Using radon-222 to study coastal groundwater/surface-water interaction in the Crau coastal aquifer (southeastern France) | Utilisation du radon-222 pour l’étude des interactions côtières eau souterraine/eau de surface dans l’aquifère côtier de La Crau (sud-est de la France) El uso de radón-222 para estudiar la interacción del agua subterránea/agua superficial costera en el acuífero costero de Crau (sureste de Francia) 利用氡-222研究(法国)东南部Crau沿海含水层沿海的地下水/地表水相互作用 Usando radônio-222 para estudar interação das águas subterrâneas costeira/águas de superficiais no aquífero costeiro do Crau (sudeste da França)
2016
Mayer, Adriano | Nguyen, Bach Thao | Banton, Olivier
Radon has been used to determine groundwater velocity and groundwater discharge into wetlands at the southern downstream boundary of the Crau aquifer, southeastern France. This aquifer constitutes an important high-quality freshwater resource exploited for agriculture, industry and human consumption. An increase in salinity occurs close to the sea, highlighting the need to investigate the water balance and groundwater behavior. Darcy velocity was estimated using radon activities in well waters according to the Hamada “single-well method” (involving comparison with radon in groundwater in the aquifer itself). Measurements done at three depths (7, 15 and 21 m) provided velocity ranging from a few mm/day to more than 20 cm/day, with highest velocities observed at the 15-m depth. Resulting hydraulic conductivities agree with the known geology. Waters showing high radon activity and high salinity were found near the presumed shoreline at 3,000 years BP, highlighting the presence of ancient saltwater. Radon activity has also been measured in canals, rivers and ponds, to trace groundwater discharges and evaluate water balance. A model of the radon spatial evolution explains the observed radon activities. Groundwater discharge to surface water is low in pond waters (4 % of total inputs) but significant in canals (55 l/m²/day).
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