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Unstable Wetting Fronts in Water‐Repellent Field Soils
Author(s) -
Hendrickx J. M. H.,
Dekker L. W.,
Boersma O. H.
Publication year - 1993
Publication title -
journal of environmental quality
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.888
H-Index - 171
eISSN - 1537-2537
pISSN - 0047-2425
DOI - 10.2134/jeq1993.00472425002200010014x
Subject(s) - soil water , water repellent , wetting , groundwater , water flow , soil science , environmental science , soil horizon , wettable powder , precipitation , hydrology (agriculture) , chemistry , geotechnical engineering , geology , materials science , composite material , meteorology , biochemistry , physics , emulsion
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.