基于ADV声学泥沙反演与扩散机制分析

ADV-based acoustical sediment inversion and diffusion mechanism in the Pearl River Estuary

利用座底三脚架观测系统于2012年洪季对珠江黄茅海河口湾底边界层沉积动力过程进行了系统观测,建立了基于现场ADV探测的高频泥沙声学反演方法,分析了泥沙浓度、泥沙扩散通量及泥沙扩散系数随潮汐变化的特征,探讨了泥沙再悬浮的湍流猝发机制。泥沙浓度、泥沙扩散通量、涡动扩散系数及泥沙扩散系数具有明显的潮汐变化特征,主要表现为急流时较大、憩流时较小。泥沙沉降速度与泥沙浓度之间的幂函数关系可以很好地描述潮周期内沉降速度的变化。湍流猝发过程中,喷射和扫射事件是泥沙垂向扩散的主要动量来源,大振幅的猝发事件对泥沙垂向扩散具有决定性影响。

Instrumented tripod observations of bottom boundary layer flows and sediment transport were conducted in the 2012 flood season in the Pearl River Estuary, South China. An inversion of highfrequency sediment concentration was performed based on the signaltonoise ratio of the acoustical Doppler velocimeter with a sampling frequency of 64 Hz. Sediment concentration, upward flux of sediment diffusion, eddy viscosity and sediment diffusivity are highly tideaffected, with large values occurring during peak tides, and small ones during slack tides. Settling velocity of sediment particles is dependent on the power of sediment concentration,rather than linearly on sediment concentration. The analyses of turbulence bursting events demonstrated that ejection and sweep are the major momentum source of sediment diffusion. The sediment diffusion is predominately controlled by the amplitude of bursting events, irrespectively of the occurrence number and duration of turbulence events. The large-amplitude bursting events were found to be responsible for upward sediment diffusion.