Parameter estimation of soil hydraulic and thermal property functions for unsaturated porous media using the HYDRUS-2D code

Abstract

Knowledge of soil hydraulic and thermal properties is essential for studies involving the combined effects of soil temperature and water input on water flow and redistribution processes under field conditions. The objective of this study was to estimate the parameters characterizing these properties from a transient water flow and heat transport field experiment. Real-time sensors built by the authors were used to monitor soil temperatures at depths of 40, 80, 120, and 160 cm during a 10-hour long ring infiltration experiment. Water temperatures and cumulative infiltration from a single infiltration ring were monitored simultaneously. The soil hydraulic parameters (the saturated water content θ s, empirical shape parameters α and n, and the saturated hydraulic conductivity Ks) and soil thermal conductivity parameters (coefficients b1, b2, and b3 in the thermal conductivity function) were estimated from cumulative infiltration and temperature measurements by inversely solving a two-dimensional water flow and heat transport using HYDRUS-2D. Three scenarios with a different, sequentially decreasing number of optimized parameters were considered. In scenario 1, seven parameters (θ s, Ks, α, n, b1, b2, and b3) were included in the inverse problem. The results indicated that this scenario does not provide a unique solution. In scenario 2, six parameters (Ks, α, n, b1, b2, and b3) were included in the inverse problem. The results showed that this scenario also results in a non-unique solution. Only scenario 3, in which five parameters (α, n, b1, b2, and b3) were included in the inverse problem, provided a unique solution. The simulated soil temperatures and cumulative infiltration during the ring infiltration experiment compared reasonably well with their corresponding observed values.

Interpretation of ponded infiltration data using numerical experiments

“…On one hand, the numerical inversion of Richards' equation represents a very powerful analytical tool. On the other hand, the numerical inversion of in-situ infiltration experiments was reported to suffer from non-uniqueness due to the lack of information about pressure head, moisture content, or temperature measured (e.g., Nakhaei and Šimůnek, 2014). Probably, for these reasons, a demand for simpler and more robust methods of infiltration experiment data processing persists.…”

Different scenarios for inverse estimation of soil hydraulic parameters from double-ring infiltrometer data using HYDRUS-2D/3D

“…Many researchers have reported that cumulative infiltration data do not provide enough information to obtain a unique set of optimized parameters, and some additional information is needed to yield a unique set of optimized parameters in inverse problems (Hopmans et al, 2002;Nakhaei and Šimůnek, 2014;Ritter et al, 2004;Russo et al, 1991). Such additional information could consist of pressure heads and/or water contents (Šimůnek and van Genuchten, 1996), solute concentrations (Abbasi et al, 2003), or temperatures (Nakhaei and Šimůnek, 2014) measured at a certain depth along the soil profile. However, our simulation results show that the simultaneous use of FC and PWP as an input increased the simulation error (Table 3).…”

“…The vadose zone has a fundamental role in many aspects of hydrology, including infiltration, soil moisture storage, evaporation, plant water uptake, groundwater recharge, runoff, and erosion (Nakhaei and Šimůnek, 2014). Knowledge of the hydraulic properties of unsaturated soils (ie the retention curve, θ(h), and the hydraulic conductivity functions, K(h)) is essential for most or all studies involving water flow and solute transport in the vadose zone (Bitterlich et al, 2004).…”

“…It is commonly reported that some additional information is needed to obtain unique solutions for a large number of parameters. Such additional information could include water contents and/or pressure heads (Šimůnek and van Genuchten, 1996), solute concentrations (Abbasi et al, 2003), or temperatures (Nakhaei and Šimůnek, 2014) measured at a certain depth in the soil profile. However, little is known about the effect of including additional data as a predictor on the efficiency and uniqueness of inverse modelling of double-ring infiltrometer data.…”

Modeling Coupled Water and Heat Transport in the Root Zone of Winter Wheat under Non-Isothermal Conditions

“…Therefore, if a model of soil water movement established under normal isothermal conditions is used to simulate soil water movement under non-isothermal conditions, the results will show a certain degree of deviation. In studying soil water movement, the effect of temperature gradient on soil water movement parameters and of heat flux on soil water movement cannot be ignored [9].…”