Probabilistic approach on course material transport under waves: Vol. 1 Theory and experiment.

The probabilistic design method of a cover layer of pipe line under the horizontal bottom is described. By assuming that the water velocity at the bottom is Rayleigh distributed, probability of bottom shear stress was derived. With a combination of the probability function of bottom shear and a simple sediment transport formula given by Madsen and Grant (1976), the expected transport rate was calculated. The results gave a warning that conventional design methods have a risk to underestimate the amount of loss.of covering material. To confirm the established formulas about inception of motion of particles and sediment transport under waves, some experiments were carried out. As for inception of particle motion, comparison between steady flow condition and wave condition was, done. It turned out that the one gives lower value than the other, and that Shields' curve gives the lower limit of the total experimental data. The data of critical velocity under waves agreed to Komar-Miller's formula which involves the factor of wave period. The critical velocity in the direction of wave propagation was found considerably higher than that against it. Sediment transport rate was measured together with velocity. As had been already presented by van de Graaff and Tilmans (1980), the transport-rate could be related to the Fourier components of the velocity. It could also be related to the maximum and minimum velocity. The influence of a phase lag between the first and second terms of the Fourier components, which is closely related to the acceleration and the deceleration of the total velocity, was not clear yet in that specific condition. Critical velocity obtained by the visual observation generally agreed to the limit line of transport-rate (zero line) on both u1 - u2 plane and u(max) - u(min) plane.