| Xiaolangdi reservoir has a total storage capacity of 12.65 billion m~3,including 7.55billion m~3 forsediment-retaining,1 billion m~3 for water and sediment regulation,and 4.05billion m~3 for long-term development.The reservoir operation methods are divided into three stages:the initial sediment-retaining period,late sediment-retaining period and the normal stage.In the initial sediment-retaining period(siltation volume of sediment storage capacity<2.2 billion m~3),the main operation mode is mainly water storage and sediment control,with the main goal of reducing siltation in the downstream river and ensuring flood control safety.In the later stage of sand blocking(2.2 billion m~3≤siltation volume≤7.55 billion m~3),moderate sediment retainning and camera sediment removal are mainly applied,and the main object is to maintain the efficient utilization of the remaining sediment storage capacity of the reservoir.During normal operation period,the reservoir reaches the balance of scouring and silting and completely loses the function of sand blocking.By October 2007,a total of 2.323 billion m~3 of silt had been deposited in Xiaolangdi reservoir.At the same time,the inflow water and sand conditions of Xiaolangdi reservoir changed directionality,and the efficiency of continuous scour of the downstream channel also decreased.Under the situation that both the new dispatching stage and the boundary conditions of the upper and lower reaches have changed,it is necessary to further optimize the dispatching mode of xiaolangdi reservoir at the later stage of sediment containment,take into account flood control and silt reduction,water supply and power generation,and adjust the response target of the downstream channel to maintain the middle-water channel.In this context,this paper chooses the topic of"Study on the Coupling Interaction between Dispatching Model for Water/Sediment/Electricity in Xiaolangdi Reservoir and Riverbed Erosion and Deposition in the lower Yellow River"as research subject.The main content includes the following parts:(1)The concept and calculation method of water and sand uncoordinated degree in the sandy river are proposed.The water and sand data of the Sanmenxia station series(1963～2017)is used as a typical representative of the water and sediment sequence entering the lower reaches of the Yellow River,and the uncoordinated state of the Yellow River water and sediment is analyzed.In terms of change,the degree of water and sand disharmony is positive before 2005,showing a state of water and sand.After 2005,it is mainly negative,showing a state of less water and less sand.(2)The empirical correlations were proposed based on the experimental,and the method and formula of calculating of density current to eject sediment is proposed.At the beginning of the sediment retaining period in the Xiaolangdi Reservoir,the sediment transport in the reservoir area was mainly caused by dredging by drowning,scouring along the course,and sand discharge by different gravity.After entering the late sand-blocking operation mode,on the basis of sediment transport in the early stage of sand-blocking,the traceability scouring mode is increased,that is,the reservoir water level is lowered to the vicinity of the delta apex,thereby reducing the sedimentation delta erosion datum surface,and forming traceability scouring on the silt delta surface.Increase the sediment concentration of the heavy gravity flow into the point.The characteristics of sediment discharge and sedimentation change of reservoirs in Xiaolangdi Reservoir are analyzed systematically.The focus is on the sedimentary delta model of the sedimentary delta in the late stage of sediment interception to the near-dam section,and the sedimentary gravity ratio of the reservoir and the backwater length of the reservoir are proposed.A calculation method for different gravity flow and sand discharge considering the scheduling process and boundary conditions of Xiaolangdi Reservoir is proposed.(3)On the basis of systematic analysis of evolution characteristics of the lower Yellow River,a calculation method of bankfull discharge is presented.It is pointed out that as the Xiaolangdi Reservoir enters the late stage of sediment interception,the coarseness of the downstream river bed and the erosion efficiency are significantly reduced.The optimization goal should be changed from increasing the overcurrent capacity to maintaining the river channel.Based on the two-dimensional mathematical model for sediment evolution in the lower Yellow River,a quasi-two-dimensional flat beach flow calculation method for the typical section of the lower Yellow River is proposed.(4)The calculation module of the above-mentioned reservoir sand discharge and river channel response is constructed,and the mathematical model of multi-objective optimal dispatching of the Dusha River Reservoir is constructed,taking into account the downstream river channel to maintain the demand of the middle water channel and the reservoir flood control and sediment reduction,power generation and water supply,and ecological environment.The model acheived the optimal scheduling of Xiaolangdi Reservoir on the annual time scale.The results of optimization scheduling for many years(2010-2017)show that the optimal scheduling scheme can achieve maximization of new win-win situation of maintaining the channel in the downstream river,alleviating the sedimentation of reservoir and improving the benefit of water supply and power generation,Based on the optimizing problem of feasible solution of coupling model,an evaluation index system and evaluation method for the optimal dispatching effect of the Xiaolangdi Reservoir in the Yellow River in the later stages of sand blocking are proposed.Then it is applied to the evaluation of the optimal dispatching effect of different schemes in 2017.The finding of this research provides theory foundation and technology support for the decision-making of reservoir multi-objective optimal dispatching schemes. |
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