The evaporation method: Extending the measurement range of soil hydraulic properties using the air‐entry pressure of the ceramic cup

Abstract

Knowledge of hydraulic functions is required for various hydrological and plant‐physiological studies. The evaporation method is frequently used for the simultaneous determination of hydraulic functions of unsaturated soil samples, i.e., the water‐retention curve and hydraulic‐conductivity function. All methodic variants of the evaporation method suffer from the limitation that the hydraulic functions can only be determined to a mean tension of ≈ 60 kPa. This is caused by the limited measurement range of the tensiometers of typically 80 kPa on the dry end. We present a new, cost‐ and time‐saving approach which overcomes this restriction. Using the air‐entry pressure of the tensiometer's porous ceramic cup as additional defined tension value allows the quantification of hydraulic functions up to close to the wilting point. The procedure is described, uncertainties are discussed, and measured as well as simulated test results are presented for soil samples of various origins, different textures (sand, loam, silt, clay, and peat) and variable dry bulk density. The experimental setup followed the system HYPROP which is a commercial device with vertically aligned tensiometers that is optimized to perform evaporation measurements. During the experiment leaked water from the tensiometer interior wets the surrounding soil of the tensiometer cup and can lead to a tension retardation as shown by simulation results. This effect is negligible when the tensiometers are embedded vertically. For coarsely textured soils and horizontal tensiometer alignment, however, the retardation must be considered for data evaluation.

Soil-Water Characteristic Curve of Residual Soil from a Flysch Rock Mass

“…Due to cavitation problems when using direct tensiometer measurements, the simplified evaporation method [37] is frequently used for measuring both the SWCC and the suction permeability curve in sands and silts. By using the tensiometer-preconditioning procedure [38], the results were obtained for matric suctions up to 130 kPa. The results obtained from the sample starting from the natural water content are denoted by HYPROP-2.…”

On the use of surrogate-based modeling for the numerical analysis of Low Impact Development techniques

“…Considering that vegetation mainly consisted of herbaceous plants, an average value of albedo of 0.23 was assumed in calculations of net short-wave radiation (Breshears et al, 1997 ]. In order to reduce the dimensionality of the optimization problem, the soil hydraulic properties of the soil substrate were measured in the laboratory using a simplified evaporation method with an extended measurement range (down to À9000 cm), as proposed by Schindler et al (2010aSchindler et al ( , 2010b. For a detailed description of the modified evaporation method, please refer to Schindler et al (2010aSchindler et al ( , 2010b.…”

“…In order to reduce the dimensionality of the optimization problem, the soil hydraulic properties of the soil substrate were measured in the laboratory using a simplified evaporation method with an extended measurement range (down to À9000 cm), as proposed by Schindler et al (2010aSchindler et al ( , 2010b. For a detailed description of the modified evaporation method, please refer to Schindler et al (2010aSchindler et al ( , 2010b. Peters and Durner (2008) conducted a comprehensive error analysis of the simplified evaporation method and concluded that it is a fast, accurate, and reliable method to determine soil hydraulic properties in the measured pressure head range, and that the linearization hypothesis introduced by Schindler (1980) causes only small errors.…”

Hydraulic properties of horticultural substrates

“…The substrate water retention curve (pF curve) and the unsaturated hydraulic conductivity function (K-function) were measured simultaneously using the Extended Evaporation Method (EEM, Schindler et al, 2010) and the HYPROP device (HYdraulic PROPerty Analyser). The measurement was executed on 250cm -3 substrate samples taken in steel cylinders.…”

“…The unsaturated hydraulic conductivity (K) is calculated according to the Darcy-Buckingham law. Using new cavitation tensiometers and applying the air entry value of the tensiometers' ceramic cup allows the range to be extended almost up to the wilting point (Schindler et al, 2010). Fig.…”