| Gravity erosion is one of the main forms of soil and water loss in the Loess Plateau.However,it is difficult to carry out quantitative and continuous observation due to the unpredictable nature of gravity erosion in timing and location,which makes the process-based data lack.Therefore,the research of gravity erosion need further study.A method to observe gravity erosion using fixed light was proposed,which was applied to artificial rainfall simulation experiments of the root-soil composite model on gully wall.The objectives of this study were to study the characteristics of gravity erosion on gully wall,and to analyze the effect of vegetation on gravity erosion.The main results are as follows:(1)A method to observe gravity erosion using fixed light was proposed,which could be used to dynamically observe and quantitatively analyze gravity erosion on gully wall.A set of equidistant laser lines was generated by MX-2016-G topography meter,which could give contour lines to slope,and the pattern was recorded by digital camera with sighting direction strabismus to the laser planes.Then,the 3D geometric shape of the slope was digitally reconstructed,and then the related parameters,such as the amount,could be determined.(2)A treatment method for complex landslide and combined avalanche was proposed,and the characteristics of gravity erosion on gully wall were studied.When calculating the total amount of gravity erosion in the rainfall events,the complex landslide or combined mass failure was counted into the amount of total gravity erosion as a whole,and the amount of single avalanche and landslide included in it must be deducted.When analyzing the proportion of various mass failure in the total amount of gravity erosion in the rainfall events,the avalanche and landslide in the combined mass failure were counted into the total amount of avalanche and landslide in each rainfall event respectively,and the complex landslide was counted into the total amount of the landslide in each rainfall event.The complex landslide and the combined mass failure occurred three times during the rainfall,the total amount of them was 38.73×10~3 cm~3,which accounted for 7%of the total gravity erosion of the root-soil composite model.(3)The effect of vegetation on gravity erosion of gully wall was studied by comparing the rainfall simulation experiments of the vegetational land model with the bare land model under the condition of slope degree 70°and height 1.5 m.The result showed that:1)the vegetation on gully wall had a certain influence on the total amount of gravity erosion under rainstorm.The average amount of gravity erosion in vegetational land was decreased by 15%compared with that in bare land after 5 groups of rainfall in this experiment.2)the vegetation on gully wall had a different influence on different types of gravity erosion.The data was got under the same underlying surface topographic conditions after the same 5 groups of rainfall.The average amount of avalanche and mudslide in vegetational land was decreased by 58%and 69%compared with that in bare land,and the maximum amount of individual avalanche in vegetational land was decreased by 66%compared with that in bare land.The average amount of landslide in vegetational land was increased by 153%compared with that in bare land,and the maximum amount of individual landslide in vegetational land was increased by22%compared with that in bare land.3)the effect of vegetation on gravity erosion was the result of many factors.The root system of vegetation had the function of"reinforcing"the soil,which may reduce the amount of gravity erosion in vegetation group;and the weight of the vegetation was the factor that intensifying the gravity erosion;in addition,the soil permeability was increased by vegetation roots broken,which could intensify landslide.The results had some reference value for analyzing the mechanism of gravity erosion. |
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