In this study, Ten Time Domain Electromagnetic (TDEM) measuring points have been conducted at four pre-selected sites along Wadi Deir Al-Kahaf in order to investigate the potential of the near subsurface deposits and ...In this study, Ten Time Domain Electromagnetic (TDEM) measuring points have been conducted at four pre-selected sites along Wadi Deir Al-Kahaf in order to investigate the potential of the near subsurface deposits and aquifer for groundwater artificial recharge applications. The surveyed results suggest well resolved geological layers such as alluvial mudflat, basalt layers and their saturation states. In addition a hydrogeophysical cross section along the studied sites was constructed which permits to locate the lateral variations in rock properties due to water saturation and or facies changes. The saturated thickness of the Upper Aquifer System in the study area was found to be changed from 5 m near TEM 1 to about 120 m near TEM 4 in thickness. The Abed Basalt Aquifer (AOB) has an average saturation thickness of about ~60 m, and forming the main aquifer (~100 m thickness) near surface to the north of the study area. TEM-3 and TEM-4 sites were found to be potential sites for groundwater artificial recharge based on the constructed hydro-geophysical model. This study recommends implementing detailed geophysical investigations particularly in the most northern parts of the study area.展开更多
This research applies Electrical Resistivity Tomography (ERT) and Time Domain Electromagnetic Method (TDEM) to study the hydrogeology of the Taubaté basin, which is characterized by half-grabens with about 850 m ...This research applies Electrical Resistivity Tomography (ERT) and Time Domain Electromagnetic Method (TDEM) to study the hydrogeology of the Taubaté basin, which is characterized by half-grabens with about 850 m of maximum sediments thickness. The study area is in Taubaté city, São Paulo State, Brazil, where the Taubaté aquifer is an important water source. The Taubaté Group is the main sedimentary package of the basin;it is formed mainly by shales that form aquicludes, and thin layers of sandstones that form the aquifer. There are 40 groundwater exploration wells in Taubaté city that provide important information. The study purpose is to characterize the geoelectrical stratigraphy of the subsurface to locate the contact between the Quaternary and Tertiary sediments and to identify the Taubaté aquifer. The ERT is used for shallow investigations (tens of meters) and the TDEM can reach a great investigation depth (hundreds of meters). Therefore, these geophysical methods are complementary. The ERT data were acquired with the pole-dipole array with 20 m of electrodes spacing and 400 m length, and the TDEM data with the central-loop array with a 200 × 200 m transmitter loop. The results permit to define the contact between the Quaternary and Tertiary sediments around 15 m depth, the Pindamonhangaba Formation between 15 m and 30 m depth and the Taubate Group between 30 m and 300 m depth. The TDEM method defined the Taubaté Group as a single geoelectric layer because the shale and the sandstone layers are all very conductive. The basement is formed by gneiss, which is a very resistive rock. The TDEM method is not able to identify a high conductor/resistor contrast. Overall, the results are consistent with the known geology and the wells information.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
A time domain electromagnetic survey was conducted in the eastern part of the Jordanian desert to image a buried Tertiary valley aquifer in the context of the characterization of groundwater resources and groundwater ...A time domain electromagnetic survey was conducted in the eastern part of the Jordanian desert to image a buried Tertiary valley aquifer in the context of the characterization of groundwater resources and groundwater resources management. The Tertiary chert-limestone rocks (B4) of the investigated valley constitute the major part of the shallow-depth aquifer (less than 100 m) which is the main source of water in the area. Thus, delineation of the geometry of the valley deems necessary for a better understanding of its structural setting and hydrogeological potential. For this purpose, 141 central-loop sounding stations were conducted in the area;they were positioned along six NE-SW directed profiles and one profile (TDEM profile 1) that extends for about 9 km in the NW-SE direction. Resistivity pseudo-sections and resistivity depth maps reveal that the subsurface is composed of two main geoelectric layers: a resistive layer of 25 - 40 ohm.m that indicates the water-bearing rocks which is composed of an alteration of massive chert and limestone. The second layer is conductive one that has a resistivity values in the range from 10 to 15 ohm.m;it consists mainly of gravel and bituminous marl. A lateral variation in resistivity that is associated with the presence of block-like structures is also noted. The good contrast in resistivity between the B4 chert-limestone water-bearing rocks and marl layer enhanced the obtained results and proved that the TDEM is efficient in imaging the boundaries of the Tertiary valley. The lateral extensions of the valley were well-imaged at three fixed-elevation slices (550, 500 and 450 m amsl). The subsurface elongation direction of the valley is confirmed by the NW-SE surface elongation of the valley. The vertical boundary of the valley is extended to an elevation of at least 450 m amsl;this corresponds to a depth of about 100 m.展开更多
Geophysical study and watershed hydrological delineation have been integrated at downstream of Alasra dam site Norh Azraq area to investigate their potential for artificial groundwater recharge. The total surface area...Geophysical study and watershed hydrological delineation have been integrated at downstream of Alasra dam site Norh Azraq area to investigate their potential for artificial groundwater recharge. The total surface area of the watershed was found to be about 195 square kilometers. The estimated annual runoff volumes for the Alasra watershed ranged between 1.2 and 1.8 MCM. Moreover, the interpretation of Ten Time Domain Electromagnetic (TDEM) soundings suggested three principal subsurface layers. The top surface layer has an intermediate resistivity (90 - 110 Ohm·m) with a thickness ranging from a few meters to around 50 m. This layer was interpreted as superficial deposits. The second subsurface layer with variably high resistivity values is composed of unsaturated massive basalt layer and probably belongs to Madhala Olivine Phyric Basalt Formation (MOB). The large variations in resistivity could be ascribed to the degree of water saturation (as a result of groundwater recharge from the nearby harvested water dam), or lithological variations (clay content) and/or due to structural control. The third subsurface layer has low resistivity values (·m to 40 Ω·m) and was found at a depth ranging from 120 to 150 m. This layer could represent a saturated basalt layer with high clay contents. The subsurface structures and major faults have been identified. Based on the results of this study, a combination of surface and subsurface artificial groundwater recharge techniques is highly recommended.展开更多
文摘In this study, Ten Time Domain Electromagnetic (TDEM) measuring points have been conducted at four pre-selected sites along Wadi Deir Al-Kahaf in order to investigate the potential of the near subsurface deposits and aquifer for groundwater artificial recharge applications. The surveyed results suggest well resolved geological layers such as alluvial mudflat, basalt layers and their saturation states. In addition a hydrogeophysical cross section along the studied sites was constructed which permits to locate the lateral variations in rock properties due to water saturation and or facies changes. The saturated thickness of the Upper Aquifer System in the study area was found to be changed from 5 m near TEM 1 to about 120 m near TEM 4 in thickness. The Abed Basalt Aquifer (AOB) has an average saturation thickness of about ~60 m, and forming the main aquifer (~100 m thickness) near surface to the north of the study area. TEM-3 and TEM-4 sites were found to be potential sites for groundwater artificial recharge based on the constructed hydro-geophysical model. This study recommends implementing detailed geophysical investigations particularly in the most northern parts of the study area.
文摘This research applies Electrical Resistivity Tomography (ERT) and Time Domain Electromagnetic Method (TDEM) to study the hydrogeology of the Taubaté basin, which is characterized by half-grabens with about 850 m of maximum sediments thickness. The study area is in Taubaté city, São Paulo State, Brazil, where the Taubaté aquifer is an important water source. The Taubaté Group is the main sedimentary package of the basin;it is formed mainly by shales that form aquicludes, and thin layers of sandstones that form the aquifer. There are 40 groundwater exploration wells in Taubaté city that provide important information. The study purpose is to characterize the geoelectrical stratigraphy of the subsurface to locate the contact between the Quaternary and Tertiary sediments and to identify the Taubaté aquifer. The ERT is used for shallow investigations (tens of meters) and the TDEM can reach a great investigation depth (hundreds of meters). Therefore, these geophysical methods are complementary. The ERT data were acquired with the pole-dipole array with 20 m of electrodes spacing and 400 m length, and the TDEM data with the central-loop array with a 200 × 200 m transmitter loop. The results permit to define the contact between the Quaternary and Tertiary sediments around 15 m depth, the Pindamonhangaba Formation between 15 m and 30 m depth and the Taubate Group between 30 m and 300 m depth. The TDEM method defined the Taubaté Group as a single geoelectric layer because the shale and the sandstone layers are all very conductive. The basement is formed by gneiss, which is a very resistive rock. The TDEM method is not able to identify a high conductor/resistor contrast. Overall, the results are consistent with the known geology and the wells information.
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.
文摘A time domain electromagnetic survey was conducted in the eastern part of the Jordanian desert to image a buried Tertiary valley aquifer in the context of the characterization of groundwater resources and groundwater resources management. The Tertiary chert-limestone rocks (B4) of the investigated valley constitute the major part of the shallow-depth aquifer (less than 100 m) which is the main source of water in the area. Thus, delineation of the geometry of the valley deems necessary for a better understanding of its structural setting and hydrogeological potential. For this purpose, 141 central-loop sounding stations were conducted in the area;they were positioned along six NE-SW directed profiles and one profile (TDEM profile 1) that extends for about 9 km in the NW-SE direction. Resistivity pseudo-sections and resistivity depth maps reveal that the subsurface is composed of two main geoelectric layers: a resistive layer of 25 - 40 ohm.m that indicates the water-bearing rocks which is composed of an alteration of massive chert and limestone. The second layer is conductive one that has a resistivity values in the range from 10 to 15 ohm.m;it consists mainly of gravel and bituminous marl. A lateral variation in resistivity that is associated with the presence of block-like structures is also noted. The good contrast in resistivity between the B4 chert-limestone water-bearing rocks and marl layer enhanced the obtained results and proved that the TDEM is efficient in imaging the boundaries of the Tertiary valley. The lateral extensions of the valley were well-imaged at three fixed-elevation slices (550, 500 and 450 m amsl). The subsurface elongation direction of the valley is confirmed by the NW-SE surface elongation of the valley. The vertical boundary of the valley is extended to an elevation of at least 450 m amsl;this corresponds to a depth of about 100 m.
文摘Geophysical study and watershed hydrological delineation have been integrated at downstream of Alasra dam site Norh Azraq area to investigate their potential for artificial groundwater recharge. The total surface area of the watershed was found to be about 195 square kilometers. The estimated annual runoff volumes for the Alasra watershed ranged between 1.2 and 1.8 MCM. Moreover, the interpretation of Ten Time Domain Electromagnetic (TDEM) soundings suggested three principal subsurface layers. The top surface layer has an intermediate resistivity (90 - 110 Ohm·m) with a thickness ranging from a few meters to around 50 m. This layer was interpreted as superficial deposits. The second subsurface layer with variably high resistivity values is composed of unsaturated massive basalt layer and probably belongs to Madhala Olivine Phyric Basalt Formation (MOB). The large variations in resistivity could be ascribed to the degree of water saturation (as a result of groundwater recharge from the nearby harvested water dam), or lithological variations (clay content) and/or due to structural control. The third subsurface layer has low resistivity values (·m to 40 Ω·m) and was found at a depth ranging from 120 to 150 m. This layer could represent a saturated basalt layer with high clay contents. The subsurface structures and major faults have been identified. Based on the results of this study, a combination of surface and subsurface artificial groundwater recharge techniques is highly recommended.
