絮凝对三峡水库泥沙沉降的影响

现场与室内实测的泥沙级配差异证实了三峡水库中存在泥沙絮凝现象,絮凝会加速水库泥沙淤积速率。为了确定絮凝对泥沙沉降速率的影响,现场采集了三峡水库原样泥沙,基于三峡水库水体环境,采用室内静水沉降试验对三峡水库中泥沙絮凝沉降规律进行了研究。研究结果表明,当试验采用的初始含沙量大于0.3 kg/m3时,部分单颗粒泥沙会聚集形成絮团,且泥沙絮凝程度以及沉速增加的幅度与水体中含沙量呈正比。参与絮团形成的单颗粒泥沙粒径均位于0.022 mm以下,小于临界粒径的泥沙占全沙的83%;采用絮凝因数和物质沉降通量因数分别表征絮凝对泥沙沉降的影响程度,这两种因数都随含沙量增加而增加,含沙量在1.5 kg/m3以下时其最大值分别为5.03和1.66,表明絮凝对三峡库区汛期的泥沙淤积有可能造成较大影响。

Regularity for sediment floc deposition in the Three Gorges Reservoir

Difference between sediment gradation measured in field and primary particles gradation indicates that there exist sediment flocs in the Three Gorges Reservoir, which may increase sediment deposition rate in the reservoir. In order to determine the influence of flocculation on sediment deposition, sediments from the Three Gorges Reservoir were collected to investigate the sediment settling process by hydrostatic settling experiments, in which the water environment is similar to that in the Three Gorges Reservoir. The results show that when sediment concentration larger than 0.3kg/m³ some particles flocculates and the extent of floc-culation gets larger when sediment concentration increases,and the maximum diameter of the primary parti-cles which may be affected by flocculation is about 0.022mm, that means that 83% of the total sediment may be influenced by flocculation. Within the concentration of the sediment in the Three Gorges Reservoir, the average settling velocity is proportional to the sediment concentration. Flocculation factor and mass set-tling flux factor is used to reflect influence of flocculation on reservoir sedimentation and it is found that both factors increase with sediment concentration at the beginning of the experiment and when sediment con-centration below 1.5kg/m³ the maximum value of flocculation factor and mass settling flux factor are 5.03 and 1.66 respectively, which indicates that flocculation may have great influence on sediment deposition in the reservoir.