The inverse slope method (ISM) was used to interpret electric sounding data to determine the geoelectric parameters of the alteration zones (continuous media) and rocky environments (discontinuous environments) of the...The inverse slope method (ISM) was used to interpret electric sounding data to determine the geoelectric parameters of the alteration zones (continuous media) and rocky environments (discontinuous environments) of the Bouna Department. Having both qualitative and quantitative interpretation, the inverse slope method (ISM) has the ability to determine the different geoelectric layers while characterizing their resistivities and true thicknesses. In the Bouna department, this method allowed us to count a maximum of four (4) geoelectric layers with a total thickness ranging from 12.99 m to 24.66 m. The alteration thicknesses calculated by the ISM in comparison with those measured in the boreholes showed a linear agreement of the coefficient of determination R2 = 0.8269 with the support of the Nash criterion which showed that this method gave thicknesses of alteration close to 76.76% of that obtained during the drillings.展开更多
The Miocene-Pliocene aquifer of Benin’s Coastal Sedimentary Basin(BSC)is the most heavily exploited aquifer for supplying water to the cities of Cotonou,Porto-Novo,and their surrounding areas,thanks to two catchment ...The Miocene-Pliocene aquifer of Benin’s Coastal Sedimentary Basin(BSC)is the most heavily exploited aquifer for supplying water to the cities of Cotonou,Porto-Novo,and their surrounding areas,thanks to two catchment fields located on the Sakete and Allada plateaus.This study,which focuses on the Sakete plateau,aims to improve knowledge of the geometry of this part of the aquifer shared with Nigeria.Inhabited by a high population density with varied economic activities,this aquifer is subject to excessive withdrawal and deterioration in water quality.Furthermore,in this part of Benin,there has been a spectacular proliferation of private wells and boreholes,often referred to as private autonomous water stations.This situation of unregulated exploitation puts further pressure on the aquifer and thus compromises the sustainable exploitation of water resources already subject to the effects of climate change.It is therefore necessary to investigate and deepen our knowledge of its geometry in order to better understand the system.In order to refine the wall and edges of the aquifer’s geometry,32 geophysical surveys were carried out along three well-defined transects,using the Time Domain Electromagnetic(TDEM)method.This method,known for its flexibility in identifying conductive soils such as clays,confirmed that the aquifer is multi-layered,interspersed with clay lenses of varying thickness in places.The aquifer wall,consisting of clay,is estimated to be between 50 and 100 m deep at the northern edge of the plateau near the Lama depression,with an outcrop of the clay layer towards Nigeria on the same cross-section.On the western profile,the wall is located between 90 and 120 m depending on the site,while on the southern profile of the plateau,the depth of the wall is almost constant at 80 m and deepens(110 m)towards the Nigerian border in the east.The Feflow numerical code was used for a finite element mesh of the aquifer.The continuous super mesh is characterized by 193,864 nodes,272,892 prism-triangle elements with 06 nodes per element.527 borehole logs and TDEM surveys were used in conjunction to establish a conceptual model of the three-dimensional geometry.展开更多
基金This research was supported by the Hydrogeology Research Group of the Geosciences and Environment Laboratory at Nangui Abrogoua University in Abidjan,Ivory Coast.
文摘The inverse slope method (ISM) was used to interpret electric sounding data to determine the geoelectric parameters of the alteration zones (continuous media) and rocky environments (discontinuous environments) of the Bouna Department. Having both qualitative and quantitative interpretation, the inverse slope method (ISM) has the ability to determine the different geoelectric layers while characterizing their resistivities and true thicknesses. In the Bouna department, this method allowed us to count a maximum of four (4) geoelectric layers with a total thickness ranging from 12.99 m to 24.66 m. The alteration thicknesses calculated by the ISM in comparison with those measured in the boreholes showed a linear agreement of the coefficient of determination R2 = 0.8269 with the support of the Nash criterion which showed that this method gave thicknesses of alteration close to 76.76% of that obtained during the drillings.
文摘The Miocene-Pliocene aquifer of Benin’s Coastal Sedimentary Basin(BSC)is the most heavily exploited aquifer for supplying water to the cities of Cotonou,Porto-Novo,and their surrounding areas,thanks to two catchment fields located on the Sakete and Allada plateaus.This study,which focuses on the Sakete plateau,aims to improve knowledge of the geometry of this part of the aquifer shared with Nigeria.Inhabited by a high population density with varied economic activities,this aquifer is subject to excessive withdrawal and deterioration in water quality.Furthermore,in this part of Benin,there has been a spectacular proliferation of private wells and boreholes,often referred to as private autonomous water stations.This situation of unregulated exploitation puts further pressure on the aquifer and thus compromises the sustainable exploitation of water resources already subject to the effects of climate change.It is therefore necessary to investigate and deepen our knowledge of its geometry in order to better understand the system.In order to refine the wall and edges of the aquifer’s geometry,32 geophysical surveys were carried out along three well-defined transects,using the Time Domain Electromagnetic(TDEM)method.This method,known for its flexibility in identifying conductive soils such as clays,confirmed that the aquifer is multi-layered,interspersed with clay lenses of varying thickness in places.The aquifer wall,consisting of clay,is estimated to be between 50 and 100 m deep at the northern edge of the plateau near the Lama depression,with an outcrop of the clay layer towards Nigeria on the same cross-section.On the western profile,the wall is located between 90 and 120 m depending on the site,while on the southern profile of the plateau,the depth of the wall is almost constant at 80 m and deepens(110 m)towards the Nigerian border in the east.The Feflow numerical code was used for a finite element mesh of the aquifer.The continuous super mesh is characterized by 193,864 nodes,272,892 prism-triangle elements with 06 nodes per element.527 borehole logs and TDEM surveys were used in conjunction to establish a conceptual model of the three-dimensional geometry.
