Microflowmeter-tension disc infiltrometer – Part I: Measurement of the transient infiltration rate

The tension disc infiltrometer is a useful tool for in situ measurements of soil hydraulic characteristics in the vadose zone. Soil hydraulic properties can be estimated from an analysis of the transient section of the cumulative infiltration curve, which is commonly measured from the water-level drop in the reservoir tower. This paper presents a new design of tension disc infiltrometer with the disc separated from a Mariotte tube, the bubble tower and the water-supply reservoir, in which the full infiltration rate curve is measured with a microflowmeter plus Mariotte tube system (MF). This disc infiltrometer was tested in the laboratory on two 1D sand columns and two 1D and 3D 2-mm sieved loam soil columns, and in the field in three different soil-structure conditions. The cumulative infiltration and infiltration rate curves recorded with the MF method were subsequently compared with the corresponding curves measured from the water-level drop in the water-reservoir tower (WLD). Although the cumulative infiltration curves calculated with the MF method fitted well with those obtained using the WLD technique, the laboratory experiments showed that the MF system allowed more accurate estimates of the infiltration rate curves. Smoothing data using a simple moving average algorithm made it possible to improve the characterization of the infiltration rate curves. These results were corroborated in field experiments, in which the MF system proved to be more robust than the standard WLD procedure. These results confirm that the disc infiltrometer design proposed here can provide a solid alternative to the classical disc infiltrometer, and, as described in the second paper of this series (), offers an alternative for estimating the soil hydraulic properties from an analysis of the infiltration rate curves.