PNNL

Abstract

Predicting flow and transport in unsaturated porous media is often hampered by insufficient and uncertain constitutive property information. Some studies have used inverse flow modeling for parameter estimation to overcome these limitations. However, determination of the soil hydraulic parameters of layered soils remains a challenge since inverting for too many parameters can lead to the non-uniqueness of parameter values. Here we propose a parameter scaling method that reduces the number of parameters to be estimated. Parameter scaling factors are determined using local-scale parameter values. By assigning scaling factors to the corresponding soil textures in the field, the reference hydraulic parameter values at the field scale can be estimated through inverse modeling of well-designed field experiments. Parameters for individual textures are then obtained through inverse scaling of the reference values using a priori relationships between reference parameter values and the specific values for each texture. The proposed method was tested using two infiltration-drainage experiments in layered soils. The numerical simulator, STOMP, was combined with the inverse modeling program, UCODE, to estimate the hydraulic parameters. The results show that the simulation errors were significantly reduced after applying parameter scaling and inverse modeling. When compared to the use of local-scale parameters, parameter scaling reduced the sum of squared weighted residue by 93-96%.