Finger flow development in layered water-repellent soils

Abstract

Finger flow in water-repellent (WR) soils influences the transport of water, solutes in soil significantly, but the mechanics of finger flow occurrence in layered WR soils is not clear. Soil chamber infiltration experiments with a total of 20 treatments, considering 5 different WR levels with 4 layer combinations, i.e., clay (or sandy) loam overlaying sand (or heavy gravel), were conducted to reveal the mechanics of finger flow occurrence in layered WR soils. The variations of the finger flow dynamics and infiltration parameters were investigated. The results showed: i) The temporal variations of cumulative infiltration (CI) decreased with the increase of the WR level. CI was generally larger when the top layer soil was sandy loam rather than clay loam; therefore, the top layer soil texture controlled CI more than the sub-layer. ii) For the wettable treatments, finger flow was clearly and uniformly generated in layered soils with a sub-layer of heavy gravel rather than with sand. But for WR layered treatments, fingers developed irregularly with the WR levels. Finger length (FL), width (FWh), and velocity (Fv and Bv) varied with the WR levels. iii) There were good power function or linear correlations between CI and cumulative wetting area (CWA), and between CI and FL. iv) Water content (θv) in the top layer was higher than sub-layer and generally decreased with the increase of WR levels. The finger flow development in layered WR soils were generally irregular and showed large extent of complexity.