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首页> 外文期刊>Earth Surface Processes and Landforms: The journal of the British Geomorphological Research Group >Volumetric displacement of flow depth by obstacles, and the determination of friction factors in shallow overland flows
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Volumetric displacement of flow depth by obstacles, and the determination of friction factors in shallow overland flows

机译：障碍物影响水深的体积位移及浅水陆流的摩擦系数确定

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摘要

Large roughness elements such as stones or plant stems (obstacles) influence the depth of overland flows in two ways. The first effect is a dynamic one, involving frictional retardation of the flow and associated reduction in flow speeds. The second influence is static, and arises from the upward volumetric displacement of flow depth because of the submerged volume of the obstacles. Depending upon the distribution of submerged obstacle volume with height above the soil surface, the proportion of he flow volume occupied (and so, the perturbation of flow depth arising from volumetric displacement) can vary irregularly or systematically with flow stage. Furthermore, the amount of volumetric displacement of flow depth would vary among surfaces carrying different cover fractions of identical obstacles. Consequently, estimates of the change in friction factors arising from the drag on flow traversing varying obstacle cover fractions are confounded with the parallel shift volumetric displacement. To understand the true frictional drag arising from obstacles, a correction must be made for the volumetric displacement. A method for making this correction is outlined. New laboratory experiments provide precise observations of depths and friction coefficients in laminar flows passing fields of regular obstacles. After making the proposed correction for volumetric displacement, increases of 40 to 75 per cent in the derived value of the Darcy-Weisbach friction factor, f, are found for an obstacle cover of 20 per cent. Many published studies of friction coefficients in shallow overland flows, such as those on stone-covered dryland soils, involve larger obstacle cover fractions, and evidently involve the significant confounding effect of volumetric displacement.
机译：诸如石头或植物茎（障碍物）之类的大粗糙度元素以两种方式影响陆上水流的深度。第一个效果是动态的，涉及流动的摩擦滞后以及相应的流速降低。第二个影响是静态的，并且由于障碍物的浸没而导致流动深度向上的体积位移而产生。根据淹没障碍物的体积随土壤表面上方高度的分布，所占流量的比例（因此，由体积位移引起的流量深度扰动）会随流量阶段不规则或系统地变化。此外，在带有相同障碍物的不同覆盖分数的表面之间，流动深度的体积位移量将变化。因此，由阻力的变化引起的摩擦因数变化的估计值与平行移动的容积位移相混淆。为了理解由障碍物引起的真正的摩擦阻力，必须对体积位移进行校正。概述了进行该校正的方法。新的实验室实验提供了对通过规则障碍物的层流中的深度和摩擦系数的精确观察。在对容积位移进行建议的校正之后，Darcy-Weisbach摩擦系数f的导出值增加了40％至75％，而障碍物覆盖率为20％。许多公开发表的关于浅层地面流动的摩擦系数的研究，例如那些在石头覆盖的旱地土壤上的摩擦系数，都涉及较大的障碍物覆盖率，并且显然涉及体积位移的显着混杂效应。

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