Integration of electrical resistivity tomography, permeability and infiltrometer tests for modelling hydraulic conductivity and infiltration rates in the field

Accurate or exact estimations of hydraulic conductivity (K) and infiltration rate are crucial for understanding soil-water interactions, optimising irrigation practices, evaluating groundwater recharge potential, and designing drainage systems. Conventionally laboratory permeability tests and in-situ infiltrometer tests, provide direct estimates of soil hydraulic behaviour. However, these methods have limitations of their point-specific nature and are unable to capture subsurface heterogeneity across larger spatial scales. In contrast, the electrical resistivity tomography (ERT) technique offers a non-invasive geophysical approach that is capable of detecting subsurface variations in soil electrical resistivity properties. The electrical resistivity estimates can further be interpreted to analyse soil types, soil layer structures, moisture and mineral contents, and pore connectivity. These are ultimately related to soil hydraulic properties, such as hydraulic conductivity and soil-water interaction behaviour, such as vertical infiltration rates. One of the accurate methods of estimating K is a pumping test, which is expensive and time-consuming. Other methods include laboratory permeameter tests, which require the collection of soil samples from the field, which often are disturbed ones and thus may produce K values with considerable uncertainties. The primary goal of this study is to establish the relationship between hydraulic conductivity (K) and electrical resistivity (ER) to replace the tests mentioned above. The second objective of this study is to establish an ER-infiltration rate relationship to convert point-based infiltration measurements into area-wide infiltration maps using resistivity data, minimizing the number of infiltrometer tests needed, saving time, manpower, and resources. Field investigations executed here involve ERT surveys using different electrode configuration arrays, such as the Wenner, Schlumberger, and dipole-dipole, across selected test sites that represent various soil textures and moisture conditions. The resistivity profiles are inverted to generate 2D subsurface sections, enabling identification of moisture zones and shallow saturation patterns. Parallelly, laboratory permeability tests are carried out on undisturbed soil samples to determine hydraulic conductivity, while infiltrometer tests are performed to obtain field-scale infiltration characteristics and steady-state infiltration rates. The combined dataset provided a comparative evaluation of resistivity variations in relation to measured soil-hydraulic parameters. Once these relationships are established, ERT can move beyond the simple imaging and serve as a fast and cost-effective way to estimate how water moves through the soil over a wider area. This will significantly reduce the need for frequent point-based tests and help capture natural variations in soil conditions that are often required in hydrological studies. Site evaluations can thus become faster and efficient, while areas with higher infiltration potential can be identified with greater confidence, and the overall planning of irrigation, drainage, and groundwater recharge strategies becomes more informed and robust.

Keywords: Electrical Resistivity Tomography (ERT); Hydro-geophysical characterization; Hydraulic Conductivity; Infiltration Rate; Groundwater recharge; Soil Heterogeneity.