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Effects of bed roughness on boundary layer mixing and mass flux across the sediment‐water interface
Author(s) -
Reidenbach M. A.,
Limm M.,
Hondzo M.,
Stacey M. T.
Publication year - 2010
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 - 10.1029/2009wr008248
Subject(s) - flume , sediment–water interface , particle image velocimetry , boundary layer , geology , surface finish , mixing (physics) , mass flux , bed load , flux (metallurgy) , sediment , surface roughness , turbulence , materials science , geotechnical engineering , sediment transport , hydrology (agriculture) , geomorphology , flow (mathematics) , mechanics , composite material , physics , quantum mechanics , metallurgy
Fine‐scale measurements of boundary layer flow and solute transport were conducted within a laboratory flume to determine how bed topography influences mixing and mass transport at the sediment‐water interface. Three different bed topographies were examined, with roughness composed of sand, gravel, or cobbles. Fluorescein dye, used as a dissolved tracer, was injected into the flow, and concentration and velocity were simultaneously measured using a combined planar laser‐induced fluorescence and particle image velocimetry technique. Enhanced turbulent mixing due to bed roughness increased mass flux across the sediment‐water interface between 1.3 times greater for the sand and 7.5 times greater for the cobble bed compared to estimates over a hydraulically smooth surface. As bed roughness increased, mass exchange became spatially more heterogeneous, coinciding with a transition from a boundary layer to a shear‐dominated mixing layer in the near‐wake region behind individual roughness elements. The enhanced flux increased pore water concentrations. However, for the same bed geometry, increased mean flow within the water column locally reduced pore water concentrations, likely due to greater downstream transport and dispersion occurring within the bed.