Assessment and application of an alternative formula to describe the hydraulic conductivity over the full moisture range

Abstract

Motivated by a versatile three‐parameter water retention curve (WRC) formula of Fredlund and Xing, we proposed an alternative expression to describe the relative hydraulic conductivity (RHC) for soils that can capture oven‐dry to water‐saturated conditions (full moisture range) with a single, closed‐form equation (without having to explicitly partitioning the capillary and film flow components). This RHC expression was tested using an existing data set that includes a wide range of soil textures, and shown to be more accurate than the other two RHC expressions. Subsequently, the new RHC expression was combined with the WRC formula of Fredlund and Xing, generating an alternative model (hereafter called the FL model) applicable to describe soil hydraulic properties over the full moisture range. The FL model requires both the known WRC and RHC data since three additional fitting parameters are involved in the present RHC expression. Furthermore, the FL model was employed in a HYDRUS‐1D numerical model for simulating the soil moisture redistribution within a lysimeter. The numerical simulation with using the FL model can accurately predict the moisture redistribution, in turn confirming the validity of the FL model despite without partitioning the capillary and film flow components.

Evaluation of a general model for multimodal unsaturated soil hydraulic properties

“…As the water content of a soil decreases, the retention of water changes from capillarity to fluid adsorption, with the mechanism of water flow changing from capillary movement to film and corner flow. For this reason, several used Mualem's model only at relatively high water contents (the capillary water range) and modeled the hydraulic conductivity at low water content (i.e., the adsorption water range) independently (e.g., Peters, 2013), or avoided the use of capillary bundle models altogether to independently describe the WRF and HCF over the whole moisture range (e.g., Luo et al, 2022).…”