Further tests of the HYPROP evaporation method for estimating the unsaturated soil hydraulic properties

Abstract

Many soil, hydrologic and environmental applications require information about the unsaturated soil hydraulic properties. The evaporation method has long been used for estimating the drying branches of the soil hydraulic functions. An increasingly popular version of the evaporation method is the semi-automated HYPROP © measurement system (HMS) commercialized by Decagon Devices (Pullman, WA) and UMS AG (München, Germany). Several studies were previously carried out to test the HMS methodology by using the Richards equation and the van-Genuchten-Mualem (VG) or Kosugi-Mualem soil hydraulic functions to obtain synthetic data for use in the HMS analysis, and then to compare results against the original hydraulic properties. Using HYDRUS-1D, we carried out independent tests of the HYPROP system as applied to the VG functions for a broad range of soil textures. Our results closely agreed with previous findings. Accurate estimates were especially obtained for the soil water retention curve and its parameters, at least over the range of available retention measurements. We also successfully tested a dual-porosity soil, as well as an extremely coarse medium with a very high van Genuchten n value. The latter case gave excellent results for water retention, but failed for the hydraulic conductivity. In many cases, especially for soils with intermediate and high n values, an independent estimate of the saturated hydraulic conductivity should be obtained. Overall, the HMS methodology performed extremely well and as such constitutes a much-needed addition to current soil hydraulic measurement techniques.

The Effect of Intraparticle Porosity and Interparticle Voids on the Hydraulic Properties of Soilless Media

“…Rates were normalized to 10°C by accounting for the temperature dependence of water viscosity. Drying curves were acquired on single samples saturated for 24 to 30 h using an automated evaporation method with a HYPROP instrument with integrated balance (UMS GmbH) (Bezerra‐Coelho et al, 2018; Schindler et al, 2016). The resulting WRCs were fitted to a bimodal, constrained van Genuchten expression, with the addition of an adsorptive water retention function ( S ad ), which forces the volumetric water content to 0 at pF 6.8 (= 618,758 kPa) (HYPROP‐FIT code 1211; Peters and Durner [2015]).…”

Capillary, Film, and Vapor Flow in Transient Bare Soil Evaporation (1): Identifiability Analysis of Hydraulic Conductivity in the Medium to Dry Moisture Range

“…Evaporation experiments in the laboratory have become a standard method to study the transport of liquid water and water vapor in soils (Or et al., 2013; Shokri et al., 2008) and to determine SHP in the laboratory (Bezerra‐Coelho et al., 2018). The determination of SHP profits from the simplicity and robustness of the experimental procedure and the reliability of determining the WRC (from full saturation to medium water content) and the HCC (in a more limited moisture range) in high resolution.…”

Modeling water fluxes through containerized soilless substrates using HYDRUS

“…Measurements ranged from substrate matric potentials of ∼2 to ∼675 hPa in the peat-based substrate and ∼2 to ∼575 hPa in the bark-based substrate. Measured values were input into HypropFit (Bezerra-Coelho, Zhuang, Barbosa, Soto, & van Genuchten, 2018) to calculate the hydraulic parameters θ s , θ r , α, n, and K s . However, unlike for the IP analysis, in the evaporative analysis, the S e and K(θ) functions were analyzed simultaneously with HypropFit, via a nonlinear algorithm to minimize the sum of weighted square residuals between measured and modeled h and θ data (Peters & Durner, 2008).…”