The effect of temperature-induced soil water repellency on transient capillary pressure-water content relations during capillary rise.

摘要

Long-term capillary rise experiments (0 to about 89 000 hour) were performed at 19 degrees C on homogenized and heat-treated podsolic forest top- and subsoil samples. These were packed into columns, the bases of which were then partially immersed, at constant depth, in water reservoirs to simulate a constant water table. Selected columns were equipped with tensiometer and TDR probes. Other columns were removed at prescribed times and divided into 2-cm horizontal segments whose volumetric water contents were determined. The degree of saturation was then estimated by comparison with the capillary rise in duplicate arrangements of samples immersed in ethanol. It was found that the heat treatments conferred increased water repellency (WR) on the soil, which increased with temperature (significantly so at greater than 60 degrees C). This had a profound effect on the capillary rise characteristics and development of water content in the soil behind the wetting front, indicating an effective, albeit slow, reduction in effective WR. This has implications for hydraulic modelling of soils with significant WR and demonstrates that sub-surface WR exerts a significant influence on capillary rise from a water table and suggests that commonly used indicators of surface WR using droplet tests may not be useful for such modelling purposes.