Cracks, fractures and macropores are typical features of natural soils and fissured rock formations, and promote preferential flow and mass transfer. Lithological heterogeneity (e.g., soil layering, lateral and vertical bedding, channels, etc.) adds its contribution to preferential flow at larger scales. In addition to these physical factors, chemical and geochemical processes (e.g., organic matter) may promote typical hydraulic behaviors leading to preferential flow (e.g., hydrophobicity and finger flow). This session focuses on experimental and theoretical challenges and state of the art of methods to characterize, measure and model preferential flows, and their effects on water infiltration into the soil, flow in the vadose zone, and their implications for the water-soil-plant-atmosphere continuum. The session also welcomes studies on the impact of preferential flows on mass transfer in the vadose zone of fractured porous media and heterogeneous soils. Preferential flows are expected to regulate the access of pollutants and solutes to soil reactive particles, and thus the efficiency of pollutant removal by soils and the geochemical processes that govern soil evolution and weathering processes (e.g., precipitation / dissolution processes). On larger scales, some landforms, such as mine waste covers are known to have highly heterogeneous properties, and yet quantifying and modelling water and solute movement in these systems is often required for regulatory and management purposes.
The proposed session will welcome studies including but limited to the following topics:
• Tracking preferential flows and mass transfers in soils using high-tech tracer techniques including MRI, tomography CAT, etc.
• Visualization or abstraction of the pore and fracture structure (pore size distribution, pore connectivity, type of macroporosity) or field heterogeneity (lithological and geological heterogeneity) and implications for preferential flow
• Linking preferential flow pattern with soil geochemical properties (e.g. organic matter and hydrophobicity)
• Coupling the physical processes of preferential flows and geochemical processes for understanding solute sorption and solute desorption, and mineral precipitation and dissolution
• Fracture network geometry and connectivity, its influence on volume-effective flow and mass transport dynamics, and on matrix-fracture interaction processes
• Recent theoretical developments for modeling preferential flows across scales – with scaling efforts from the pore and fracture to the Darcian and landscape scales
• Quantification and modelling of water flow and solute transport within heterogeneous substrates and complex geological structures such as mine wastes (e.g. tailings and waste rocks), mine waste covers and rocky/gravelly substrate

The analysis of infiltration, especially when infiltration experiments are used to estimate soil hydraulic properties, is becoming increasingly important for the geosciences community. Indeed, infiltration process is an important component of the hydrological cycle; it refers to the entry into the soil of water and all substances transported by it. Thus, estimates of soil infiltrability are mandatory key tasks to be performed on a number of hydrologic, agronomic, ecological or environmental studies. Under natural conditions, infiltration is characterized by high spatial variability resulting from a high degree heterogeneity of both soil texture and structure. On the other hand, local infiltration experiments are sensitive to space-time variability of the unsaturated soil properties. High-resolution infiltration measurement is crucial to properly describe and analyze soil water properties needed to model soil water flow. The aim of the session focus is on the principles, capabilities, and applications of both infiltration techniques and models at different scales, including, but not limited to: - field infiltration measurements for a wide variety of infiltration devices, from the most simple to the most sophisticated and complete, combined to complementary information provided by other methods (i.e., TDR probes, GPR, ERT, etc.), - new or revisited numerical and analytical models to account for multiple-porosity, hydrophobicity, organic matter, or swelling on infiltration, clogging, biofilm development; and many other factors that are not taken into account in classic infiltration models, - estimation of soil hydraulic parameters, among which the saturated-unsaturated hydraulic conductivity and sorptivity which are fundamental in soil science. We will explore diverse topics of infiltration and interactions encompassing soil processes. The session is not limited by methodology or approach and we welcome studies including laboratory or numerical simulation of infiltration, in-situ studies of water and solutes infiltration. We welcome contributions from simulated and real data investigations in the laboratory or field, successful and failed case studies as well as the presentation of new and promising infiltration approaches.

The continuum approach is a classical framework to describe and understand the soil—water dynamics and the soil effective—stress state in unsaturated soils. This approach is greatly dependent on the soil—water constitutive laws, viz soil—water retention curve, relative hydraulic conductivity, and those derived by these two principal ones. They link the real soil and its model. Advancements along their development and the comprehension of their role stand at the intersection of experimental measurements, mathematical representation and modelling, numerical solutions, theoretical understandings and practical applications. The growing possibility of monitoring soil moisture with rather simple tools has allowed to perform many field experiments devoted to understand the links between environmental variables and soil moisture. Also, climate change research has boosted this field of knowledge. Many terrestrial critical zone observatories have been installed, therefore new information both at the local and at the catchment scale is now available. Many open issues still exist in understanding the role of soil moisture in the environment, in combination with other factors such as soil and air temperature, air humidity, carbon and nitrogen availability, etc. Also, it is necessary the study of the structure of time and spatial variability of soil moisture itself, for example to combine the different scales of measurements. Usually soil moisture is measured at the local scale, but hydrogeophysics allows to have larger scale measurements and micrometeorological tools such as eddy covariance provide even larger scale estimation of gas and energy fluxes. The cosmic ray have increasing applications and the remote sensing images are powerful tools, therefore interesting issues regard the spatial upscaling, and the sampling frequency.

We invite contributions related to the understanding of the soil--water constitutive laws and to soil moisture monitoring, both finalised to understand the effects of its time and spatial variability, and to study soil moisture itself.

Scientists working both in the biogeosciences, and in soil sciences field are encouraged to participate, for example with study related to the implications of soil moisture on carbon and nitrogen dynamics, as well as on root and plant growth. The growing possibility of monitoring soil moisture with rather simple tools has allowed to perform many field experiments devoted to understand the links between environmental variables and soil moisture. Also, climate change research has boosted this field of knowledge. Many terrestrial critical zone observatories have been installed, therefore new information both at the local and at the catchment scale is now available.