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Congratulations to INTERFACES fellow, Tamara Kolbe, who published her first paper last week.  Tamara’s work has been published by the Journal of Hydrology (DOI:10.1016/j.jhydrol.2016.05.020) and is available free for a short period of time at http://dx.doi.org/10.1016/j.jhydrol.2016.05.020.    

Coupling 3D groundwater modeling with CFC-based age dating to classify local groundwater circulation in an unconfined crystalline aquifer

Tamara Kolbe, Jen Marçais, Zahra Thomas, Benjamin W. Abbott, Jean-Raynald de Dreuzy, Pauline Rousseau-Gueutin, Luc Aquilina, Thierry Labasque, Gilles Pinay

Nitrogen pollution of freshwater and estuarine environments is one of the most urgent environmental crises. Shallow aquifers with predominantly local flow circulation are particularly vulnerable to agricultural contaminants. Water transit time and flow path are key controls on catchment nitrogen retention and removal capacity, but the relative importance of hydrogeological and topographical factors in determining these parameters is still uncertain. In the recent published paper, we used groundwater dating and numerical modeling techniques to assess transit time and flow path in an unconfined aquifer in Brittany, France. We found that groundwater flow was highly local (mean travel distance = 350 m), while CFC-based ages were quite old (mean = 40 years). Sensitivity analysis revealed that groundwater travel distances were not sensitive to geological parameters (i.e. arrangement of geological layers and permeability profile) within the constraints of the CFC age data. However, circulation was sensitive to topography in the lowland area where the water table was near the land surface, and to recharge rate in the upland area where water input modulated the groundwater table.

We propose a new indicator (rGW-LOCAL) to quantify these groundwater table controls. The ratio rGW-LOCAL is sensitive to recharge conditions as well as topography and it could be used to compare controls on groundwater circulation within or between catchments.