Weibull distribution models for describing soil hydraulic properties over the entire matric suction range

Abstract

Accurate descriptions of soil hydraulic properties over the entire matric suction range require the consideration of both capillary and noncapillary processes. This study extended the Weibull distribution models of hydraulic properties to complete dryness by the modular frameworks of Peters-Durner-Iden (PDI) and Brunswick (BW). Model-data comparison results showed that the original Weibull distribution models, accounting solely for capillary phenomena, provided inadequate descriptions of measurements in the dry range of water retention curve and hydraulic conductivity curve. The improved models of PDI and BW, accounting for both capillary and noncapillary processes, effectively described the hydraulic properties data from saturation to complete dryness, although the BW model violated the linearity requirement for water retention in dry soils with wide pore-size distributions. The PDI model overall performed better than the BW model in terms of their capability to fit the retention data and predict the conductivity data. Adopting the physically-based approach developed recently, the improved PDI and BW models can reliably predict the hydraulic conductivity along the complete matric suction range from water retention only, without use of fitted conductivity parameters. Thus, the improved PDI and BW models are applicable to cases where measured conductivity data (particularly noncapillary-dominated range) are not available.