Effective Hydraulic Properties Determined from Transient Unsaturated Flow in Anisotropic Soils

An important requirement for accurate modeling of field‐scale unsaturated transport using local‐scale parameters is a method to account for multiscale heterogeneity and the connectivity of the facies that control flow. A series of infiltration tests were conducted at the Hanford Site along a 60‐m‐long transect, instrumented at 1‐m intervals to measure water content (θ) and capillary pressure head ( h ) to quantify the spatial correlation structure of hydraulic properties and assess connectivity of the facies. Hydraulic parameters including the pore connectivity–tortuosity tensor ( L i ) were inversely estimated using the Subsurface Transport Over Multiple Phases (STOMP) numerical simulator coupled with the parameter estimation code, UCODE. Results show that six of eight parameters required for a modified van Genuchten–Mualem model could be inversely estimated using θ measured during transient infiltration from a surface line source and approximated prior information. Soils show evidence of saturation‐dependent anisotropy that was well described with the connectivity tensor. Variability of the vertical saturated hydraulic conductivity, K sv , was larger than the horizontal, K sh The autocorrelation ranges for K sh , K sv , the inverse of the air‐entry value, α, and the horizontal connectivity, L h , were between 2.4 and 4.6 m, whereas the van Genuchten shape parameter, n , and saturated water content, θ s , showed no autocorrelation. Accurate upscaling of hydraulic properties requires the correct assessment of the connectivity of facies.