scholarly journals Review: Hydrogeology of weathered crystalline/hard-rock aquifers—guidelines for the operational survey and management of their groundwater resources

2021 ◽  
Author(s):  
Patrick Lachassagne ◽  
Benoît Dewandel ◽  
Robert Wyns
Keyword(s):  
Hydraulic Conductivity ◽  
Conceptual Model ◽  
Hard Rock ◽  
Groundwater Resources ◽  
Ground Surface ◽  
Fracture Network ◽  
Weathering Processes ◽  
Hard Rocks ◽  
Geological Discontinuities ◽  
Hard Rock Aquifers

AbstractHard rocks or crystalline rocks (i.e., plutonic and metamorphic rocks) constitute the basement of all continents, and are particularly exposed at the surface in the large shields of Africa, India, North and South America, Australia and Europe. They were, and are still in some cases, exposed to deep weathering processes. The storativity and hydraulic conductivity of hard rocks, and thus their groundwater resources, are controlled by these weathering processes, which created weathering profiles. Hard-rock aquifers then develop mainly within the first 100 m below ground surface, within these weathering profiles. Where partially or noneroded, these weathering profiles comprise: (1) a capacitive but generally low-permeability unconsolidated layer (the saprolite), located immediately above (2) the permeable stratiform fractured layer (SFL). The development of the SFL’s fracture network is the consequence of the stress induced by the swelling of some minerals, notably biotite. To a much lesser extent, further weathering, and thus hydraulic conductivity, also develops deeper below the SFL, at the periphery of or within preexisting geological discontinuities (joints, dykes, veins, lithological contacts, etc.). The demonstration and recognition of this conceptual model have enabled understanding of the functioning of such aquifers. Moreover, this conceptual model has facilitated a comprehensive corpus of applied methodologies in hydrogeology and geology, which are described in this review paper such as water-well siting, mapping hydrogeological potentialities from local to country scale, quantitative management, hydrodynamical modeling, protection of hard-rock groundwater resources (even in thermal and mineral aquifers), computing the drainage discharge of tunnels, quarrying, etc.

scholarly journals Hydrogeological conceptual model of andesitic watersheds revealed by high-resolution heliborne geophysics

2019 ◽  
Vol 23 (5) ◽  
pp. 2321-2338 ◽  
Author(s):  
Benoit Vittecoq ◽  
Pierre-Alexandre Reninger ◽  
Frédéric Lacquement ◽  
Guillaume Martelet ◽  
Sophie Violette
Keyword(s):  
Hydraulic Conductivity ◽  
Conceptual Model ◽  
Preferential Flow ◽  
Groundwater Resources ◽  
Watershed Scale ◽  
Volcanic Island ◽  
Multidisciplinary Study ◽  
Hydrogeological Characteristics ◽  
Volcanic Islands ◽  
Very High

Abstract. We conducted a multidisciplinary study at the watershed scale of an andesitic-type volcanic island in order to better characterize the hydrogeological functioning of aquifers and to better evaluate groundwater resources. A heliborne Time Domain ElectroMagnetic (TDEM) survey was conducted over Martinique in order to investigate underground volcanic structures and lithology, characterized by high lateral and vertical geological variability and resulting in a very high heterogeneity of their hydrogeological characteristics. Correlations were made on three adjacent watersheds between resistivity data along flight lines and geological and hydrogeological data from 51 boreholes and 24 springs, showing that the younger the formations, the higher their resistivity. Correlation between resistivity, geology and transmissivity data of three aquifers is attested: within the interval 10–100 ohm m and within a range of 1 to 5.5 Ma, the older the formation, the lower its resistivity, and the older the formation, the higher its transmissivity. Moreover, we demonstrate that the main geological structures lead to preferential flow circulations and that hydrogeological watersheds can differ from topographical watersheds. The consequence is that, even if the topographical watershed is small, underground flows from an adjacent watershed can add significant amounts of water to such a catchment. This effect is amplified when lava domes and their roots are situated upstream, as they present very high hydraulic conductivity leading to deep preferential groundwater flow circulations. We also reveal, unlike basaltic-type volcanic islands, that hydraulic conductivity increases with age in this andesitic-type volcanic island. This trend is interpreted as the consequence of tectonic fracturing associated with earthquakes in this subduction zone, related to andesitic volcanic islands. Finally, our approach allows characterization in detail of the hydrogeological functioning and identification of the properties of the main aquifer and aquitard units, leading to the proposition of a hydrogeological conceptual model at the watershed scale. This working scale seems particularly suitable due to the complexity of edifices, with heterogeneous geological formations presenting high lateral and vertical variability. Moreover, our study offers new guidelines for accurate correlations between resistivity, geology and hydraulic conductivity for volcanic islands. Finally, our results will also help stakeholders toward a better management of water resources.

scholarly journals Improving the Methods for Processing Hard Rock Aquifers Boreholes’ Databases. Application to the Hydrodynamic Characterization of Metamorphic Aquifers from Western Côte d’Ivoire

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3219
Author(s):  
Aoulou Kouassi Aristide ◽  
Severin Pistre ◽  
Oga Yéï Marie Solange ◽  
Dewandel Benoît ◽  
Lachassagne Patrick
Keyword(s):  
Cote D'ivoire ◽  
Côte D’Ivoire ◽  
Hard Rock ◽  
Research Work ◽  
Geological Data ◽  
Cote D’Ivoire ◽  
Weathering Processes ◽  
Percentile Method ◽  
Côte D'ivoire ◽  
Hard Rock Aquifers

Statistical analysis of a borehole database, linear discharges, and water strikes processing enabled an understanding of the structure, geometry and hydrodynamic properties of the metamorphic hard rock aquifers from the Montagnes District, Western Côte d’Ivoire. The database comprises 1654 boreholes among which 445 only were usable for this research work after its pre-processing. Analysis shows that the structure of the aquifer is similar to that observed in several other areas in the world: it developed due to weathering processes, comprises the capacitive saprolite, 10–20 m thick on average, and an underlying transmissive fractured layer, overlying the unweathered impermeable hard rock. The fractured layer is 80 m thick, the first 40 to 45 metres being its most productive zone, with a 11.3 m3/h median productivity. This research shows that metamorphic aquifers exhibit similar aquifer properties (thickness, hydrodynamic parameters) as plutonic ones and that there is interest in using such databases for research and other purposes. However, a rigorous pre-treatment of the data is mandatory, and geological data from published maps must be used instead of the geological data from the database. A previous methodology aiming at processing the boreholes’ linear discharges was improved. It notably appears that the slope method must be preferred to the percentile method.

scholarly journals Assessment of Aquifer Vulnerability Using Integrated Geophysical Approach in Weathered Terrains of South China

2019 ◽  
Vol 11 (1) ◽  
pp. 1129-1150 ◽  
Author(s):  
Muhammad Hasan ◽  
Yanjun Shang ◽  
Weijun Jin ◽  
Gulraiz Akhter
Keyword(s):  
South China ◽  
Hard Rock ◽  
Groundwater Resources ◽  
Aquifer Vulnerability ◽  
X Ray Diffraction ◽  
Fractured Aquifer ◽  
Formation Factor ◽  
X Ray ◽  
Hard Rock Aquifers ◽  
Groundwater Reserves

Abstract Despite being rich in groundwater resources, assessment of hard-rock aquifers in many areas of Asia is difficult given their strong heterogeneity. However, delineation of such aquifers is essential for estimation of the groundwater reserves. In addition, the vulnerability of hard-rock aquifers is controlled by the weathered/fractured zones because it is the place where most of the groundwater reserves are contained. In this work, an integrated approach of the electrical resistivity tomography (ERT), high precision magnetic, X-ray Diffraction (XRD), physicochemical analysis and pumping test data was performed to investigate the hard-rock aquifers occurring in the weathered terrains. This approach reveals seven fractures/faults (F1 to F7) and four discrete layers such as the topsoil cover, highly weathered, partly weathered and unweathered rock. The groundwater resources are estimated as a function of different parameters i.e., aquifer resistivity (ρo), transverse unit resistance (Tr), hydraulic conductivity (K), transmissivity (T), rock formation factor (F) and rock porosity (Φ). These parameters divide the groundwater resources into four aquifer potential zones with specific ranges of ρo, Tr, K, T, F and Φ i.e., high, medium, poor, and negligible potential aquifers. The results suggest that the high potential aquifer reserves are contained within the weathered/fractured and fault zones. The X-ray diffraction (XRD) technique analyzes quartz as the major mineral (>50%). The physicochemical and geophysical analysis suggests good groundwater quality in the investigated area. The integrated results are highly satisfied with the available borehole information. This integrated geophysical approach for the estimation of groundwater resources is not only applicable in the weathered terrains of South China, but also in many other areas of the weathered/fractured aquifer in Asia and beyond.

Fracture network analysis of the St-Eustache quarry, Quebec, Canada, for groundwater resources management

2009 ◽  
Vol 46 (7) ◽  
pp. 828-841 ◽  
Author(s):  
Jean-Michel Lemieux ◽  
Donna Kirkwood ◽  
René Therrien
Keyword(s):  
Rock Mass ◽  
Hydraulic Conductivity ◽  
Statistical Data ◽  
Groundwater Resources ◽  
Geometric Model ◽  
Fracture Network ◽  
Limited Information ◽  
Resources Management ◽  
Bedding Planes ◽  
Hydrogeological Study

A detailed structural survey has been conducted on a fractured sedimentary rock formation in the St-Eustache quarry, Quebec, Canada, to supplement a hydrogeological study. The two main types of discontinuities in the quarry are horizontal bedding planes and vertical joints. The fracture network is classified as a stratabound network that could be considered as an equivalent porous medium (EPM) for groundwater flow for a volume of rock of 25 to 100 m3. Using detailed statistical data of the fracture network, a geometric model is used to infer a range of hydraulic conductivity values for the low permeability fractures not directly measured with hydraulic tests and treated as EPM for their interpretation. This analysis shows that the vertical and horizontal fractures have about the same permeability in the rock mass, except for a few high hydraulic-conductivity bedding planes. Hydraulic conductivity of single fractures ranges between 1.7 × 10−3 and 1.7 × 10−1 m/s. The porosity of the bulk rock mass inferred from fracture spacing measurements was found to be between 0.03% and 0.3%. Because vertical boreholes provide limited information on vertical fractures, the interpretation of hydraulic tests at the site was greatly improved by the structural surveys.

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