Dewandel Benoit - Academia.edu (original) (raw)

Uploads

Papers by Dewandel Benoit

Research paper thumbnail of Evaluation of aquifer thickness by analysing recession hydrographs. Application to the Oman ophiolite hard-rock aquifer

Journal of Hydrology, 2003

For more than a century, hydrologists and hydrogeologists have been investigating the processes o... more For more than a century, hydrologists and hydrogeologists have been investigating the processes of stream and spring baseflow recession, for obtaining data on aquifer characteristics. The Maillet Formula [Librairie Sci., A. Hermann, Paris (1905) 218], an exponential equation widely used for recession curve analysis, is an approximate analytical solution for the diffusion equation in porous media whereas the equation proposed by Boussinesq [C. R. Acad. Sci. 137 (1903) 5; J. Math. Pure Appl. 10 (1904) 5], that depicts baseflow recession as a quadratic form, is an exact analytical solution. Other formulas currently used involve mathematical functions with no basis on groundwater theory. Only the exact analytical solutions can provide quantitative data on aquifer characteristics. The efficiency of the two methods was compared on the basis of recession curves obtained with a 2D cross-sectional finite differences model that simulates natural aquifers. Simulations of shallow aquifers with an impermeable floor at the level of the outlet show that their recession curves have a quadratic form. Thus, the approximate Maillet solution largely overestimates the duration of the 'influenced' stage and underestimates the dynamic volume of the aquifer. Moreover, only the Boussinesq equations enable correct estimates of the aquifer parameters. Numerical simulations of more realistic aquifers, with an impermeable floor much deeper than the outlet, proves the robustness of the Boussinesq formula even under conditions far from the simplifying assumptions that were used to integrate the diffusion equation. The quadratic form of recession is valid regardless of the thickness of the aquifer under the outlet, and provides good estimates of the aquifer's hydrodynamic parameters. Nevertheless, the same numerical simulations show that aquifers with a very deep floor provide an exponential recession. Thus, in that configuration, the Maillet formula also provides a good fit of recession curves, even if parameter estimation remains poor. In fact, the recession curve appears to be closer to exponential when flow has a very important vertical component, and closer to quadratic when horizontal flow is dominant. As a consequence, aquifer permeability anisotropy also changes the recession form.

Research paper thumbnail of Improving pumping tests interpretation in carbonate aquifers with diagnostic plot method

Study of groundwater resources using pumping test started with Theis solution. It allows estimati... more Study of groundwater resources using pumping test started with Theis solution. It allows estimating the hydraulic parameters of porous aquifers such as transmissivity and storage coefficient from the water drawdown. Various methods exist to interpret well-test for different boundary conditions in porous or fractured aquifers. Assumptions are still needed to apply the Theis solution and its derivatives to karst aquifers. The diagnostic plot method is a method to assist hydrogeologist to interpret the pumping test. It appears to be useful to identify flow regime and discriminate conduit and matrix flows in karstic aquifers. This study aims to carry out pumping test and apply diagnostic plot method in two geological settings to improve the hydrogeological understanding of karst aquifer. We also discuss how the diagnostic plot method enhances the classical pumping test interpretation. This study concerns the carbonate aquifer of the Huveaune watershed near Marseille city in southern Fra...

Research paper thumbnail of Assessing water availability in a semi-arid watershed of southern India using a semi-distributed model

Appropriate groundwater resource management becomes a priority for the States of the semi-arid so... more Appropriate groundwater resource management becomes a priority for the States of the semi-arid southern India. Because of the highly increasing groundwater demand, the number of drought-prone regions where the groundwater resource is classified as over-exploited by the Government is critically increasing. Thus there is a need to develop quantitative methodologies adapted to the regional context that are capable to assess water resources at watershed scale and the impact of management measures. This study demonstrates the calibration and use of an integrated water resource assessment model (SWAT) in an 84 km 2 representative semi-arid crystalline watershed of southern India with no perennial surface water source. The model can reproduce (i) the recharge rate estimates derived independently by a groundwater balance computation, (ii) runoff and surface water storage occurring in tanks that spread along the drainage system, (iii) groundwater table fluctuations monitored at a monthly time step. Results show that even if the calibration period (2006-2010) was more humid than long-term average, the watershed is sensitive to the monsoon inter-annual variability with water-stress during the dry years and an associated loss in agricultural production. The impact of these dry years is spatially variable with higher vulnerability for sub-basins having proportionally larger irrigated paddy areas, lower groundwater resource, and/or lower recharge potential (i.e., due to land use and repartition of percolation tanks). The scope for additional recharge by means of managed aquifer recharge structures is limited and demand-side management measures are needed to mitigate pumping. A wishful management objective may be to see groundwater reserves as a supplementary resource in case of monsoon failure and not as the main water resource to be used indiscriminately. SWAT proved to be an adequate modeling framework for the simulation of water resource in semi-arid hard-rock context where groundwater vertical fluxes largely prevail over regional lateral flows at kmscale. It provides interesting capabilities for water availability mapping and the simulation of different types of scenarios (e.g., land use changes, climate change).

Research paper thumbnail of Water Quality Evolution During Managed Aquifer Recharge (MAR) in Indian Crystalline Basement Aquifers: Reactive Transport Modeling in the Critical Zone

Procedia Earth and Planetary Science, 2014

The present study investigates the role of MAR (Managed Aquifer Recharge) on groundwater quality ... more The present study investigates the role of MAR (Managed Aquifer Recharge) on groundwater quality overexploited crystalline aquifers in semi-arid context (South India). A 1D transient reactive transport model was conceived to simulate the infiltration of a recharge tank through the critical zone. The model takes into account hydrodynamics, evaporation, kinetic weathering of minerals (precipitation/dissolution), adsorption, cationic exchange. Results show the beneficial effect of MAR on groundwater quality, in particular on Fluoride accumulation, a widespread problem in the Indian context, strongly depending on seasonal climatic variations.

Research paper thumbnail of Analytical solutions for analysing pumping tests in a sub-vertical and anisotropic fault zone draining shallow aquifers

Journal of Hydrology, 2014

Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We ... more Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We present new analytical solutions for examining the influence, during a pumping test in a well, of an infinite linear and anisotropic strip-aquifer that drains shallow aquifers of different diffusivity and thickness. The whole system is confined and the aquifer geometry can be represented by a 'T', an aquifer geometry resembling a sub-vertical fault or a sub-vertical vein cross-cutting shallower aquifers. The proposed solutions are based upon an unconventional application of well-image theory, without limitation of the diffusivity contrast between the three domains. Solutions for drawdown were developed for the three domains, i.e. the strip-aquifer and the two shallow compartments, and flow signatures are discussed in detail and compared to numerical modelling. The proposed solutions are not shown to be exact solutions to the appropriate partial differential equation, but very good and useful approximations. The solutions were applied to a 63-day pumping test in a steep fault zone in crystalline aquifer rock of Brittany, France. After that, the flow contributions of the fault zone and of the shallow aquifers deduced from groundwater dating were compared to analytical solutions. The solutions and theoretical type-curve examples can help in understanding flow processes from tests conducted in settings that are similar to such a conceptual model.

Research paper thumbnail of Analytical solutions for analysing pumping tests in a sub-vertical and anisotropic fault zone draining shallow aquifers

Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We ... more Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We present new analytical solutions for examining the influence, during a pumping test in a well, of an infinite linear and anisotropic strip-aquifer that drains shallow aquifers of different diffusivity and thickness. The whole system is confined and the aquifer geometry can be represented by a 'T', an aquifer geometry resembling a sub-vertical fault or a sub-vertical vein cross-cutting shallower aquifers. The proposed solutions are based upon an unconventional application of well-image theory, without limitation of the diffusivity contrast between the three domains. Solutions for drawdown were developed for the three domains, i.e. the strip-aquifer and the two shallow compartments, and flow signatures are discussed in detail and compared to numerical modelling. The proposed solutions are not shown to be exact solutions to the appropriate partial differential equation, but very good and useful approximations. The solutions were applied to a 63-day pumping test in a steep fault zone in crystalline aquifer rock of Brittany, France. After that, the flow contributions of the fault zone and of the shallow aquifers deduced from groundwater dating were compared to analytical solutions. The solutions and theoretical type-curve examples can help in understanding flow processes from tests conducted in settings that are similar to such a conceptual model.

Research paper thumbnail of Evaluation of aquifer thickness by analysing recession hydrographs. Application to the Oman ophiolite hard-rock aquifer

Journal of Hydrology, 2003

For more than a century, hydrologists and hydrogeologists have been investigating the processes o... more For more than a century, hydrologists and hydrogeologists have been investigating the processes of stream and spring baseflow recession, for obtaining data on aquifer characteristics. The Maillet Formula [Librairie Sci., A. Hermann, Paris (1905) 218], an exponential equation widely used for recession curve analysis, is an approximate analytical solution for the diffusion equation in porous media whereas the equation proposed by Boussinesq [C. R. Acad. Sci. 137 (1903) 5; J. Math. Pure Appl. 10 (1904) 5], that depicts baseflow recession as a quadratic form, is an exact analytical solution. Other formulas currently used involve mathematical functions with no basis on groundwater theory. Only the exact analytical solutions can provide quantitative data on aquifer characteristics. The efficiency of the two methods was compared on the basis of recession curves obtained with a 2D cross-sectional finite differences model that simulates natural aquifers. Simulations of shallow aquifers with an impermeable floor at the level of the outlet show that their recession curves have a quadratic form. Thus, the approximate Maillet solution largely overestimates the duration of the 'influenced' stage and underestimates the dynamic volume of the aquifer. Moreover, only the Boussinesq equations enable correct estimates of the aquifer parameters. Numerical simulations of more realistic aquifers, with an impermeable floor much deeper than the outlet, proves the robustness of the Boussinesq formula even under conditions far from the simplifying assumptions that were used to integrate the diffusion equation. The quadratic form of recession is valid regardless of the thickness of the aquifer under the outlet, and provides good estimates of the aquifer's hydrodynamic parameters. Nevertheless, the same numerical simulations show that aquifers with a very deep floor provide an exponential recession. Thus, in that configuration, the Maillet formula also provides a good fit of recession curves, even if parameter estimation remains poor. In fact, the recession curve appears to be closer to exponential when flow has a very important vertical component, and closer to quadratic when horizontal flow is dominant. As a consequence, aquifer permeability anisotropy also changes the recession form.

Research paper thumbnail of Improving pumping tests interpretation in carbonate aquifers with diagnostic plot method

Study of groundwater resources using pumping test started with Theis solution. It allows estimati... more Study of groundwater resources using pumping test started with Theis solution. It allows estimating the hydraulic parameters of porous aquifers such as transmissivity and storage coefficient from the water drawdown. Various methods exist to interpret well-test for different boundary conditions in porous or fractured aquifers. Assumptions are still needed to apply the Theis solution and its derivatives to karst aquifers. The diagnostic plot method is a method to assist hydrogeologist to interpret the pumping test. It appears to be useful to identify flow regime and discriminate conduit and matrix flows in karstic aquifers. This study aims to carry out pumping test and apply diagnostic plot method in two geological settings to improve the hydrogeological understanding of karst aquifer. We also discuss how the diagnostic plot method enhances the classical pumping test interpretation. This study concerns the carbonate aquifer of the Huveaune watershed near Marseille city in southern Fra...

Research paper thumbnail of Assessing water availability in a semi-arid watershed of southern India using a semi-distributed model

Appropriate groundwater resource management becomes a priority for the States of the semi-arid so... more Appropriate groundwater resource management becomes a priority for the States of the semi-arid southern India. Because of the highly increasing groundwater demand, the number of drought-prone regions where the groundwater resource is classified as over-exploited by the Government is critically increasing. Thus there is a need to develop quantitative methodologies adapted to the regional context that are capable to assess water resources at watershed scale and the impact of management measures. This study demonstrates the calibration and use of an integrated water resource assessment model (SWAT) in an 84 km 2 representative semi-arid crystalline watershed of southern India with no perennial surface water source. The model can reproduce (i) the recharge rate estimates derived independently by a groundwater balance computation, (ii) runoff and surface water storage occurring in tanks that spread along the drainage system, (iii) groundwater table fluctuations monitored at a monthly time step. Results show that even if the calibration period (2006-2010) was more humid than long-term average, the watershed is sensitive to the monsoon inter-annual variability with water-stress during the dry years and an associated loss in agricultural production. The impact of these dry years is spatially variable with higher vulnerability for sub-basins having proportionally larger irrigated paddy areas, lower groundwater resource, and/or lower recharge potential (i.e., due to land use and repartition of percolation tanks). The scope for additional recharge by means of managed aquifer recharge structures is limited and demand-side management measures are needed to mitigate pumping. A wishful management objective may be to see groundwater reserves as a supplementary resource in case of monsoon failure and not as the main water resource to be used indiscriminately. SWAT proved to be an adequate modeling framework for the simulation of water resource in semi-arid hard-rock context where groundwater vertical fluxes largely prevail over regional lateral flows at kmscale. It provides interesting capabilities for water availability mapping and the simulation of different types of scenarios (e.g., land use changes, climate change).

Research paper thumbnail of Water Quality Evolution During Managed Aquifer Recharge (MAR) in Indian Crystalline Basement Aquifers: Reactive Transport Modeling in the Critical Zone

Procedia Earth and Planetary Science, 2014

The present study investigates the role of MAR (Managed Aquifer Recharge) on groundwater quality ... more The present study investigates the role of MAR (Managed Aquifer Recharge) on groundwater quality overexploited crystalline aquifers in semi-arid context (South India). A 1D transient reactive transport model was conceived to simulate the infiltration of a recharge tank through the critical zone. The model takes into account hydrodynamics, evaporation, kinetic weathering of minerals (precipitation/dissolution), adsorption, cationic exchange. Results show the beneficial effect of MAR on groundwater quality, in particular on Fluoride accumulation, a widespread problem in the Indian context, strongly depending on seasonal climatic variations.

Research paper thumbnail of Analytical solutions for analysing pumping tests in a sub-vertical and anisotropic fault zone draining shallow aquifers

Journal of Hydrology, 2014

Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We ... more Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We present new analytical solutions for examining the influence, during a pumping test in a well, of an infinite linear and anisotropic strip-aquifer that drains shallow aquifers of different diffusivity and thickness. The whole system is confined and the aquifer geometry can be represented by a 'T', an aquifer geometry resembling a sub-vertical fault or a sub-vertical vein cross-cutting shallower aquifers. The proposed solutions are based upon an unconventional application of well-image theory, without limitation of the diffusivity contrast between the three domains. Solutions for drawdown were developed for the three domains, i.e. the strip-aquifer and the two shallow compartments, and flow signatures are discussed in detail and compared to numerical modelling. The proposed solutions are not shown to be exact solutions to the appropriate partial differential equation, but very good and useful approximations. The solutions were applied to a 63-day pumping test in a steep fault zone in crystalline aquifer rock of Brittany, France. After that, the flow contributions of the fault zone and of the shallow aquifers deduced from groundwater dating were compared to analytical solutions. The solutions and theoretical type-curve examples can help in understanding flow processes from tests conducted in settings that are similar to such a conceptual model.

Research paper thumbnail of Analytical solutions for analysing pumping tests in a sub-vertical and anisotropic fault zone draining shallow aquifers

Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We ... more Pumping test Compartmented aquifer Fault Crystalline aquifer Groundwater dating s u m m a r y We present new analytical solutions for examining the influence, during a pumping test in a well, of an infinite linear and anisotropic strip-aquifer that drains shallow aquifers of different diffusivity and thickness. The whole system is confined and the aquifer geometry can be represented by a 'T', an aquifer geometry resembling a sub-vertical fault or a sub-vertical vein cross-cutting shallower aquifers. The proposed solutions are based upon an unconventional application of well-image theory, without limitation of the diffusivity contrast between the three domains. Solutions for drawdown were developed for the three domains, i.e. the strip-aquifer and the two shallow compartments, and flow signatures are discussed in detail and compared to numerical modelling. The proposed solutions are not shown to be exact solutions to the appropriate partial differential equation, but very good and useful approximations. The solutions were applied to a 63-day pumping test in a steep fault zone in crystalline aquifer rock of Brittany, France. After that, the flow contributions of the fault zone and of the shallow aquifers deduced from groundwater dating were compared to analytical solutions. The solutions and theoretical type-curve examples can help in understanding flow processes from tests conducted in settings that are similar to such a conceptual model.