废黄河口海域的悬沙输运机制研究

THE MECHANISM OF SUSPENDED SEDIMENT TRANSPORT IN THE ABANDONED HUANGHE RIVER DELTA

废黄河三角洲是南黄海内陆架的重要物源。为深入探索废黄河口海域沉积物输运机制,利用2015~2016年夏季与冬季在废黄河口外海域10个站位获取的现场沉积动力数据,计算潮不对称参数、余流、悬沙输运量等。分析结果表明,废黄河口海域沉积物输运模式存在显著的空间差异,大部分海域悬沙沿等深线向南输运,仅在近岸侧局部悬沙向岸或向北输运、离岸最远处站位向北输运但输运率较小;近岸浅水海域以平流输沙为主,其他离岸区域以再悬浮作用为主。由于流速和悬沙浓度之间的相位差,导致余流(净水输运)方向与净悬沙输运方向存在差异。研究沉降速度与悬沙输运涨落潮不对称的关系,发现沉降速度越大,悬沙输运的不对称性就越显著;沉降速度是造成近底部流速与悬沙浓度相位差的主要原因,导致废黄河口外净悬沙输运存在显著的垂向差异。

The abandoned Huanghe(Yellow) River delta is an important source of sediment on the inner shelf of the South Yellow Sea.To understand the mechanisms of sediment transport in the coastal ocean of the abandoned Huanghe River subaqueous delta,the tidal asymmetry parameters,residual flows,and suspended sediment transport flux were calculated based on in-situ data obtained in the 10 stations located from nearshore to offshore in summer and winter of 2015~2016.Results show that the suspended sediment transport patterns varied significantly in space.Suspended sediment in most sea areas is transported southward along the isobaths,and only a part of them is transported shoreward or northward on the nearshore side,and in the farthest offshore station is transported northward but the transportation rate is small.The suspended sediment transport in the nearshore shallow water is dominated by advection while that of other offshore areas is dominated by resuspension.The direction of net suspended sediment transport diverges from the direction of residual flow(net water transport) due to that flow velocity and suspended sediment concentration are sometimes out of phase.The relationship between sediment settling velocity and the asymmetry of suspended sediment transport flux shows that the larger the settling velocity,the higher asymmetry degree of suspended sediment transport.The small settling velocity is responsible for the temporal inconsistence between near-bottom velocities and suspended sediment concentrations,resulting in vertical differences in net suspended sediment transport rates in the abandoned Huanghe River delta.