Understanding water and mass fluxes through the various compartments of the external terrestrial layers. Examples: Flow in a fractured vadose zone and exchange flow at the sediment-water interface of river systems
Understanding water and mass fluxes through the various compartments of the external terrestrial layers is currently considered as a common challenge in different environmental and energetic applications. This seminar discusses two examples. The first one deals with the study of climate change impact on water resources in a fractured aquifer/spring system in Lebanon. The main goal is to investigate the effects of fractures on predictions of available water resources under climate change conditions. This requires simulations of unsaturated flow in fractured vadose zones. Current models and simulators involve significant simplifications as they cannot consider preferential flows. We developed a new model based on an explicit description of fractures and we implemented advanced numerical techniques to allow for large scale simulations, both in space and time. The results show that, neglecting the preferential flow processes leads to an overestimation of the amount of available water.
The second example deals with the study of water and mass fluxes at the sediment-water interface (SWI) of rivers. This interface is a critical boundary for river dynamics where hydrological and biogeochemical processes tightly control pesticide dissipation. Transport processes govern pesticide transit time and distribution across the SWI depending on the water flow and hyporheic exchanges. Simultaneously, reactive processes such as sorption and biodegradation are responsible for retardation or actual degradation of pesticides within the porous sediment. Knowledge on the interplay of these processes at the SWI remain sparse mostly because a physically-based generalized framework to model transport and reactivity at fluid-porous interfaces is still lacking. Here, we combine multi-physical model development and laboratory experiments to investigate the effects of representative hydrological conditions on pesticide transport at the SWI.