New Analytical Model for Cumulative Infiltration into Dual-Permeability Soils

Abstract

In the vadose zone, preferential flow and transport are much more common than uniform water flow and solute transport. In recent decades, several models have been developed for preferential water flow and physical non-equilibrium solute transport. Among these models, the dual-permeability approach is an interesting tool for the conceptualization and modeling of preferential flow. However, this approach has been mainly studied from a numerical point of view. In this study, we developed a new analytical model for water infiltration into dual-permeability soils. The model is based on the analytical model originally proposed for single-permeability soils. The pro-posed model relies on the assumption that the water exchange rate at the interface between the matrix and fast-flow regions does not change cumu-lative infiltration at the soil surface, so that the total cumulative infiltration can be set equal to the sum of independent cumulative infiltrations into each region. This assumption was investigated using numerically generated data. The proposed analytical model was then used to evaluate the effects of fast-flow region hydraulic properties and hydraulic conditions on total cumulative infiltration for the case of single-and multi-tension water infiltra-tion experiments. Finally, both single-and dual-permeability models were evaluated with respect to their ability to fit experimental data and associ-ated problems of non-uniqueness in optimized parameters. The proposed model could serve as a new tool for modeling and characterizing preferen-tial flow in the vadose zone. Abbreviations: BOF, basic oxygen furnace; CVRMSE, coefficient of variation of the root mean square error; DP, dual-permeability; MTI, multiple-tension infiltration; NSE, Nash– Sutcliffe coefficient; SP, single-permeability; STI, single-tension infiltration. Water quality must be protected because water is used for many different purposes (e.g., drinking, irrigation, and industry) and provides a living environment for marine, aquatic, and continental ecosystems, yet climate change is predicted to drastically impact the water cycle and reduce water resources in many terrestrial environments, requiring proper management of their quantity and quality (McDonald et al., 1996; Gascoin et al., 2009). Additionally, there is a large spectrum of chemical substances that are released into the environment by human activities and that constitute a risk to groundwater quality. In particular, in urban areas, runoff water carries significant loads of pollutants, including heavy metals, hydrocarbons, pesticides, bacteria, and nutrients (Mikkelsen et al., 1997). In recent decades, field and laboratory studies have demonstrated that water flow and solute transport in the unsaturated zone often occur through a small fraction of the soil along preferential flow paths (Flury et al., 1994; Buttle and Leigh, 1997; Allaire-Leung et al., 2000a, 2000b). Preferential flow reduces the access of pollutants to the soil matrix and thus their opportunity to adsorb onto soil particles (Lassabatere et al., 2004; Lassabatere et al., 2007; Lamy et al., 2009). Therefore, there is an urgent need for scien-tific advances in developing new measurement techniques and theoretical approaches to better understand preferential water flow and physical nonequilibrium solute transport,