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Impact of Vegetation on Bed Load Transport Rate and Bedform Characteristics
Author(s) -
Yang J. Q.,
Nepf H. M.
Publication year - 2019
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2018wr024404
Subject(s) - bedform , flume , bed load , vegetation (pathology) , sediment transport , geology , hydrology (agriculture) , sediment , ripple marks , volume (thermodynamics) , flux (metallurgy) , ripple , flow (mathematics) , environmental science , soil science , geomorphology , geometry , geotechnical engineering , materials science , medicine , physics , mathematics , pathology , quantum mechanics , voltage , metallurgy
The impacts of aquatic vegetation on bed load transport rate and bedform characteristics were quantified using flume measurements with model emergent vegetation. First, a model for predicting the turbulent kinetic energy, k t , in vegetated channels from channel average velocity U and vegetation volume fraction ϕ was validated for mobile sediment beds. Second, using data from several studies, the predicted k t was shown to be a good predictor of bed load transport rate, Q s , allowing Q s to be predicted from U and ϕ for vegetated channels. The control of Q s by k t was explained by statistics of individual grain motion recorded by a camera, which showed that the number of sediment grains in motion per bed area was correlated with k t . Third, ripples were observed and characterized in channels with and without model vegetation. For low vegetation solid volume fraction ( ϕ ≤ 0.012), the ripple wavelength was constrained by stem spacing. However, at higher vegetation solid volume fraction ( ϕ =0.025), distinct ripples were not observed, suggesting a transition to sheet flow, which is sediment transport over a plane bed without the formation of bedforms. The fraction of the bed load flux carried by migrating ripples decreased with increasing ϕ , again suggesting that vegetation facilitated the formation of sheet flow.