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This article in JEQ

  1. Vol. 22 No. 1, p. 109-118
     
    Received: Jan 24, 1992
    Published: Jan, 1993


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doi:10.2134/jeq1993.00472425002200010014x

Unstable Wetting Fronts in Water-Repellent Field Soils

  1. J. M. H. Hendrickx *,
  2. L. W. Dekker and
  3. O. H. Boersma
  1. Hydrology Program, Dep. of Geoscience, New Mexico Inst. of Mining and Technol., Socorro NM 87801;
    The Winand Staring Centre for Integrated Land, Soil and Water Res., Wageningen, the Netherlands.

Abstract

Abstract

Study objectives are to (i) investigate the effects of a water-repellent top layer on water flow and solute transport and (ii) examine whether unstable wetting front theories can be used to predict the occurrence of preferential flow in water-repellent field soils. The study took place on two adjacent plots with grasscover near Ouddorp (The Netherlands)—one plot with a water-repellent top layer, the other plot with a wettable top layer. The soil at the experimental site is a sand soil of marine origin—mesic Typic Psammaquent. We conducted three different tests to obtain experimental evidence for our hypothesis that flow through a water-repellent soil would be unstable. An I coloring technique showed an unstable wetting front with preferential flow paths in the water-repellent soil; flow through the wettable soil resulted in a homogeneous, stable wetting front. The variability of the soil water contents in the water-repellent soil was larger than in the wettable soil, indicating that flow through the water-repellent soil was less stable. A Br tracer experiment, under conditions of natural precipitation, revealed that solutes in the water-repellent soil travelled faster to the groundwater than in the wettable soil. After 5 wk with 120 mm precipitation, the Br amounts in the groundwater under the water-repellent top layer were 6 to 13 times higher than those under the wettable top layer. These experimental results demonstrate that unstable wetting front theories can be used to predict the occurrence of preferential flow in water-repellent field soils.

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