A significant number of subsurface phenomena and environmental problems involve preferential flow and solute transport in variably-saturated porous media. Relatively large connected void spaces or highly permeable pore regions such as macropores, root holes, structural voids, channel-like openings or coarse-textured sediment structures in the vadose zone have been widely documented to provide rapid pathways for spreading and transmission of nutrients and contaminants (e.g. pesticides, heavy metals, NAPL), particles and microorganisms, and radionuclides from the soil surface to drains, ditches, surface waters, and deep aquifers. An improved understanding of the key governing processes and thus the ability to reliably predict the rate and direction of preferential flow and contaminant transport in variably-saturated media would be of great economic benefit, for example in the planning and implementation of remediation programs at contaminated macroporous and fractured sites and in the improved management of soil landscapes. The question of how to upscale pore or Darcy-scale descriptions of preferential flow and transport to the larger scales relevant for management (e.g. fields, farms, catchments and landscapes) is one key unresolved issue, which hampers reliable prediction of the fate of contaminants and the development of optimal management strategies and practices.

The objectives of this session are to stimulate papers dedicated to preferential flow processes at scales ranging from structured macroporous soils to complex landscapes, with the aim to support the development of more sustainable land and water management, the improved and efficient use of soil and water resources and the prevention of environmental pollution.

Major topics include:
1. Model development, theoretical approaches and experimental evidence of preferential flow and transport at different scales (pedon-hillslope-field-landscape);
2. Linking soil structure forming/degrading processes (e.g. effects of earthworm burrowing activity and plant root systems, soil tillage) to the preferential flow process;
3. Relation between infiltration and surface runoff in the context of preferential flow processes;
4. Preferential transport of contaminants, particles, colloids, and microorganisms;
5. Reactions, transformations and matter dynamics in and along preferential flow paths;
6. Advanced techniques for visualizing preferential flow paths at relevant scales;
7. Methodologies to link preferential flow across scales, including hydropedological approaches.