Sediment dispersion pattern off the present Huanghe (Yellow River) subdelta and its dynamic mechanism during normal river discharge period

Hydrological observations were conducted synchronically along three transects in the southeast, middle and northeast off the present Huanghe (Yellow River) subdelta during normal-discharge (approximately 200 m3 s−1) period on August 8–13, 2003. Suspended sediment fluxes and dispersion patterns off the present Huanghe subdelta were studied based on the hydrographic data collected in these surveys. Along each survey transect, tidal shear fronts were identified that in combination with the tidal currents were the dominant factors controlling the pattern of sediment dispersal. Most of the river-laden suspended sediment from the river mouth was transported via hypopycnal flow and was limited within the 5 m isobath off the mouth due to the barrier effect of the tidal shear front and the weak river flow. In northern and southern areas off the subdelta, the sediment fluxes at stations farther from the coast were much higher than those at the nearshore ones, indicating that the river-laden sediments were transported to north and south offshore via deeper water areas at both sides of the river mouth. The tidal shear fronts revealed in the northern and southern nearshore areas of the subdelta, jointly with tidal currents barred the sediment transport from offshore to nearshore. This resulted in offshore sediment deposition on the northern and southern parts of the subaqueous subdelta, rather than in the nearshore area, thus forming nearshore erosion and offshore accumulation areas, respectively.