| Since the 1970 s,water circulation processes and water resources conditions have changed significantly in the Loess Plateau.The changes in the hydrological characteristics of the Loess Plateau affect the people's livelihood and environmental issues such as flood control,water resources allocation and water ecological protection in the Yellow River Basin.With the implementation of soil and water conservation measures and the implementation of the guidelines of “Returning farmland to forests”,the vegetation coverage in most parts of the Loess Plateau has recovered significantly.Therefore,under the background of vegetation cover and underlying surface characteristics recovered significantly,whether the mechanism of flow production and convergence in the Loess Plateau has changed has become an issue that needs to be studied in depth.This paper is under the support of the “Thirteenth Five-Year Plan” National Science and Technology Support Plan“Mechanism and Trends of Water and Sediment Changes in the Yellow River Basin”.The Jingle Station Control Basin in the upstream of Fenhe River and Zuli River Basin are selected as typical research areas,analyzed the patterns of production and confluence of flood in the Loess Plateau region,And explored whether the mechanism of runoff production and confluence changed with the change of underlying surface,and provide reference for relevant research in other regions.The main research contents and results of this paper are as follows:(1)Analysis of Characteristics of Underlying Surface Condition in the Loess Plateau.On the basis of collecting data on the hydro-meteorological data,land use and human activities in the Loess Plateau,and combining previous studies,the characteristics of the underlying surface of the Loess Plateau were analyzed.The results show that the underlying surface of the Loess Plateau has changed significantly in the past 40 years,which is reflected in changes in vegetation,silt dams,reservoirs,terraces and so on.(2)Analysis on Characteristics of Underlying Surface and Runoff in Typical Basins.Jingle Station Control Basin in the upstream of Fenhe River and Zuli River Basin are selected as as typical basins for research.First,remote sensing data at different periods in a typical watershed are interpreted and the characteristics of the underlying surface of the basin are analyzed.Then according to the data of rainfall flood process,calculated the characteristics of storm floods and analyzed their characteristics.(3)Analysis of runoff Production and Confluence Mechanisms in Typical Basins.On the basis of the analysis of rainfall and runoff characteristics,the runoff production patterns and confluence characteristics were identified.The study found that the composition of runoff changes in Jingle Station Control Basin,and the proportion of infiltration-excess runoff decreases,and the proportion of saturation-excess runoff increases.The Zuli River Basin is still dominated by infiltration-excess runoff,based on previous studies and analysis of underlying surface,it has been found that changes in the underlying surface have not resulted in major changes in the runoff production and confluence mechanism of the Zuli River Basin.(4)Analysis on the Changing Years and Causes of Runoff Production and Confluence Mechanisms in Typical River Basins.According to the double-accumulation curve and the eigenvalues trendency of runoff production and confluence,it was found that after 1998,the mechanism of the production and confluence of Jingle Station Control Basin changed significantly.And the flood volume is reduced by about 43%,the runoff coefficient is reduced by 50%,the peak flow rate is reduced by about 40%,and the flood peak delay is increased by 21.9%.It was found that due to the increase of forest coverage,groundwater discharge capacity,ground infiltration capacity,and water storage capacity in the river basin were increased,resulting in the changes of runoff production and confluence characteristics. |
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