Upscaling unsaturated hydraulic parameters for flow through heterogeneous anisotropic sediments
We compare two methods for determining the upscaled water characteristics and saturation-dependent anisotropy in unsaturated hydraulic conductivity from a field-scale injection test. In both approaches an effective medium approximation is used to reduce a porous medium of M textures to an equivalent homogeneous medium. The first approach is a phenomenological approach based on homogenization and assumes that moisture-based Richards? equation can be treated like the convective-dispersive equation (CDE). The gravity term, dKz(S)/d(S), analogous to the vertical convective velocity in the CDE, is determined from the temporal evolution of the plume centroid along the vertical coordinate allowing calculation of an upscaled Kz(S). As with the dispersion tensor in the CDE, the rate of change of the second spatial moment in 3D space is used to calculate the water diffusivity tensor, D(S), from which an upscaled K(S) is calculated. The second approach uses the combined parameter scale inverse technique (CPSIT). Parameter scaling is used first to reduce the number of parameters to be estimated by a factor M. Upscaled parameters are then optimized by inverse modeling to produce an upscaled K(S) characterized by a pore tortuosity-connectivity tensor, L. Parameters for individual textures are finally determined from the optimized parameters by inverse scaling using scale factors determined a priori. Both methods produced upscaled K(S) that showed evidence of saturation dependent anisotropy. Flow predictions with the STOMP simulator, parameterized with upscaled parameters, were compared with field observations. Predictions based on the homogenization method were able to capture the mean plume behavior but could not reproduce the asymmetry caused by heterogeneity and lateral spreading. The CPSIT method captured the effects of heterogeneity and anisotropy and reduced the mean squared residual by nearly 90% compared to local-scale and upscaled parameters from the homogenization method.
- Research Organization:
- Pacific Northwest National Laboratory (PNNL), Richland, WA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC05-76RL01830
- OSTI ID:
- 877546
- Report Number(s):
- PNNL-SA-45568; 830403000
- Journal Information:
- Advances in Water Resources, Journal Name: Advances in Water Resources Journal Issue: 2 Vol. 29
- Country of Publication:
- United States
- Language:
- English
Similar Records
A Combined Parameter Scaling and Inverse Technique to Upscale the Unsaturated Hydraulic Parameters for Heterogeneous Soils
Effective Hydraulic Properties Determined from Transient Unsaturated Flow in Anisotropic Soils