This session combines presentations on recent developments and state-of-the-art in understanding, measuring, and modelling subsurface hydrology and solute/vapor transport processes in both the saturated (groundwater) and unsaturated (vadose) zones, as well as across boundaries.

The correct quantification of transport processes, which occur at different spatial and temporal scales, is challenging and strongly influences predicted spreading, dilution and mixing rates. However, dispersion, mixing and chemical reactions are local phenomena that strongly depend on the interplay between large-scale system heterogeneity and smaller-scale processes. Much effort has been placed in the fundamental understanding of these processes since they are of practical relevance to identify the fate of contaminants in surface and subsurface water that can affect human health and the environment.

The aim of this session is to discuss the effect of flow heterogeneity on transport at different scales, from pore scale up to catchment scale - including theory, modeling, laboratory and field experiments as well as applications. Our contributions deal with the questions: Is macrodispersivity a meaningful parameter? Under which conditions does spatially variable flow enhance mixing and chemical reactions? What is the role played by diffusive processes in modeling transport in porous media? How to upscale dispersion and reactive transport from pore to field-scale? What is the relation between ADE models and dynamic structures of catchment hydrology like travel time distributions? What are appropriate methods to characterize the relevant properties? What are the recent improvements in transport measurement technologies?
(The session is cosponsored by the Ground Water Commission of IAHS)