Factors driving riverbed scouring and sedimentation in the Bayangaole to Toudaoguai reaches of the Upper Yellow River

Abstract

The Inner Mongolia reaches of the Yellow River face problems of severe sedimentation caused by a variety of complex factors. The sedimentation process in those reaches has been characterized using the sediment balance method, and the key factors affecting the process have been analyzed using the correlation analysis method. The results show that during the period 1952–2012 the Bayangaole (Bayan Gol) to Toudaoguai reaches in Inner Mongolia have undergone successive processes of accumulative sedimentation, then relative balance, and then accumulative sedimentation once again. The total annual sedimentation is 12.0341×108 m3, of which accumulations from July to October account for 95.1% and the reaches from Sanhuhekou to Toudaoguai account for 98.5%. The main factor affecting scouring and sedimentation of the Bayangaole to Sanhuhekou reaches is the combined water and sediment condition. The critical conditions for equilibrium are an incoming sediment coefficient 700 m3·s–1. The main factor affecting scouring and sedimentation of the Sanhuhekou to Toudaoguai reaches is the incoming sediment from the tributaries on the south bank and the combined water and sediment condition of the main stream. The critical conditions of the main stream for maintaining equilibrium status are a flow discharge of the main stream exceeding 800 m3·s–1 and a comprehensive incoming sediment coefficient < 0.005 kg·s·m–6. The incoming sediment from the tributaries has little impact on the main stream when the annual sediment load is less than 0.1×108 t. The incoming sediment coefficient of the main stream and the incoming sediment from the tributaries both play vital roles in the riverbed evolution of the Inner Mongolia reaches, but the latter contributes the most.