Study on preliminary operation of Xiaolangdi Reservoir and flow-sediment regulation of the Yellow River

The study on some topics concerning reservoir sedimentation and flow-sediment regulation in the preliminary operation of Xiaolangdi Reservoir is presented in this paper.The quantitative expressions of trapping coarse particles and sluicing fine particles and their control conditions have been derived.The percentage of reservoir deposition and ratio of sediment sluiced from the lower reach are closely related and their relation has been demonstrated by both theory and field data.For a certain reservoir the relation is single-valued and it is reliable to connect the reservoir sedimentation and downstream erosion.The important effect of the flow-sediment regulation of Xiaolangdi Reservoir to the improvement of channel in the lower Yellow River has been analyzed.The expression of second channel-forming discharge and the relation between second channel-forming discharge and the ban-full discharge in the lower Yellow River have been discussed and then the possibility for increasing the channel-forming discharge at present and in the future is demonstrated.Finally it has been shown that it is necessary to change the practical operation mode from reservoir planning.