Role of Reef-Flat Plate on the Hydrogeology of an Atoll Island: Example of Rangiroa

On atoll islands, the fresh water lens (FWL) constitutes, for island population, a very important resource various usages. Its shape and thickness highly depend on underground characteristics of several rock formations which constitute island: upper Holocene sediments lower Pleistocene limestone rocks separated by Unconformity. In this study, simple investigation methods were applied Pacific Rangiroa in order to characterize aquifer hydrodynamics their impact FWL. A budget was proposed, including deep infiltration Pumping tests tidal analysis demonstrated confined character its main hydrodynamic properties (storage hydraulic conductivity). The role reef-flat plate hydrogeology highlighted. impermeable nature contributes reduce aquifer. It also flow regime aquifer, inducing high fast level fluctuations due tide forces, consequently increase saline mixing zone. Both phenomena contribute FWL, is only 2 m-thick that atoll.