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Steady nonuniform shallow flow within emergent vegetation

Publication ,  Journal Article
Wang, WJ; Huai, WX; Thompson, S; Katul, GG
Published in: Water Resources Research
December 1, 2015

Surface flow redistribution on flat ground from crusted bare soil to vegetated patches following 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 downstream boundaries mimicking the nonuniformity encountered in nature. In natural settings, such H(x) variations 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 (Cd) 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 Cd must be varying in x beyond what a local or bulk Reynolds number predicts. Inferred Cd(x) from the flume experiments exhibited a near-parabolic shape most peaked in the densest canopy cases. The outcome of such Cd(x) variations is then summarized in a bulk resistance formulation that may be beneficial to modeling runon-runoff processes on shallow slopes using SVE.

Duke Scholars

Published In

Water Resources Research

DOI

EISSN

1944-7973

ISSN

0043-1397

Publication Date

December 1, 2015

Volume

51

Issue

12

Start / End Page

10047 / 10064

Related Subject Headings

  • Environmental Engineering
  • 4011 Environmental engineering
  • 4005 Civil engineering
  • 3707 Hydrology
  • 0907 Environmental Engineering
  • 0905 Civil Engineering
  • 0406 Physical Geography and Environmental Geoscience
 

Citation

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Wang, W. J., Huai, W. X., Thompson, S., & Katul, G. G. (2015). Steady nonuniform shallow flow within emergent vegetation. Water Resources Research, 51(12), 10047–10064. https://doi.org/10.1002/2015WR017658
Wang, W. J., W. X. Huai, S. Thompson, and G. G. Katul. “Steady nonuniform shallow flow within emergent vegetation.” Water Resources Research 51, no. 12 (December 1, 2015): 10047–64. https://doi.org/10.1002/2015WR017658.
Wang WJ, Huai WX, Thompson S, Katul GG. Steady nonuniform shallow flow within emergent vegetation. Water Resources Research. 2015 Dec 1;51(12):10047–64.
Wang, W. J., et al. “Steady nonuniform shallow flow within emergent vegetation.” Water Resources Research, vol. 51, no. 12, Dec. 2015, pp. 10047–64. Scopus, doi:10.1002/2015WR017658.
Wang WJ, Huai WX, Thompson S, Katul GG. Steady nonuniform shallow flow within emergent vegetation. Water Resources Research. 2015 Dec 1;51(12):10047–10064.
Journal cover image

Published In

Water Resources Research

DOI

EISSN

1944-7973

ISSN

0043-1397

Publication Date

December 1, 2015

Volume

51

Issue

12

Start / End Page

10047 / 10064

Related Subject Headings

  • Environmental Engineering
  • 4011 Environmental engineering
  • 4005 Civil engineering
  • 3707 Hydrology
  • 0907 Environmental Engineering
  • 0905 Civil Engineering
  • 0406 Physical Geography and Environmental Geoscience