Risk Analysis Of Joint Flood Control Operation For Lower Cascade Reservoirs In Jinsha River And Three Gorges Cascade

In recent years,the frequent occurrence of extreme hydrological events caused by global climate change has posed a great threat to social economy.In order to reduce the risk of flood control caused by extreme hydrological events,we should strengthen the construction of flood control and disaster reduction system and optimize the allocation of resources.With the construction and operation of large-scale controlled reservoirs in the basin,a large-scale joint flood control dispatching system has been initially formed.Due to the influence of multiple uncertainties such as hydrology,hydraulics and dispatching delay,the dispatching processes,which are characterized by randomness and complexity,affect the safe and stable operation of reservoirs.From the perspective of flood control safety,the management of dispatching risk is of great significance.Therefore,this paper focuses on the key scientific problems of flood control dispatching risk analysis under the background of high efficiency,safety and economic operation of downstream Jinsha River-Three Gorges cascade reservoir.According to different risk definitions,the risk analysis of flood control dispatching of reservoir group is carried out based on stochastic simulation method and frequency curve of flood control reservoir.The main research contents and innovative achievements are as follows.(1)Based on the normal distribution,lognormal distribution and other commonly used distribution functions as well as the maximum entropy principle,the distribution law of runoff forecast error is studied.Firstly,a neural network model based on improved weed optimization algorithm is established,and short-term runoff forecasting is carried out for Yichang Station to obtain prediction errors in different periods.Then,based on this data,the distribution law of prediction errors in early flood season,main flood season and late flood season are deduced by using maximum entropy theory and various commonly used distributions respectively.Taking the inflow of the Three Gorges Reservoir from 2001 to 2010 as a case,the results show that the prediction errors in different periods have different distribution laws,and the prediction values generally have a larger tendency.(2)In view of the joint flood control dispatching system of reservoirs in the upper reaches of the Yangtze River,the risk analysis of joint flood control dispatching of reservoirs based on stochastic simulation method is carried out.Considering the influence of different operation modes and various uncertainties of reservoirs,and combining with the stochastic simulation method of multivariate runoff,the risk variation law of reservoirs is analyzed,and then the multi-attribute risk decision of scheduling schemes is made with the subjective preferences and objective information of decision makers.The study shows that the uncertainty of flood forecasting of Three Gorges Reservoir inflow has a great influence on the risk rate of upstream reservoirs.The joint flood control dispatch of reservoirs can effectively reduce the risk of downstream reservoirs and improve the overall flood control benefits of the basin.Multi-attribute risk decision-making can comprehensively consider the importance of river basin flood control dispatching task and give the optimal dispatching scheme,which provides a basis for reservoir flood control dispatching decision-making.(3)According to the requirement of real-time flood risk analysis for reservoirs,an innovative method for calculating the frequency curve of flood control reservoir capacity based on a long series of historical measured runoff data is proposed.Based on this,the risk analysis model of reservoir real-time flood control dispatching is established,and the variation law of flood control risk in different periods of flood season of the Three Gorges Reservoir is analyzed.Furthermore,considering the geographical location,hydrological connection and flood control demand of cascade reservoirs,the frequency curves of flood control reservoirs under different operation scenarios of the Three Gorges Reservoir are analyzed,and the interoperability of flood control reservoir capacities between upstream reservoirs and downstream reservoirs is explored.The results show that the frequency curve of flood control reservoir capacity can reflect the risk change characteristics of the Three Gorges Reservoir in different periods of flood season,and it can be helpful to judge the current flood control situation.Rational utilization of the interoperability of flood control reservoir capacity can effectively reduce the flood control risk of the Three Gorges Reservoir and provide a new idea for risk analysis of real-time flood control operation of the reservoir.