STATISTICAL PROPERTIES OF BOTTOM VELOCITIES IN A WAVE PLUS CURRENT CONDITION

A statistical description of the results of three experimental campaigns focused on orthogonal waves-current interaction in the presence of a sandy bed, a gravel bed and a rippled bed is presented. Higher order statistics have been determined for the velocity components in a current only and a wave plus current conditions. It was found that when current only data are analyzed, no matter on the bed roughness conditions, the probability density of the velocity close to the bed is somewhat similar to a Gaussian distribution; far from the bed this similarity is less perceived. Skewness and Kurtosis, with respect to the Gaussian values, decreases and increases respectively when the distance from the bed increases. When a wave is superimposed on the current, the frequency distribution appears to be double peaked, with the highest peak always corresponding to the lower velocity range. This occurrence has been explained by means of a phase analysis which showed that the more frequent values are smaller than the average velocity.