三峡水库泥沙絮凝特征及影响因素分析

Flocculation characteristics of sediment in Three Gorges Reservoir and influential factors analysis

以三峡水库奉节河段和庙河河段的现场取样资料为基础,通过现场测量和室内实验分析,发现819个现场取样点中,99.4%的测点存在泥沙絮凝现象,其中83.6%的泥沙絮团直径约为单颗粒直径的3~8倍,表明在条件适合的情况下三峡水库泥沙絮凝具有普遍性,絮凝的临界粒径为0.02 mm。从库区泥沙絮凝的分布来看,主要集中在中上层水体中,并且顺水流方向呈现衰减的趋势,庙河河段的絮凝度明显小于奉节河段。库区泥沙絮凝的临界流速为0.7 m/s,流速小于0.7 m/s有利于泥沙絮凝的形成,但由于库区泥沙颗粒间的相对动能较小,泥沙絮凝难以形成稳定的大絮团,主要表现为弱絮凝。

Field measurements are carried out at Miaohe and Fengjie reaches in Three Gorges Reservoir,and the sediments are sampled for the laboratory experiments. The analysis results show that the flocculation phenomenon exists in 99. 4% of the 819 measuring points,and the diameter of 83. 6% flocs is 3 to 8 times larger than that of the single particle,indicating that the flocculation is universal under suitable conditions in Three Gorges Reservoir and the critical diameter of the floc is 0. 02 mm. In the perspective of the sediment flocculation distribution,the flocculation mainly concentrates in the upper and middle layer of waters,which attenuates along the flow direction,namely the extent of flocculation of Miaohe reach is much smaller than that of Fengjie reach. The critical velocity of flocculation is 0. 70 m / s,it is conducive to the formation of sediment flocculation below 0. 7m / s.The formation of stable and large floc groups is difficult and weak flocculation is dominant in Three Gorges Reservoir due to the small relative kinetic energy of sediment particles.