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Effects of water repellency on infiltration rate and flow instability

Abstract:

Laboratory infiltration experiments were carried out to quantify the effects of soil water-repellency on infiltration rate and the wetting front instability. A two-dimensional transparent chamber (41.5 cm wide, 50 cm high and 2.8 cm thick) was constructed for infiltration experiments using three water-repellent Ouddorp sands (The Netherlands) and a wettable silicon sand. The results showed that if the water-ponding depth (h0) at the soil surface was lower than the water-entry value (hwe) of repellent sands, infiltration would not start until the water drop penetration time (WDPT) is exceeded; and contrary to infiltration in wettable soils, the infiltration rate increased with time. However, infiltration could immediately start at any time when we- The wetting front was unconditionally unstable for resulting in fingered flow. However, the flow was conditionally stable for zwe if the soil was not layered in a fine-over-coarse or wettable-over-repellent configuration, and if soil air was not compressed during infiltration. The occurrence of stable and unstable flow in repellent soils was consistent with the pbkp_rediction based on a linear instability analysis. The findings can be used to improve irrigation efficiencies in water repellent soils, e.g. using high-ponding irrigation methods. © 2003 Elsevier Ltd. All rights reserved.