Fractal features of soil particle size distribution in layered sediments behind two check dams: Implications for the Loess Plateau, China
Abstract The layered sediment deposited behind a check dam can provide useful information about soil erosion processes in the dam controlled area. This study aims to evaluate the possible fractal nature of layered sediments behind check dams, assessing whether fractal dimension can serve as a feasible index for evaluating the impact of land use types on the area controlled by the check dam. Fractal dimension measurement was employed to analyze the features of soil particle size distribution (PSD) for different layered sediments of the Shipanmao and Zhangshan check dams in the Dalihe River Basin of the Loess Plateau, China. Results show that the predominant soil particle sizes of the sediment layers behind the Shipanmao and Zhangshan dams are silt clay CV for the coarse sand fraction is highest, followed by the fine sand and the silt clay size fractions. Larger soil particle sizes coincide with larger CV values. The fractal dimension D m of the PSD ranges from 2.111 to 2.219, and 2.144 to 2.447 for Shipanmao and Zhangshan, respectively. The D m values tend to increase and decrease for the layered sediments from top to bottom with some turning points. The turning points of D m are related to the trends of the soil PSDs in the adjacent sediment layers. Although D m has significant positive and negative correlations with the silt clay and the fine sand size fractions, respectively, no correlation with the coarse sand fraction was observed. Soil PSD is a more dominant factor affecting D m than the time lag between soil erosion and sediment deposition. Overall, D m decreased for Shipanmao during the deposition period (1972 1979) The total increment of the C factor in the universal soil loss equation and the soil erosion amount per rainfall erosivity were applied to analyze land use changes between 1972 and 1979 for the dam controlled area of the Shipanmao dam. The total increment of C during 1972 1979 was 0.021 and the soil erosion amount per rainfall erosivity was smaller in 1972 than in 1979, indicating desertification in the dam controlled area. In addition, the land use types prevalent in 1979 were more prone to soil loss than those in 1972. D m is a useful parameter to assess land use types and soil degradation processes in dam controlled areas of the Loess Plateau.