Plume bulge observed in the Pearl River Estuary in summer: Spatiotemporal characteristics and influencing factors

Plume bulges were once thought to be less prone to form in an estuary with trumpet-like characteristics, such as the Pearl River Estuary (PRE), where no plume bulge has previously been detected by hydrological observations. However, based on large scale simultaneous observations, the formation dynamic of a plume bulge in the PRE during the flood-ebb tidal cycle is characterized in this paper. The influences of discharge change on the plume bulge are revealed through the different motion processes of the surface-advected plume and tidal plume. The results show that during spring tide with a weak SE wind and high river discharge (20,725 m3 s−1), a plume bulge in the PRE is produced on the south side of the Dawanshan Islands outside the estuary. Based on the standardization stratification coefficient calculation method and the salinity decomposition method, it was found that the tidal plume is the main component forming the plume bulge rather than the surface-advected plume. The 25 isohaline indicated the boundary of the PRE plume bulge. However, when the discharge was reduced by approximately 43%, no plume bulge was observed. River discharge had a considerable impact on the formation of plume bulges as higher discharge was favorable in enhancing the momentum and flux of the tidal plume in the longitudinal Lantau Channel, whereas lower discharge was favorable for the formation of a surface-advected plume flowing along the west bank.