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Reference : UMR6118-JORHEY-003
Workplace : RENNES
Date of publication : Friday, November 08, 2019
Type of Contract : FTC Scientist
Contract Period : 12 months
Expected date of employment : 4 March 2020
Proportion of work : Full time
Remuneration : 2500/2900€ without taxes
Desired level of education : PhD
Experience required : 1 to 4 years
The hyporheic zone – named from the Greek hypo (under) - rheos (flow) –, is a sharp and puzzling interface connecting surface water (rivers) to the groundwater (aquifers). Sharp, because its thickness (a few meters) is small compared to the typical scales involved in the critical zone (several kilometers), and also because strong biogeochemical gradients develop in this layer, in response to mixing between surface and subsurface water of differing ages and compositions (Fig 1). Puzzling, because of its key, yet debated, role in altering biogeochemical signals at the basin scale, notably on greenhouse gases such as nitrous oxide (via denitrification), carbon7(via biomass production) and other contaminants such as arsenic (via redox reactions)8and nitrates (via nitrification). Today, a better understanding of the small-scale flow processes occurring through the hyporheic interface is necessary to correctly model hyporheic exchanges of river beds. An appealing strategy to gather such new knowledge is via the experimental study simplified analogical models of the hyporheic zone.
The first objective (6 months) of the post-doctoral project is to develop an experimental setup to monitor hyporheic fluxes under controlled surface and groundwater flow conditions, notably via the index-matching technique. This technique has been developed by the host team during several years and has reach a great level of maturity. The next objective (6 months) is to map the spatio-temporal distribution of conservative and reactive exchanges inside the sediment bed as a function of the roughness and permeability of the interface to evidence the main mechanisms for hyporheic mixing and compare them to field observations. This objective will be achieved owing to smart fluorescent probes that can be visualized with laser induced fluorescence.
The applicant should have obtained a PhD degree in Fluid mechanics, Physics, or Geosciences during the last 4 years, and already published at least 1 scientific paper as first author. Strong experimental skills with fluids are required, with additional knowledge in data and image processing. Theoretical skills in continuum mechanics and notions of chemistry are also sought-after. Knowledge of scientific programming is mandatory (including Python, Matlab, OpenFoam, ...).
The Géosciences Rennes laboratory team gathers 160 scientists of various background: physics, fluid mechanics, geophysics, geochemistry and geomorphology. It is located in a dynamical campus in the middle of an historical town, Rennes, at 1h25 of Paris. Hyporheic exchanges have been already considered in the lab through river-groundwater exchanges at medium to large scales (1m-1km) in local rivers (Olivier Bour, Alain Crave, Camille Bouchez). In turn, the recent experimental breakthroughs in porous columns (ERC ReactiveFronts, Tanguy Le Borgne) offer promising perspective for a finer characterization of hyporheic flows linking pore scale to the reach scale, and a possible reinterpretation of field data. The post-doctoral project is part of a 4 years research project founded by the French National Science Agency and starting in 2020. The Post-Doctoral researcher will work in relative autonomy, in close collaboration 2 senior researchers (Joris Heyman and Tanguy Le Borgne), 1 Engineer, 4 post-doc researchers and 4 PhD students. The project offer possible collaborations with Australian and Austrian colleges. If desired, the post-doc may take part in under-graduate teaching in the university, with a complement salary.
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