Erosion and sediment particle sorting characteristics of sand-covered loess slope during thawing period
SU Yuanyi1,2, ZHANG Yang3, YANG Zhi4, LI Peng1,2, LI Zhanbin1,2, WANG Tian1,2, ZHANG Naichang5
1. State Key Laboratory of Eco-hydraulic Engineering in Arid Area, Xi'an University of Technology, 710048, Xi'an, China; 2. Key Laboratory of National Forestry Administration on Ecological Hydrology and Disaster Prevention in Arid Regions, 710048, Xi'an, China; 3. Agriculture Rural and Water Bureau, Administration Committee of Xi'an International Trade & Logistics Park, 710026, Xi'an, China; 4. Ningxia Hui Autonomous Region Soil and Water Conservation Monitoring Station, 750002, Yinchuan, China; 5. Northwest Engineering Corporation Limited, 710065, Xi'an, China
Abstract:[Background] Soil erosion in the wind water erosion crisscross zone of the Loess Plateau in spring thawing period is usually the result of water erosion, wind erosion and freeze-thaw erosion. However, the problem of soil erosion caused by joint action is far more than the harm of single action erosion itself. The superposition of different erosion types will lead to great changes in soil erosion.[Methods]In order to explore the influence of thawing water erosion on sand-covered loess slopes during the thawing period, 4 types of non-frozen bare slope (U0), non-frozen sand-covered slope (U1), frozen-soil bare slope (F0), and frozen-soil sand-covered slope(F1) were selected. The slope surface (with a thickness of 1 cm of sand cover) was the research object. A 2 m long slope surface and a flow rate of 1 L/min were designed to conduct an indoor water discharge scour test in order to understand the slope erosion process and the separation characteristics of sediment particles.[Results]1) The initial runoff generation time of the frozen-soil slopes (F0 and F1) was significantly shorter than that of the non-frozen slopes (U0 and U1), and the initial runoff generation time of the sand-covered slopes (U1 and F1) was significantly later than that of the bare slopes (U0 and F0).2) The average runoff and sediment yield rates of each slope were U0 < U1 < F0 < F1, and U0 < U1 < F0 < F1. The average runoff and sediment yield rates of U0 were significantly different from those of U1, F0 and F1 (P<0.05). 3) The average value of mean weight diameter (MWD) of sediment particles on each slope was as follows:Loess substrate < F0 < U0 < F1 < U1 < Sandy soil substrate. During the experiment, MWD of the bare slopes fluctuated little with the extension of runoff generation time, and MWD of the sand-covered slope increased and decreased significantly in two processes. Under the condition of erosion, sand and coarse silt were more easily carried away by runoff, and sand was more easily eroded on the sand-covered slopes, while coarse silt was more easily eroded on the bare slopes.[Conclusions]Sand cover on slope results in the delay of the initial runoff generation time, and the delay effect is more obvious with the increase of sediment cover thickness. Froze soil will significantly reduce the initial runoff generation time on the slope. Froze soil will break large soil particles, resulting in the increase of fine particles on the slope.
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