Groundwater flows in weathered crystalline rocks: Impact of piezometric variations and depth-dependent fracture connectivity

Guihéneuf, Nicolas; Boisson, Alexandre; Bour, Olivier; Dewandel, Benoı̂t; Perrin, José; Dausse, Amélie; Viossanges, Mathieu; Chandra, S.; Ahmed, Shakeel; Maréchal, Jean-Christophe

doi:10.1016/j.jhydrol.2014.01.061

Cited by 108 publications

(100 citation statements)

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“…1c) dominate with a depth density decreasing relationship as frequently observed in a superficial fractured context (Dewandel et al, 2006;Guihéneuf et al, 2014;Hencher et al, 2011;Martel, 2006;Twidale, 1973). These horizontal fractures present weathering traces, induced by oxygenated water circulation in this superficial part of the aquifer and are mainly developed west of the MFT80 well (see Figs.…”

Section: Geological Contextsupporting

confidence: 54%

“…Groundwater resources in igneous and metamorphic crystalline rocks are often restricted within weathered subsurface fractured bedrock and saprolite that typically extends up to 50 m depth (Dewandel et al, 2006;Guihéneuf et al, 2014;Hencher et al, 2011;Maréchal et al, 2004;Wright, 1992). In deeper part of the bedrock, groundwater flows is mainly controlled by the presence of fractures in an impervious matrix (Banks et al, 2002(Banks et al, , 1996Clauser, 1992;Singhal and Gupta, 2010).…”

Section: Introductionmentioning

confidence: 99%

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Groundwater sources and geochemical processes in a crystalline fault aquifer

Roques

Aquilina

Bour

et al. 2014

Journal of Hydrology

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International audienceThe origin of water flowing in faults and fractures at great depth is poorly known in crystalline media.This paper describes a field study designed to characterize the geochemical compartmentalization of adeep aquifer system constituted by a graben structure where a permeable fault zone was identified. Analysesof the major chemical elements, trace elements, dissolved gases and stable water isotopes reveal theorigin of dissolved components for each permeable domain and provide information on various watersources involved during different seasonal regimes. The geochemical response induced by performinga pumping test in the fault-zone is examined, in order to quantify mixing processes and contributionof different permeable domains to the flow. Reactive processes enhanced by the pumped fluxes are alsoidentified and discussed.The fault zone presents different geochemical responses related to changes in hydraulic regime. Theyare interpreted as different water sources related to various permeable structures within the aquifer.During the low water regime, results suggest mixing of recent water with a clear contribution of olderwater of inter-glacial origin (recharge temperature around 7 C), suggesting the involvement of watertrapped in a local low-permeability matrix domain or the contribution of large scale circulation loops.During the high water level period, due to inversion of the hydraulic gradient between the major permeablefault zone and its surrounding domains, modern water predominantly flows down to the deep bedrockand ensures recharge at a local scale within the graben.Pumping in a permeable fault zone induces hydraulic connections with storage-reservoirs. The overlaidregolith domain ensures part of the flow rate for long term pumping (around 20% in the present case).During late-time pumping, orthogonal fluxes coming from the fractured domains surrounding the majorfault zone are dominant. Storage in the connected fracture network within the graben structure mainlyensures the main part of the flow rate (80% in the present case). Reactive processes are induced by mixingof water from different sources and transfer conditions. A specific approach is applied to quantify thereaction rate involved along the pumping time. Autotrophic denitrification coupled with iron mineralsoxidation is highlighted and water rock interaction is clearly enhanced by the flux changes induced bypumping

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Section: Geological Contextsupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Groundwater sources and geochemical processes in a crystalline fault aquifer

Roques

Aquilina

Bour

et al. 2014

Journal of Hydrology

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“…Due to lack of this information, fractured rock zones are sometimes used as disposal areas for radioactive waste (Neuman, 2005). In addition, since most of the fractured rock aquifers are shallow aquifers, usually up to 50 m deep (Guiheneuf et al, 2014), they are susceptible to inter-annual climate variabilities, particularly in drier environments (Lapworth et al, 2013). Understanding dominant hydrogeological processes in fractured rock formations is the first step to sustainable management of the resource regardless of climatic conditions.…”

Section: Introductionmentioning

confidence: 99%

Groundwater recharge and flow processes as revealed by stable isotopes and geochemistry in fractured Hornblende-biotite-gneiss, Rivirivi Catchment, Malawi

Kambuku¹,

Tsujimura²,

Kagawa³

2018

Afr. J. Environ. Sci. Technol.

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To enable sustainable management of groundwater resources, knowledge of dominant hydrogeological processes is fundamental. In this study, stable isotopes of water [δ 18O and δD] and major inorganic ions were used to investigate recharge and groundwater flow processes in a catchment underlain by fractured and faulted hornblende-biotite-gneiss. Spatial and temporal geochemical distributions consistently showed Mg-Ca-HCO 3 dominated water facies. Evaporation was established to be the main process affecting isotopic enrichment in the study area. Stable isotopic and geochemical data revealed that a combination of thin overburden soil of up to 30 mm thickness and presence of fractures seem to enable localized rapid preferential recharge processes of isotopically enriched rainwater in shallow groundwater around the ridge section. However, the thicker overburden soil (up to 3 m) along the valley seems to allow only isotopically depleted large rain events to recharge deeper groundwater. The isotopically enriched small rain events seem to be allowed to evaporate before recharging groundwater in areas with thicker overburden soils. It was further established that the valley section also receives regional lateral groundwater recharge from high altitude areas. Regional groundwater flow system in the northwest-southeast (NW-SE) direction was thus established with local flows confirmed around the ridge section. It was also revealed that Ntcheu Fault acts as a conduit of regional groundwater flow in the NW-SE direction. Inter-aquifer connectivity and surface water and groundwater interaction were construed around the ridge section and around B12 and R8, respectively. The rapid recharge and flow phenomena in this type of geological media make the resource susceptible to pollution and inter-annual climatic variabilities. It is prudent therefore to consider such information when implementing other developmental plans in the catchment.

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“…In this type of aquifer, the occurrence and pattern of water rely on the existence and degree of fracturing, as the water is stored and transmitted through crevices, joints and fractures [11,12,13]. Groundwater flow and storage in this area have always been a major issue due to its abundant heterogeneity and anisotropy, with an irregular distribution of groundwater pathways.…”

Section: Introductionmentioning

confidence: 99%