Abstract: The vertical distribution of tidal ellipse parameters (amplitude of the major axis, ellipticity, direction and phase) of the dominant M₂ tidal current in Sanggou Bay are analyzed based on in-situ observed current profile data during kelp-free and kelp-mature periods. The results indicate that the suspended kelp culture has a remarkable effect on vertical structure of tidal current. The parameters of M₂ tidal ellipse vary little in the vertical direction during kelp-free period. In contrast, due to the impact of the suspended kelp, the M₂ tidal ellipse parameters show a significant vertical variation during kelp-mature period. Specifically, moving away from the middle layer towards both surface and bottom boundary layers, the maximum velocity decreases rapidly, the ellipticity increases, the direction of the maximum velocity veers clockwise and the appearing time of maximum velocity becomes earlier. The observed data also indicate that at the middle entrance of Sanggou Bay, the direction of the maximum velocity turns from the north-south direction during the kelp-free period to the northwest-southeast direction during the kelp mature period, which was found to be caused by the relevant change of sea level gradient.

Key words: Sanggou Bay, suspended kelp culture, vertical tidal current structure, M₂ tidal current