Saltwater wedge variation in a non-anthropogenic coastal karst aquifer influenced by a strong tidal range (Burren, Ireland)

Perriquet, Marie; Léonardi, Véronique; Henry, Tiernan; Jourde, Hervé

doi:10.1016/j.jhydrol.2014.10.006

Cited by 19 publications

(11 citation statements)

References 32 publications

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“…3d) and springs (Figs. 7 and 8a) in correspondence of faults has been recognized in many geological realms of the word such as the Carboniferous limestones of Western Ireland (Gillespie et al 2001; Perriquet et al 2014), in the Triassic dolomitic limestones in Austria (Bauer et al 2016), and in the Jurassic limestones of Central and Southern Italy (Galdenzi and Menichetti 1995; Billi et al 2007; Petrella et al 2007; Barberio et al 2017). Notably, the coupling of low values of effective flowing porosity and rigorous modelling of fault permeability (see the left side of Fig.…”

Section: Discussionmentioning

confidence: 99%

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Medici

West

Chapman

et al. 2019

Environ Sci Pollut Res

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Viruses and bacteria which are characterized by finite lives in the subsurface are rapidly transported via fractures and cavities in fractured and karst aquifers. Here, we demonstrate how the coupling of a robust outcrop characterization and hydrogeophysical borehole testing is essential for prediction of contaminant velocities and hence wellhead protection areas. To show this, we use the dolostones of the Permian Magnesian Limestone aquifer in NE England, where we incorporated such information in a groundwater flow and particle tracking model. Within this aquifer, flow in relatively narrow (mechanical aperture of~10 −1-1 mm) fractures is coupled with that in pipe cavities (~0.20-m diameter) following normal faults. Karstic cavities and narrow fractures are hydraulically very different. Thus, the solutional features are represented within the model by a pipe network (which accounts for turbulence) embedded within an equivalent porous medium representing Darcian flowing fractures. Incorporation of fault conduits in a groundwater model shows that they strongly influence particle tracking results. Despite this, away from faulted areas, the effective flow porosity of the equivalent porous medium remains a crucial parameter. Here, we recommend as most appropriate a relatively low value of effective porosity (of 2.8 × 10 −4) based on borehole hydrogeophysical testing. This contrasts with earlier studies using particle tracking analyses on analogous carbonate aquifers, which used much higher values of effective porosity, typically~10 2 times higher than our value, resulting in highly non-conservative estimates of aquifer vulnerability. Low values of effective flow porosities yield modelled flow velocities ranging from~100 up to~500 m/day in un-faulted areas. However, the high fracturing density and presence of karstic cavities yield modelled flow velocities up to~9000 m/day in fault zones. The combination of such flow velocities along particle traces results in 400-day particle traces up to 8-km length, implying the need for large well protection areas and high aquifer vulnerability to slowly degrading contaminants.

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Section: Discussionmentioning

confidence: 99%

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Medici

West

Chapman

et al. 2019

Environ Sci Pollut Res

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“…As the bulk resistivity of a granular medium is a function of the porosity, pore fluid resistivity, and clay content (Archie 1942;Waxman and Smits 1968), reduced resistivities suggest faults and/or karst zones. Inversions of a theoretical model (Figure 3d) that simulate the field acquisition procedure for the T1 DD array (Figure 3(b,c)), with added errors to account 1670, 790, 2190, 1520, 2600, 1500, and 1270, respectively. random noise equivalent to 5%, provide a non-unique approximation for the observed resistivities, suggesting the presence of two large diameters approximately 10 to 25 m), water filled conduits (assumed = 20 Ωm water resistivity similar to inland values from Perriquet et al [2014]). This forward model is also subject to uncertainties around clay content and mass fraction.…”

Section: Terrestrial Profilesmentioning

confidence: 99%

“…Groundwater flow within the catchment is via well-developed near-surface (upper 5 m to 10 m) epikarst and through linked pathways of fissures, joints, and large conduits, which allow rapid vertical flow, probably ~20-150 m hr -1 as in neighbouring catchments (Cronin et al 1999;Perriquet et al 2014). The region is characterised by a strong tidal range (Cave and Henry 2011).…”

Section: Geology and Hydrogeology Of Southern Galway Baymentioning

confidence: 99%

“…Electrical resistivity tomography (ERT) has been used effectively in many hydrogeological applications, e.g., aquifer characterisation (Comte et al 2012), groundwater/surface water interactions (Nyquist, Freyer and Toran 2008), seawater contamination (Khalil 2006;Nguyen et al 2009;Martorana et al 2014), salinity studies of lakes and reservoirs (Amidu and Dunbar 2008), and the detection of conduits for groundwater movement through typically heterogeneous karst regions (Zhu, Currens and Dinger 2011). It can be used in combination with methods that have traditionally been used for the investigation of SGD, including, e.g., monitoring of freshwater outputs using seepage metres, piezometres and natural (geochemical) tracers, water balance approaches, hydrograph separation techniques, and theoretical tant role in the coastal hydrogeology (Cave and Henry 2011;Smith and Cave 2012;Wilson and Rocha 2012;McCormack et al 2014;Perriquet et al 2014). This paper describes the use of surface-towed ERT to examine SGD in a coastal karst aquifer setting.…”

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confidence: 99%

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Terrestrial and marine electrical resistivity to identify groundwater pathways in coastal karst aquifers

O’Connell

Daly

Henry

et al. 2017

Near Surface Geophysics

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Groundwater movement in karst aquifers is characterised by high‐velocity fissure and conduit flow paths, and in coastal karst aquifers, these act as pathways for saline intrusion and freshwater discharge to the sea. This paper examines groundwater movement in two neighbouring catchments in the west of Ireland that represent canonical coastal karst aquifers dominated by discharges in the intertidal zone and at offshore submarine springs. Terrestrial and surface‐towed marine electrical resistivity tomography, coupled with ancillary hydrogeological data, identifies the influence of faulting and conduits on groundwater egress/saltwater ingress. The on‐shore and off‐shore subsurface geometry of major fault zones is identified, and the tidal influence of seawater and ground‐water flow is demonstrated in these zones and karst springs. Imaging of these sub‐surface structures is a pre‐requisite for numerical modelling of current and future climate‐driven freshwater–seawater interactions in karst coastal aquifers.

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“…In highly heterogeneous coastal aquifers, in particular for fractured and karst systems, networks of high-permeability geologic structures are found to conduct intruding saltwater along preferential flow paths, deteriorating nearshore fresh groundwater resources (Bonacci & Roje-Bonacci, 1997;Hendrickx & Flury, 2001;Kung, 1990;Perriquet et al, 2014;Webb & Anderson, 1996;Xu et al, 2016). Numerical models have been developed to simulate groundwater flow and solute transport through fractured and karst aquifer systems (e.g., Reimann et al, 2013;Shoemaker et al, 2008;Smith & Schwartz, 1984;Xu et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Preferential Flow Enhances Pumping‐Induced Saltwater Intrusion in Volcanic Aquifers

Geng

Michael

2020

Water Resources Research

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Preferential flow can result in rapid contamination of groundwater resources. This is particularly true in aquifers with connected, high permeability geologic structures and in coastal systems where the oceanic source of contamination is ubiquitous. We consider saltwater intrusion due to pumping in volcanic aquifers with lava tubes represented as connected high-K structures and compare salinization responses to those of heterogeneous aquifers with different structure and equivalent homogeneous systems. Three-dimensional simulations of variable-density groundwater flow and salt transport show that conduits formed by lava flows create preferential groundwater flow in volcanic aquifers. These conduits allow fresh groundwater to extend further offshore than in other systems. However, onshore pumping causes saltwater to migrate landward quickly through the conduits relative to the other models, resulting in more severe saltwater intrusion, particularly at shallow depths. The geometry of geologic heterogeneity in volcanic aquifers leads to increased risk of salinization of fresh groundwater as well as substantial uncertainty due to significant spatial variation in saltwater intrusion. The findings illustrate the importance of considering geologic heterogeneity in assessing the vulnerability of coastal freshwater resources in volcanic and other aquifers with connected high-permeability geologic structures.Plain Language Summary The findings of this study provide insight into vulnerability of volcanic coastal aquifers to salinization due to groundwater pumping. Our results reveal significant landward movement of saltwater due to onshore pumping, which has important implications for vulnerability of coastal freshwater resources in volcanic and other aquifers with connected geologic structures. In coastal regions, the control of saltwater intrusion often relies on salinity detection in monitoring wells located near the shoreline. Our results demonstrate significant spatial variations in saltwater intrusion along the coastline that are strongly correlated to geologic heterogeneity. These variations are difficult to predict; thus, intrusion may easily bypass monitoring wells. These results highlight the importance of considering geologic heterogeneity in studies of saltwater intrusion in volcanic and other heterogeneous aquifers.

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Saltwater wedge variation in a non-anthropogenic coastal karst aquifer influenced by a strong tidal range (Burren, Ireland)

Cited by 19 publications

References 32 publications

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Prediction of contaminant transport in fractured carbonate aquifer types: a case study of the Permian Magnesian Limestone Group (NE England, UK)

Terrestrial and marine electrical resistivity to identify groundwater pathways in coastal karst aquifers

Preferential Flow Enhances Pumping‐Induced Saltwater Intrusion in Volcanic Aquifers

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