Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—2. Application of the methodology

Abstract

Sarkar et al. (this issue) proposed a laboratory measurement method for obtaining the hydraulic conductivity of soil at near‐saturated moisture conditions, bridging the gap between measurements that can be obtained with the evaporation method in the medium dry region, and measurements of the saturated conductivity by traditional methods. The method is based on a tension infiltration on a limited part of the surface of a soil sample and drainage of the sample at the same tension, leading to a divergent flow field. Despite equal tensions at top and bottom of the sample (“unit gradient”), the water flux in the sample is smaller than the corresponding value of the soil hydraulic conductivity at the applied tension. From numerical analysis of the flow problem, they concluded that unsaturated conductivity can be obtained with an accuracy of 10% for all texture classes of the USDA soil texture triangle. In this paper, we test the methodology for three different soil types using an appropriate apparatus. The results match well with independent saturated conductivity measurements on the wet side, and with unsaturated conductivity measurements in the medium moisture range that were obtained with the evaporation method.

Measuring near‐saturated hydraulic conductivity of soils by quasi unit‐gradient percolation—1. Theory and numerical analysis

“…This is illustrated exemplarily in Fig. for one of the real experiments ( Sarkar et al., ). In the virtual experiments, the time steps in boundary conditions had different durations (5 to 50 minutes per step) for the twelve different soil classes, depending on their hydraulic properties and state of suction, in order to ensure that steady state conditions were always reached, which was checked by the equality of inflow and outflow rates to three significant digits, i.e ., .…”

“…) and to evaluate them systematically. Based on the findings of the numerical study, we performed and evaluated real measurements, which will be documented in a companion paper ( Sarkar et al., ).…”

“…The choice of the geometry data was determined by our physical experiments, where we used a diameter of the infiltrating disk of 4.5 cm in contact with a soil column with a diameter of 8.0 cm ( Sarkar et al., ). Hydraulic parameters for all 12 soil classes of the USDA soil triangle were taken from Carsel and Parrish (), as shown in Tab.…”

“…Typical example of time dependent boundary conditions: stepwise varying pressure head for four rounds (real data example for first sample of soil SAU from Sarkar et al., ).…”

“…Our strategy to investigate these fundamental questions was creating ''synthetic'' experimental data with numerical modelling (section 2.2) and to evaluate them systematically. Based on the findings of the numerical study, we performed and evaluated real measurements, which will be documented in a companion paper (Sarkar et al, 2019).…”