野外放水条件下坡面流水动力学特征

Hydrodynamic characteristics of surface runoff on field scour

坡面流是土壤侵蚀的主要动力因素之一,也是侵蚀泥沙搬运、农业面源污染的重要载体,为探讨坡面流水力学特征变化规律,本文通过径流小区放水冲刷试验,研究不同坡面覆盖和放水条件下坡面流水动力学特征。结果表明:坡面流雷诺数和弗劳德数受植被覆盖情况和坡面坡度的影响较小,受放水流量影响较显著。其中,坡面流入流断面雷诺数和弗劳德数随时间基本保持不变;出流断面雷诺数动态变化呈增加趋势,弗劳德数呈缓慢下降趋势,其动态变化幅度随植株密度增加而趋于平缓,植株布设方式对雷诺数和弗劳德数的动态变化影响较小。流量和植株密度增加会引起阻力系数增长,阻力系数随冲刷历时呈增长趋势,坡度和植株密度可以控制这种增长趋势。

Background Soil erosion harms the development of national economy. Water erosion is the most important form of soil erosion in China. Overland flow is the main driving force of water erosion and main carrier of sediment transport which is a key factor of water erosion. Reynolds number, Froude number and resistance coefficient of overland flow are important parameters reflecting overland flow characteristics. [ Methods ] To investigate mechanical properties of overland flow, the study on the dynamic changes of Reynolds number, Froude number and resistance coefficient with 3 plant density （0, 20, and 30 plants/m2）, 2 vegetation distributions （row arrangement and random arrangement）, two slopes （5° and 10°） and 3 scouring flow （1, 2, 3 m3/h） were studied by field scour simulation experiment. [ Results] The results showed that effect on Reynolds number of inflow section by plant coverage density and slope was not significant, and only effected by flow rate. Dynamic changes on Reynolds number of inflow section remained stable over time, while that in outflow section showed an increasing trend which was affected by plant density. And the increasing rate of dynamic changes in outflow section slowed down with the increase of the plant density, however, influence by plant arrangement was not significant. Compared to the inflow section, Reynolds number of outflow section was smaller, indicating that the kinetic energy of the overland flow reduced during scouring process. Froude number was both less than 1 in two observation section, which were slow flow. Froude number of inflow section only increased with flow rate increasing, and the influences on Froude number of inflow section by plant coverage density and slope were not significant. The same as Reynolds number of inflow section, Froude number of inflow section also remained stable over time. The dynamic change of Froude number in outflow section decreased with time slowly, which was effected by plant densiy significantly, and the influence on it by plant arrangement was not significant. The dynamic changes of Froude number leveled off even plant density increased. Effect on resistance coefficient by slope was not significant, which was effected by plant density and flow rate, and the influence of plant arrangement was not significant. Stepwise regression analysis on resistance coefficient showed that f = 2. 350t0.012q-3.178 c0.084, indicating that dynamic changes of resistance coefficient showed an increase trend that could be controlled by increase of slope and plant density. [ Conclusions] Dynamic changes of resistance coefficient on bare slope had greater increase rate than slopes covered by vegetation, and resistance coefficient changing with time tend to be gentle with the plant density increased. Meanwhile, change range of resistance coefficient in plant random arrangement slope was smaller than slope in plant row arrangement.