Analysis of water demand for channel forming and sediment transport in the Upper Reaches of the Yellow River in Inner Mongolia

Health of a river mainly depends on water demand for channel forming and sediment transport, particularly on the rational allocation of water resources in alluvial river. In this paper, energy balance equation was used to investigate the energy dissipation of sediment-carrying water flow, and distribution mode for water flow channel forming and sediment-carrying energy in the Upper Reaches of Yellow River in Inner Mongolia. Energy dissipated in alluvial river can be divided into two parts: one is to form a certain scale of river channel against boundary resistance of riverbed; another for transporting sediment. Silting or scouring of the riverbed during transportation can be an inherent indicator for the energy balance of water flow. Combined with the characteristics of flow and sediment movement in alluvial rivers, a complex relationship was proposed including the bank full discharge, the incoming sediment load, and the amount of scour and silting, in order to determine the water demand for channel forming and sediment transport. A calculation method was used to present the water demand for channel forming and sediment transport in a state of scour and silting in alluvial river. A calculation equation of water demand for channel forming and sediment transport was also established based on the measured data of the Inner Mongolia Reaches from 1960 to 2013. The calculated results showed that the incoming sediment load into the Inner Mongolia reaches was 70-110 million tons in flood season, and the water demand required for channel forming and sediment transport was 9.46-14.12 billion m3, providing that the silting ratio in these reaches was controlled below 30%, and a median water river channel in a scale of 2 000-3 000 m3/s. The water demand for channel forming and sediment transport mainly depends on incoming sediment loads, scales of river channels, and various levels of silting. In the case of the water demand higher required for channel forming and sediment transport, three trends can be obtained, including that, 1) the silting ratio can be lower control in an incoming sediment load and same scale of median water river channel; 2) the scale of median water river channel can be larger in an incoming sediment load and same silting ratio controlled, and 3) the incoming sediment load in flood season can be higher in the same silting ratio controlled and requirement on scale of median water river channel. There was agreement with the calculation results and the variation law of the water demand for channel forming and sediment transport of the Inner Mongolia reach, and the energy dissipation of alluvial rivers as well. The change law of water demand was obtained for channel forming and sediment transport under various conditions of sediment level, river channel scales and siltation levels. The findings can provide a sound technical support for the regulation of water resources in the Upper Reaches of Yellow River in Inner Mongolia.