| Summary: | The most common method for in situ measurement of saturated hydraulic conductivity (<i>K</i><sub>sat</sub>) of the vadose zone is the constant head well permeameter method. Our general objective is to provide an empirical method for determining volume of water required for measuring <i>K<sub>sat</sub></i> using this procedure. For one-dimensional infiltration, steady state reaches as time (<i>t</i>) → ∞. For three-dimensional water flow from a cylindrical hole under a constant depth of water, however, steady state reaches rather quickly when a saturated bulb forms around the hole. To reach a quasi-steady state for measuring <i>K<sub>sat</sub></i>, we assume an adequate volume of water is needed to form the saturated bulb around the hole and increase the water content outside of the saturated bulb within a bulb-shaped volume of soil, hereafter, referred to as wetted soil volume. We determined the dimensions of the saturated bulb using the Glover model that is used for calculating <i>K<sub>sat</sub></i>. We then used the values to determine the volume of the saturated and wetted bulbs around the hole. The volume of water needed to reach a quasi-steady state depends on the difference between the soil saturated and antecedent water content (Δ<i>θ</i>). Based on our analysis, between 2 and 5 L of water is needed to measure <i>K<sub>sat</sub></i> when Δ<i>θ</i> varies between 0.1 and 0.4 m<sup>3</sup> m<sup>−3</sup>, respectively.
|
|---|