工程堆积体坡面植物篱的控蚀效果及其机制研究

工程堆积体极易产生水土流失,是生产建设项目水土流失防治的重点。为探明工程堆积体植物篱控蚀效果和机理,通过野外模拟径流冲刷试验,该文采用35、45、55 L/min 3种放水流量,对24°、28°、32°三种坡度的植物篱(H)及裸露对照小区(C)堆积体边坡(20 m×5 m标准监测小区)进行模拟放水冲刷试验,选取产沙率、径流含沙量、减沙量、径流挟沙力、剪切力、剥蚀率和径流功率等因子对堆积体坡面植物篱的控蚀效果及其机理进行分析。结果表明:堆积体侵蚀时间段集中在产流中后期(10~32 min),侵蚀位置主要在坡面中上段(0~10 m),植物篱具有10%~45%的减沙效益,其控蚀能力与冲刷历时之间存在二次函数的关系,临界时间随坡度和流量的增加而提前;植物篱坡面产流后期径流含沙量超过裸坡,这与其在侵蚀过程中的"源-汇"转变有关;植物篱可降低坡面土壤剥蚀率,提高坡面的临界剪切力和临界径流功率,能抑制细沟向坡面下部的发育,基于径流功率,其可蚀性参数(3.58 g/(N·m))大于对照坡面的可蚀性参数(2.83 g/(N·m))。研究结果可为坡面植物篱的合理利用提供一定的理论支撑,也能为工程堆积体措施条件下土壤侵蚀预报模型的建立提供部分参数支持。

Erosion resistance effects and mechanism of hedgerows in slope of engineering accumulation

Engineering accumulation body generated during the process of engineering construction has a unique soil composition and complex underlying surface. This sort of deposit is characterized by weak anti-scour ability attributed to the surface structure of soil loss, loose soil, and plant roots and organic matter deficiency, which may result in the runoff conditions easily causing severe soil erosion. Engineering accumulation body is prone to soil and water loss, which is the emphasis of water and soil conservation in production and construction project. As an effective soil and water conservation measure, hedgerows have been widely used in various types of arable lands. In the present study, hedgerows are adopted to improve the erosion resistance of the slope by runoff scouring tests. The hydrodynamic characteristics are a premise and foundation to understand erosion processes on engineering accumulation body under the condition of hedgerow measure. Thus, a series of studies were conducted for the simulation of runoff erosion process in order to reveal the relationships of main hydrodynamic parameters, such as runoff velocity, depth, flow shear stress, stream power and other relevant parameters, and to explore the erosion control mechanisms of hedgerow on engineering accumulation slope. The study area is located at the Changwu Agricultural Ecological Experimental Station on the Loess Plateau (35°14′24.5″N, 107°40′21.2″E). The established plot was 20 m long and 5 m wide, with 0.5 m thickness of soil generated from slope excavation. There were 3 flow discharges (35, 45, 55 L/min) and 3 slopes (24°, 28°, 32°), and a hedgerow plot was set for each slope and at the same time a bare slope was set as the control; in the hedgerow plot, 4 hedgerows were uniformly arranged from top down. The distance between the highest hedgerow and the upper edge of the slope is 3 m, and the hedgerow spacing is 4 m. A total of 18 field trials were designed in this study. The results showed that the erosion time of the engineering accumulation body focused on the late period of runoff (10-32 min), and the main erosion position was in the middle-upper slope (0-10 m). The cumulative sediment yields of hedgerows plot are reduced by 10%-45% compared to control plot. The relationship between erosion control capability and scouring duration could be stated with quadratic function in which critical time became more early with the increase of slope and flow discharge. In later stage, the sediment concentration in runoff of hedgerows plot exceeded control plot, which could be related to transformation of hedgerows between source and sink. Hedgerows reduce soil detachment rate, increase critical shear stress and critical stream power, and curb rill evolution to develop toward the lower slope. Based on the runoff power, hedgerow slope erodibility (3.58 g/(N·m)) was higher than that of the control surface erodibility parameter (2.83 g/(N·m)). Different slopes and rainfall intensities under the condition of engineering accumulation of hedgerows have good runoff and sediment reduction effect, which may provide a theoretical reference for the rational use of slope protection measures. Meanwhile, fitting the relations between hydrodynamic parameters and soil erosion rate, rill erodibility and critical runoff power can also provide basic parameters for the study on soil erosion on engineering accumulation slope under hedgerow.