This research examines the phenomenon of saltwater intrusion in the Yellow River estuary (YRE) through utilization of shipboard surveys and mooring investigations. Hydrographic data were gathered in May and October 2023 to elucidate the relationship between saltwater intrusion in YRE and various factors, including tides, winds, and river discharge. The fortnightly cycle of the diurnal tide within the estuary is controlled by the declination of the moon above and below the equator, rather than by the lunar phase, as is the case in a semidiurnal system. The spring tides occur two days after the maximum lunar declination and neap tides occur two days following the zero value of lunar declination. Surface salinity within estuary demonstrates semidiurnal fluctuations, with an initial peak occurring prior to high tide and a subsequent peak during early ebb phase. The earlier peak is attributed to interplay between upstream tidal currents and downstream fluvial flow, while the later peak is likely influenced by saltwater which has intruded into river channel. Conversely, bottom salinity exhibits diurnal variations, as seawater is driven into and out of river channel by diurnal tidal currents. The peak salinity levels in the estuary correspond to fortnightly variations in water elevation, indicating stronger intrusion during spring tides than in neap tides. Additionally, strong northeasterly winds can enhance saltwater intrusion; however, intrusion is hindered once the winds subside in following day. This phenomenon of wind-induced hindrance has not been previously documented and may be attributed to significant accumulation of freshwater within the river due to northeasterly winds. Overall, saltwater intrusion is more intense during winter and spring than in summer and autumn. • Salt intrusion process within the Yellow River Estuary was investigated through shipboard surveys and mooring investigations. • Salinity in the bottom layer varied diurnally following the flood-ebb tidal cycle, while surface salinity exhibited semi-diurnal variations, where the first peak is induced by saltwater intrusion and the second peak is from downstream saltwater advection. • The spring-neap tidal cycle within YR Estuary is controlled by the declination of the moon above and below the equator, rather than the lunar phase. • Saltwater intrusion was more pronounced during spring tides than in neap tides, with a maximum intrusion distance of 4.5 km under southerly winds and spring tide conditions. • Strong northeasterly winds enhanced saltwater intrusion but hindered this process once the winds subsided the following day.
Hu et al. (Sat,) studied this question.