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Longitudinal and transverse dispersion coefficients in unsaturated plainfield sand
Author(s) -
Yule D. F.,
Gardner W. R.
Publication year - 1978
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/wr014i004p00582
Subject(s) - inflow , transverse plane , dispersion (optics) , analytical chemistry (journal) , diffusion , tracer , outflow , physics , materials science , mineralogy , chemistry , optics , mechanics , chromatography , thermodynamics , meteorology , nuclear physics , structural engineering , engineering
The relationship between the longitudinal and transverse dispersion coefficients ( D L and D τ ) and the pore water velocity (υ) and the effective diffusion coefficient ( D e ) was determined for 0.01 < υ < 0.28 cm/min in a vertical unsaturated column ( L = 23 cm) of C horizon Plainfield sand. The inflow and outflow control systems on the soil column consisted of rows of porous ceramic tubes with individual adjustable pressure controls. Uniform inflow and outflow were achieved across the column, and υ was maintained constant during each experiment. An analysis of the transverse spread produced indicated that the effect of apparatus‐induced dispersion was <10%. D L (cm 2 /min) was linearly related to υ (cm/min) ( D L = 0.216υ + 0.0032; r 2 = 0.90). Slightly larger D L was found in experiments with H 2 O replacing Cl than in experiments with Cl replacing H 2 O. D L at the lowest υ was 2 orders of magnitude greater than D e . D T (cm 2 /min) was essentially independent of υ( D T = 0.0035υ + 0.0031; r 2 = 0.15) and was about 2 orders of magnitude greater than D e at the lowest υ studied. The spread of tracer at the outflow was inversely proportional to υ, and transverse dispersion had reduced the concentration peak of the inflow by 84% at L = 23 cm and υ = 0.01 cm/min. The ratio D L / D T was proportional to υ and ranged from ∼ 1 (υ = 0.01 cm/min) to ∼20 (υ = 0.28 cm/min).