Characterisation of karst hydrogeology in Western Ireland using geophysical and hydraulic modelling techniques

McCormack, Ted; O’Connell, Yvonne; Daly, Eve; Gill, Laurence; Henry, Tiernan; Perriquet, Marie

doi:10.1016/j.ejrh.2016.12.083

Cited by 33 publications

(39 citation statements)

References 31 publications

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“…Zones of deep karstification and high densities of perpendicular fractures were found in the deep borehole (BH1) at depths between 93 and 110 mbgl, corresponding to the sea level of the most recent ice age (McCormack et al 2017).…”

Section: Hydrogeologymentioning

confidence: 99%

“…The groundwater flow is conduit-dominated from south to north, i.e. updip, as in the neighbouring catchment in the west, and the main groundwater discharge from the catchment is believed to have occurred via SiGD into Bell Harbour bay (Perriquet et al 2012;McCormack et al 2017). Bell Harbour bay has a very shallow topography, largely influenced by tidal oscillation: in the long term, 89% of water in the bay is drained during ebb tide.…”

Section: Hydrogeologymentioning

confidence: 99%

“…A shallow conduit following south-north within the valley was detected by McCormack et al (2017). This conduit is assumed to connect the two turloughs in the valley, Gortboyheen (T1) and Luirk (T2), allowing the turloughs to rapidly fill following persistent periods of rain, and similarly to almost empty again.…”

Section: Hydrogeologymentioning

confidence: 99%

“…While the DCN approach only accounts for groundwater flow in conduits or in connections between fractures, the semi-distributed pipe network model used here also includes additional diffuse groundwater recharge in interception catchments. Multiple groundwater flow dynamics and SiGD were modelled using InfoWorks ICM ® version 7.0 commercial software (Innovyze, Tweed Heads, Australia), guided by principles outlined in Gill et al (2013) and McCormack et al (2017). The pipe model resembles diffuse groundwater recharge in permeable pipes modelled as laminar flow following Darcy's law, combined with the outline of major conduit flow horizons connected to the turlough (T1) on the surface, considering open channel and pressurised flow hydraulic conditions.…”

Section: Pipe Network Modelmentioning

confidence: 99%

“…However, until recently, the discharge of coastal karst aquifers in Ireland has largely been conceptualised as intertidal discharge or shallow SGD close to the shore-for example, the Bell Harbour catchment in the Burren plateau located in the west of Ireland McCormack et al 2017). Groundwater discharge into Bell Harbour bay is known to occur as submarine discharge as well as in the vicinity of intertidal springs, hence SiGD.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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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 Bpollution 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 m 3 /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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Section: Hydrogeologymentioning

confidence: 99%

Section: Hydrogeologymentioning

confidence: 99%

Section: Hydrogeologymentioning

confidence: 99%

Section: Pipe Network Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2018

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Toward a new conceptual model for groundwater flow in merokarst systems: Insights from multiple geophysical approaches

Sullivan

Zhang

Behm

et al. 2020

Hydrological Processes

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Merokarst aquifers — relatively thin (<1–2 m) karstified carbonate units interbedded between mudstone, shale, or sandstone — constitute a significant proportion of carbonate terrain and underlie a large portion of the west‐ and south‐central USA, yet few advances have been made in our understanding of porosity development and flow‐path generation in these complex systems in decades. Toward this end, we used a multi‐geophysical approach at the well‐studied Konza Prairie Biological Station (KPBS), a part of the larger Flint Hills (25,734 km2), underlain by thin limestone units (1–2 m thick) interbedded with mudstone/shale units (2–4 m thick), to elucidate hydrologic connectivity and potential controls on known groundwater flow directions. We combined electrical resistivity tomography (ERT), surface and borehole nuclear magnetic resonance (NMR), and ground penetrating radar (GPR) measurements across a low order catchment where over 25 boreholes and groundwater wells sampling perched aquifers could be used to constrain interpretation of lithology, potential flow paths, and permeability. Data revealed that groundwater export may be an unappreciated component of lateral‐flow‐dominated models used to represent merokarst in that: (a) potentiometric surfaces from two limestone units showed groundwater flows toward a hydrologic depression, opposite the direction of stream flow, in the upstream portion of the catchment, (b) long term measures of groundwater levels revealed a greater variance and overall water storage in this same upstream area compared to wells near the outlet, and (c) ERT and NMR results indicate pronounced lateral heterogeneity within a given unit, suggestive of a greater degree of vertical hydrological connectivity than usually considered for horizontally‐layered merokarst. Our data suggest vertical connectivity can shunt water to depth in these “sandwiched” merokarst aquifers, yielding atypical groundwater flow directions and unrealized deep export of weathering solutes and carbon.

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Characterization of seasonal groundwater origin and evolution processes in a geologically heterogeneous catchment using geophysical, isotopic and hydro‐chemical techniques (Lough Gur, Ireland)

O’Connell

Rocha

Daly

et al. 2022

Hydrological Processes

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Lough Gur is a shallow groundwater fed eutrophic lake situated within a small agricultural catchment containing volcanic and karst rock features in mid‐west Ireland. Seasonally active conduits linking two spring discharge locations from the lake under high flow conditions were revealed using dye tracing and a terrestrial geophysical survey, highlighting the architecture of the conduit flow path from Lough Gur to its discharge spring. A radon survey combined with a lake geophysical survey identified the locations of in‐lake discharge springs and thickness of the lakebed sediments. Falling head hydraulic characterization experiments illustrated the heterogenous nature of lakebed sediments and hydrograph analysis coupled with stable isotopes of water (δ18O and δ2H) revealed significant surface water ‐ groundwater interaction during high flow periods. Significantly, δ18O and δ2H signatures plot above the global meteoric water line and local meteoric water line indicating hydration of silicate minerals and direct isotope exchange of δ18O between water and rock minerals. Groundwater δ18O and δ2H signatures during low flow periods indicate that recharge sources are influenced by enriched surface waters and precipitation while a wider range of signatures during high flow periods indicates a greater variation of sources. D‐excess signatures illustrate rapid rainfall infiltration under high flow conditions, thereby demonstrating the vulnerability of the groundwater, while lake water signatures confirm widespread surface water‐groundwater interaction/mixing. Hydrochemical analyses confirm both silicate weathering and carbonate dissolution as primary geochemical processes with Mg/Ca ratios suggesting greater groundwater residence time during low flow periods. Correlations between δ13CDIC and dissolved organic carbon suggest a seasonal switch in the source of DIC to groundwaters between the oxidation of organic matter in summer and dissolution of carbonate minerals in winter. The SI saturation index for calcite (SIC) illustrates calcium carbonate precipitation along with CO2 evasion to be a perennial processes. Finally, the spatial variation for nitrate isotopic signatures (δ18ONO3‐ and δ15NNO3‐) suggests a number of nitrate sources to groundwaters including soil organic nitrogen, manure and/or domestic effluent with indications of denitrification processes under low flow conditions.

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Characterisation of karst hydrogeology in Western Ireland using geophysical and hydraulic modelling techniques

Cited by 33 publications

References 31 publications

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

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

Toward a new conceptual model for groundwater flow in merokarst systems: Insights from multiple geophysical approaches

Characterization of seasonal groundwater origin and evolution processes in a geologically heterogeneous catchment using geophysical, isotopic and hydro‐chemical techniques (Lough Gur, Ireland)

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