Study On Flood Forecasting Of Huanren Reservoir Under The Change Of Underlying Surface

As one of the most common and serious natural disasters in nature,flood disaster has brought immeasurable losses to human beings in history.As one of the most important non engineering measures for flood control,flood forecasting plays an important role in decision support in the process of flood control.In recent years,with the intensification of human activities,the underlying surface conditions of the basin have been changed,which in turn affected the characteristics of the basin's runoff and confluence,and reduced the accuracy of the original flood forecasting scheme.Taking Huanren Reservoir as the background,this paper studies the basin flood forecasting under the change of underlying surface.Firstly,the original forecasting scheme of Huanren Reservoir and its existing problems are analyzed,then the change trend of flood influencing factors is studied,and finally the flood forecasting scheme of Huanren Reservoir under the change of underlying surface is studied.The main achievements are as follows:(1)Study on the change trend of flood influencing factors.Firstly,the trend analysis method and MK nonparametric rank correlation test method are used to analyze the change trend of flood characteristics of Huanren Reservoir.The results show that there is no obvious change trend of flood characteristics;Then,using remote sensing data,the spatial and temporal changes of land use in Huanren basin since 1980 s are analyzed.It is found that the main land use types in Huanren basin are woodland and cultivated land,accounting for more than 90%,and the overall changes of various land use types are very small;Finally,the quantity,storage capacity and spatial distribution of water conservancy projects in Huanren basin since 1950 s are analyzed statistically.The results show that the changes of water conservancy projects in the middle and upper reaches of Huanren basin are relatively large.It can be considered that the main factor affecting the accuracy of flood forecast is the small and medium-sized water conservancy projects in the basin.(2)Study on flood forecasting scheme of Huanren Reservoir without considering the influence of water conservancy project.According to the characteristics of Huanren basin,XAJ model is selected as the flood forecasting model,and 77 historical floods from 1967 to2013 are used for unit and subunit simulation.The results show that the subunit XAJ model takes into account the temporal and spatial heterogeneity of rainfall,and the simulation results are better.The qualified rate of runoff and confluence forecast is 79.2% and 68.8%respectively,but the verification rate of confluence forecast in the calibration period is significantly lower than that in the regular period.The analysis shows that the reason is that a large number of water conservancy projects have been built in the upstream,which leads to different characteristics of runoff and confluence in different years.(3)Study on flood forecasting scheme of Huanren Reservoir Considering the influence of water conservancy project.According to the temporal and spatial variation characteristics of underlying surface in Huanren Basin,the historical floods are divided into four periods:1967-1977,1997-2004,1978-1996 and 2005-2013.Firstly,based on the idea of aggregating reservoirs,the water conservancy projects in the upper reaches of the basin are aggregated into different reservoirs;Then,according to the basic regulation and storage law of each water conservancy project,the storage discharge relationship curve of the aggregated reservoir is established;Finally,the flood forecasting model of Huanren Reservoir Considering the influence of upstream water conservancy projects is constructed by combining the storage and discharge relationship curve of aggregated reservoir with XAJ model.The flood of four periods are simulated respectively,and the storage and discharge law of upstream small and medium-sized reservoir projects is excavated,and the influence process of water conservancy projects on flood process is analyzed.The results show that the established reservoir storage and discharge relationship curve is basically in line with the storage and discharge law of medium and small reservoirs in the upstream,and the simulation accuracy is greatly improved.