Mathematical modeling of karstogenesis: an approach based on fracturing and hydrogeological processes

The karstogenesis of a synthetic aquifer is analyzed as a function of the matrix permeability and the fracture density affecting the carbonate reservoir. The synthetic carbonate aquifer generation results from numerical simulations based on Discrete Fracture Network (DFN) and groundwater flow simulations. The aim is to simulate karstogenesis processes in an aquifer characterized by a fracture network, while matching field reality and respecting geometrical properties as closely as possible. DFN are simulated with the soft REZO3D that allows the generation of 3-D realistic fracture networks, especially regarding the relative position of fractures that control the overall network connectivity. These generated DFN are then meshed and considered to perform groundwater flow simulation with the model GroundWater (GW). At each time step and for each fracture element, flow velocity and the mean groundwater age are extracted and used in an analogical dissolution equation that computes the aperture evolution. This equation relies on empirical parameters calibrated with former speleogenesis studies. In this paper, karstogenesis simulations are performed using fixed-head hydraulic boundary conditions within a single stratum as a function of two fracture density settings. The results are interpreted in terms of head fields, mean groundwater age distributions; while total flow rate and average aperture are analyzed as a function of time. The effect of fracture density and rock matrix permeability are then assessed

Tanis

L’année 2019 a été particulièrement riche en activités diverses pour la Mission française des fouilles de Tanis (MFFT). La campagne de recherches proprement dite (fouilles, épigraphie, architecture) menée au printemps s’est en effet prolongée en s’articulant progressivement avec le projet de mise en valeur du site archéologique, faisant suite aux travaux initiés par la mission elle-même depuis quelques années, désormais portés, avec le concours étroit de celle-ci, par l’Ifao conjointement ave..

Les fractures et les paléoncontraintes du granite hercynien de Millas (zone axiale des Pyrénées) : un cas d’étude de la tectonique cassante d’un aquifère de socle

International audienc

Inspection des conduites de fluides par sondes à centrales inertielles et transducteurs

International audienc

Les fractures et les paléoncontraintes du granite hercynien de Millas (zone axiale des Pyrénées) : un cas d’étude de la tectonique cassante d’un aquifère de socle

International audienc

Qualitative and Comparative Study of Different Methods of Interpolation for the Mapping of Groundwater Salinity: Case Study of Thermal Waters Used for Irrigation in Northeastern Algeria

International audienceFaced with the scarcity of surface water accentuated by climate change, particularly in many arid and semi-arid countries, the quality of groundwater used for irrigation is a concern to agronomists and hydrogeologists. When these waters are of deep origin, they may have high mineralization and chemical compositions unsuitable for irrigation; in particular, they may alter soils and crops. It is therefore important to optimize the spatial estimation of the salinity of these waters and contribute to better knowledge of their quality, through an adapted and robust statistical and geostatistical approach. In the case of north-eastern Algeria, the objective of this study is to characterize the quality of deep waters and to test two interpolation methods (Inverse distance weight and ordinary Kriging) of their electrical conductivity (EC) as an indicator of their salinity and of the risk of damaging irrigated soils. 51 groundwater samples were taken in this region where there are many thermal springs, the water of which is used for irrigation and often is highly mineralized (EC between 0.6 and 26.6 dS/m). The geology is composed of karstic rocks crossed by large faults that allow deep water to rise. Based on major elements contents, analysis of the hydrochemical facies of these waters shows that the main facies are hyperchlorinated sodium (38%) and sulfated calcium (32%). The RSC (Residual Sodium Carbonate) and SAR (Irrigation water salt) indexes were used to assess the water quality. The results indicate that the majority of the sampled groundwater present a risk for soils irrigated with these waters (almost 1/3 presents a strong risk). The risk for the soils seems to be explained by the positive value of the residual alkalinity, and the high risks of sodization and alkalinization. The geostatistical analysis reveals strong heterogeneity in electrical conductivity (salinity). The maps based on this analysis allow the identification of risk areas. The comparison of Inverse distance weight and ordinary Kriging methods indicates similar results being obtained through both methods. However, ordinary kriging appears to be more accurate, less biased, and seemingly better represents the organization of the groundwater resources, as NE-SW alignments are visible. With the proposed approach, it is possible to calculate the surface areas of the different salinity thresholds and then optimize the use of deep groundwater for irrigatio

Étude géochimique et hydrodynamique du Bassin du Lac Tchad (la nappe phréatique dans les régions du Kadzell (Niger oriental) et du Bornou (Nord-Est du Nigéria))

MONTPELLIER-BU Sciences (341722106) / SudocSudocFranceF