Dataset on onshore groundwaters and offshore submarine spring of a Mediterranean karst aquifer during flow reversal and saltwater intrusion

Description

This dataset was generated to study the behavior of a Mediterranean coastal (Thau lagoon, southern France) karst aquifer for which the flow reversal phenomenon has occurred several times in the past through a submarine karst spring located at -29.5 meters below the lagoon level. Since the 1960s, seven flow reversal phenomena have occurred, the last one occurring between 11/28/2020 and 03/14/2022. During these phenomena, which can last from a few weeks to several months, the salty water is absorbed from the lagoon to the conduit of the submarine spring, which leads to the salinization of the underlying karst aquifer. The equipment and the monitoring of the submarine spring constitute a key element of the research project to understand of the hydrogeological functioning of the karst system during regular conditions, when fresh groundwater flows out of the submarine spring, as well as during disruptive events, when flow reversal and salty water intrusion through the spring occur. The submarine spring flow dataset is contained in the Vise_Submarine_Spring.xlsx file, which contains three excel sheets. The first sheet named "Flow" contains the data of the hourly averages of the flow rates measured at a time step of 5 minutes between 06/26/2019 and 12/31/2022. During regular flowing conditions (i.e. groundwater flows out of the spring), the flow rate is positive. During flow reversal periods, the flow rate becomes negative. The "Comments" column is used to qualify this flow context. The second sheet named "SpC" and the third sheet named "Temp" contain, data of the hourly averages of water specific conductivity and temperature data, respectively, measured at a 5 minutes time step between 06/26/2019 and 10/13/2022. During flow reversal periods, the specific conductivity and temperature measured are those of the lagoon water, these measurements make it possible to qualify the physico-chemical properties of the salty water infiltrated by the karst spring during disruptive events. The lagoon water level dataset is contained in the Thau_Lagoon.xlsx file. The sheet named “WaterLevel” contains the hourly data of the lagoon water levels measured at the H-lagoon site. The data is expressed in meters above sea level. Measured lagoon water level fluctuations were repeatedly checked at the reference point using a manual water level gauge. The groundwater dataset is contained in the Thau_karst_groundwater.xlsx file, which has 9 sheets, one for each of the following stations referenced to the BRGM groundwater database (BSS number with hypertext links). Each sheet contains piezometric data (expressed in m.a.s.l) between 01/01/2017 and 12/31/2022 for the longest time series. The sheets also provides the groundwater temperature and specific conductivity data (with the exception of point BSS002JEKD). Information on the depth of the measurement probe is indicated into the metadata section of each excel sheet.

Steps to reproduce

An experimental device was especially design for collect and measure the flow rate at the submarine spring. The submarine spring discharge was measured with a one-meter-diameter flowmeter (Optiflux 4300W model, Krohne) connected to a data logger installed on the lagoon shore. Water level, water electric conductivity and temperature of submarine spring were measured in the experimental device with two OTT PLS C in situ probes connected on land to an OTT NetDL data logger equipped with a GPRS modem. The measuring lagoon water level is performed in a strainer tube using an ultrasonic sensor. Water level, water specific conductivity (SpC) at 25 °C and temperature of karst aquifer were measured at springs and boreholes with Dipper PETC data logger (SEBA Hydrometry) equipped with a GPRS modem.

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