High frequency saltwater intrusion monitoring using borehole geophysical tools (SMD)

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

High frequency saltwater intrusion monitoring using borehole geophysical tools (SMD)

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

Monitoring the groundwater quality/quantity from your desktop – application to salt water intrusion monitoring EMI: Environmental data Management Interface

More and more data of groundwater quantity and quality is acquired and exists. The means to collect it (GPRS, Radio, IoT…) have been developed during the last years. Storing this data is not a problem. But, having a mean to have all the different data gathered in the same platform with the possibility to display and analyse them in a simple and rapid way doesn’t exist enough. A web application has been developed to answer this problem. This application enables to store all type of groundwater data (water table elevation, groundwater quality, borehole information, water extraction data…) in order to display it. The organisation of this application allows displaying all the data by site. Several tools to analyse the data are included (calculation of hydrogeological parameters, statistics, interpolation) allowing a first data interpretation, in particular for salt water intrusion issues. This web application was born from collaboration between IT experts and environmental engineers

Monitoring the groundwater quality/quantity from your desktop – application to salt water intrusion monitoring EMI: Environmental data Management Interface

More and more data of groundwater quantity and quality is acquired and exists. The means to collect it (GPRS, Radio, IoT…) have been developed during the last years. Storing this data is not a problem. But, having a mean to have all the different data gathered in the same platform with the possibility to display and analyse them in a simple and rapid way doesn’t exist enough. A web application has been developed to answer this problem. This application enables to store all type of groundwater data (water table elevation, groundwater quality, borehole information, water extraction data…) in order to display it. The organisation of this application allows displaying all the data by site. Several tools to analyse the data are included (calculation of hydrogeological parameters, statistics, interpolation) allowing a first data interpretation, in particular for salt water intrusion issues. This web application was born from collaboration between IT experts and environmental engineers

Reaction-induced volume change triggers brittle failure at eclogite facies conditions

International audienceMetamorphic reactions can lead to important changes in rock strength and density. Eclogitization constitutes one of the most emblematic transformations in continental subduction zones, where conversion of lower crustal rocks into eclogite facies rocks correlates with the occurrence of seismogenic events. The relationship between eclogitization and seismicity has been highlighted in several studies, but the processes that trigger brittle failure remain highly debated. Indeed, whether the change in density (from ∼2850 kg.m−3 to ∼3300 kg.m−3) or the change in rheology can lead to embrittlement is still enigmatic. Here we show that eclogitization-induced volume change occurring out of equilibrium can, by itself, generate sufficient shear stress to fail the rocks at high-pressure conditions. Intermediate-depth earthquakes in continental subduction zones could therefore be explained by volume changes, even without considering rheological modifications induced by mineral reactions. Our results also indicate that interplay between negative volume change and frictional plastic yielding can enhance the propagation of the eclogitization process by a runaway mechanism as long as the reaction is not limited by the lack of reactants