Soil water infiltration measurements using electrical impedance tomography

Characterizing hydraulic properties of different types of soils is of great importance for agricultural and geological studies. In situ measurement of soil hydraulic conductivity is a time-consuming task since data has to be recorded at fixed time intervals over a period of minutes or hours depending on the type of soil. Moreover, it is still necessary to use real data for validating models. This paper presents the design of a multimodal infiltrometer which consists of an automated soil infiltration single-ring measurement device and Electrical Impedance Tomography (EIT) data acquisition system. A data logger measures the liquid level change of the 100 cm Marriotte-type column, as the water infiltrates at a rate by maintaining a small positive pressure on the water as it moves out of the infiltrometer. A phantom fitted with 16 plate-type electrodes is embedded in the measurement site underneath the water outlet for EIT measurements. The automated infiltrometer data is used for determining soil saturated hydraulic conductivity whereas the EIT measurement system produces images of the water movement through the material below the land surface whose water saturation fluctuates. The equipment was tested in laboratory and in situ trials on four different types of soil (silt loam, clay loam, silty clay and sandy loam) around the Cuitzeo lake watershed (19°58′N, 101°08′W). The results suggest that EIT can be used to image the dynamics of water infiltration of different types of soils, and the automated infiltrometer can provide better information that visually recorded measurements. Thus, a set of images can be used for measuring drainage properties as well. This has important implications for improving computer modelling and soil characterization.