Temporal evolution of nearshore tidal currents field in the Yellow River Delta over the past four decades

Abstract

Over the past four decades, the water and sediment fluxes of the Yellow River to the sea and the deltaic coastal morphology have changed markedly under the combined influence of human activities and natural processes. There is an urgent need to quantitatively investigate how shoreline adjustments driven by outlet migration and the embayment north of the river mouth affect the nearshore tidal‐current field. In this study, Landsat imagery and multi‐year bathymetric data were used to resolve shoreline changes, subaqueous topographic evolution, and outlet shifts of the Yellow River Delta in 1987, 2000, and 2023. A numerical hydrodynamic model was established to quantitatively evaluate the influence of different outlet and shoreline configurations on the nearshore tidal regime and to reveal the response mechanisms of the tidal‐current field to shoreline evolution, river‐mouth deflection and changes in runoff intensity. The results indicate the following: (1) Nearshore tidal currents are predominantly rectilinear, and an elliptical high‐velocity zone (>0.8 m/s) that migrates with the river mouth has persisted. Northward deflection of the river mouth has created an embayment between the Gudong seawall and the mouth, where current speed has decreased significantly, with a maximum reduction of 0.46 m/s, corresponding to a change rate of 78.23%. (2) Runoff intensity strongly modulates water levels and tidal currents near the river mouth. The runoff‐dominated area expands with increasing discharge, and under extreme runoff (4000 m ³ /s), the influence can extend up to approximately 10 km offshore beyond the mouth. (3) The distribution and strength of the tidal‐current field are significantly affected by the outlet course and shoreline configuration. Corresponding adjustments of the tidal‐current field are observed in regions of intense erosion and accretion, such as the Gudong nearshore area and the active and abandoned river mouths. These findings are of considerable engineering value for understanding delta morphodynamics and informing nearshore environmental management.