Robinson, T.O.; (2007) Gravity currents in the presences of water waves. Doctoral thesis , University of London.

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Abstract

This thesis describes a laboratory study on the effect of free surface progressive waves on high Reynolds number gravity currents generated by instantaneous release of finite volumes of dense homogeneous fluid. The waves and gravity currents are studied as two-dimensional and the flows across the width of the flume are assumed to be constant. The engineering applications of this investigation will provide an insight into the processes by which dredging plumes are dispersed and flows propagate into estuaries at the coastline. This investigation examines the process at a fundamental level and gives a summary of the key characteristics and trends of the gravity current in the marine environment. This work has been carried out in the wave current flume at UCL using a number of advanced flow measuring techniques such as Laser Doppler Velocimetry to measure the orbital velocities of the waves and Particle Image Velocimetry to measure the internal dynamics of the gravity current. The position and density profiles of the gravity current were measured using digital images. In a static environment a gravity current spreading in two directions has symmetry in shape and distance from the point of release. In the presence of waves, the gravity current fronts propagate with and against the wave direction. The wave motion induces an asymmetry in the shape and rate of propagation of the gravity current fronts. Under certain wave conditions the overall length of the gravity current is found to be unchanged by the presence of the waves and the characteristics of the gravity current are similar to the case in static ambient water. However, in some cases the overall distance is severely modified by the wave motion. In addition to modifying the propagation rate of the gravity current the wave-induced mean flow modifies the profile of the gravity current head. The direction of the gravity current relative to the wave motion is vital in determining the rate of dispersion and the height of the density current.

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