2009 Volume 111 Pages 9-16
We examined effects of soil water repellency on hydrological processes in various scales from small plot to catchment in a Japanese cypress plantation. We measured soil water repellency and infiltration rate along a hillslope transect, and monitored overland flow at small plots (1 × 2 m) with sparse and dense fern cover and a large plot (8 × 25 m) and stream discharge at the outlet of a small catchment (0.43 ha). Strong water repellency in surface soil horizon was partially associated with Hortonian over-land flow, which volume potentially depended on sever-ity of water repellency. Relationships between matric po-tential and soil water content indicate that changes in the soil water repellency and consequently runoff coefficient of overland flow could occur during a single storm event. Greater amounts of overland flow at small plots compared to ones at large plot suggests that overland flow generated in hillslope was discontinuously transferred. Higher infil-tration rate at the bottom of hillslope likely caused little contribution of overland flow on catchment runoff. Despite the substantial overland flow generated in hillslope due to soil water repellency, water repellency was not a dominant factor accelerating runoff directly at the small catchment scale.
