A Point‐Source Method for Rapid Simultaneous Estimation of Soil Hydraulic and Chemical Transport Properties

Abstract

Hydraulic and chemical transport properties are needed for accurate prediction of water and chemical movement through the vadose zone. Field methods used to estimate such properties are often hampered by extensive labor and time constraints. One of the objectives of this study was to develop an experimental setup and a procedure for a point-source method that facilitates rapid and simultaneous measurements of soil hydraulic and chemical transport properties at multiple locations. Another objective was to evaluate the pointsource method by comparing the parameters with those produced by ponded and tension infiltrometers. The experimental setup consisted of three dripper lines equipped with pressure-compensating drippers. The setup was evaluated on a greenhouse soil pit. Determined hydraulic properties were the saturated hydraulic conductivity (K s ) and the macroscopic capillary length (λ c ). Hydraulic properties (from the point-source method) were determined by applying four consecutive discharge rates on the soil surface and measuring their corresponding steady-state saturated areas. Determined chemical transport parameters were the immobile water fraction (θ im /θ) and the mass exchange coefficient (α). They were determined by applying a sequence of conservative fluorobenzoate tracers. The point-source method gave consistent and reliable estimates for both sets of properties. Except for α, there was no significant difference between the two procedures (point source vs. infiltrometers) in determining both sets of properties. The study showed that the point-source setup could be utilized for rapid and simultaneous estimation of soil hydraulic and chemical transport properties at multiple locations with minimum labor requirements. and Collins, 1971; van Genuchten and Wierenga, 1976;Clothier et al., 1992; Jaynes et al., 1995), there have been Hydraulic and chemical transport properties are needed for accu- ABSTRACT

A review of model applications for structured soils: a) Water flow and tracer transport

“…A single applied tension yielded one set of values for the hydraulic conductivity, K, the total water content, θ, the water content of the immobile zone, θ im , and the mass transfer coefficient, α (Alletto et al, 2006), while several tracer infiltrations conducted at different tensions produced K, θ, θ im , and α, as near-saturated functions of the matric potential (Casey et al, 1998). Al-Jabri et al (2002) suggested a variant of this method for simultaneous measurement at multiple locations based on point-source dripper lines. They used the Wooding's (1968) analytical solution for estimating K and the capillary length, λ c , while MIM transport parameters were estimated according to Jaynes et al (1995).…”

“…They used the Wooding's (1968) analytical solution for estimating K and the capillary length, λ c , while MIM transport parameters were estimated according to Jaynes et al (1995). In an application with several dripping rates, the saturated hydraulic conductivity, K s , the ratio of the immobile and the saturated water content, θ im /θ s , and λ c were similar, while α was different compared to corresponding values derived using the disk infiltrometer (Al-Jabri et al, 2002). The dripper line method was further extended by the installation of a TDR probe beneath each infiltration spot to also measure solute breakthrough to yield the dispersion coefficient in the mobile region (Al-Jabri et al, 2006).…”

Comparison of alternative models for simulating anomalous solute transport in a large heterogeneous soil column

“…For example, Brusseau et al (1994) used the gravimetrical mass balance method to measure the mobile water fraction and determined mass transfer coefficient in an aggregated soil in terms of Fick's law. In addition, these two parameters can be determined by experimental methods such as tension disk infiltrometer (Casey et al, 1999), point-source method (Al-Jabri et al, 2002), and time domain reflectometry (TDR) method (Lee et al, 2000). However, determining these two parameters independently is still a non-trivial task as they appear to be somewhat correlated, and the robust physical meaning of them needs further investigation (Griffioen et al, 1998;Maraqa, 2001).…”

Saturated Soil Hydraulic Conductivity

“…2.48) until the ponded zone approaches a constant circular or nearly circular area at some finite infiltration time. Once this saturated disk is formed, water continues spreading laterally on the soil surface forming an unsaturated zone (Yitayew et al 1998;Shani et al 1987;Al-Jabri et al 2002a). The unsaturated front is identified by the change of the soil color from wet to dry conditions.…”