How to unravel relationships between soil structure and preferential flow in structured soils with fast tomography at the continuum scale?

Abstract:

The modeling of water flow in the vadose zone and the understanding of processes and mechanisms that control preferential flow is still a challenge for many environmental issues. Since a long time, tridimensional X-ray images have been used to characterize the structures of intact soil cores. Conversely, imaging of water dynamics in soil structures was scarcely developed except on quite small samples in the order of a few centimeters to a few millimeters. As soil structure is a key-controlling factor, the understanding of the complex relationships between the topology and morphology of the pore space on flow distribution and hydraulic properties cannot be undertaken on such small samples. Therefore, we recently proposed the visualization and characterization of flow processes at the core scale (soil volumes of dimensions above 10 cm) with 3D image sequences acquired in a X-ray medical scanner. Last generation of these scanners combining a helical acquisition mode to the multislice capability can now provide very short acquisition times in the order of few seconds for a decimeter column. The 3D image sequences acquired during simulated rainfall events within the scanner were processed and analyzed with new ad hoc tools. Results will focus on 1) the recognition of the functional part of the macropore network related to the flow distribution, 2) its comparison to the entire structure and 3) the estimation of the macroscopic surface exchange between the active macropore network and the soil matrix obtained during the recording of water infiltration.