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Impact of Vegetation‐Generated Turbulence on the Critical, Near‐Bed, Wave‐Velocity for Sediment Resuspension
Author(s) -
Tang Caihong,
Lei Jiarui,
Nepf Heidi 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 - 10.1029/2018wr024335
Subject(s) - turbulence , wave shoaling , amplitude , turbulence kinetic energy , critical ionization velocity , mechanics , sediment , breaking wave , volume fraction , physics , wave propagation , geology , optics , geomorphology , longitudinal wave , mechanical wave , thermodynamics
Laboratory experiments examined the impact of model vegetation on wave‐driven resuspension. Model canopies were constructed from cylinders with three diameters ( d = 0.32, 0.64, and 1.26 cm) and 12 densities (cylinders/m 2 ) up to a solid volume fraction ( ϕ ) of 10%. The sediment bed consisted of spherical grains with d 50 = 85 μm. For each experiment, the wave velocity was gradually adjusted by increasing the amplitude of 2‐s waves in a stepwise fashion. A Nortek Vectrino sampled the velocity at z = 1.3 cm above the bed. The critical wave orbital velocity for resuspension was inferred from records of suspended sediment concentration (measured with optical backscatter) as a function of wave velocity. The critical wave velocity decreased with increasing solid volume fraction. The reduction in critical wave velocity was linked to stem‐generated turbulence, which, for the same wave velocity, increased with increasing solid volume fraction. The measured turbulence was consistent with a wave‐modified version of a stem‐turbulence model. The measurements suggested that a critical value of turbulent kinetic energy was needed to initiate resuspension, and this was used to define the critical wave velocity as a function of solid volume fraction. The model predicted the measured critical wave velocity for stem diameters d = 0.64 to 2 cm. Combining the critical wave velocity with an existing model for wave damping defined the meadow size for which wave damping would be sufficient to suppress wave‐induced sediment suspension within the interior of the meadow.