Effective Suction Control for Infiltration Water Sampling in Unsaturated Soils

Abstract

We investigated the applicability of the infiltration water sampling system using a suction-controlled flux sampler in various soils. When a glass filter was used in a sandy soil, the simulation results from HYDRUS-2D model indicated that once the matric potential above the filter (h_C) decreased rapidly by suction application, a zone of low water content was remained above the filter. When the next infiltration water approached the filter, the low water content zone was packed between the filter and the infiltration water. That was showing a lower h_C than the matric potential in the natural soil profile (h_L, h_R). This phenomenon was also observed when a glass filter was applied to loam and silt loam soils. In contrast, h_C was higher than h_L and h_R when using a porous plate and membrane filters, which have low permeability. These results indicated that appropriate selection of a sampling filter and boundary condition was required for better sampling, when a suction-controlled flux sampler was applied to various soils. Because the filter permeability and soil properties affected the criterion for suction control, their combination and the existence of low water content zone between the filter and soil should be considered.