Change Of Soil Surface Microrelief And Their Effects On Soil Erosion In Purple Soil Area

Soil surface microrelief is one of the important factors that affect the slope erosion process, it influenced people’s understanding of water erosion mechanism and the reasonable layout of conservation tillage measures due to the randomness and vagueness of topographical distribution in erosion process. Therefore, this paper took the purple soil in Hilly Area of Central Sichuan Basin as the research object, used the method of combining indoor artificial rainfall simulation experiment and GIS technology, integrated soil erosion theories and fractal method, researched the variation characteristics of microrelief under different rainfall regimes, slopes and erosion stages, investigated the effects of microrelief on flow confluence process, surface runoff and sediment yield, the results were beneficial to elucidate the change of soil surface roughness, and provided theory basis for understanding the mechanism of water erosion and soil erosion prediction further. The main results were as bellowing:(1)The elevation reduced area increased from 48.56% to 63.14% under increasing rainfall series, and decreased from 38.59% to 35.12% under decreasing rainfall series. The variation range of soil surface roughness in whole slope were-0.25%,1.51% and 2.80% for the former,2.30%,1.97% and 1.97% for the latter. The width of fractal dimension AD and singular index △a increased gradually under increasing rainfall series, and the opposite trend expressed under decreasing rainfall series./(a) max were 2.1559,△f(a) were 0 in two rainfall patterns.(2)The surface runoff density decreased from 19.95 to 19.80 m m-2 under increasing rainfall condition, AD of flow path decreased from 1.1551 to 0.9662, runoff density increased from 21.61 to 22.57 m m’2 under decreasing rainfall condition, and △D increased from 1.1799 to 1.2554. The variation range of △a of flow path were 11.88%,-18.09% and -7.78% during increasing rainfall series,-10.45%、18.83% and 0.01% during decreasing rainfall series. The total runoff of increasing rainfall series was 5.82% higher than decreasing rainfall series, but its sediment yield was 35.83% higher than latter. The influence of rainfall regimes on runoff was lower than the influence on sediment yield. Predicting runoff and sediment well by using multifractal parameters and soil surface roughness index.(3)In single rainstorm, the elevation increased area were more than 70% in 10° and 15° plots, when the slope was 20°, the elevation reduced area achieved 72.11%. With the increase of slope, the variation range of soil surface roughness were-3.71%,-5.29%and-1.72%. When the slope was 10° and 15°,△D,△a and △f(a) both increased after rain, topography tended to smooth, the opposite trend expressed in 20° plot. The flow sinuosity decreased with the increase of slope, the stability of stream network aggravated. After rainfall, runoff density increased and flow defused in 10° and 15° plots, the 20° plot had opposite change tendency too. When slope were different, there had no obvious relationship between flow path and microrelief based on multifractal methods. In three slopes, the total runoff were 34.54,31.82 and 38.65 L m 2, the sediment yield were 0.571, 0.696 and 0.821 kg m-2. Correlation analysis results show that, in the same condition of rainfall event, the ground runoff was significantly influenced by microrelief, but sediment was mainly affected by slope.(4)In splash erosion, soil surface roughness both decreased in different slope; In sheet erosion, the variation range of soil surface roughness was-1.39%,0.46% and 2.98% in 10°,15° and 20° plot respectively; In rill erosion, it was 0.74%,2.62% and 7.95% respectively. The soil surface roughness was more stable in upslope than that in midslop and downslope. Multifractal characteristics of topography were different between different erosion stages. On the whole, the special distribution and morphological of microrelief changed very little under 10° treatment;The special different increased significantly in sheet erosion under 15° treatment; The special different with the development of erosion stages under 20° treatment, and the topography tended to rough. Correlation analysis results show that △f(a) of flow path was significant positive correlation with △f(a) of microrelief in sheet and rill erosion.(5) With the increase of slope, the upslope splash erosion enhanced first and then became lower, downslope splash erosion and total splash erosion were enhanced gradually, splash erosion was mainly affected by slope, but little affected by initial roughness. In sheet erosion, soil surface roughness was 10°>15°>20°, the change of runoff and sediment were same with roughness. In rill erosion, the change of runoff was contrary to the change of soil surface rougness, sediment yield was little affected by initial roughness.