Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geoph... more Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geophysical techniques offer non-invasive and integrative methods that help interpreting such systems as a whole. Among these techniques, gravimetry has been increasingly used in the last decade to characterize the hydrological behavior of complex systems, e.g. karst environments or volcanoes. We present a continuous microgravimetric monitoring of 3 years in the karstic area of Rochefort (Belgium), that shows multiple occurrences of caves and karstic features. The gravity record includes measurements of a GWR superconducting gravimeter, a Micro-g LaCoste gPhone and an absolute FG5 gravimeter. Together with meteorological measurements and a surface/in-cave hydrogeological monitoring, we were able to improve the knowledge of hydrological processes. On the one hand, the data allowed identifying seasonal groundwater content changes in the unsaturated zone of the karst area, most likely to be linked to temporary groundwater storage occurring in the most karstified layers closed to the surface. Combined with additional geological information, modelling of the gravity signal based on the vertical potential of the gravitational attraction was then particularly useful to estimate the seasonal recharge leading to the temporary subsurface groundwater storage. On the other hand, the gravity monitoring of flash floods occurring in deeper layers after intense rainfall events informed on the effective porosity gradient of the limestones. Modelling was then helpful to identify the hydrogeological role played by the cave galleries with respect to the hosting limestones during flash floods. These results are also compared with measurements of an in-cave gravimetric monitoring performed with a gPhone spring gravimeter. An Electrical Resistivity Tomography monitoring is also conducted at site and brings additional information useful to verify the interpretation made with the gravimetric monitorin
Des essais de traçage quantitatifs ont été réalisés en mars, avril et septembre 2013. La rivière ... more Des essais de traçage quantitatifs ont été réalisés en mars, avril et septembre 2013. La rivière souterraine est accessible via différents réseaux karstiques permettant l'installation de fluorimètres en plusieurs points stratégiques et la multiplication des sites d'injection (en uranine et rhodamine). Dans la région de Furfooz (6 km au SE de Dinant), la Lesse s'infiltre partiellement en sa rive droite dans la perte des Nutons et parcourt un petit kilomètre pour résurger en aval au Trou de La Loutre. La particularité de ce système est d'une part le double recoupement de méandre de la Lesse aérienne par la Lesse souterraine et d'autre part la présence d'une importante masse d'eau (le lac du Trou qui Fume-Puits des Vaux) sur le trajet de la Lesse souterraine qui elle s'écoule à des débits relativement faibles (de 5l/s à l'étiage jusqu'à 65 l/s en crue). Les différentes courbes de restitution obtenues après injection à la perte des Nutons sont Enf...
Le plateau de Hesbaye est situe au Nord-Est de la Belgique. Sa nappe aquifere, logee dans les cra... more Le plateau de Hesbaye est situe au Nord-Est de la Belgique. Sa nappe aquifere, logee dans les craies du Cretace, est sollicitee a raison de 30 millions de m 3 par an afin d'alimenter en eau potable la ville de Liege et ses environs. Bien que protegee par une epaisseur de 5 a 20 metres de limon, de nombreux indices montrent une lente mais reelle degradation de la qualite de ses eaux souterraines, notamment par les nitrates. Les teneurs minimales en nitrates ( a 30 mg/l) sont respectivement observees lorsque la nappe est captive sous des depots tertiaires, semi-captive sous des alluvions des rivieres et libre. Les teneurs maximales (> a 40 mg/l) sont observees dans la partie libre de la nappe situee en milieu urbanise demontrant que les concentrations en nitrates presentent de fortes variations spatiales tributaires non seulement du contexte hydrogeologique mais egalement de l'occupation du sol; Verticalement, les teneurs en nitrates diminuent avec la profondeur selon un gr...
Communications in agricultural and applied biological sciences, 2008
In the Walloon Region of Belgium, a committee of intervention has been created to investigate pro... more In the Walloon Region of Belgium, a committee of intervention has been created to investigate problems of pesticide contamination of various catchments use for drinking water production. This committee involves the Agricultural Research centre--Wallonia (CRA-W, project coordinator) and some University experts. It is funded by the Société Publique de Gestion des Eaux (SPGE). The diagnosis method, base on the AQUAPLAINE method (Arvatis-France), consists of 4 steps. The first step is the preparation of diagnosis (at the office) that takes into account the paper risk of active ingredients. and their uses, the identification of the agricultural parcels, the collection of cartographic and numeric data, the description of the hydrogeological and pedological contexts and the study of the meteorological data in relation with the period of pollution. The second step consists of making a plot diagnosis (on the field) to identify the way of transfer inside the plot and collecting data. At the t...
Communications in agricultural and applied biological sciences, 2009
In the Walloon Region (Belgium), a Committee of Investigation was created in 2007 to investigate ... more In the Walloon Region (Belgium), a Committee of Investigation was created in 2007 to investigate and determine the potential pesticides pollution sources in drinkable water catchments. This Committee, constituted by a multidisciplinary team of experts i.e agronomists, soil scientists, phyto-chemists, hydrogeologists, is coordinated by the Walloon Agricultural Research Centre (CRA-W) and funded by the Société Publique de Gestion des Eaux (SPGE). The diagnosis method is inspired of the AQUAPLAINE method (Arvalis, France), and is composed of four steps: 1/preparing the diagnosis using existing data, 2/diagnosis using data bank completed by field observations, 3/meeting and discussion with the pesticide users, 4/final diagnosis and remediation proposal. In a rural district of Walloon Region, a water producer who possesses two catchments ("Les marroniers" (P1) and "Puits N2" (P2)) has problems with pesticides. The pollution started in 1998 with atrazine and bromacile ...
La nappe aquifère de Hesbaye, logée dans les craies du Crétacé, est sollicitée à raison de trente... more La nappe aquifère de Hesbaye, logée dans les craies du Crétacé, est sollicitée à raison de trente millions de mètres cubes par an. Bien que naturellement protégée par une épaisseur de 5 à 20 mètres de limons, de nombreux indices montrent une dégradation de la qualité des eaux souterraines, notamment par les nitrates. Les concentrations en nitrates atteignent 15 à 25 mg.l-1 dans la partie semi-captive de la nappe et sont systématiquement supérieures à 35 mg.l-1 dans la partie libre. Malgré de fortes fluctuations temporelles, les teneurs augmentent en moyenne de 0,35 mg.l-1 à 0,7 mg.l-1 par an selon la situation semi-captive ou libre de la nappe. La détermination des paramètres hydrodynamiques et de transport de la craie par plus de 35 traçages répartis sur 11 sites, a permis de réaliser un modèle local (10 km2) de transport simulant la propagation des nitrates dans la nappe. Le modèle a montré que cette dernière est, malgré une certaine homogénéisation, très sensible aux apports de s...
In this paper we demonstrate the ability of the recently enhanced object-distance based method to... more In this paper we demonstrate the ability of the recently enhanced object-distance based method to reconstruct the 3D conduit shapes of the Furfooz karstic system (Belgium). Various data (maps, cross-sections, GPS points) are used to define the network skeleton and to constrain the 3D conduit envelop generation thanks to a Gibbs sampling algorithm. This preliminary work shows that the basic version of the object-distance based method is quite efficient to model basic drains. However, the last improvements in order to take into account a geological knowledge are necessary to get realistic models of some elongated conduits developed along fractures. The computation of the section areas and volumes on one modelled conduit shows important differences compared to those corresponding to the common ellipsoidal conduit approximation. As these differences should strongly impact flow simulations, this preliminary work tends to comfort the interest toward a better modelling of karst conduit sha...
SUMMARY Along the North-Pas-de-Calais coast between a point south of Boutonnière du Boulonnais an... more SUMMARY Along the North-Pas-de-Calais coast between a point south of Boutonnière du Boulonnais and the Authie River, Cretaceous rocks are limited to the east by a paleocliff that overlooks the Quaternary coastal and dune deposits. The chalk aquifer is connected to the Quaternary aquifers and further west to the sea water. Close to the seashore the top of the chalk plateau falls rapidly from 20 m above sea level to 20 m below sea level, causing the aquifer to grade from being unconfined in the east to confined in the west. This chalky aquifer is eut by several faults. A structural survey (LOUCHE et al, 1997) based on borehole data was carried out to evaluate whether the rate and direction of groundwater flow are controlled by the différent faults. Two major fault groups striking N030° and N110° hâve been revealed by the structural map, with a third minor group (N 160-170°) to the north of the Canche. The two major groups, created during tectonic activity from the Palaeozoic to the pr...
Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geoph... more Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geophysical techniques offer non-invasive and integrative methods that help interpreting such systems as a whole. Among these techniques, gravimetry has been increasingly used in the last decade to characterize the hydrological behavior of complex systems, e.g. karst environments or volcanoes. We present a continuous microgravimetric monitoring of 3 years in the karstic area of Rochefort (Belgium), that shows multiple occurrences of caves and karstic features. The gravity record includes measurements of a GWR superconducting gravimeter, a Micro-g LaCoste gPhone and an absolute FG5 gravimeter. Together with meteorological measurements and a surface/in-cave hydrogeological monitoring, we were able to improve the knowledge of hydrological processes. On the one hand, the data allowed identifying seasonal groundwater content changes in the unsaturated zone of the karst area, most likely to be linked to temporary groundwater storage occurring in the most karstified layers closed to the surface. Combined with additional geological information, modelling of the gravity signal based on the vertical potential of the gravitational attraction was then particularly useful to estimate the seasonal recharge leading to the temporary subsurface groundwater storage. On the other hand, the gravity monitoring of flash floods occurring in deeper layers after intense rainfall events informed on the effective porosity gradient of the limestones. Modelling was then helpful to identify the hydrogeological role played by the cave galleries with respect to the hosting limestones during flash floods. These results are also compared with measurements of an in-cave gravimetric monitoring performed with a gPhone spring gravimeter. An Electrical Resistivity Tomography monitoring is also conducted at site and brings additional information useful to verify the interpretation made with the gravimetric monitorin
Des essais de traçage quantitatifs ont été réalisés en mars, avril et septembre 2013. La rivière ... more Des essais de traçage quantitatifs ont été réalisés en mars, avril et septembre 2013. La rivière souterraine est accessible via différents réseaux karstiques permettant l'installation de fluorimètres en plusieurs points stratégiques et la multiplication des sites d'injection (en uranine et rhodamine). Dans la région de Furfooz (6 km au SE de Dinant), la Lesse s'infiltre partiellement en sa rive droite dans la perte des Nutons et parcourt un petit kilomètre pour résurger en aval au Trou de La Loutre. La particularité de ce système est d'une part le double recoupement de méandre de la Lesse aérienne par la Lesse souterraine et d'autre part la présence d'une importante masse d'eau (le lac du Trou qui Fume-Puits des Vaux) sur le trajet de la Lesse souterraine qui elle s'écoule à des débits relativement faibles (de 5l/s à l'étiage jusqu'à 65 l/s en crue). Les différentes courbes de restitution obtenues après injection à la perte des Nutons sont Enf...
Le plateau de Hesbaye est situe au Nord-Est de la Belgique. Sa nappe aquifere, logee dans les cra... more Le plateau de Hesbaye est situe au Nord-Est de la Belgique. Sa nappe aquifere, logee dans les craies du Cretace, est sollicitee a raison de 30 millions de m 3 par an afin d'alimenter en eau potable la ville de Liege et ses environs. Bien que protegee par une epaisseur de 5 a 20 metres de limon, de nombreux indices montrent une lente mais reelle degradation de la qualite de ses eaux souterraines, notamment par les nitrates. Les teneurs minimales en nitrates ( a 30 mg/l) sont respectivement observees lorsque la nappe est captive sous des depots tertiaires, semi-captive sous des alluvions des rivieres et libre. Les teneurs maximales (> a 40 mg/l) sont observees dans la partie libre de la nappe situee en milieu urbanise demontrant que les concentrations en nitrates presentent de fortes variations spatiales tributaires non seulement du contexte hydrogeologique mais egalement de l'occupation du sol; Verticalement, les teneurs en nitrates diminuent avec la profondeur selon un gr...
Communications in agricultural and applied biological sciences, 2008
In the Walloon Region of Belgium, a committee of intervention has been created to investigate pro... more In the Walloon Region of Belgium, a committee of intervention has been created to investigate problems of pesticide contamination of various catchments use for drinking water production. This committee involves the Agricultural Research centre--Wallonia (CRA-W, project coordinator) and some University experts. It is funded by the Société Publique de Gestion des Eaux (SPGE). The diagnosis method, base on the AQUAPLAINE method (Arvatis-France), consists of 4 steps. The first step is the preparation of diagnosis (at the office) that takes into account the paper risk of active ingredients. and their uses, the identification of the agricultural parcels, the collection of cartographic and numeric data, the description of the hydrogeological and pedological contexts and the study of the meteorological data in relation with the period of pollution. The second step consists of making a plot diagnosis (on the field) to identify the way of transfer inside the plot and collecting data. At the t...
Communications in agricultural and applied biological sciences, 2009
In the Walloon Region (Belgium), a Committee of Investigation was created in 2007 to investigate ... more In the Walloon Region (Belgium), a Committee of Investigation was created in 2007 to investigate and determine the potential pesticides pollution sources in drinkable water catchments. This Committee, constituted by a multidisciplinary team of experts i.e agronomists, soil scientists, phyto-chemists, hydrogeologists, is coordinated by the Walloon Agricultural Research Centre (CRA-W) and funded by the Société Publique de Gestion des Eaux (SPGE). The diagnosis method is inspired of the AQUAPLAINE method (Arvalis, France), and is composed of four steps: 1/preparing the diagnosis using existing data, 2/diagnosis using data bank completed by field observations, 3/meeting and discussion with the pesticide users, 4/final diagnosis and remediation proposal. In a rural district of Walloon Region, a water producer who possesses two catchments ("Les marroniers" (P1) and "Puits N2" (P2)) has problems with pesticides. The pollution started in 1998 with atrazine and bromacile ...
La nappe aquifère de Hesbaye, logée dans les craies du Crétacé, est sollicitée à raison de trente... more La nappe aquifère de Hesbaye, logée dans les craies du Crétacé, est sollicitée à raison de trente millions de mètres cubes par an. Bien que naturellement protégée par une épaisseur de 5 à 20 mètres de limons, de nombreux indices montrent une dégradation de la qualité des eaux souterraines, notamment par les nitrates. Les concentrations en nitrates atteignent 15 à 25 mg.l-1 dans la partie semi-captive de la nappe et sont systématiquement supérieures à 35 mg.l-1 dans la partie libre. Malgré de fortes fluctuations temporelles, les teneurs augmentent en moyenne de 0,35 mg.l-1 à 0,7 mg.l-1 par an selon la situation semi-captive ou libre de la nappe. La détermination des paramètres hydrodynamiques et de transport de la craie par plus de 35 traçages répartis sur 11 sites, a permis de réaliser un modèle local (10 km2) de transport simulant la propagation des nitrates dans la nappe. Le modèle a montré que cette dernière est, malgré une certaine homogénéisation, très sensible aux apports de s...
In this paper we demonstrate the ability of the recently enhanced object-distance based method to... more In this paper we demonstrate the ability of the recently enhanced object-distance based method to reconstruct the 3D conduit shapes of the Furfooz karstic system (Belgium). Various data (maps, cross-sections, GPS points) are used to define the network skeleton and to constrain the 3D conduit envelop generation thanks to a Gibbs sampling algorithm. This preliminary work shows that the basic version of the object-distance based method is quite efficient to model basic drains. However, the last improvements in order to take into account a geological knowledge are necessary to get realistic models of some elongated conduits developed along fractures. The computation of the section areas and volumes on one modelled conduit shows important differences compared to those corresponding to the common ellipsoidal conduit approximation. As these differences should strongly impact flow simulations, this preliminary work tends to comfort the interest toward a better modelling of karst conduit sha...
SUMMARY Along the North-Pas-de-Calais coast between a point south of Boutonnière du Boulonnais an... more SUMMARY Along the North-Pas-de-Calais coast between a point south of Boutonnière du Boulonnais and the Authie River, Cretaceous rocks are limited to the east by a paleocliff that overlooks the Quaternary coastal and dune deposits. The chalk aquifer is connected to the Quaternary aquifers and further west to the sea water. Close to the seashore the top of the chalk plateau falls rapidly from 20 m above sea level to 20 m below sea level, causing the aquifer to grade from being unconfined in the east to confined in the west. This chalky aquifer is eut by several faults. A structural survey (LOUCHE et al, 1997) based on borehole data was carried out to evaluate whether the rate and direction of groundwater flow are controlled by the différent faults. Two major fault groups striking N030° and N110° hâve been revealed by the structural map, with a third minor group (N 160-170°) to the north of the Canche. The two major groups, created during tectonic activity from the Palaeozoic to the pr...
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