Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

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Vol15 No.4: 738-751

Title】Effects of slope gradient on runoff from bare-fallow purple soil in China under natural rainfall conditions

Author】KOMATSU Yoshitaka1*; KATO Hiroaki2; ZHU Bo3; WANG Tao3; YANG Fan1; RAKWAL Randeep4; ONDA Yuichi2

Addresses】1 Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan; 2 Center for Research in Isotopes and Environmental Dynamics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan; 3 Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, No. 9, Block 4, Renminnan Road, Chengdu 610041, China; 4 Faculty of Health and Sport Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8574, Japan

Corresponding author】KOMATSU Yoshitaka

Citation】Komatsu Y, Kato H, Zhu B, et al. (2018) Effects of slope gradient on runoff from bare-fallow purple soil in  China under natural rainfall conditions. Journal of Mountain Science 15(4). https://doi.org/10.1007/s11629-017-4714-3

DOI】10.1007/s11629-017-4714-3

Abstract】Purple soil is highly susceptible for overland flow and surface erosion, therefore understanding surface runoff and soil erosion processes in the purple soil region are important to mitigate flooding and erosion hazards. Slope angle is an important parameter that affects the magnitude of runoff and thus surface erosion in hilly landscapes or bare land area. However, the effect of slope on runoff generation remains unclear in many different soils including Chinese purple soil. The aim of this study was to investigate the relationship between different slope gradients and surface runoff for bare-fallow purple soil, using 5 m × 1.5 m experimental plots under natural rainfall conditions. Four experimental plots (10°, 16°, 20° and 26°) were established in the Yanting Agro-ecological Experimental Station of Chinese Academy of Science in central Sichuan Basin. The plot was equipped with water storage tank to monitor water level change. Field monitoring from July 1 to October 31, 2012 observed 42 rainfall events which produced surface runoff from the experimental plots. These water level changes were converted to runoff. The representative eight rainfall events were selected for further analysis, the relationship between slope and runoff coefficient were determined using ANOVA, F-test, and z-score analysis. The results indicated a strong correlation between rainfall and runoff in cumulative amount basis. The mean value of the measured runoff coefficient for four experimental plots was around 0.1. However, no statistically significant relationship was found between slope and runoff coefficient. We reviewed the relationship between slope and runoff in many previous studies and calculated z-score to compare with our experimental results. The results of z-score analysis indicated that both positive and negative effects of slope on runoff coefficient were obtained, however a moderate gradient (16°-20° in this study) could be a threshold of runoff generation for many different soils including the Chinese purple soil.

Keywords】Surface runoff; Slope gradient; Natural rainfall; Purple soil; Runoff plot