Kg. Villholth et Kh. Jensen, FLOW AND TRANSPORT PROCESSES IN A MACROPOROUS SUBSURFACE-DRAINED GLACIAL TILL SOIL - II - MODEL ANALYSIS, Journal of hydrology, 207(1-2), 1998, pp. 121-135
The experimental results from a field-scale tracer experiment in a sub
surface-drained glacial till soil were analyzed by the application of
a single/dual porosity model (MACRO), optionally accounting for concur
rent and interacting flow and transport in the bulk soil porosity as w
ell as in the macropores. The model analysis showed that macropore flo
w is essential in describing the observed transport phenomenon on a sh
ort as well as a longer time scale. The diffusive exchange of solute b
etween the matrix and the macropores was very sensitive and critical f
or the model prediction of the drainage concentration. The exchange wa
s overpredicted and too rapid when the soil aggregate size (distance b
etween macropores) obtained from an image analysis of soil cores was u
sed in the model. On this basis, the model assumption of instant equil
ibration of the solute across the matrix porosity, disregarding small-
scale concentration gradients, is questioned. Decreasing the domain ex
change resulted in an improved model correspondence with the drainage
chemograph. The drainage flow pattern was altered between drainage sea
sons owing to the changes in hydraulic efficiency of surface-vented ma
cropores influenced by the physical disturbance and compaction of the
soil surface. Hypothetically introducing fully surface-connected macro
pores into the calibrated model resulted in a 22% increase in the loss
of solute to the drain, indicating the significance of the hydraulic
conditions at the soil surface and the model specification thereof. (C
) 1998 Elsevier Science B.V. All rights reserved.