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Prediction of Dispersivity for Undisturbed Soil Columns from Water Retention Parameters
Author(s) -
Perfect E.,
Sukop M. C.,
Haszler G. R.
Publication year - 2002
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj2002.6960
Subject(s) - pedotransfer function , hydraulic conductivity , soil water , soil science , loam , dispersion (optics) , water retention curve , environmental science , soil texture , water retention , geotechnical engineering , mathematics , geology , physics , optics
Dispersivity (α) is a required input parameter in solute‐transport models based on the advection‐dispersion equation (ADE). Normally α is obtained from miscible‐displacement experiments. This dependency on inverse procedures imposes a severe limitation on our predictive capability. If solute breakthrough curves and soil hydraulic properties were measured simultaneously, pedotransfer functions could be developed to predict α from independent measurements. In this study, short (6 cm long) undisturbed columns were employed to investigate the relationship between α and the water‐retention curve as parameterized by the air‐entry value (ψ a ) and Campbell exponent ( b ). We worked with 69 columns from six soil types ranging in texture from loamy sand to silty clay, conventional‐till and no‐till management practices, steady‐state saturated flow conditions, and a step decrease in CaCl 2 concentration from 0.009 to 0.001 M Breakthrough curves were measured by monitoring changes in effluent electrical conductivity using a computerized data acquisition system. Estimates of α (calculated using the method of moments) ranged from 1 to 192 mm for the six soil types. Stepwise multiple‐regression analysis explained ∼50% of the total variation in α, and indicated that dispersion increased as ψ a and b increased. Since both ψ a and b increase with increasing clay content, α also increases moving from coarse‐ to fine‐textured soils. Our regression equation can be used as a pedotransfer function to predict α from existing databases of soil hydraulic properties. Further research is needed to independently validate its predictive capability, and to develop strategies for upscaling the model predictions.