The term “geoelectric null-array” is used for direct current electrode configurations yielding a ... more The term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture. The main objective is to determine which array(s) best localise vertical structures. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately. The numerical analysis served as basis to interpret the field results too. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-g null-array showed to be the most efficient and accurate in localising fractures. This study shows that geoelectrical null-arrays are better than classical arrays for localisation of fractures.
ABSTRACT A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), We... more ABSTRACT A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture, both in profiling and in azimuthal mode is presented. The term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space.The main objective is to determine which array(s) best localise vertical structures or best identify their orientation. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately, while the midpoint null-array combined with the Schlumberger null-array allows accurate orientation of a fracture. Field test measurements were carried out to verify the theoretical results above a quarry in Les Breuleux with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-g null-array showed to be the most efficient and accurate in localising fractures. The orientations of the fractures in accordance with the numerical results, were most efficiently determined with midpoint null-array, however Schlumberger null-array adds accuracy to the results. This study shows that geoelectrical null-arrays are better than classical arrays for the characterisation of fracture geometry.
Tiefengrundwasser findet sich in allen grosstektonischen Einheiten der Schweiz. Die bekannten, te... more Tiefengrundwasser findet sich in allen grosstektonischen Einheiten der Schweiz. Die bekannten, teilweise genutzten Vorkommen von Tiefengrundwas-ser und insbesondere die chemische Zusammensetzung dieser Wasser wird fur die verschiedenen Einheiten aufgezeigt. Im Hinblick auf mogliche Nutzungskon-flikte werden die gesetzlichen Grundlagen und Massnahmen zum Schutz dieser Ressource diskutiert.
I also want to thank all people working at Chyn for creating such a pleasant and amusing working ... more I also want to thank all people working at Chyn for creating such a pleasant and amusing working environment, which makes it almost the 'second home'. In particular, I would like to thank Daniel Hunkeler, Heinz Surbeck and Pierre Schnegg for their involvment in this project, leading to numerous results and very fruitful discussions. Without the close collaboration with the Cyprus Water Development Department, field work in Cyprus would not have been possible. Their interest and support and fruitful discussions were very much appreciated. Special thanks go to Dr. Andreas Christodoulides, whose personal involvement in helping us with anything we needed during the field campaigns in Cyprus will remain unforgettable. Special thanks go to the managements of the Lanitis and Phasouri plantations, who authorised the implementation of the monitoring wells and who provided a lot of logistical support. A very special thank goes to Fabien Cornaton for all the support and help he has given me throughout these years, with many discussions leading onto new tracks. Also, I want to thank him for all the long-distance trouble-shooting and debugging across the oceans and corrections he did for me in the last phase of the work. My parents and family I want to thank so much for all the unforgettable support I got from them, particularly in the very last and difficult phase of the work. My father's patience in correcting my 'awkward' english and his pertinent comments and advice kept me going.
I also want to thank all people working at Chyn for creating such a pleasant and amusing working ... more I also want to thank all people working at Chyn for creating such a pleasant and amusing working environment, which makes it almost the 'second home'. In particular, I would like to thank Daniel Hunkeler, Heinz Surbeck and Pierre Schnegg for their involvment in this project, leading to numerous results and very fruitful discussions. Without the close collaboration with the Cyprus Water Development Department, field work in Cyprus would not have been possible. Their interest and support and fruitful discussions were very much appreciated. Special thanks go to Dr. Andreas Christodoulides, whose personal involvement in helping us with anything we needed during the field campaigns in Cyprus will remain unforgettable. Special thanks go to the managements of the Lanitis and Phasouri plantations, who authorised the implementation of the monitoring wells and who provided a lot of logistical support. A very special thank goes to Fabien Cornaton for all the support and help he has given me throughout these years, with many discussions leading onto new tracks. Also, I want to thank him for all the long-distance trouble-shooting and debugging across the oceans and corrections he did for me in the last phase of the work. My parents and family I want to thank so much for all the unforgettable support I got from them, particularly in the very last and difficult phase of the work. My father's patience in correcting my 'awkward' english and his pertinent comments and advice kept me going.
In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling... more In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling from irrigation is superimposed on the effects of seawater intrusion. Water quality degradation of irrigation pumping wells caused by seawater intrusion further enhances salinisation by irrigation, as the extracted solute mass is recycled and is not withdrawn from the system. The main objective of this study is the investigation and quantification of the impact of solute recycling from irrigation relative to seawater intrusion. A solute mass budget was established by expressing the solute mass return flow as fraction of the extracted solute mass from wells by means of a solute mass return flow ratio ðr r Þ: The obtained expression for the relative contribution of solute recycling from irrigation is an exponential function of the return flow ratio r r and normalised time t only (time versus system turnover time). This expression was applied to an example, the Kiti aquifer (Southern Cyprus), where field observations suggest that solute return flow is a superimposed salinisation mechanism. The contribution from solute recycling normalised with the solute mass flux entering from the sea after 20 years was found to be 1.5-8.5% in the extracted solute mass flux, depending on the estimation of the system turnover time. Subsequently, a coupled finite element model, reflecting the main features of the Kiti aquifer was used as a possible 'synthetic reality', to test the relative impact of solute recycling on the spatial salinity distribution in a complex hydrogeological and geometrical setting. This was done by running two simulation scenarios: (1) recycling all the extracted solute back into the system and (2) leaving solute recycling aside and comparing the results of these two scenarios relative to each other and to patterns observed in the field. The results showed, that by introducing solute recycling into the numerical model as coupled boundary condition does not only respect the overall solute mass balance but can have an important impact on the salinity distribution, leading to a significant spreading of the mixing zone, similar to what was observed in the field.
Emergency responses in humanitarian contexts require rapid setup of water supply. Boreholes are o... more Emergency responses in humanitarian contexts require rapid setup of water supply. Boreholes are often drilled where the needs are highest and not where hydrogeological conditions are most favourable. The Rapid Groundwater Potential Mapping (RGWPM) methodology was therefore developed as a practical tool to support borehole siting when time is critical, allowing strategic planning of geophysical campaigns. RGWPM is based on the combined analysis of satellite images, digital elevation models and geological maps, obtained through spatial overlay of the two main hydrogeological variables controlling groundwater potential: water availability (WA) and reservoir capacity (RC). The WA associates hydrogeomorphological features to groundwater dynamic processes, while the RC reflects estimates of the hydraulic conductivity. RGWPM maps are produced through an overlay of WA and RC with the overall groundwater potential (GWP) characterized as 'very low', 'low', 'medium', and 'high', with each zone associated to a specific water supply option. The first RGWPM map was elaborated during a drilling campaign in Northern Uganda. The average yield for the eight boreholes sited 'with' RGWPM was 35 m 3 /h versus 3 m 3 /h for the 92 preexisting boreholes that were sited 'without' RGWPM. Statistical comparison of the classified yields of all hundred boreholes with the RGWPM predicted-yield ranges revealed a good correlation for the 'low' GWP unit, highlighting areas where well siting for motorised systems should be avoided. A rather poor correlation of 33% was found for the 'medium' GWP unit, believed to be artificially induced by the numerous hand pumps (low yields) located in potentially higher yielding areas.
The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refug... more The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refugee camps and local community. Risk of well salinisation and water level depletion has led to the concerns regarding sustainability of groundwater management. A methodology was developed to quantify groundwater recharge, based on hydrogeological data analysis, linking river discharge rates to groundwater recharge by combining remote sensing techniques with surface/groundwater numerical modelling. Also, the risk of salinisation of wells was assessed by means of numerical modelling combined with data provided from a groundwater monitoring network. Groundwater recharge estimates yielded 50 to 100 times higher values than previous studies, suggesting a multi-layered aquifer system. Since abstractions are concentrated within only one aquifer horizon of the system, they were found to be close to recharge rates. Hence, groundwater prospection of deeper horizons could reveal a potential for new groundwater resources in the area.
A framework for a process-based salinisation risk assessment methodology is proposed that allows ... more A framework for a process-based salinisation risk assessment methodology is proposed that allows separation and mapping of areas prone to primary salinisation, such as seawater intrusion, agrochemical pollution or geogenic contamination and secondary salinisation derived from irrigationinduced solute recycling. By adaptation of the boundary conditions, the bulk salinity distribution is decomposed into components derived from the different salinisation processes. To obtain the respective risk index distributions, both the 'present state' and salinisation potentials (steady state salinity distributions) have to be simulated. The respective salinisation risk indices are defined as the potential of further salinisation induced by the respective salinisation process and are obtained by deducting the components of the 'present state' salinity distributions from the respective salinisation potentials. The risk index distribution maps are then overlaid with a defined threshold salinity, revealing areas requiring remediation or conservation measures. The risk index distributions are strictly related to a given exploitation scheme. Modification of an exploitation scheme leads therefore to modified risk index distributions which highlight areas that will suffer further salinisation from areas for which the modified exploitation scheme will have a remediating effect. The risk maps obtained for a real case site (Akrotiri aquifer, Southern Cyprus) are then presented, revealing the outcomes of the approach, as well as its limitations.
Close to half a million refugees live in Dadaab, Kenya and rely on groundwater from the Merti Aqu... more Close to half a million refugees live in Dadaab, Kenya and rely on groundwater from the Merti Aquifer. Preliminary hydrogeological mapping indicates over exploitation of the fresh water aquifer could result in salt water intrusion, which would put the security of water supply for the refugee camps and host population at risk. UNHCR together with University of Neuchâtel has embarked on a comprehensive study of the Merti Aquifer including remote monitoring, and numerical modelling of the aquifer in order to develop a sustainable groundwater management plan for the aquifer which supplies water to all the refugee camps in Dadaab, Kenya.
The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refug... more The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refugee camps and local community. Risk of well salinisation and water level depletion has led to the concerns regarding sustainability of groundwater management. A methodology was developed to quantify groundwater recharge, based on hydrogeological data analysis, linking river discharge rates to groundwater recharge by combining remote sensing techniques with surface/groundwater numerical modelling. Also, the risk of salinisation of wells was assessed by means of numerical modelling combined with data provided from a groundwater monitoring network. Groundwater recharge estimates yielded 50 to 100 times higher values than previous studies, suggesting a multi-layered aquifer system. Since abstractions are concentrated within only one aquifer horizon of the system, they were found to be close to recharge rates. Hence, groundwater prospection of deeper horizons could reveal a potential for new g...
A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g nu... more A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture, both in profiling and in azimuthal mode is presented. The term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space.The main objective is to determine which array(s) best localise vertical structures or best identify their orientation. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately, while the midpoint null-array combined with the Schlumberger null-array allows accurate orientation of a fracture. Field test measurements were carried out to verify the theoretical results above a quarry in Les Breuleux with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real fiel...
Kurzfassung in einem Porengrundwasserleiter aus Niederterrassenschottern bei Pratteln, Schweiz, w... more Kurzfassung in einem Porengrundwasserleiter aus Niederterrassenschottern bei Pratteln, Schweiz, wurde ein Markierungsversuch mit Uranin durchgeführt, um die gefährdung eines trinkwasserbrunnens durch ein 760 m talaufwärts gelegenen ablagerungsstandort zu bewerten. Dabei wurde eine maximale abstandsgeschwindigkeit von 127 m/d und ein Wiedererhalt von 0,93 % festgestellt. Der tracer wurde auch in zwei intermediären beobachtungsbrunnen nachgewiesen. Diese Studie diskutiert die Ursachen dieser hohen Fließgeschwindigkeit. Durch drei verschiedene analytische Modelle konnten die Durchgangskurven simuliert und transportparameter bestimmt werden. erst die anwendung eines zweidimensionalen numerischen Modells (FeFLOW) mit vereinfachter geometrie liefert aber eine hydrogeologisch konsistente, mögliche erklärung aller Versuchsergebnisse. Demnach handelt es sich vermutlich um einen relativ homogenen grundwasserleiter. Der steile gradient (6 ‰) und die hohe Durchlässigkeit (3 • 10-2 m/s) verursachen die hohen Fließgeschwindigkeiten. Der hauptteil der tracerwolke strömt seitlich an den brunnen vorbei. Durch später durchgeführte Kleinpumpversuche wurde diese Modellvorstellung weitgehend bestätigt. Diese befunde sollten bei Schutz-und Sanierungskonzepten berücksichtigt werden. Tracer experiments and modelling for risk assessment of a drinking water well Abstract a tracer experiment with uranine in a gravel aquifer aimed to assess the risk of a drinking water well near Pratteln, Switzerland, resulting from a contaminated site 760 m further upgradient. the experiment revealed a maximum linear flow velocity of 127 m/d and a mass recovery of 0.93 %. the tracer was also detected at two intermediate monitoring wells. this paper discusses the causes of this high flow velocity. Three different analytical models allowed simulation of the breakthrough curves and determination of transport parameters. a two-dimensional numerical model (FEFLOW) with simplified geometry provided a hydrogeologically consistent and probable explanation of all results. the aquifer is most likely relatively homogeneous, the steep hydraulic gradient (6 ‰) and high conductivity (3 • 10-2 m/s) cause high flow velocities, and most of the tracer passed northeast of the wells. recently conducted small scale pumping tests largely confirmed this conceptual model. These findings should be considered for future protection measures. Keywords alluvial aquifer • flow velocity • scale effect • groundwater protection • tracer test • analytical and numerical modeling Einleitung bei der ausweisung von trinkwasserschutzzonen in Porengrundwasserleitern wird die Verweilzeit meist als wichtigstes Kriterium herangezogen; in der Schweiz gelten 10, in Deutschland 50 tage zur abgrenzung der Zone ii. auch für andere Fragen des grundwasserschutzes sind Verweil-Dr. N. goldscheider (), Dr. e. Milnes centre d'hydrogéologie (chYN),
A framework for a process-based salinisation risk assessment methodology is proposed that allows ... more A framework for a process-based salinisation risk assessment methodology is proposed that allows separation and mapping of areas prone to primary salinisation, such as seawater intrusion, agrochemical pollution or geogenic contamination and secondary salinisation derived from irrigationinduced solute recycling. By adaptation of the boundary conditions, the bulk salinity distribution is decomposed into components derived from the different salinisation processes. To obtain the respective risk index distributions, both the 'present state' and salinisation potentials (steady state salinity distributions) have to be simulated. The respective salinisation risk indices are defined as the potential of further salinisation induced by the respective salinisation process and are obtained by deducting the components of the 'present state' salinity distributions from the respective salinisation potentials. The risk index distribution maps are then overlaid with a defined threshold salinity, revealing areas requiring remediation or conservation measures. The risk index distributions are strictly related to a given exploitation scheme. Modification of an exploitation scheme leads therefore to modified risk index distributions which highlight areas that will suffer further salinisation from areas for which the modified exploitation scheme will have a remediating effect. The risk maps obtained for a real case site (Akrotiri aquifer, Southern Cyprus) are then presented, revealing the outcomes of the approach, as well as its limitations.
Interception of aquifers by tunnel excavation results in water inflow and leads to drawdown of th... more Interception of aquifers by tunnel excavation results in water inflow and leads to drawdown of the water table which may induce ground settlement. In this work, analytical and numerical models are presented which specifically address these groundwater related processes in tunnel excavation. These developed models are compared and their performance as predictive tools is evaluated. Firstly, the water inflow in deep tunnels is treated. It is shown that introducing a reduction factor accounting for the effect of effective stress on hydrodynamic parameters avoids overestimation. This effect can be considered in numerical models using effective stress-dependent parameters. Then, quantification of ground settlement is addressed by a transient analytical solution. These solutions are then successfully applied to the data obtained during the excavation of the La Praz exploratory tunnel in the Western Alps (France), validating their usefulness as predictive tools.
In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling... more In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling from irrigation is superimposed on the effects of seawater intrusion. Water quality degradation of irrigation pumping wells caused by seawater intrusion further enhances salinisation by irrigation, as the extracted solute mass is recycled and is not withdrawn from the system. The main objective of this study is the investigation and quantification of the impact of solute recycling from irrigation relative to seawater intrusion. A solute mass budget was established by expressing the solute mass return flow as fraction of the extracted solute mass from wells by means of a solute mass return flow ratio ðr r Þ: The obtained expression for the relative contribution of solute recycling from irrigation is an exponential function of the return flow ratio r r and normalised time t only (time versus system turnover time). This expression was applied to an example, the Kiti aquifer (Southern Cyprus), where field observations suggest that solute return flow is a superimposed salinisation mechanism. The contribution from solute recycling normalised with the solute mass flux entering from the sea after 20 years was found to be 1.5-8.5% in the extracted solute mass flux, depending on the estimation of the system turnover time. Subsequently, a coupled finite element model, reflecting the main features of the Kiti aquifer was used as a possible 'synthetic reality', to test the relative impact of solute recycling on the spatial salinity distribution in a complex hydrogeological and geometrical setting. This was done by running two simulation scenarios: (1) recycling all the extracted solute back into the system and (2) leaving solute recycling aside and comparing the results of these two scenarios relative to each other and to patterns observed in the field. The results showed, that by introducing solute recycling into the numerical model as coupled boundary condition does not only respect the overall solute mass balance but can have an important impact on the salinity distribution, leading to a significant spreading of the mixing zone, similar to what was observed in the field.
Groundwater salinisation is a major groundwater contamination issue worldwide and can be caused b... more Groundwater salinisation is a major groundwater contamination issue worldwide and can be caused by different processes, such as seawater intrusion, agrochemical pollution, geogenic contamination and irrigation-induced salinisation. In many areas, several salinisation processes are superimposed. Since remedial measures vary for different salinisation processes, correct identification is fundamental for adequate design of management strategies: different strategies may be required in one and the same aquifer, depending on which salinisation process is active where in the domain. A simulation-based salinisation risk assessment methodology is proposed, based on the principle of linear superposition of total dissolved solutes in groundwater. In a first step, the measured bulk salinity distribution is used to calibrate a numerical groundwater flow and transport model, accounting for all identified salinisation processes. Then, the bulk salinity distribution is decomposed into different salinity components by adapting the boundary conditions, running a simulation for each salinisation process separately. These simulation results yield the necessary components to calculate the risk index distributions, which are a measure of the respective future potential salinity increase. Overlaying the risk index distributions with a defined threshold concentration reveals risk areas requiring remediation or conservation measures with respect to each process. The risk area maps resulting from this methodology are a promising tool for the design of groundwater management schemes. They condense relevant information from complex dynamic processes obtained from numerical simulations and visualise the results in simple and static maps, accessible to decision makers who are not familiar with groundwater dynamics. The different steps of the salinisation risk assessment procedure are first described and illustrated on a synthetic example and then applied to a real aquifer system in Southern Cyprus (Akrotiri), where three major salinisation processes are superimposed.
The term "geoelectric null-array" is used for direct current electrode configurations yielding a ... more The term "geoelectric null-array" is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-γ null-array and Schlumberger null-array in response to a fracture, both in profiling and in azimuthal mode. The main objective is to determine which array(s) best localise fractures or best identify their orientation. Forward modelling of the three null-arrays revealed that the Wenner-γ and Schlumberger null-arrays localise vertical fractures the most accurately, whilst the midpoint null-array combined with the Schlumberger null-array allows accurate orientation of a fracture. Numerical analysis then served as a basis to interpret the field results. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null-arrays and classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-γ null-array proved to be the most efficient and accurate in localising fractures. The orientations of the fractures according to the numerical results were most efficiently determined with the midpoint null-array, whilst the Schlumberger null-array adds accuracy to the results. This study shows that geoelectrical null-arrays are more suitable than classical arrays for the characterisation of fracture geometry.
The term “geoelectric null-array” is used for direct current electrode configurations yielding a ... more The term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture. The main objective is to determine which array(s) best localise vertical structures. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately. The numerical analysis served as basis to interpret the field results too. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-g null-array showed to be the most efficient and accurate in localising fractures. This study shows that geoelectrical null-arrays are better than classical arrays for localisation of fractures.
ABSTRACT A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), We... more ABSTRACT A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture, both in profiling and in azimuthal mode is presented. The term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space.The main objective is to determine which array(s) best localise vertical structures or best identify their orientation. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately, while the midpoint null-array combined with the Schlumberger null-array allows accurate orientation of a fracture. Field test measurements were carried out to verify the theoretical results above a quarry in Les Breuleux with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-g null-array showed to be the most efficient and accurate in localising fractures. The orientations of the fractures in accordance with the numerical results, were most efficiently determined with midpoint null-array, however Schlumberger null-array adds accuracy to the results. This study shows that geoelectrical null-arrays are better than classical arrays for the characterisation of fracture geometry.
Tiefengrundwasser findet sich in allen grosstektonischen Einheiten der Schweiz. Die bekannten, te... more Tiefengrundwasser findet sich in allen grosstektonischen Einheiten der Schweiz. Die bekannten, teilweise genutzten Vorkommen von Tiefengrundwas-ser und insbesondere die chemische Zusammensetzung dieser Wasser wird fur die verschiedenen Einheiten aufgezeigt. Im Hinblick auf mogliche Nutzungskon-flikte werden die gesetzlichen Grundlagen und Massnahmen zum Schutz dieser Ressource diskutiert.
I also want to thank all people working at Chyn for creating such a pleasant and amusing working ... more I also want to thank all people working at Chyn for creating such a pleasant and amusing working environment, which makes it almost the 'second home'. In particular, I would like to thank Daniel Hunkeler, Heinz Surbeck and Pierre Schnegg for their involvment in this project, leading to numerous results and very fruitful discussions. Without the close collaboration with the Cyprus Water Development Department, field work in Cyprus would not have been possible. Their interest and support and fruitful discussions were very much appreciated. Special thanks go to Dr. Andreas Christodoulides, whose personal involvement in helping us with anything we needed during the field campaigns in Cyprus will remain unforgettable. Special thanks go to the managements of the Lanitis and Phasouri plantations, who authorised the implementation of the monitoring wells and who provided a lot of logistical support. A very special thank goes to Fabien Cornaton for all the support and help he has given me throughout these years, with many discussions leading onto new tracks. Also, I want to thank him for all the long-distance trouble-shooting and debugging across the oceans and corrections he did for me in the last phase of the work. My parents and family I want to thank so much for all the unforgettable support I got from them, particularly in the very last and difficult phase of the work. My father's patience in correcting my 'awkward' english and his pertinent comments and advice kept me going.
I also want to thank all people working at Chyn for creating such a pleasant and amusing working ... more I also want to thank all people working at Chyn for creating such a pleasant and amusing working environment, which makes it almost the 'second home'. In particular, I would like to thank Daniel Hunkeler, Heinz Surbeck and Pierre Schnegg for their involvment in this project, leading to numerous results and very fruitful discussions. Without the close collaboration with the Cyprus Water Development Department, field work in Cyprus would not have been possible. Their interest and support and fruitful discussions were very much appreciated. Special thanks go to Dr. Andreas Christodoulides, whose personal involvement in helping us with anything we needed during the field campaigns in Cyprus will remain unforgettable. Special thanks go to the managements of the Lanitis and Phasouri plantations, who authorised the implementation of the monitoring wells and who provided a lot of logistical support. A very special thank goes to Fabien Cornaton for all the support and help he has given me throughout these years, with many discussions leading onto new tracks. Also, I want to thank him for all the long-distance trouble-shooting and debugging across the oceans and corrections he did for me in the last phase of the work. My parents and family I want to thank so much for all the unforgettable support I got from them, particularly in the very last and difficult phase of the work. My father's patience in correcting my 'awkward' english and his pertinent comments and advice kept me going.
In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling... more In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling from irrigation is superimposed on the effects of seawater intrusion. Water quality degradation of irrigation pumping wells caused by seawater intrusion further enhances salinisation by irrigation, as the extracted solute mass is recycled and is not withdrawn from the system. The main objective of this study is the investigation and quantification of the impact of solute recycling from irrigation relative to seawater intrusion. A solute mass budget was established by expressing the solute mass return flow as fraction of the extracted solute mass from wells by means of a solute mass return flow ratio ðr r Þ: The obtained expression for the relative contribution of solute recycling from irrigation is an exponential function of the return flow ratio r r and normalised time t only (time versus system turnover time). This expression was applied to an example, the Kiti aquifer (Southern Cyprus), where field observations suggest that solute return flow is a superimposed salinisation mechanism. The contribution from solute recycling normalised with the solute mass flux entering from the sea after 20 years was found to be 1.5-8.5% in the extracted solute mass flux, depending on the estimation of the system turnover time. Subsequently, a coupled finite element model, reflecting the main features of the Kiti aquifer was used as a possible 'synthetic reality', to test the relative impact of solute recycling on the spatial salinity distribution in a complex hydrogeological and geometrical setting. This was done by running two simulation scenarios: (1) recycling all the extracted solute back into the system and (2) leaving solute recycling aside and comparing the results of these two scenarios relative to each other and to patterns observed in the field. The results showed, that by introducing solute recycling into the numerical model as coupled boundary condition does not only respect the overall solute mass balance but can have an important impact on the salinity distribution, leading to a significant spreading of the mixing zone, similar to what was observed in the field.
Emergency responses in humanitarian contexts require rapid setup of water supply. Boreholes are o... more Emergency responses in humanitarian contexts require rapid setup of water supply. Boreholes are often drilled where the needs are highest and not where hydrogeological conditions are most favourable. The Rapid Groundwater Potential Mapping (RGWPM) methodology was therefore developed as a practical tool to support borehole siting when time is critical, allowing strategic planning of geophysical campaigns. RGWPM is based on the combined analysis of satellite images, digital elevation models and geological maps, obtained through spatial overlay of the two main hydrogeological variables controlling groundwater potential: water availability (WA) and reservoir capacity (RC). The WA associates hydrogeomorphological features to groundwater dynamic processes, while the RC reflects estimates of the hydraulic conductivity. RGWPM maps are produced through an overlay of WA and RC with the overall groundwater potential (GWP) characterized as 'very low', 'low', 'medium', and 'high', with each zone associated to a specific water supply option. The first RGWPM map was elaborated during a drilling campaign in Northern Uganda. The average yield for the eight boreholes sited 'with' RGWPM was 35 m 3 /h versus 3 m 3 /h for the 92 preexisting boreholes that were sited 'without' RGWPM. Statistical comparison of the classified yields of all hundred boreholes with the RGWPM predicted-yield ranges revealed a good correlation for the 'low' GWP unit, highlighting areas where well siting for motorised systems should be avoided. A rather poor correlation of 33% was found for the 'medium' GWP unit, believed to be artificially induced by the numerous hand pumps (low yields) located in potentially higher yielding areas.
The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refug... more The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refugee camps and local community. Risk of well salinisation and water level depletion has led to the concerns regarding sustainability of groundwater management. A methodology was developed to quantify groundwater recharge, based on hydrogeological data analysis, linking river discharge rates to groundwater recharge by combining remote sensing techniques with surface/groundwater numerical modelling. Also, the risk of salinisation of wells was assessed by means of numerical modelling combined with data provided from a groundwater monitoring network. Groundwater recharge estimates yielded 50 to 100 times higher values than previous studies, suggesting a multi-layered aquifer system. Since abstractions are concentrated within only one aquifer horizon of the system, they were found to be close to recharge rates. Hence, groundwater prospection of deeper horizons could reveal a potential for new groundwater resources in the area.
A framework for a process-based salinisation risk assessment methodology is proposed that allows ... more A framework for a process-based salinisation risk assessment methodology is proposed that allows separation and mapping of areas prone to primary salinisation, such as seawater intrusion, agrochemical pollution or geogenic contamination and secondary salinisation derived from irrigationinduced solute recycling. By adaptation of the boundary conditions, the bulk salinity distribution is decomposed into components derived from the different salinisation processes. To obtain the respective risk index distributions, both the 'present state' and salinisation potentials (steady state salinity distributions) have to be simulated. The respective salinisation risk indices are defined as the potential of further salinisation induced by the respective salinisation process and are obtained by deducting the components of the 'present state' salinity distributions from the respective salinisation potentials. The risk index distribution maps are then overlaid with a defined threshold salinity, revealing areas requiring remediation or conservation measures. The risk index distributions are strictly related to a given exploitation scheme. Modification of an exploitation scheme leads therefore to modified risk index distributions which highlight areas that will suffer further salinisation from areas for which the modified exploitation scheme will have a remediating effect. The risk maps obtained for a real case site (Akrotiri aquifer, Southern Cyprus) are then presented, revealing the outcomes of the approach, as well as its limitations.
Close to half a million refugees live in Dadaab, Kenya and rely on groundwater from the Merti Aqu... more Close to half a million refugees live in Dadaab, Kenya and rely on groundwater from the Merti Aquifer. Preliminary hydrogeological mapping indicates over exploitation of the fresh water aquifer could result in salt water intrusion, which would put the security of water supply for the refugee camps and host population at risk. UNHCR together with University of Neuchâtel has embarked on a comprehensive study of the Merti Aquifer including remote monitoring, and numerical modelling of the aquifer in order to develop a sustainable groundwater management plan for the aquifer which supplies water to all the refugee camps in Dadaab, Kenya.
The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refug... more The Merti aquifer (Kenya) is the only permanent water resource for the supply of the Dadaab refugee camps and local community. Risk of well salinisation and water level depletion has led to the concerns regarding sustainability of groundwater management. A methodology was developed to quantify groundwater recharge, based on hydrogeological data analysis, linking river discharge rates to groundwater recharge by combining remote sensing techniques with surface/groundwater numerical modelling. Also, the risk of salinisation of wells was assessed by means of numerical modelling combined with data provided from a groundwater monitoring network. Groundwater recharge estimates yielded 50 to 100 times higher values than previous studies, suggesting a multi-layered aquifer system. Since abstractions are concentrated within only one aquifer horizon of the system, they were found to be close to recharge rates. Hence, groundwater prospection of deeper horizons could reveal a potential for new g...
A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g nu... more A comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-g null-array and Schlumberger null-array in response to a fracture, both in profiling and in azimuthal mode is presented. The term “geoelectric null-array” is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space.The main objective is to determine which array(s) best localise vertical structures or best identify their orientation. Forward modelling of the three null-arrays revealed that the Wenner-g and Schlumberger null-arrays localise vertical fractures the most accurately, while the midpoint null-array combined with the Schlumberger null-array allows accurate orientation of a fracture. Field test measurements were carried out to verify the theoretical results above a quarry in Les Breuleux with the three null arrays and many classical arrays. The results were cross-validated with quarry-wall geological mapping. In real fiel...
Kurzfassung in einem Porengrundwasserleiter aus Niederterrassenschottern bei Pratteln, Schweiz, w... more Kurzfassung in einem Porengrundwasserleiter aus Niederterrassenschottern bei Pratteln, Schweiz, wurde ein Markierungsversuch mit Uranin durchgeführt, um die gefährdung eines trinkwasserbrunnens durch ein 760 m talaufwärts gelegenen ablagerungsstandort zu bewerten. Dabei wurde eine maximale abstandsgeschwindigkeit von 127 m/d und ein Wiedererhalt von 0,93 % festgestellt. Der tracer wurde auch in zwei intermediären beobachtungsbrunnen nachgewiesen. Diese Studie diskutiert die Ursachen dieser hohen Fließgeschwindigkeit. Durch drei verschiedene analytische Modelle konnten die Durchgangskurven simuliert und transportparameter bestimmt werden. erst die anwendung eines zweidimensionalen numerischen Modells (FeFLOW) mit vereinfachter geometrie liefert aber eine hydrogeologisch konsistente, mögliche erklärung aller Versuchsergebnisse. Demnach handelt es sich vermutlich um einen relativ homogenen grundwasserleiter. Der steile gradient (6 ‰) und die hohe Durchlässigkeit (3 • 10-2 m/s) verursachen die hohen Fließgeschwindigkeiten. Der hauptteil der tracerwolke strömt seitlich an den brunnen vorbei. Durch später durchgeführte Kleinpumpversuche wurde diese Modellvorstellung weitgehend bestätigt. Diese befunde sollten bei Schutz-und Sanierungskonzepten berücksichtigt werden. Tracer experiments and modelling for risk assessment of a drinking water well Abstract a tracer experiment with uranine in a gravel aquifer aimed to assess the risk of a drinking water well near Pratteln, Switzerland, resulting from a contaminated site 760 m further upgradient. the experiment revealed a maximum linear flow velocity of 127 m/d and a mass recovery of 0.93 %. the tracer was also detected at two intermediate monitoring wells. this paper discusses the causes of this high flow velocity. Three different analytical models allowed simulation of the breakthrough curves and determination of transport parameters. a two-dimensional numerical model (FEFLOW) with simplified geometry provided a hydrogeologically consistent and probable explanation of all results. the aquifer is most likely relatively homogeneous, the steep hydraulic gradient (6 ‰) and high conductivity (3 • 10-2 m/s) cause high flow velocities, and most of the tracer passed northeast of the wells. recently conducted small scale pumping tests largely confirmed this conceptual model. These findings should be considered for future protection measures. Keywords alluvial aquifer • flow velocity • scale effect • groundwater protection • tracer test • analytical and numerical modeling Einleitung bei der ausweisung von trinkwasserschutzzonen in Porengrundwasserleitern wird die Verweilzeit meist als wichtigstes Kriterium herangezogen; in der Schweiz gelten 10, in Deutschland 50 tage zur abgrenzung der Zone ii. auch für andere Fragen des grundwasserschutzes sind Verweil-Dr. N. goldscheider (), Dr. e. Milnes centre d'hydrogéologie (chYN),
A framework for a process-based salinisation risk assessment methodology is proposed that allows ... more A framework for a process-based salinisation risk assessment methodology is proposed that allows separation and mapping of areas prone to primary salinisation, such as seawater intrusion, agrochemical pollution or geogenic contamination and secondary salinisation derived from irrigationinduced solute recycling. By adaptation of the boundary conditions, the bulk salinity distribution is decomposed into components derived from the different salinisation processes. To obtain the respective risk index distributions, both the 'present state' and salinisation potentials (steady state salinity distributions) have to be simulated. The respective salinisation risk indices are defined as the potential of further salinisation induced by the respective salinisation process and are obtained by deducting the components of the 'present state' salinity distributions from the respective salinisation potentials. The risk index distribution maps are then overlaid with a defined threshold salinity, revealing areas requiring remediation or conservation measures. The risk index distributions are strictly related to a given exploitation scheme. Modification of an exploitation scheme leads therefore to modified risk index distributions which highlight areas that will suffer further salinisation from areas for which the modified exploitation scheme will have a remediating effect. The risk maps obtained for a real case site (Akrotiri aquifer, Southern Cyprus) are then presented, revealing the outcomes of the approach, as well as its limitations.
Interception of aquifers by tunnel excavation results in water inflow and leads to drawdown of th... more Interception of aquifers by tunnel excavation results in water inflow and leads to drawdown of the water table which may induce ground settlement. In this work, analytical and numerical models are presented which specifically address these groundwater related processes in tunnel excavation. These developed models are compared and their performance as predictive tools is evaluated. Firstly, the water inflow in deep tunnels is treated. It is shown that introducing a reduction factor accounting for the effect of effective stress on hydrodynamic parameters avoids overestimation. This effect can be considered in numerical models using effective stress-dependent parameters. Then, quantification of ground settlement is addressed by a transient analytical solution. These solutions are then successfully applied to the data obtained during the excavation of the La Praz exploratory tunnel in the Western Alps (France), validating their usefulness as predictive tools.
In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling... more In coastal aquifers which are exploited for agricultural purposes, salinisation by salt recycling from irrigation is superimposed on the effects of seawater intrusion. Water quality degradation of irrigation pumping wells caused by seawater intrusion further enhances salinisation by irrigation, as the extracted solute mass is recycled and is not withdrawn from the system. The main objective of this study is the investigation and quantification of the impact of solute recycling from irrigation relative to seawater intrusion. A solute mass budget was established by expressing the solute mass return flow as fraction of the extracted solute mass from wells by means of a solute mass return flow ratio ðr r Þ: The obtained expression for the relative contribution of solute recycling from irrigation is an exponential function of the return flow ratio r r and normalised time t only (time versus system turnover time). This expression was applied to an example, the Kiti aquifer (Southern Cyprus), where field observations suggest that solute return flow is a superimposed salinisation mechanism. The contribution from solute recycling normalised with the solute mass flux entering from the sea after 20 years was found to be 1.5-8.5% in the extracted solute mass flux, depending on the estimation of the system turnover time. Subsequently, a coupled finite element model, reflecting the main features of the Kiti aquifer was used as a possible 'synthetic reality', to test the relative impact of solute recycling on the spatial salinity distribution in a complex hydrogeological and geometrical setting. This was done by running two simulation scenarios: (1) recycling all the extracted solute back into the system and (2) leaving solute recycling aside and comparing the results of these two scenarios relative to each other and to patterns observed in the field. The results showed, that by introducing solute recycling into the numerical model as coupled boundary condition does not only respect the overall solute mass balance but can have an important impact on the salinity distribution, leading to a significant spreading of the mixing zone, similar to what was observed in the field.
Groundwater salinisation is a major groundwater contamination issue worldwide and can be caused b... more Groundwater salinisation is a major groundwater contamination issue worldwide and can be caused by different processes, such as seawater intrusion, agrochemical pollution, geogenic contamination and irrigation-induced salinisation. In many areas, several salinisation processes are superimposed. Since remedial measures vary for different salinisation processes, correct identification is fundamental for adequate design of management strategies: different strategies may be required in one and the same aquifer, depending on which salinisation process is active where in the domain. A simulation-based salinisation risk assessment methodology is proposed, based on the principle of linear superposition of total dissolved solutes in groundwater. In a first step, the measured bulk salinity distribution is used to calibrate a numerical groundwater flow and transport model, accounting for all identified salinisation processes. Then, the bulk salinity distribution is decomposed into different salinity components by adapting the boundary conditions, running a simulation for each salinisation process separately. These simulation results yield the necessary components to calculate the risk index distributions, which are a measure of the respective future potential salinity increase. Overlaying the risk index distributions with a defined threshold concentration reveals risk areas requiring remediation or conservation measures with respect to each process. The risk area maps resulting from this methodology are a promising tool for the design of groundwater management schemes. They condense relevant information from complex dynamic processes obtained from numerical simulations and visualise the results in simple and static maps, accessible to decision makers who are not familiar with groundwater dynamics. The different steps of the salinisation risk assessment procedure are first described and illustrated on a synthetic example and then applied to a real aquifer system in Southern Cyprus (Akrotiri), where three major salinisation processes are superimposed.
The term "geoelectric null-array" is used for direct current electrode configurations yielding a ... more The term "geoelectric null-array" is used for direct current electrode configurations yielding a potential difference of zero above a homogeneous half-space. This paper presents a comparative study of the behaviour of three null-arrays, midpoint null-array (MAN), Wenner-γ null-array and Schlumberger null-array in response to a fracture, both in profiling and in azimuthal mode. The main objective is to determine which array(s) best localise fractures or best identify their orientation. Forward modelling of the three null-arrays revealed that the Wenner-γ and Schlumberger null-arrays localise vertical fractures the most accurately, whilst the midpoint null-array combined with the Schlumberger null-array allows accurate orientation of a fracture. Numerical analysis then served as a basis to interpret the field results. Field test measurements were carried out above a quarry in Les Breuleux (Switzerland) with the three null-arrays and classical arrays. The results were cross-validated with quarry-wall geological mapping. In real field circumstances, the Wenner-γ null-array proved to be the most efficient and accurate in localising fractures. The orientations of the fractures according to the numerical results were most efficiently determined with the midpoint null-array, whilst the Schlumberger null-array adds accuracy to the results. This study shows that geoelectrical null-arrays are more suitable than classical arrays for the characterisation of fracture geometry.
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Papers by Ellen Milnes