Modified Fickian model for solute uptake by runoff

  • Richardson C
  • Parr A
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Abstract

A 1-dimensional Fickian diffusion model for entrainment of interstitial soil water by overland flow is modified to account for early non-Fickian mass transfer obsd. during lab. runoff expts. Modification involves specifying a time-dependent diffusion coeff. that decreases with time and asymptotically approaches the const. Fickian value with time. Results show that this asymptotic diffusion coeff. varies with the square of the quantity V*?k, where V* is shear velocity and k is media permeability. Modifying the model entails the development of type curves for a range of convective time scales, or times of non-Fickian mass transfer. A graphical curve-matching technique using dimensionless cumulative mass loss data provides a means of estg. the entrainment, or mass transfer, coeff. as a function of the convective time scale. This procedure shows that the entrainment coeff. varies linearly with V*?k. Reasonable prediction of mass loss results using the asymptotic diffusion coeffs., an empirical relation for the entrainment coeff., and a convective time scale of 5 min as model input. [on SciFinder (R)]

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Authors

  • C P Richardson

  • A D Parr

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