| 5·12 Wenchuan earthquake triggered a large number of landslides. It is estimated that there are over 197,000 landslide accumulation body. Most of these landslide accumulation body were Rock-soil aggregate (RSA), its loose structure, vegetation coverage is low, and widely distribute in the upper reaches of Minjiang River. On the one hand landslide accumulation body prone secondary disasters, destroying towns, roads, irrigation and other infrastructure, endangering the lives and property of local residents; the other hand under rainfall, runoff, earthquakes and other external force, landslide accumulation body vulnerable to soil erosion, not only cause great difficulties for ecological restoration, at the same time the loss of sediment into the river, reducing river water quality, threating ecological environment of the Minjiang River Downstream. It is visible that carrying out research work on landslide accumulation body is great significance for the reconstruction in earthquake area. We studied landslide accumulation body from the perspective of soil erosion in the wenchuan earthquake area and analysised landslide accumulation body slope soil erosion characteristics. This paper provided a reasonable basis for evaluating earthquake landslide accumulation body soil erosion hazards, while carrying out ecological restoration and for earthquake disaster zone governance laid a theoretical foundation.This paper selected landslide accumulation body as the research object in Wenchuan earthquake area. It applied soil erosion, soil science, hydrology theory. On the basis of field surveying, we understood the spatial distribution of landslide accumulation body in Wenchuan earthquake area and analysised the physical properties of the accumulation body. In the room using artificial rainfall, studied soil erosion law of landslide accumulation body and explored the influence of soil-rock ratio, rainfall intensity, slope on soil erosion. The main findings are as follows:(l)Landslide showed linear distribution in the study area, a larger number of landslide accumulation body in the east, widely distributed in the Minjiang River, most accumulation body altitude lower 2000m, landslide accumulation body distribution and spatial distribution of the local population has a certain similarity. Slope is mainly between 30°40°. Height ranged from a few meters to several hundred meters, the accumulation of more than 80% were between 10-150m. The differences of moisture profile are significant in the different layers of the accumulation body. The moisture content increased with increasing depth, increased multiples were 2.83,1.38,1.03. 0-10cm layer moisture content was significantly lower than non-landslide accumulation body surface, The moisture content of the other layers and non landslide accumulation body is insignificant compared to the corresponding layer. Soil content increased with increasing depth between different layers of the accumulation body, the amount of 0-10cm layer of soil content less than non-landslide accumulation body surface,10-20cm,20-30cm layer is greater than the corresponding layer of non-landslide accumulation body.10-20cm layer of soil content from its base to the top of the hill there is an increasing trend, For other layers, there was no significant change in the law of slope length. Grain composition was good in 10-20cm and 20-30cm of landslide accumulation body, other layers was not good. Particle size composition of different layers were moderate gravel (60-10mm), accounting for more than 50%. Most of soil particle composition was sand particles, accounting for about 70%.(2)On the condition of artificial rainfall, infiltration of accumulation body was different with soil-rock ratio varying. When ratio is 1:4 and three kinds of rain intensity, rainfall were all into the accumulation body. While ratio is 1:1 and 1:2, infiltration process were more consistent, infiltration rate continuously decreased with times, to a certain time to reach steady infiltration rate. The rule of steady infiltration rate was not obvious in different of soil and rock ratio and slope. Surface runoff increased with increasing rainfall intensity. When ratio is 1:4, there was no surface runoff. When ratio is 1:2, rainfall intensity is 1.0mm/min, there was also no surface runoff. It showed that there is a critical point of soil-rock ratio. When it smaller than the threshold, there is no runoff no matter how strong the rainfall intensity. When it greater than the threshold, if the rainfall intensity is small, there is also no runoff. The curves of sediment concentration were inconsistent over time under different conditions of rainfall intensity. Slope is 35° and ratio is 1:1, rainfall intensity is 1.5mm/min, the sediment concentration began to have an increasing trend, gradually decrease small. Under other conditions, sediment concentration increased with rainfall duration decreasing, but the magnitude of reduce was different. Averaged sediment concentration decreased with decreasing soil-rock ratio. The process of the rate surface sediment is divided into two phases:a rapid increase phase and fluctuations stage, the average production rate decreased with soil-rock ratio and rain intensity. The relationship between surface runoff and sediment yield over a period of time, cumulative runoff and sediment yield can be expressed by a power function, R2 is respectively between 0.8504-0.9848 and 0.9962-0.9993.(3)There is a peak that the process of interflow changes over time, but the peak duration is different with varying soil-rock ratio and rainfall intensity. It is represented by linear relationship between the cumulative runoff and time, R2 is 0.94 or more. The smaller soil-rock ratio, the greater average runoff. The concentration of runoff decreased with time, it is fast at the beginning, gradually it is more slowly. The relationship between the cumulative sediment yield of interflow and time is difference along with the soil-rock ratio varies. When soil-rock ratio is 1:1 and 1:2, the relationship is a function of logarithmic. When soil-rock ratio is 1:4, it is a function of linear. There is complex relationship between the period interflow and sediment yield, sediment yield increased with interflow at the beginning, then sediment yield decreased at a certain time. The relationship between cumulative runoff of interflow and sediment yield is the same as the surface runoff, it is represented by a function of power, R2 is ranged from 0.9086 to 0.9995.(4)The time of occurring surface runoff decreased with increasing rainfall intensity and increased with soil-rock ratio decreasing. There was no obvious regularity between the time of occurring interflow and soil-rock ratio and rainfall intensity. The time of occurring interflow were within 10min, and the time of occurring surface runoff shortest 2.7min, up to 38.9min. The time of surface runoff was longer than most of the time of occurring interflow. The amount of runoff increased with rainfall intensity increasing. On the different soil-rock ratio conditions, the contribution of surface runoff and interflow to the total runoff was different, when soil-rock ratio is 1:1 and 1:2, the rainfall intensity is 2.0 mm/min, the contribution of surface runoff greater than interflow, but when the rainfall intensity is 1.0mm/min, the contribution of interflow greater than surface runoff. When soil-rock ratio is 1:4, there was no surface runoff, the total amount of runoff came from interflow. Soil-rock ratio and slope have little effect on the amount of runoff. The contribution of interflow increased with the soil-rock ratio decreasing. The relationship between slope and contribution of the surface runoff and interflow was more complex. When soil-rock ratio is 1:1, the contribution of surface runoff increased with slope increasing. When soil-rock ratio is 1:2, the contribution of surface runoff decreased with slope increasing. The total amount of sediment increased with increasing rainfall intensity, the contribution of surface sediment and interflow sediment to the total amount of sediment was consistent with the law of runoff. The of the total amount of sediment decreased with soil-rock ratio decreasing, the contribution of surface sediment to the total amount of sediment increased with soil-rock ratio increasing. When soil-rock ratio is 1:1, the total yield of sediment increased with increasing slope. When soil-rock ratio is 1:2, the total yield of sediment tended to decrease with increasing slope. |
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