Simulating liquid water distribution at the pore scale in snow: water retention curves and effective transport properties

Abstract

Liquid water flows by gravity and capillarity in snow, drastically modifying its properties. Unlike dry snow, observing wet snow remains a challenge and data from 3D pore-scale imaging are scarce. This limitation hampers our understanding of the water, heat, and vapor transport processes in wet snow, as well as their modeling. Here, we explore a simulation-based approach, namely a pore morphology model, to simulate the distribution of liquid water in the pore space of snow for various water contents. Using the Young-Laplace equation and pore radius as a probe, liquid water is gradually introduced and then removed during wetting (imbibition) and drying (drainage) simulations, respectively. This model was applied to a set of 34 3D tomography images of dry snow of varied microstructures. For each microstructure, a series of 3D images of wet snow at different stages of drainage and imbibition was obtained. From these series, we examine key properties for the modeling of wet snow processes. First, we describe the water retention curves obtained for imbibition and drainage for the different microstructures. The classical van Genuchten model is used to describe our simulated water retention curves. The obtained model parameters, i.e., the shape parameters (αvg and nvg) and the residual water content, are compared to the ones obtained in laboratory experiments from literature. New parameterizations of these parameters based on snow density, grain size, and the interfacial mean curvature are proposed. Then, we present estimates of hydraulic conductivity, water permeability, effective thermal conductivity, and water vapor diffusivity, computed on the simulated wet snow images. We study their evolution in relation to water content, density, and snow type. Our estimates are compared to existing parameterizations of the wet snow properties; new parameterizations are proposed when needed. Our simulations are a first step toward a better characterization of the micro-scale distribution of liquid water in snow, and contribute to improving the modeling of the hydraulic and physical properties of wet snow.