Field Scale Vertical Transport from Horizontally Variable Local Scale Transport Parameters

Abstract

In field soils, transport properties vary vertically and horizontally. With experimental measurements it is distinctly easier to consider the vertical than the horizontal variability. We present a simple approach for considering the horizontal variability of the transport behavior of the soil in a one‐dimensional transport model. The model approach assumes independence on depth of the vertical dispersion coefficient, which is justified by the relatively small effects of the vertical dispersion in comparison to those of the horizontal dispersion only. The approach is based on numerical experiments using different parameter statistics. An analytical expression of the dependence of effective parameters, describing the transport at the field scale, on the statistical lognormal distributions of transport parameters at the local scale is derived heuristically by careful inspection of the numerical experimental results. The model was tested in (1) a reevaluation of a one‐dimensional field experiment with chloride tracer in a heavy loam soil of Roth (1989), and (2) a two‐dimensional leaching field experiment with the same tracer in a sandy soil plot of 5600 m2. For both experiments the model using lognormal local parameter distributions provides a satisfactory representation of field averages of the vertical transport derived from local measurements.