Water Movement and Finger Flow Characterization in Homogeneous Water-Repellent Soils

Soil water repellency (SWR) is a widespread property in soils around the world. It influences soil water movement and causes unstable flow. The mechanics of finger flow occurrence in water-repellent soils are not clearly understood. Slab chamber infiltration experiments consisting of increasing SWR persistence in clay and sandy loam soils were conducted to compare wetting front advancement and mechanics of finger flow development. The temporal variation curves of cumulative infiltration (CI) decreased with an increase in SWR persistence. For wettable soils, the wetting front advanced regularly with time, but for water-repellent soils, it became unstable and finger flow occurred as the SWR persistence increased. Water movement in soils with higher SWR persistence tended to be more unstable. Water repellency contributed to finger flow development, especially for sandy loam. There were strong correlations among CI, finger length, and the cumulative wetting area. In the strongly, severely, and extremely water-repellent sandy loam soils, the power function relationship fit better than the linear function. The average soil water content decreased with a higher SWR persistence, which meant that less water was available in the profile. Finger flow development was related to the more severe water-repellent conditions and tended to be more easily formed in the water-repellent sandy loam soils than the clay loam soils due to the faster infiltration rate.