Study On Snowmelt Erosion Of Hillslope In Snowmelt Period At Black Soil Region Of North East China

The northeast black soil area has the characteristics of slopes with gentle slope length.The soil erosion caused by snowmelt in spring is an important form of erosion in this area,especially in the sloping land planted on the ridge,the rills and breaks ridges caused by the snowmelt reult in runoff erosion.The ridges and other forms of broken have caused different degrees and different forms of damage to different slopes of the sloping farmland in the area.At present,the relevant researches in this area are mostly concentrated in the rainfall period.The research reports on the snowmelt period are relatively few,and the lack of basic research has greatly restricted the development of black land protection technology.In order to explore the soil erosion characteristics of sloping farm land during the snowmelt period,the influencing factors and erosion process of the sloping lands in this period are clarified.The paper analyzes the distribution of snow,the nature of snow,the process of snowmelt,the depth of thawing of surface soil and the distribution of rills in slope farmland through field in situ observation.And the content of the runoff ridge and other ridges,and then the characteristics of snowmelt erosion in the sloping farmland.The paper uses the nuclide tracer method to determine the long-term erosion results of various erosion camping forces on the slope surface,and compares the similarities and differences of the combination of snowmelt erosion and various erosion camping forces on different part of slopes,and further clarifies the characteristics of snowmelt erosion.By comparing the snow distribution and snow melting process in the typical measures of the “three lines of defense”,the mechanism and effect of typical measures on soil erosion control during the snowmelt period are clarified.By observing the snow distribution,snowmelt runoff,sediment concentration,erosion amount and thawing depth of the sloping farmland,the average snow depth increased from 20.9 cm to 25.7 cm from the bottom of the slope.The erosion time is concentrated on 4 d.The observation of the snowmelt process shows that the correlation between snowmelt runoff and sediment concentration is not significant,but it has a significant relationship with the amount of erosion.It shows the characteristics of the erosion process of snowmelt erosion which is different from the rainfall erosion.According to the correlation between thawing depth and sediment concentration and soil erosion,it is found that the thawing depth and the erosion amount are linearly fitted,indicating that the thawing depth is one of the important factors affecting the erosion amount during the snowmelt period.The unthawed soil layer is the important control effect of snowmelt runoff and sediment.The analysis of the lag relationship between daily runoff and sediment concentration suggests that the sediment collected in the lower part of the slope mainly originates from the confluence of the middle and lower slopes of the slope due to the difference between the snow distribution and the snowmelt production and convergence.In the concave slope section,the snow-sand erosion sediment in the middle-uphill section has a limited migration distance during a snowmelt runoff process.The observation of rills caused by snowmelt erosion in slope farmland shows that the shape of rills during snowmelt can be divided into three types: ridge,ridge and composite.Different ridges broken position reflect the erosion characteristics and erosion degree of snowmelt runoff at different slopes.For the sloping land cultivated by the horizontal ridge,the ridge-type rill is the most common in all slopes,and it is also the rill pattern with the most erosion.The amount of rill erosion increases first and then decreases along the slope,and the morphological development features are in the form of narrow and deep ridges along the ridge and erosion ridges.The tracer observation of the sloping farmland in the none soil and water conservation protection measures shows that the composite camp erosion results are characterized by the strongest slope erosion,which weakens to the slope and increases sharply under the slope.The gully erosion during the snowmelt period is more distributed in the upslope section.The concavity and confluence of the snowmelt runoff in the middle and lower sections of the slope has the ability to break through the ridges more strongly,which has a greater potential risk to the occurrence of gully erosion.Calculating the route of the snowmelt runoff erosion,the average slope degree decreases from 37.1° to 22.7° with the change of the slope length and the increase of the confluence,reflecting that the runoff scouring ability is gradually stronger.It can be seen that the form of soil erosion during the snowmelt period is characterized by rill erosion in the uphill section and concentrated erosion of the snowmelt runoff in the middle and lower slopes.Finally,the influence of the "three lines of defense" typical measures on the snow distribution and the interception effect of the snowmelt runoff are compared.The results show that the "three lines of defense" water conservation measures affect the snowmelt runoff by affecting the distribution of snow and the process of snowmelt.Preventing runoff scouring has a significant effect.The main innovation of the thesis is that through the observation of the field runoff sediment process in the field,it is found that the snowmelt runoff erosion is different from the rainfall runoff erosion.The snowmelt erosion is observed in the field,and found that the snowmelt runoff is further clarified on different slopes.The effect of snowmelt erosion is unique comparing to multiple external forces erosion;in comparison with the snowmelt process of typical measures,the snowmelt period measures are discussed by analyzing the snow distribution and runoff interception effects.