Study of Groundwater Circulation Using Stable Isotopes : the Example of the Punaruu Watershed (Tropical Oceanic Island of Tahiti, French Polynesia)

Abstract:

The increasing demand for drinking and industrial water, especially in the most populated areas of the tropical oceanic Island of Tahiti in French Polynesia (South central Pacific), makes it necessary to conduct hydrological and hydrogeological studies on water resources and management. Our investigation area represents the second largest watershed of Tahiti called Punaruu. The largest industrial zone of Tahiti occupies the minor low valley of this catchment and is particularly impacted by dredging of the stream and rock removals since several decades whereas the major high part is naturally well preserved. This study aims to identify the main infiltration areas of the aquifers of this industrial zone as well as the areas at low elevations to be protected from potential pollutions. During the period between May 2013 and July 2015, we have collected rainwater samples from five rain gauges located at elevations ranging from 0 to 1420 m. We have also performed water sampling from the main rivers and three springs up to altitudes of 800 m as well as six pumping boreholes in the industrial zone. Chemical (major elements) and stable isotopic (^_δ18O and ^_δ2H) analyses have been done from all these water samples and help us to constrain a conceptual model of groundwater circulation within such a complex discontinuous volcanic structure.