Analysis Of Runoff Evolution Rules And Mid-long Term Runoff Forecast In Minjiang River Under The Influence Of Reservoirs

In the construction phase of the reservoir groups,the irreversible changes caused by artificially changing land utilization and soil vegetation cover,which have generated drastic influence in the hydrological process.In the stage of the reservoir groups operation,while the reservoir groups fulfil economic benefits such as flood control,power generation,and irrigation,they also have ecological and environmental impact on the discharge of the river runoff,which is mainly reflected in hydrological condition changes,degradation of river ecosystems,etc.Therefore,in order to clarify the degree of changes with the runoff characteristics led by hydropower development,and quantitatively evaluate the effects of underlying surface changes and reservoir operation,meanwhile carry out mid-long-term runoff forecasting under the background of reservoir group operation,which is of great significance to rationally develop and utilize water resources,protect resources and environment,and optimize the scheduling of water conservancy projects.The Minjiang River is the largest tributary of water and an important base for hydropower resources development in the upper reaches of the Yangtze River.This paper takes the Lancang River Basin as study area,and carries out an in-depth study of the runoff evolution rule analysis,hydrological process simulation and medium and long-term runoff forecasting under the operation of reservoir groups.The main findings are as follows:(1)Considering the impact of the reservoir groups'construction and operation on runoff,the runoff sequence of the export station(Gaochang hydrometrical station)was taken as the research object,and using the trend rate method,moving T test,Mann-Kendall test and wavelet analysis to explores the trend of runoff inner and interannual variation law,quantitatively determine the degree of runoff changes with the impact weight of the index through the IHA and CRITIC methods.The results show that with the increase of the reservoir number,the maximum(minimum)flow has larger amplitude;the reservoir construction and operation have the most significant impact on runoff during the flood season especially during June-October,in which the six indicators of June-October average flow and annual maximum flow take up a large weight;Gaochang hydrometrical station have a moderate degree of change in runoff.(2)In order to study the impact of land use and vegetation cover change on runoff caused by reservoir group construction,using the SWAT model and the control variable method to set up two kinds of hydrological simulation scenarios.Using the Parasol analysis in SWAT-CUP to carry out the parameter sensitivity analysis,and quantitatively determine the impact of land use/soil cover and reservoir operation on runoff changes.The results showed that the changes of land use and vegetation cover reduced the runoff by 45 m~3/s,and the operation of the reservoir reduced runoff by 75 m~3/s.It indicates that the reservoir discharge has significant impact on runoff.(3)In view of the medium and long-term runoff forecast under the influence of reservoir storage and discharge,this paper starts with the physical causes,and integrates the meteorological forecasting factors with the reservoir drainage factors,establishing model of multiple regression,BP neural network and support vector machine based on PSO.Then comparing the forecast results to determine the impact of reservoir operation on the accuracy of medium and long-term runoff forecasting.The results show that the accuracy of the prediction scheme for increasing the drainage factor is increased by 7.01%when using multiple regression models;Using the BP neural network model,the accuracy of the prediction scheme for increasing the drainage factor is increased by 4.17%;Using the SVM model,the accuracy of the prediction scheme for increasing the drainage factor is increased by 2.33%.