This paper presents a study of the variation of the elevation of Tongguan, which is located in the backwater zone of the Sanmenxia Reservoir, in response to changes in flow runoff. The analysis indicated that the rise of the eleva- tion of Tongguan, which is defined as the stage corresponding to a discharge of 1000 m3/s at Tongguan station, is controlled by the stream energy. A close relationship existed between the elevation of Tongguan and the superimposed stream en- ergy that integrates the current and the preceding years’ flow and dam operation conditions. When the flow runoff remains relatively constant and the pool level of the dam has a rela- tively large range of variations, then the elevation of Tong- guan is primarily controlled by the dam operation conditions. On the other hand, if the flow runoff has a relatively large range of variations and the pool level of the dam remains relatively constant, then the elevation of Tongguan is primar- ily controlled by the flow conditions. These findings are of importance for optimizing the dam operation in order to lower and control the elevation of Tongguan, and therefore to minimize the backwater effect of the dam operation. This paper presents a study of the variation of the elevation of Tongguan, which is located in the backwater zone of the Sanmenxia Reservoir, in response to changes in flow runoff. The analysis indicated that the rise of the eleva- tion of Tongguan, which is defined as the stage corresponding to a discharge of 1000 m3 / s at Tongguan station, controlled by the stream energy. A close relationship existed between the elevation of Tongguan and the superimposed stream en- ergy that integrates the current and the preceding years’ flow When the flow runoff remains relatively constant and the pool level of the dam has a rela- tively large range of variations, then the elevation of Tong- guan is primarily controlled by the dam operation conditions. On the other hand, if the flow runoff has a relatively large range of variations and the pool level of the dam remains relatively constant, then the elevation of Tongguan is primar- ily controlled by the flow conditi ons. These findings are of importance for optimizing the dam operation in order to lower and control the elevation of Tongguan, and therefore to minimize the backwater effect of the dam operation.