Impacts of tidal species on water level variations in Pearl River Delta channel networks

Abstract

Variations in the water level of tide-influenced deltas are strongly related to the evolution of tides as the tidal waves propagate upriver. However, the impacts of tidal species on these water level variations are not well understood, particularly in delta channel networks. Therefore, a one-dimensional hydrodynamics model of the Pearl River Delta channel networks was established to investigate the impacts of different tidal species on the distribution of the water level. Spatial distributions of the amplitude of four main tidal species (the diurnal (D1), semidiurnal (D2), quarterdiurnal (D4), and fortnightly (D1∕14) tidal species) were extracted using the continuous wavelet transform method. The results reveal that the diurnal and semidiurnal tidal species dominate the fluctuation in the water level near the river outlets, but are significantly attenuated in the upstream direction. The quarterdiurnal tidal species strengthens in shallow waters and then decays farther upriver. However, the fortnightly tidal species grows upriver. There is a strong resemblance between the distribution patterns of the water level and that of the amplitude of the fortnightly tidal species in the Pearl River Delta channel networks. Moreover, in the upstream channels, dominant fortnightly tides lead to the occurrence of lowest low water levels on neap tides rather than the expected spring tides. The results of this study have significant implications for the investigation of hydrodynamic processes and the management of navigation safety in delta channel networks.