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Vertical variation of mixing within porous sediment beds below turbulent flows
Author(s) -
Chandler I. D.,
Guymer I.,
Pearson J. M.,
van Egmond R.
Publication year - 2016
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 - 10.1002/2015wr018274
Subject(s) - sediment , mixing (physics) , soil science , sediment–water interface , hydrology (agriculture) , reynolds number , turbulence , geology , porosity , mechanics , environmental science , geotechnical engineering , geomorphology , physics , quantum mechanics
Abstract River ecosystems are influenced by contaminants in the water column, in the pore water and adsorbed to sediment particles. When exchange across the sediment‐water interface (hyporheic exchange) is included in modeling, the mixing coefficient is often assumed to be constant with depth below the interface. Novel fiber‐optic fluorometers have been developed and combined with a modified EROSIMESS system to quantify the vertical variation in mixing coefficient with depth below the sediment‐water interface. The study considered a range of particle diameters and bed shear velocities, with the permeability Péclet number, P e Kbetween 1000 and 77,000 and the shear Reynolds number, R e * , between 5 and 600. Different parameterization of both an interface exchange coefficient and a spatially variable in‐sediment mixing coefficient are explored. The variation of in‐sediment mixing is described by an exponential function applicable over the full range of parameter combinations tested. The empirical relationship enables estimates of the depth to which concentrations of pollutants will penetrate into the bed sediment, allowing the region where exchange will occur faster than molecular diffusion to be determined.