Aquifer Compartmentalization in the Lower Rhine Embayment

Faults that are part of the Roer Valley Rift System compartmentalize groundwater flow systems in the Lower Rhine Embayment. We hypothesize that these faults cutting through the unconsolidated sediments of the Lower Rhine Embayment act as combined conduit-barrier systems. In such systems fluid flowing vertically along faults will be enhanced while fluids flowing across-faults will be impeded. We propose that this dual behaviour can be understood by assuming the simultaneous shear of sand and the smear of clay along the fault plane. The barrier properties of faults in the Lower Rhine Embayment are noticeable by strong hydraulic head gradients that are enhanced by groundwater extractions that are impacting regional scale groundwater flow. Preliminary, idealized models show that these head drops can coexist with vertically enhanced fluid migration. However, hydraulic head data alone are not sufficient to demonstrate this behaviour. For this purpose we have collected a suite of groundwater samples for detailed hydrochemical analyses. These samples have been analyzed for stable isotope ratios, trace metals, groundwater ages, and noble gasses. The results of these analyses are being integrated using two- and three-dimensional hydrogeological models that are used to calculate transient hydraulic head, temperature and groundwater age distributions.