Identification And Adaptability Of The Pre-release Index Thresholds For Flood Control Of A Reservoir

With the improvement of the meteorology-hydrology coupling forecasting technology and flood control operation engineering system,the flood control pre-release operation method based on the flood forecast information has become an effective measure to scientifically deal with the flood exceeding the downstream flood control standard(excessive flood).However,the pre-release start-and stop-points are difficult to identify and the prerelease water volume lacks of dynamic adjustment in the current reservoir pre-release operation method.As for these problems,the pre-release index connotation is analyzed and the mathematical expression of the pre-release index is introduced in this thesis.The identification method of the pre-release index thresholds including the pre-release start-and stop-thresholds and pre-release depth threshold is introduced.Taking the Shuifumiao reservoir as a case,a pre-release operation model based on the pre-release index threshold is established and the feasibility and adaptability of the pre-release operation model are evaluated.The main investigation contents and corresponding conclusions are as follows:(a)The pre-release index connotation is defined and the mathematical expression of the pre-release index is introduced.It is determined that the main factors influencing the prerelease operation are the reservoir water storage,peak discharge and time,and flood volume using the principal component analysis.The mathematical expression of the pre-release index,which is used to quantify the forecast-release information,is established by analyzing the dimensionless numbers constructed by these factors.(b)The identification method of the pre-release start-and stop-thresholds and pre-release depth threshold is introduced.Some characteristic historical flood progresses are simulated using the flood control optimal operation with an optimization-simulation method.According to the identification results obtained by this method,the pre-release start-and stop-thresholds and pre-release depth threshold of Shuifumiao reservoir are 0.59,0.34,and 4.706 × 107 m3,respectively.(c)A pre-release operation model based on the pre-release index threshold is established and applied in the flood control operation simulation of Shuifumiao reservoir.By comparing with the reservoir current operation method and flood routing calculation,the adaptability for floods with different frequencies and flood storage and delaying effects of the pre-release operation model are evaluated.The results show that:in the cases with excessive floods P=0.1,0.2,and 1%),the operation time with the out-flow rate exceeding the downstream safety flow rate and the operation time with the water level exceeding the flood control high water level are 17.2%and 9.7%shorter on average than those of the flood routing calculation and 14.0%and 6.3%shorter on average than those of the current operation method,which can effectively enhance the reservoir and downstream flood control safety.(d)The adaptability of the pre-release operation model based on the pre-release index threshold considering the influence of the flood forecasting error is evaluated.The results show that:the in-flow flood forecasting error of Shuifumiao reservoir exhibits a negatively skewed distribution.Considering the random forecasting error satisfying the negatively skewed distribution with the confidence level of the maximum relative error being 80%,the maximum out-flow rates and reservoir water levels obtained using the pre-release operation method are lower than those obtained using the current operation method and flood routing calculation in floods with P<1%and more than 85%of the maximum out-flow rates and reservoir water levels obtained using the pre-release operation method are lower than those obtained using the current operation method and flood routing calculation in floods with P=3.33 and 5%.Research results of this thesis can provide a theoretical basis and technical guidance for the reservoir pre-release operation based on the flood forecasting results to enhance the regulation and storage capacity of the reservoir for excessive floods and provide a technical reference to further develop the flood control forecast-pre-release coupling operation of the basin reservoir group.