Geological and climate control on regional groundwater flow

Groundwater constitutes a crucial ressource in many regions of the world. The main challenge derives from the heterogeneity of the geological media and its impact on groundwater flow at the regional scale. We describe the influence of geodynamic processes on aquifer compartmentalisation in crystalline media and the role of large scale structures on fluid flows and resources. The main objectives are: i) identifying the factors controlling the permeability in different geodynamic or geomorphologic contexts (ie. stress, weathering processes); ii) characterizing the link between geomorphology and fluid flow at the regional scale (origin of water, recharge processes and resident times), and iii) quantifying the impact of climate changes on recharge and groundwater flow. 

Flow and transport processes in porous and fractured media: the interwell scale

While hydrogeophysical methods at the borehole scale are relatively mature, there is a dearth of reliable methods to characterize the geometries of flow paths at larger scales, i.e. between boreholes, and their impact on transport. We develop innovative field methods that aims at characterizing hydraulic and transport properties of fractured reservoirs, as well as reactive processes involved during transport and mixing. We use new range of multidisciplinary technologies, including high resolution flow tomography to infer hydraulic properties of fractured reservoirs, fiber-optic measurements of the spatial distribution of temperature to investigate flow dynamic, subsurface and borehole geophysical methods to image hydraulically active structures, multi-tracer transport experiments to quantify transport properties, dissolved gases monitoring to infer residence times, mixing and related water-rock interaction processes.

Relationship between hydrodynamic conditions and reactive processes in aquifers

Although of prime interest for many applications, the link between flow dynamic and reactive processes is poorly understood at the field scale. We run a specific research program to analyse the impact of transient hydrodynamic conditions on specific (bio)geochemical reaction involved at different scales, from pumped site contexts (mainly denitrification processes) to the watershed scale. We could describe transient reaction kinetics involved in long-term groundwater abstraction conditions by coupling statistical approach and end-member mixing analysis. We have notably identified the role of secondary mineral phases in providing the electron needed for the autotrophic denitrication to be sustained. We have also demonstrated that microbial community composition was driven by groundwater residence time and hydrological conditions in three different groundwater abstraction sites.

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© 2017 by Clément Roques