THE MOTION OF LARGE BOTTOM PARTICLES (COBBLES) IN A WAVE-INDUCED OSCILLATORY FLOW

The purpose of this paper is to present the results of a series of exp eriments aimed at better understanding the dynamics of the motion of l arge bottom particles (cobbles) in a wave-induced oscillatory flow. Th is problem is closely related to the motion of cobbles along the botto m in an oscillatory flow such as occurs in coastal waters beyond the r egion of wave breaking. The aims of the study were (i) to mimic this p rocess in laboratory experiments and (ii) to develop a physical model to predict cobble movements. The oscillatory flow was created in a lon g tank of rectangular cross-section using standing waves of large ampl itude, objects of different shapes (spheres and disks) were placed in the flow and their subsequent motion along the tank floor was studied. The results of the observations were compared with the predictions of a theoretical model. For the range of parameters used in the experime nts (shape, size, aspect ratio and density of cobbles, amplitude and f requency of the oscillatory flow and bottom friction), reasonable agre ement between the measured and calculated values of the cobble displac ements as a function of time was obtained. (C) 1998 Elsevier Science B .V. All rights reserved.