Sediment transport off the Huanghe (Yellow River) delta and in the adjacent Bohai Sea in winter and seasonal comparison

Abstract

Based on the data on the current velocity, water temperature, salinity, turbidity and concentration of suspended sediment collected in November 2006 along three survey transects at three time-series, ship-based stations off the Huanghe (Yellow River) delta, and at twenty-four grid survey stations in the adjacent Bohai Sea, sediment transport off the Huanghe delta and in the adjacent Bohai Sea under winter regime were studied and compared with those from the summer season. The homogeneous distribution of salinity, temperature and sediment in the water column indicated a well-mixed body of water. A zone of high suspended sediment concentrations (SSC) >100 mg l −1 with a width of 35 km was identified along the delta coast. Two highest SSC centers were found in the surface and middle water layers around the abandoned Diaokou Huanghe river mouth and the present Huanghe river mouth, and the third one in the bottom layer around the abandoned Qingshuigou Huanghe river mouth. These three highest SSC centers become major sediment source areas in winter. Based on the location of the high bottom shear stress zone, the prevailing wave directions and the protuberant topography of the river mouths, we identified the resuspension origin of the three highest SSC centers caused mostly by the winter storm waves, partially by tidal currents. Suspended sediment flux (SSF) along the three coastal transects indicated that the sediment in the northwest part of the delta was transported northeastward and southeastward along the coast of the recent delta lobe. The SSC and SSF were higher in winter than summer by 1.7–27.1 and 2–122.5 times, respectively, except around the present river mouth. This indicates that the intensity of sediment transport in winter is much stronger than in summer due to the powerful effect of winter storms although the river water and sediment discharges to the sea were much greater in summer. The massive Huanghe sediment to the sea was accumulated in a narrow coastal area due to weak hydrodynamics in summer, and then strongly resuspended mostly by storm waves in winter and transported to the offshore area. The coastal area off the Huanghe delta acts as a sediment sink in summer and converted to be a sediment source in winter in response to the seasonal variation of the East Asian monsoon in this region. The erosion–accumulation pattern of the Huanghe subaqueous delta from 1976 to 2003 illustrates that river-laden sediment is deposited mainly in the southern part off the coastal area and it is also the result of intensive southward sediment transport in winter.