A large inverted siphon of Middle Route Project of South to North Water Diversion passes through a sand mining riv-er. The sand mining lowered the river bed elevation and the inverted siphon was exposed to the river bed, resulting in water level rising and silting in the upstream and scouring in the downstream of the siphon. In order to guarantee the safe operation of the in-verted siphon, two solutions of horizontal protection and vertical protection are suggested. Through comprehensive comparison and considering the safety of the siphon, the vertical protection scheme is recommended and the clear requirements on the problems to be paid attention to in construction and operation of the siphon are put forward.%南水北调中线某大型渠道倒虹吸管穿越的采砂河段，因采砂活动导致河道地形下降，主河床部位倒虹吸管顶出露，致使河道行洪时倒虹吸管上游河道的水位壅高、河床淤积，而下游河床发生冲刷。为保证倒虹吸管的安全运行，设计提出了水平和垂直两种防护方案，经综合比选，从倒虹吸本身的工程安全考虑，推荐垂直防护方案，并对工程施工和运行期间应注意的问题提出了明确要求。
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