Dynamics Governing the Response of Tidal Current in Jiaozhou Bay Mouth to Land Reclamation

Abstract:

The data collected from previous observation studies and numerical models show that the tidal current in Jiaozhou (JZB) mouth becomes apparently weaker while the spatial asymmetry (stronger flooding in the north and stronger ebbing in the south) remains nearly unchanged during the past several decades of significant land reclamation. In this study, a theoretical analysis is carried out to explain the dynamics that determines the phenomenon found in observation and modelling studies. The analytic solution of the tidal motion in an idealized bay indicates that the tidal current in a small coastal bay such as the JZB is linearly proportional to its spatial dimension, if is far less than a quarter of the tidal wave length. This suggests that the decrease in the tidal current speed in JZB mouth is owing to land reclamation inside the bay (the remote factor). Because of the insensitivity of tidal range to , a linear relationship between bay areas and tidal current of JZB mouth can be derived, according to which the change of the amplitude of tidal current after the land reclamation can be well predicted. The results of mean tidal current amplitude derived by simple theoretical method agree well with previous 3D model studies. We also found that the spatial asymmetry of the tidal current in JZB mouth is determined by the predominate role of advection in tidal motion which is controlled by the sharp Tuandao headland (the local factor). Unchanged shoreline around Tuandao headland leads to the stable spatial asymmetry of tidal current. Numerical experiments indicate it is the nonlinear process of advection that generates the tidal residual current in JZB mouth. Therefore, the weaker tidal current can lead to weaker residual current, while the unchanged asymmetry of tidal current results in the unaltered pattern of inflow in the north and outflow in the south for the tidally induced residual current in JZB mouth.