Papers by Jean-Christophe Comte
HAL (Le Centre pour la Communication Scientifique Directe), Dec 5, 2008
Hydrogeology Journal, May 10, 2015
The process of accounting for heterogeneity has made significant advances in statistical research... more The process of accounting for heterogeneity has made significant advances in statistical research, primarily in the framework of stochastic analysis and the development of multiple-point statistics (MPS). Among MPS techniques, the direct sampling (DS) method is tested to determine its ability to delineate heterogeneity from aerial magnetics data in a regional sandstone aquifer intruded by low-permeability volcanic dykes in Northern Ireland, UK. The use of two two-dimensional bivariate training images aids in creating spatial probability distributions of heterogeneities of hydrogeological interest, despite relatively 'noisy' magnetics data (i.e. including hydrogeologically irrelevant urban noise and regional geologic effects). These distributions are incorporated into a hierarchy system where previously published density function and upscaling methods are applied to derive regional distributions of equivalent hydraulic conductivity tensor K. Several K models, as determined by several stochastic realisations of MPS dyke locations, are computed within groundwater flow models and evaluated by comparing modelled heads with field observations. Results show a significant improvement in model calibration when compared to a simplistic homogeneous and isotropic aquifer model that does not account for the dyke occurrence evidenced by airborne magnetic data. The best model is obtained when normal and reverse polarity dykes are computed separately within MPS simulations and when a probability threshold of 0.7 is applied. The presented stochastic approach also provides improvement when compared to a previously published deterministic anisotropic model based on the unprocessed (i.e. noisy) airborne magnetics. This demonstrates the potential of coupling MPS to airborne geophysical data for regional groundwater modelling.
Frontiers in Ecology and Evolution
Karst ecosystems represent up to 25% of the land surface and recent studies highlight their poten... more Karst ecosystems represent up to 25% of the land surface and recent studies highlight their potential role as a sink for atmospheric methane. Despite this, there is limited knowledge of the diversity and distribution of methane-oxidizing bacteria (MOB) or methanogens in karst caves and the sub-surface environment in general. Here, we performed a survey of 14 shotgun metagenomes from cave ecosystems covering a broad set of environmental conditions, to compare the relative abundance and phylogenetic diversity of MOB and methanogens, targeting biomarker genes for methane monooxygenase (pmoA and mmoX) and methyl-coenzyme M reductase (mcrA). Taxonomic analysis of metagenomes showed 0.02–1.28% of classified reads were related to known MOB, of which Gammaproteobacterial MOB were the most abundant making up on average 70% of the surveyed caves’ MOB community. Potential for biogenic methane production in caves was also observed, with 0.008–0.39% of reads classified to methanogens and was dom...
Unearthed, 2016
Mapping a waste disposal site using Tellus airborne geophysical data' in M.E. Young (ed.), Uneart... more Mapping a waste disposal site using Tellus airborne geophysical data' in M.E. Young (ed.), Unearthed: impacts of the Tellus surveys of the north of Ireland. Dublin. Royal Irish Academy.
NSG2020 26th European Meeting of Environmental and Engineering Geophysics, 2020
Advances in Geoethics and Groundwater Management : Theory and Practice for a Sustainable Development, 2021
Across the Island of Ireland, hard rock aquifers which are found to underlie over 65% of Ireland ... more Across the Island of Ireland, hard rock aquifers which are found to underlie over 65% of Ireland (Robins and Misstear, 2000) are commonly referred to as poorly productive bedrock aquifers (PPA), characterised by low well yields (GSI, 2006). Despite their limited role in water supply, PPAs are found to contribute significantly to the maintenance of river baseflow levels, especially in upland catchments during sustained dry periods (Comte et al., 2012). Typically, these units are considered to be devoid of intrinsic matrix porosity: instead, the flow of groundwater is confined to secondary porosity generated through interconnected fractures and fissures. Previous studies have highlighted the challenges in characterising PPA systems due to the heterogeneity of geological structures at micrometre–metre (cf. Neuman, 2005) and regional scales (km to 10s km, cf. Krasny, 2002). This is particularly the case in hard rock environments where the permeability of bedrock is largely dictated by t...
Journal of Hydrology, 2021
Sedimentology, 2021
Sediments deposited by glacial meltwaters (for example, ice‐contact delta deposits) form permeabl... more Sediments deposited by glacial meltwaters (for example, ice‐contact delta deposits) form permeable packages in the subsurface that can act as reservoirs for both water and hydrocarbons. They are also an important source of aggregate for the construction industry. As reservoirs they are challenging to characterize in terms of their structure, flow and storage properties due to their complex depositional history. In this study, ice‐contact deltas of Salpausselkä I and II end moraines in Southern Finland are studied using a combination of geomorphological mapping, sedimentological studies and near surface geophysical methods. Sedimentary logs from isolated outcrops were correlated to ground penetrating radar (GPR) profiles to unravel the internal structure and depositional history of these ice‐contact deltas. Subsequently, electrical resistivity tomography (ERT) and gravity data were analysed to estimate the depth to bedrock and to model porosity distribution within the sediments. Resu...
Environmental Modelling & Software, 2021
Hydrogeology Journal, 2021
Understanding the role of geological heterogeneity on the performance of managed aquifer recharge... more Understanding the role of geological heterogeneity on the performance of managed aquifer recharge (MAR) in terms of effective groundwater storage is crucial to design MAR systems. Natural aquifers are affected by a variety of geologic strata and structures at different scales, which are responsible for wide ranging hydraulic properties. This study combines physical experiments and numerical modeling to investigate the effect of geologic structures commonly encountered in sedimentary environments, on MAR-induced groundwater flow patterns using injection wells. Models were conceptualized and parametrized based on the hydrogeological conditions of Tailan River basin in arid NW China, which hosts a typical, structurally complex, alluvial-fan aquifer system affected by sediment layering, clay lenses and anticline barriers, and is extensively studied for the strategic potential of MAR in addressing water shortages in the region. Results showed that, compared to a homogeneous scenario, high-permeability aquifer layers shortened groundwater ages, decreased the thickness of the artificially recharged water lenses (ARWLs), and shifted the stagnation points downstream. Clay lenses increased groundwater residence times but had little effect on spatial flow patterns due to their elongation parallel-to-flow direction. Overall groundwater ages, as well as the thickness of ARWLs created through injection on the upstream side of an anticline, increased, and this to a larger extent than through injection on the downstream side, which did not increase significantly compared to the homogeneous scenario. Results provide insights for MAR optimization in naturally heterogeneous aquifer systems, along with a benchmark tool for application to a wide range of typical geological conditions.
Journal of Hydrology, 2021
Hydrogeology Journal, 2020
The Nairobi volcano-sedimentary regional aquifer system (NAS) of Kenya hosts >6 M people, incl... more The Nairobi volcano-sedimentary regional aquifer system (NAS) of Kenya hosts >6 M people, including 4.7 M people in the city of Nairobi. This work combines analysis of multi-decadal in-situ water-level data with numerical groundwater modelling to provide an assessment of the past and likely future evolution of Nairobi’s groundwater resources. Since the mid-1970s, groundwater abstraction has increased 10-fold at a rate similar to urban population growth, groundwater levels have declined at a median rate of 6 m/decade underneath Nairobi since 1950, whilst built-up areas have increased by 70% since 2000. Despite the absence of significant trends in climatic data since the 1970s, more recently, drought conditions have resulted in increased applications for borehole licences. Based on a new conceptual understanding of the NAS (including insights from geophysics and stable isotopes), numerical simulations provide further quantitative estimates of the accelerating negative impact of abs...
Advances in Water Resources, 2020
Journal of Soils and Sediments, 2019
Purpose The aim of this work was to identify and analyze the records of flood-drought cycles as p... more Purpose The aim of this work was to identify and analyze the records of flood-drought cycles as preserved in the sediments of the Notwane reservoir, southern Botswana, in order to better understand how extreme events affect water and sediment quality. This work represents the first attempt to study the reservoir sediments in arid to semi-arid environments and suggests that they could be used as proxies for the characterization of the effects of flood-drought cycles. Materials and methods For the first time in an arid context like Botswana, sediments from artificial reservoirs were explored through correlating sediment records with the presence and quantity of pollutants in the reservoir’s wider arid and semi-arid catchment after the latest extreme flood event of 2017. Sediments from the Notwane reservoir were collected with a push corer to a maximum depth of 80 cm. Sediments were then analyzed for grain size distribution, organic matter content, and concentrations of heavy metals (F...
Hydrological Sciences Journal, 2018
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Papers by Jean-Christophe Comte