Abstract
In February 2016, two remote controlled geophysical monitoring tools (SMD) have been installed for the first time in the Reunion Island. Settled into two piezometers drilled into a basaltic coastal aquifer, between the ocean and a production well, they allow the record of groundwater electrical conductivity (ECw) logs on a 30 min basis. Thanks to those two tools, water operator continuously knows the shape and the position of the SWI as data are available online on a secured web application designed especially for SWI data management. During the observation period a 5,15 m rise of SWI interface has been recorded. Knowing the average porosity, water table elevation and SWI interface position it is possible to estimate available fresh groundwater volume. Along a 1 km band between extraction well and the ocean, available fresh groundwater volume was found to be 1 259 000 m3 in June 2016. In June 2017, due to SWI progression this volume was found to be 777 000 m3, that to say a 480 000 m3 volume of freshwater replaced by brackish water. SMD network will now be spread in the Reunion Island to improve coastal extraction well management knowing SWI shape and position on a high frequency basis.
Highlights
Due to a high demographic pressure, Reunion Island coastal aquifers are more and more subject to saltwater intrusion
Two remote controlled geophysical monitoring tools (SMD) have been installed into two piezometers settled in between the coastline and a production wells. They allow the record of hourly EC vertical logs to know on an hourly basis SWI interface position
Those geophysical tools are connected to a Web application (EMI) used by water operator to adapt fresh water extraction flow rate according to SWI
Summary
Due to a high demographic pressure, Reunion Island coastal aquifers are more and more subject to saltwater intrusion. Some coastal wells settled too close from the shore, in basaltic aquifers has to be abandoned, and new ones have to be drilled farthest from the coastline inducing financial damaged. As saltwater intrusion is increasing years after years on this island, it demands strong investments to precisely monitor fresh/saline interface position and its evolution according freshwater abstractions To achieve this objective, two remote controlled geophysical monitoring tools (SMD) have been installed into two piezometers settled in between the coastline and a production wells. Two remote controlled geophysical monitoring tools (SMD) have been installed into two piezometers settled in between the coastline and a production wells They allow the record of hourly EC vertical logs to know on an hourly basis SWI interface position. Those geophysical tools are connected to a Web application (EMI) used by water operator to adapt fresh water extraction flow rate according to SWI
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