三峡库区泥沙絮凝临界条件现场测量

Field measurements of the critical conditions of sediment flocculation in the Three Gorges Reservoir

三峡库区絮凝现象是细颗粒泥沙淤积的重要原因,泥沙絮凝临界条件对三峡库区泥沙淤积规律和模拟具有重要意义。在三峡库区忠县和奉节河段开展泥沙絮凝的现场测量,基于声学多普勒流速仪(Acoustic Doppler Velo-cimeter,ADV)和泥沙采样测得同步的瞬时流速和含沙量,通过泥沙扩散理论反算现场泥沙沉速及絮团粒径,得到了三峡库区泥沙絮凝度及其与粒径、流速和含沙量的关系。结果表明:库区细颗粒泥沙发生絮凝,且多为中轻度絮凝,重度絮凝较少;库区泥沙絮凝的临界粒径约为0. 018 mm,临界流速约为0. 7 m/s,临界含沙量约为0. 8 kg/m^3。研究结果可为三峡库区泥沙的运动规律以及泥沙淤积模拟等提供一定的理论支撑。

Flocculation is the primary cause of fine sediment deposition in the Three Gorges Reservoir (TGR),and the critical conditions of flocculation is of great significance to the law and simulation of the sedimentation in the TGR.Field measurements of sediment flocculation were carried out at the Zhongxian and Fengjie reaches in the TGR during the flood season. Based on the acoustic backscatter intensity from ADV and sediment sampling,the instantaneous flow velocities and sediment concentrations were measured synchronously. The sediment settling velocities and floc sizes were calculated using the sediment diffusion theory. The relationships between flocculation degree and particle size,flow velocity and sediment concentration were obtained,respectively. Results show that the sediment flocs are mostly in the region of middle and light flocculation,but less in the region of heavy flocculation. The critical particle size of the sediment flocs is about 0. 018 mm,the critical flow velocity is about 0. 7 m/s,and the critical sediment concentration is about 0. 8 kg/m^3. This research can provide theoretical supports for the basic law of sediment transport and simulation of sedimentation in the TGR.