Application And Risk Analysis Of Ensemble Rain Forecast In Dynamic Control Of Flood Limit Water Level Of Parallel Reservoirs

Water resources in China are unevenly distributed in time and space,flood disasters coexist with the contradiction between water supply and demand.On the basis of ensuring the safety of flood control,the use of advanced science and technology to play the beneficial role of water conservancy projects and increase the utilization rate of flood resources are important measures to alleviate the current situation of water shortages in my country.Using flood forecast information and rainfall forecast information to carry out dynamic control of the flood limit water level of the reservoir is an effective method to improve the utilization rate of flood resources.Applying high-precision rainfall forecast information to the dynamic control of the flood limit water level of the reservoir group can further explore the compensation effect of the reservoir capacity and improve the profitability.However,the existence of forecast uncertainty also has an impact on the flood control safety of the reservoir and downstream.This paper takes Qing-Chai Parallel Reservoirs as the research object.On the basis of clarifying the application method of ECMWF ensemble rainfall forecast information in the research basin,this paper applies it to increase the upper limit of the dynamic control domain of the flood limit water level of Qing-Chai Parallel Reservoirs,and Analyze the impact of different forecast information on the flood control benefits of the reservoir.Then,based on the storage capacity compensation,this paper makes a quantitative description of the risk transformation relationship of parallel reservoirs and the risk transmission relationship between the reservoir and the downstream,and provides decision-makers with Qing-Chai Parallel Reservoirs capacity allocation plan from the perspective of flood control safety.The main research contents and results are as follows:(1)The application of ECMWF ensemble rainfall forecast information in Qing-Chai parallel basin is clarified.Through the "three rates" analysis of ECMWF ensemble forecast statistics products and Taylor chart analysis,it is clear that the forecast values of ECMWF ensemble rainfall forecasts in the Qingchai River Basin need to be determined by comprehensively using the 90% quantile value and the average of the standardized accuracy rate.Based on this,a joint distribution function of rainfall forecast errors with and without correlation is constructed under different forecast situations,and the impact of the correlation of rainfall forecast errors on the flood control safety and benefit benefits of parallel reservoirs is quantitatively analyzed.It is clarified that in Qing-Chai parallel basin,the uncertainty description of forecast without considering the correlation of rainfall between basins can be used to guide the flood season operation of parallel reservoirs.(2)The ECMWF ensemble rainfall forecast information was applied to improve the profitability of parallel reservoirs,and risk analysis was carried out.First,combining the improved pre-discharge capacity constraint method and the "aggregation-decomposition" method,the upper limit relationship curve of the dynamic control domain of the flood limit water level of the Qing-Chai Parallel Reservoirs is constructed,and the maximum upper limit of the two reservoirs is increased to 129.5m and 108 m,respectively.Based on this,the risk of using only rainfall forecast information for pre-storage and pre-discharge is analyzed,and the results show that the use of rainfall forecast information can also improve the flood control benefits of the reservoir.Then,the risk of the comprehensive utilization of rainfall forecast information and flood forecast information coupled with pre-storage and pre-discharge and forecast dispatching methods is analyzed,and the influence of the use of different forecast information on the flood control benefits of the reservoirs is clear through comparison.(3)Quantitatively describe the risk transformation relationship of parallel reservoirs and the risk transfer relationship between upstream and downstream of the reservoir,then provide support for the reasonable allocation of the storage capacity of parallel reservoirs from the perspective of flood control safety.Based on the storage capacity conversion of Qing-Chai Parallel Reservoirs,the reservoirs and downstream risks of different storage capacity allocation schemes of Qing-Chai Parallel Reservoirs are calculated,and the risk conversion relationship of Qing-Chai Parallel Reservoirs parallel reservoirs and the risk transfer relationship from the parallel reservoirs to the downstream Shifosi station are quantitatively described.The proposed water level adjustment of Qing-Chai Parallel Reservoirs under different flood control needs is given,under the circumstance that the overall profitability of the reservoir group remains unchanged.Constructed the Qing-Chai Parallel Reservoirs joint forecasting and dispatching model,obtained three sets of joint forecasting dispatching rules with the goal of multiple storage of Qinghe Reservoir,multiple storage of Caihe Reservoir,and storage of two reservoirs with the same weight.Explored the law of risk transmission and risk transformation under different rules.