波流作用下海底边界层沉积物再悬浮与影响因素研究

Sediment resuspension of bottom boundary layer under waves and currents

海底沉积物再悬浮及其分布取决于海洋水动力、沉积物类型与床面形态之间复杂的相互作用,准确地理解和确定沉积物再悬浮过程对于沉积物输运的研究具有重要的意义。本文在祥云湾海洋牧场典型海域开展现场原位观测,获取研究区波浪、海流及悬浮沉积物浓度数据;分析了波、流作用下海底边界层悬浮沉积物垂向分布特征,并探究了海洋水动力和床面形态对悬浮沉积物垂向分布的影响。结果表明,研究区波流之间的相互作用不显著,沉积物再悬浮受控于风暴浪作用,风暴浪作用下底床切应力可以达到沉积物临界切应力的10~15倍,沉积物的再悬浮滞后于风暴浪作用2~3 h。在波浪荷载微小的情况下,悬浮沉积物垂向分布呈现"I"型,波浪荷载下,悬浮沉积物垂向分布呈现幂指函数分布,表现为"L"型;床面形态随波、流作用而演化,影响沉积物的再悬浮过程,u*w/u*c=1.00可作为波浪和海流起主导控制作用的床面形态的判别依据,纯波浪荷载作用下的u*w/u*c显著高于波浪主控作用下,但二者之间的界线随着波浪荷载的增加而升高。

Resuspension and its distribution of sediment depend upon three interacting components namely the characteristics of the mobile sediment, the bed forms and the forcing hydrodynamics. A good understanding of the process of sediment resuspension is important in sediment transport. In this paper, in-situ measurements of wave,current, and suspended sediment concentration profiles in the marine ranching of Xiangyun Bay were carried out.The vertical distribution characteristics of suspended sediment in the bottom boundary layer under the wave-current action were analyzed. The results show that the resuspension of seabed sediments in the study area is controlled by storm-waves. The bottom shear stress under storm wave is 10-15 times of the critical shear stress of sediment, resuspension of sediment lags behind storm-wave for 2-3 hours. The type of vertical distribution of suspended sediment is "I" under small wave load, the vertical distribution of suspended sediment in the bottom boundary layer presents a power exponential function, which is "L" type under storm-wave. Bedforms evolved with wave and can be used as a criterion to distinguish the bedfroms under the dominant control of wave or current. The value of higher than that under the dominant control of wave, and the cutoff value between them increased with the increase of wave load.