基于ADCP测量的长江口推移质运动速度研究

Measuring bed load with an acoustic Doppler current profiler in Changjiang Estuary

利用ADCP测量底床推移质运动是近年来水下泥沙研究的新动向。长江河口南港和北港为粉砂-细砂质河床,采用ADCP定点观测方法对其底床推移质运动速度进行研究。结果表明:近底高浓度悬沙对ADCP现场监测推移质运动可能存在一定的影响,但是其影响不随近底悬沙浓度和厚度的变化而变化;床沙普遍运动是利用ADCP底跟踪方法在野外现场监测推移质运动速度的适用条件;南港床沙普遍运动的临界起动流速为1.0m/s,北港床沙普遍运动的临界起动流速为0.9m/s;在满足床沙普遍运动条件下,Va与τsk的2.1次呈幂函数相关,满足水槽实验研究中两者相关性的结果。说明利用ADCP方法估算推移质运动速度合理有效,可用作底沙输运机制现场研究。

Measuring bedload transport with ADCP is a new trend for subaqueous sediment transport study.The river beds of North Channel and South Channel in the Changjiang Estuary consist of silt-fine sand,and this paper tried to use ADCP with fixed point observation to study bedload transport. The results showed that high concentration of near-bottom suspended sediment might influence the observation of bedload transport with ADCP,but the influence did not change by the variation of the concentration and thickness of near-bottom suspended sediment. Measuring bedload speed（ V）awith ADCP is applicable to the situation that bed particles are generally moving. The critical incipient velocity for bed particles of North Channel and South Channel are0. 9 m / s and 1. 0 m / s respectively. Under the condition of bed particles in generally movement,the relationship between bedloadspeed（V）aand shear stress（ τsk） can be approximated by a power function of shear stress with an exponent about 2. 1,which is agreement with the results of flume experiments. Therefore,using ADCP to estimate bedload speed is reasonable and effective,and it can be used to study bedload transport mechanisms in the field.