Konstantinos Chalikakis

Three-dimensional magnetic resonance imaging for groundwater

The surface nuclear magnetic resonance method (SNMR) is an established geophysical tool routinely used for investigating one-dimensional (1D) and sometimes 2D subsurface water-saturated formations. We have expanded the tool by developing a 3D application. 3D-SNMR is a large-scale method that allows magnetic resonance imaging of groundwater down to about 80?m. Similar to most surface geophysical methods, 3D-SNMR has limited resolution, but it is effective for investigating water-saturated geological formations larger than several tens of meters. Because the performance of the method depends on variable survey conditions, we cannot estimate it in general. For demonstration purposes, we present an example of numerical modeling under fixed conditions. Results show that under certain conditions it is possible to detect a water volume as small as 500?m3 and the detection threshold depends on the ambient electromagnetic noise magnitude and on the location of the target volume relative to the SNMR loops. The 3D-SNMR method was used to investigate accumulated water within the T?te Rousse glacier (French Alps). Inversion of the field measurements made it possible to locate the principal reservoir in the central part of the glacier and estimate the volume of accumulated water. These results were verified by 20 boreholes installed after the 3D-SNMR results were obtained and by pumping water out of the glacier. Very good correspondence between the 3D-SNMR and borehole results was observed.

On the inclusion of ground-based gravity measurements to the calibration process of a global rainfall-discharge reservoir model: case of the Durzon karst system (Larzac, southern France)

This work examines the relevance of the inclusion of ground-based gravity data in the calibration process of a global rainfall-discharge reservoir model. The analysis is performed for the Durzon karst system (Larzac, France). The first part of the study focuses on the hydrological interpretation of the ground-based gravity measurements. The second part of the study investigates further the information content of the gravity data with respect to water storage dynamics modelling. The gravity-derived information is found unable to either reduce equifinality of the single-objective, discharge-based model calibration process or enhance model performance through assimilation.

Management and research strategies of karst aquifers in Greece: Literature overview and exemplification based on hydrodynamic modelling and vulnerability assessment of a strategic karst aquifer

Karst aquifers are valuable water resources in terms of quantity and quality, hence, their protection and rational management is of utmost importance to sustain water supply. An overview of research articles regarding Karst aquifers in Greece was obtained revealing that progressively the initial simple statistical analysis was replaced from advanced tools but rarely coupled. Additionally, a combined approach including the concept of groundwater vulnerability and pollution risk in conjunction with statistical and hydrodynamic analysis was performed in the complex karst aquifer of Damasi-Titanos in Thessaly Central Greece. The karst aquifer discharges via three springs and it is in dynamic interaction with one of the two rivers that cross the system. The water demands of the area are mainly met with groundwater from the karst aquifer rendering its protection fundamental priority for the sustainability of the area. The hydrodynamic analysis of the karst system was performed by pairing statistical techniques and KarstMod. The analysis revealed a high correlation between the springs that highlights the karstification maturity of the aquifer. Additionally, spring discharge is mainly controlled by the percolation of River Titarisios rather than precipitation. Following the hydrodynamic analysis, the PaPRIKa method was applied and validated using sensitivity analysis in order to assess the intrinsic vulnerability. The vulnerability and hazard maps were combined to produce the pollution risk map of the karst aquifer. The majority of the karst aquifer is characterized by high to very high vulnerability as well as pollution risk. The case study and the obtained overview revealed that a holistic approach can provide mutually supported results increasing their reliability. In this base, a four-step road map including hydrogeological observation, statistical analysis, modelling and vulnerability assessment is suggested in order to obtain the sustainable exploration and integrated management of karst aquifers in Greece.

Hydrochemical constraints between the karst Tabular Middle Atlas Causses and the Saïs basin (Morocco): implications of groundwater circulation

The karst Tabular Middle Atlas Causses reservoir is the main drinking-water supply of Fez-Meknes region (Saïs Basin) in Morocco. Recent analyses showed a decline in associated groundwater chemical quality and increased turbidity. To understand this hydrosystem, four surveys were undertaken during fall and spring, 2009–2011. Hydrogeochemical studies coupled with isotopic analyses (δ18O, δD and 222Rn) showed that the aquifers between the causses (mountains) and the Saïs Basin are of Liassic origin and at the southern extremities are of Triassic origin. Five recharge zones of different altitudes have been defined, including two main mixing zones in the south. Deuterium excess results suggest local recharge, while a plot of δ18O versus δD characterizes a confined aquifer in the eastern sector. 222Rn results reveal areas of rapid exchanges with an upwelling time of less than 2xa0weeks. A schematic conceptual model is presented to explain the groundwater circulation system and the behavior of this karst system.RésuméLe réservoir des Causses karstiques du Moyen Atlas tabulaire constitue la principale source d’approvisionnement en eau potable de la région de Fez-Meknes (bassin de Saïs) au Maroc. Des analyses récentes ont montré une diminution de la qualité chimique des eaux souterraines associée à une turbidité accrue. Pour comprendre cet hydrosystème, quatre campagnes ont été réalisées en automne et printemps de 2009 à 2011. Des études hydrogéochimiques associées à des analyses isotopiques (δ18O, δD et 222Rn) ont montré que les aquifères situés entre les causses (montagnes) et le bassin de Saïs sont d’origine liasique et d’origine triasique au niveau des extrémités méridionales. Cinq zones de recharge de différentes altitudes ont été définies, y compris deux zones principales de mélange dans le sud. Les résultats en excès en deutérium suggèrent une recharge locale, alors qu’un graphique δ18O versus δD caractérise un aquifère confiné dans le secteur oriental. Les résultats du 222Rn révèlent des zones d’échanges rapides avec un temps de remontées des eaux de moins de deux semaines. Un modèle conceptuel schématique est. présenté pour expliquer le système de circulation des eaux souterraines et le comportement de ce système karstique.ResumenEl reservorio kárstico Tabular Middle Atlas Causses es el principal suministro de agua potable de la región de Fez-Meknes (cuenca de Saïs) en Marruecos. Los análisis recientes mostraron una disminución en la calidad química del agua subterránea asociada y un aumento de la turbidez. Para comprender este sistema hidrológico, se realizaron cuatro estudios durante el otoño y la primavera del período 2009–2011. Los estudios hidrogeoquímicos asociados a análisis isotópicos (δ18O, δD and 222Rn) mostraron que los acuíferos entre los causses (montañas) y la Cuenca Saïs son de origen Liásico y en las extremidades meridionales son de origen Triásico. Se han definido cinco zonas de recarga a diferentes altitudes, incluyendo dos zonas principales de mezcla en el sur. Los resultados de exceso de deuterio sugieren la recarga local, mientras que un diagrama de δ18O versus δD caracteriza un acuífero confinado en el sector oriental. Los resultados arrojados revelan áreas de intercambio rápido con un tiempo de surgencia de menos de dos semanas. Se presenta un modelo conceptual esquemático para explicar el sistema de circulación de aguas subterráneas y el comportamiento de este sistema kárstico.摘要岩溶Tabular Middle Atlas高原是摩洛哥Fez-Meknes地区(Saïs盆地)主要的饮用水供水地。最近的分析显示地下水化学质量下降及浑浊度增加。为了了解这个水系统,在2009–2011年秋季和春季进行了四次调查。水文地球化学研究结果与同位素分析(δ18O、 δD 及 222Rn)显示,高原(山脉)和 Saïs盆地之间的含水层属于里阿斯统,在最南端属于三叠纪。确定了不同高度的的五个补给带,包括南部的两个混合带。穿超量结果显示出有本地补给,而18O 与 δD图表明在东部有一个承压含水层。222Rn结果揭示了上涌时间不到两个星期的快速交换区。提出了随机概念模型以解释地下水循环系统和这个岩溶系统的特性。ResumoO reservatório cárstico dos Causses Tabulares do Atlas Médio é o principal fornecimento de água potável da região de Fez-Meknes (Bacia de Saïs) no Marrocos. Análises recentes mostraram um declínio na qualidade química associada às águas subterrâneas e ao aumento da turbidez. Para entender este hidrossistema, quatro pesquisas foram realizadas durante o outono e a primavera, 2009–2011. Estudos hidrogeoquímicos, juntamente com análises isotópicas (δ18O, δD e 222Rn), mostraram que os aquíferos entre os causses (montanhas) e a Bacia de Saïs são de origem Liássica e nas extremidades do sul são de origem Triássica. Foram definidas cinco zonas de recargas de diferentes altitudes, incluindo duas zonas principais de mistura no sul. Os resultados de excesso de deutério sugerem uma recarga local, enquanto que o gráfico de δ18O versus δD caracteriza um aquífero confinado no setor oriental. Resultados de 222Rn revelam áreas de trocas rápidas com um tempo de ressurgência menor que duas semanas. Um modelo esquemático conceitual é apresentado para explicar o sistema de circulação de águas subterrâneas e o comportamento deste sistema cárstico.