金沙江堰塞湖溃决后淤积河段疏浚措施实验研究

Experimental Research on the Dredging Measures for the Silted River Section after the Collapse of the Jinsha River Barrier Lake

2018年金沙江上游因强降雨发生大型山体滑坡形成堰塞湖,堰塞湖溃决后大量泥沙随溃坝洪水向下游输移,导致下游河道形态及水流特性突变。某规划电站尾水河段受该事件影响,床面淤积6~10 m。为保障该电站如期正常建设,针对尾水河段上下游3 km河道,开展动床物理模型试验研究,探索尾水河段设计水位恢复方案。河道演变分析表明,堰塞湖溃决后的第1年,工程河段河床单向显著冲刷;至2022年汛前,河道整体表现为上冲下淤,尤其弯道下游石滩显著生长发育。通过模型试验预测了工程河段2027年地形,届时河道床而仍较堰塞湖溃决前高1~6 m,需要采取疏浚措施才能保障规划电站尾水口水位降低至设计水位。为有效减小疏浚范围及疏浚量,详细分析了弯道下游新生石滩段的水沙特性及演变趋势,提出了下游先期局部疏浚,通过自然演变调整床面,再开展整体疏浚的整治方案。试验证明,该方案较直接疏浚方案缩短了疏浚长度,可减少约6.88万m3疏浚量。继续针对新方案开展淤积试验,由于上游电站已陆续建成使用,其拦蓄作用大幅减少了研究河段来沙量,在5个典型年的水沙作用下,研究河段床面整体保持相对稳定,仅尾水出口下游左侧呈现一定程度淤积,建议管理单位定期按需要进行必要的局部疏浚维护,以保障电站安全运行。

In 2018,a large-scale landslide occurred in the upstream of the Jinsha River due to heavy rainfall,forming a barrier lake.After the breach of the barrier lake,large amounts of silt and sediment were transported downstream with the floodwaters,resulting in significant changes in the morphology and flow characteristics of the downstream river channel.The tailwater section of a certain planned power station was affected by this event,with a sediment deposition of 6 to 10 meters.In order to ensure the normal construction of the power station as scheduled,a physical model test was conducted to explore the restoration plan for the tailwater section of the river,covering a distance of 3 kilometers upstream and downstream.An analysis of the channel evolution showed significant unidirectional erosion of the engineered section of the river in the first year after the breach of the lake.By the pre-flood season of 2022,the overall trend of the river channel was characterized by upstream erosion and downstream deposition,particularly evident in the significant growth and development of gravel bars downstream of bends.The topography of the engineered section of the river in 2027 was predicted by using model tests,which showed that the riverbed would still be 1 to 6 meters higher than the pre-burst level of the barrier lake.Therefore,dredging measures would be necessary to lower the tailwater level of the planned power station to the design level.In order to effectively reduce the dredging area and volume,a detailed analysis of the water and sediment characteristics and evolution trend of the newly formed gravel bar segment downstream of the bends was conducted.A remediation plan was proposed,which involved an initial local dredging downstream,followed by adjusting the riverbed through natural evolution before conducting an overall dredging.The test confirmed that this plan could reduce the length of dredging and save approximately 68800 cubic meters of dredging volume compared to a direct dredging approach.Sedimentation tests are carried out for the new plan,as the upstream power stations have been gradually built and put into use,their detention effect has significantly reduced the sediment inflow to the research river section.Under the water and sediment effects of five typical years,the overall bed of the river section remains relatively stable,and only a certain degree of sedimentation appears on the left side downstream of the tail water outlet.It is recommended that the local dredging as needed be regularly carried out to ensure the safe operation of the power station.