An observational study of saltwater intrusion into the Yellow River estuary

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 estuary is characterized by diurnal tides and diurnal tidal currents. The fortnightly cycle of tidal elevation within the estuary is influenced by tropical dynamics, displaying spring tides occurring two days after the maximum lunar declination and neap tides two days following the zero value. 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 within the river due to northeasterly winds. Overall, saltwater intrusion is more intense during winter and spring than in summer and autumn.