Insights into saline intrusion and freshwater resources in coastal karstic aquifers using a lumped Rainfall–Discharge–Salinity model (the Port-Miou brackish spring, SE France)

Abstract

. Insights into saline intrusion and freshwater resources in coastal karstic aquifers using a lumped Rainfall-Discharge-Salinity model (the Port-Miou brackish spring, SE France). Journal of Hydrology, Elsevier, 2016, 540, pp.148-161. 10.1016/j.jhydrol.2016 Accepted Manuscript This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe aim of this study was to develop a conceptual model of saline intrusion within coastal karst aquifers by analyzing rainfall-discharge-salinity data and to assess freshwater resources using a lumped modeling approach. In a first step, we analyzed 4 years of data (rainfall, discharge and salinity times series) of the Port-Miou brackish submarine spring in South France (400 km²). A conceptual model of the aquifer was then designed to differentiate a deep brackish reservoir and a shallower fresh one. Salinity variations at the spring are assumed to be controlled mainly by dilution originating from the fresh water in the shallower reservoir. In a second step, a lumped modeling approach was developed based on the conceptual model to simulate discharge as well as salinity over time. We proposed a reservoir-model to take into account slow and fast components in the shallower part of the aquifer and a saline intrusion in the deeper one. This Rainfall-Discharge-Salinity model was calibrated and validated for two periods of 1.5 years at a daily time step and was also tested to reproduce a multi-annual evolution of the available discharge and salinity time series. Good simulation results were obtained to reproduce water and mass budgets as well as discharge and salinity dynamics 2 during several hydrological cycles. The simultaneous modeling of hydrodynamics and quality data showed the robustness of the model in addition to its easy implementation. Our results led us to propose a new type of seawater mixing mechanism for brackish springs: the dilution type, in addition to the well-known Ventury suction and Head balance types. The application of the lumped model on the Port-Miou brackish spring validated the hydrogeological processes deduced from experimental data, given an initial quantification of the freshwater resources available in such complex brackish karstic aquifers.

Groundwater management of a highly dynamic karst by assessing baseflow and quickflow with a rainfall-discharge model (Dardennes springs, SE France)

“…This reorganization generated deep phreatic karst systems connected to vauclusian springs by chimney-shafts, with perascensum speleogenesis (Mocochain et al, 2011). In the saturated zone of the aquifer, these chimney-shafts may act as connecting or draining channels between the deep part of the aquifer and the current base level, as was shown in the submarine spring of Port-Miou (Arfib and Charlier, 2016) located 34 km westward of the Dardennes case-study.…”

“…The two lower reservoirs can be in parallel and separated (Bezès, 1976), or in parallel with water exchange between them (Rimmer and Hartmann, 2012), or in parallel but water from the matrix has to pass the conduit system before it reaches the spring (Geyer et al, 2007). Other structures also exist: Hartmann et al (2012) tested two lower reservoirs in series, while Arfib and Charlier (2016) added a third reservoir. These models were used to discuss the regional karst groundwater resources (Bakalowicz, 2005;Fleury et al, 2009;Ladouche et al, 2014), as a tool for the identification and quantification of flow (Fleury et al, 2007), to assess the vulnerability (Butscher and Huggenberger, 2008), to estimate the groundwater balance (Jukić and Denić-Jukić, 2009), or for flood hazard (Fleury et al, 2013).…”

Submarine and intertidal groundwater discharge through a complex multi-level karst conduit aquifer

“…The development of coastal karst systems may be related to glaciation and glacial maxima, sea level changes, and tectonics, such as the large-scale event of the Messinian salinity crisis which lowered the level of the Mediterranean to as much as 1500 m below the present level (Doerflinger et al 2009). A result of that may be coastal karst aquifers with multiple outlet levels, such as Port-Miou in the Mediterranean (Fleury et al 2007), which consists of a deep brackish conduit reservoir up to 223 mbsl and a shallow freshwater reservoir (Arfib and Charlier 2016).…”

Accuracy and sensitivity of radium mass balances in assessing karstic submarine groundwater discharge in the stratified Calanque of Port-Miou (Mediterranean Sea)

“…This case study offers two main advantages: i) the shape of the calanque limits the exchanges (inflow and outflow) with the open sea at the mouth of the natural cove ii) the discharge and salinity of the submarine spring are monitored by continuous in-situ sensors at a gauging station in the flooded karst conduit located 500 meters upstream of the sea (underground laboratory). Moreover, this spring is one of the major sources of SGD to the Mediterranean Sea in Europe (Tulipano et al 2005;Custodio 2010;Arfib and Charlier, 2016). In addition, there is no sediment or runoff, which means that a simplified radium mass balance can be performed.…”