The main-channel restoration objective and the relevant flow regime required for the lower Yellow River

摘要

The main-channel of the lower Yellow River is the main path of water and sediment transportation. In this paper, we put forth a suggestion that the bank-full discharge of the main-channel in the lower Yellow River should be no less than 4000 m~3/s, which is based on the demand from effective sediment transportation (or riverbed scouring), the demand of flood control on morphology of the cross section of the main-channel, and the possible riverbed-forming force of future flood. The forming of the main-channel is the process for the flood force to overcome the resistance from the riverbed. The forming of the main-channel configuration comes from the competition between riverbed-forming force of flood and resistance from the riverbed. Regarding the flood with medium or less sediment content and without floodplain inundated, the main-channel forming mechanism can be simplified as the relationship between the change of cross section area and W~αQ~β. For forming same main-channel, the needed flood force W~(0.32)Q~(0.37) is definite, i.e., when the discharge is large, the flood volume can be smaller; if some flood is able to scour the main-channel, its force W~(0.32)Q~(0.37) should be larger than 41. Not all floods that inundate floodplain have the function of silting in floodplain and scouring main-channel. Regarding flood with medium or less sediment content, only when the flood discharge is over 1.5 times of the relevant bankfull discharge, obvious scouring effect can occur in the main-channel.