Steady nonuniform shallow flow within emergent vegetation [electronic resource]

• Ngôn ngữ: eng
• Ký hiệu phân loại: 512.5 Linear algebra
• Thông tin xuất bản: Washington, D.C. : Oak Ridge, Tenn. : United States. Dept. of Energy. Office of Science ; Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy, 2015
• Mô tả vật lý: Size: p. 10047-10064 : , digital, PDF file.
• Bộ sưu tập: Metadata
• ID: 260998
• Chủ đề: 1. 54 environmental sciences; 2. 60 applied life sciences

Tóm tắt

 Surface flow redistribution on flat ground from crusted bare soil to vegetated patches follow-ing intense rainfall events elevates plant available water above that provided by rainfall. The significance of this surface water redistribution to sustaining vegetation in arid and semiarid regions is undisputed. What is disputed is the quantity and spatial distribution of the redistributed water. In ecohydrological models, such nonuniform flows are described using the Saint-Venant equation (SVE) subject to a Manning roughness coefficient closure. To explore these assumptions in the most idealized setting, flume experiments were conducted using rigid cylinders representing rigid vegetation with varying density. Flow was induced along the streamwise x direction by adjusting the free water surface height H(x) between the upstream and down-stream boundaries mimicking the nonuniformity encountered in nature. In natural settings, such H(x) varia-tions arise due to contrasts in infiltration capacity and ponded depths during storms. The measured H(x) values in the flume were interpreted using the SVE augmented with progressively elaborate approximations to the roughness representation. The simplest approximation employs a friction factor derived from a drag coefficient (C<
 sub>
 d<
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 ) for isolated cylinders in a locally (but not globally) uniform flow and upscaled using the rod density that was varied across experiments. Comparison between measured and modeled H(x) suggested that such a ??naive?? approach overpredicts H(x). Blockage was then incorporated into the SVE model calculations but resulted in underestimation of H(x). Biases in modeled H(x) suggest that C<
 sub>
 d<
 /sub>
  must be varying in x beyond what a local or bulk Reynolds number predicts. Inferred C<
 sub>
 d<
 /sub>
 (x) from the flume experiments exhibited a near-parabolic shape most peaked in the densest canopy cases. The outcome of such C<
 sub>
 d<
 /sub>
 (x) variations is then summarized in a bulk resistance formulation that may be beneficial to modeling runon-runoff processes on shallow slopes using SVE.