Channel‐Trapped Convergence and Divergence of Lateral Velocity in the Pearl River Estuary: Influence of Along‐Estuary Variations of Channel Depth and Width

Abstract

AbstractA cruise survey was conducted in the Pearl River Estuary (PRE) in May 2014. In situ observations during this cruise reveal that at the surface in the central channel of the PRE there was a strong convergence of lateral velocity during an ebb tide and a divergence during a flood tide. The ebb tide convergence was also observed in satellite synthetic aperture radar imagery. The Finite‐Volume Coastal Ocean Model was executed in the PRE domain to accurately simulate the convergence and divergence of the cross‐estuary velocity during ebb and flood tides, respectively. Numerical experiments in an idealized estuary domain are implemented with three distinct forcing scenarios: tide, river discharge, and a combination of both. Model results show that the cross‐estuary momentum balance plays a significant role in the dynamics of the velocity convergence and divergence in the PRE. Additionally, the interaction between tide and river discharge enhances the surface convergence on ebb tide and generates the surface divergence on flood tide. The model results reveal that the along‐estuary variation of channel depth and width is responsible for the tide‐induced lateral velocity convergence and divergence in the channel, supported by the fact that when the channel depth and width are set to constant values in the model, the channel‐trapped ebb convergence substantially weakens, and the flood divergence disappears. This study provides an indication for other wide estuaries.