Effect of mining subsidence on soil erosion in mountainous area of the Loess Plateau

Abstract: Mining subsidence reshapes the surface structure and morphology in a mountainous area. However, surface deformation and movement rules in a mountainous area influenced by mining subsidence are quite different from rhose in a flat area, which result mainly from the superposition of ground subsidence and surface moving caused by slippage. Research about change of the soil erosion caused by the above phenomenon is very necessary. In this paper, based on mining subsidence rules and models, a DEM of the subsidence area was constructed referring to the subsidence parameters in the research area. On this basis, the soil erosion changes of three major factors-slope, slope length factor, and vegetation coverage factor caused by mining subsidence in a revised universal soil loss equation in mountainous area were measured for the first time, and the other three parameters that were not disturbed by mining in a revised universal soil loss equation were calculated according to relevant research studies. Finally, soil erosion quantity in the research area was calculated. The results showed that: From 2001-2010, the average slope decreased by 0.025°, caused by mining in the study area, average slope length factor decreased by 0.139, the area that soil erosion unchanged，reduced and increased in subsidence area was respectively3.083,3.412 and 4.707km2, and the area in which soil erosion reduced and increased out of the subsidence area was respectively 0.143 and 0.023km2, the totally soil erosion amount decreased by 78426.95t, 689.892t/km2 in average per year, which was mainly caused by the decrease of slope length and slope. The impact on soil erosion affected by mining subsidence in the upstream area will influence in part the area of the watershed where outside the mining area, and ending in the position where the slope length is ended, because mining subsidence changes the flow direction, and furthermore, flow length is changed as a result. In the basin of the subsidence area, the subsidence value was basically the same, slope and flow direction doesn't change. Nevertheless, the physical and chemical properties of the soil are changed, the vegetation was injured, and the vegetation cover factor became the main factor influencing soil erosion in this region. Soil erosion affected by mining subsidence in a mountainous area is quite different from flat ground. On flat ground, mining subsidence will absolutely intensify soil erosion except in the subsidence basin, because the slope and slope length are increased, but in a mountainous area, there is no absolute positive or negative influence, and the result is closely related to the original landform, subsidence magnitude, and location. The research conclusions can provide a scientific basis for soil erosion predictions in a mountainous mining area.