Abstract: This paper presents an extreme stage-extreme discharge analysis and a specific-gauge analysis on the change in the lower Weihe River stage during the past 70 years to explore the characteristics and mechanism of river stage changes and their causes under the combined effects of water-sediment conditions and erosion base level. Considering the three operating modes of the Sanmenxia reservoir, we divide the time series (1950-2017) into periods of P1 (1950-1959), P2 (1960-1973), P3 (1974-2002), and P4 (2003-2017). The water stage was generally on the rise at Huaxian; it fluctuated at Xianyang in P1 and P2, while continuously decreased in P3 and P4. The rise in the erosion base level, represented by Tongguan elevation, caused a large-scale sedimentation in the lower Weihe and thus became the major cause for the Huaxian stage rising. The Xianyang hydrologic station was less affected by the base level. Its water stage downtrend was originated from riverbed scour caused by the drastic reduction in incoming sediment, and comprehensive management of river channels promoted this trend. By our predictions, the water stage in the lower Weihe may continue its downtrend in the future. The results help the management of the lower Weihe basin and other similar rivers.

Key words: water-sediment conditions, erosion base level, water stages, lower Weihe River, Tongguan elevation