead of the original assumption of constant buoyancy, gave results that agreed closely with the experimental velocity versus time histories.