| The phenomenon of water and soil loss in the Three Gorges reservoir area is prone to occur frequently,and the soil erosion in small watersheds is often a difficult problem in the ecological environment protection in the Three Gorges reservoir area.Due to the complex composition of soil types in small watersheds,the water and soil loss model in the watersheds cannot be calculated according to the hydraulic erosion model of single slope soil.In addition,under the action of rainfall,the exposed soil in the small watershed will be affected by long-term rainfall erosion,and the composition and structure of the surface soil will change,which is often manifested as discontinuous gradation of the surface soil and low content of fine particles.In serious cases,it will further lead to landslides,debris flows and other disasters.To sum up,it is necessary to study the law of runoff and sediment yield of soil in small watershed under the action of rainfall for supplementing the corresponding scientific theory and guiding the practical application of the project.Fu Gou small watershed in Wan Zhou District belongs to the Yangtze River basin,and the soil erosion type is mainly composed of hydraulic erosion,which has the typical characteristics of water and soil loss in the Three Gorges reservoir area.Therefore,this paper takes the soil in the natural slope runoff plots under different land use conditions in Fu Gou small watershed of Wan Zhou District,Chongqing as the research object.Physical tests such as mechanical composition,chemical tests such as organic matter content,and soil erosion tests under artificial simulated rainfall were carried out on different types of soil with different physical and chemical properties.On this basis,the study on the law of runoff and sediment yield of soil in small watershed under different rainfall intensity and slope combinations was carried out.Based on the linear regression equation,the soil and water loss model of soil in small watershed under rainfall was established.Finally,the hydrodynamic characteristics of slope surface flow under different rainfall intensity and slope combinations were analyzed.The research conclusions of this paper are as follows:(1)The Fu Gou small watershed in Tian Cheng Street,Wan Zhou District was selected as the research object to conduct a detailed survey of the topography,climate and meteorology,water physical properties,soil conditions,etc.on the site,and the local vegetation,land,landform,elevation and other data were obtained through UAV.The typical soil samples in Fu Gou small watershed were selected for routine indoor physical tests,and the basic physical data of soil samples in the region were obtained.It lays a foundation for the subsequent analysis of sediment and runoff yield and hydrodynamic characteristics of this type of region.(2)The indoor artificial simulation test was conducted to study the sediment and runoff yield of soil samples in Fu Gou small watershed under different rainfall intensity and slope combinations.It is found that the discharge and sediment yield are closely related to the rainfall intensity and slope.In addition,there is a critical slope where the sediment yield and sediment yield reach the extreme value.On this basis,the linear regression equation of sediment and runoff yield under artificial simulated rainfall is established,and the calculation method of critical slope is proposed.(3)The hydrodynamic parameters such as average velocity of slope,hydraulic radius,Reynolds number,Froude number,Darcy-Wesbach resistance coefficient and so on are selected to analyze the hydrodynamic characteristics.According to the hydrodynamic parameters,the flow pattern of slope flow is laminar flow,the flow state of slope flow is slow flow,and the resistance coefficient of purple soil is greater than that of lime(rock)soil.Through the correlation analysis between the hydrodynamic parameters and the average sediment yield,the correlation between the hydrodynamic parameters of each soil sample was obtained. |
PDF Full Text Request