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

Schuler, Philip; Duran, L.; McCormack, T.; Gill, L.

Submarine and intertidal groundwater discharge through a complex multi-level karst conduit aquifer | Submarine und intertidale Grundwasserschüttung durch einen komplexen Mehrebenen-Karströhrenaquifer Décharge sous-marine et intertidale d’eaux souterraines d’un complexe aquifère karstique à conduits étagés Descarga de agua subterránea submarina e intermareal a través de un acuífero kárstico complejo de conductos multiniveles 复杂多级岩溶管道含水层的水下和潮汐间地下水排泄 Descarga submarina e entremarés de águas subterrâneas através de um complexo aquífero cárstico de condutos multiníveis

2018

Schuler, Philip | Duran, L. | McCormack, T. | Gill, L.

The quantification of submarine and intertidal groundwater discharge (SiGD) or purely submarine groundwater discharge (SGD) from coastal karst aquifers presents a major challenge, as neither is directly measurable. In addition, the expected heterogeneity and intrinsic structure of such karst aquifers must be considered when quantifying SGD or SiGD. This study applies a set of methods for the coastal karst aquifer of Bell Harbour in western Ireland, using long-term onshore and offshore time series from a high-resolution monitoring network, to link catchment groundwater flow dynamics to groundwater discharge as SiGD. The SiGD is estimated using the “pollution flushing model”, i.e. a mass-balance approach, while catchment dynamics are quantified using borehole hydrograph analysis, single-borehole dilution tests, a water balance calculation, and cross-correlation analysis. The results of these analyses are then synthesised, describing a multi-level conduit-dominated coastal aquifer with a highly fluctuating overflow regime draining as SiGD, which is in part highly correlated with the overall piezometric level in the aquifer. This concept was simulated using a hydraulic pipe network model built in InfoWorks ICM [Integrated Catchment Modeling]® version 7.0 software (Innovyze). The model is capable of representing the overall highly variable discharge dynamics, predicting SiGD from the catchment to range from almost 0 to 4.3 m³/s. The study emphasises the need for long-term monitoring as the basis for any discharge studies of coastal karst aquifers. It further highlights the fact that multiple discharge locations may drain the aquifer, and therefore must be taken into consideration in the assessment of coastal karst aquifers.

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