Assessing groundwater resources in coastal area: a case study in Myanmar

Coastal aquifers are of a great relevance for human needs because coastal areas are often densely populated. To meet the needs of the people living in coastal area and to assess the groundwater resources for the future, we need to know the main characteristics of these aquifers. A preliminary hydrogeological assessment is conducted in order to point out the main questions encountered. Then, a geophysical survey is designed to answer these questions. Finally, the economical impact of integrated hydro-geophyscial approach is calculated. This paper presents the main results of a survey conducted in Myanmar. We found that the joint use of hydrogeological data (boreholes and pumping tests) with appropriate geophysics (magnetic resonance sounding and electrical resistively measurements) improves significantly the knowledge of coastal groundwater resources. The presence of groundwater, its available quantity but also its salinity can be reasonably estimated from surface geophysical measurements

Can groundwater secure drinking-water supply and supplementary irrigation in new settlements of North-West Cambodia ?

Since the end of the Cambodian Civil War in 1998, the population of the Oddar Meanchey province has drastically increased despite the lack of adequate infrastructure, including basic amenities such as drinking-water supply. To improve the access to drinking water, governmental and aid agencies have focussed on drilling shallow boreholes. The use of groundwater for irrigation is also a growing concern to cope with the occasional late arrival of the rainy season or to produce food during the dry season. Since the groundwater resource in the province has not been documented, a 4-year study was undertaken (2011-2014), aiming to estimate the capability of groundwater to supply domestic needs and supplementary irrigation for rice production. Aquifer properties were estimated by combined use of hydrogeological techniques with the geophysical magnetic resonance sounding method. Groundwater storage and recharge were estimated based on new developments in the application of the geophysical method for quantifying specific yield. The median groundwater storage of the targeted sandstone aquifer is 173 mm, the recharge is diffuse and annually ranges from 10 to 70 mm, and the transmissivity is low to medium. Simulations of pumping indicate that the aquifer can easily supply 100 L of drinking water per capita daily, even considering the estimated population in 2030. However, the shallow aquifer can generally not deliver enough water to irrigate paddy fields of several hectares during a 2-month delay in the onset of the monsoon

The use of transient electro-magnetism method to localize saline water intrusion in Sri Lanka

On the east coast of Sri Lanka, groundwater resources mainly consist in coastal aquifers, which are exploited for both irrigation and domestic purposes. In case of an intensive exploitation, saline water intrusions can occur, which make the water in wells improper for consumption. Considering the future resettlements of internally displaced families in coastal areas, and in order to evaluate the potential of these coastal aquifers (before launching a well implementation program), one need to locate the extent of this saline water intrusion. This information can be obtained by intrusive means such as piezometers monitoring, or non-intrusive means with geophysical methods. Transient Electro Magnetism (TEM) method has been used on different coastal sites on the east coast of Sri Lanka and has given good results for estimating the aquifers geometrical parameters. This first study will be followed by a more complete geophysical survey involving other methods

Joint use of singular value decomposition and Monte-Carlo simulation for estimating uncertainty in surface NMR inversion

This work was supported by a grant from Labex OSUG@2020 (Investissements d'avenir – ANR10 LABX56). We also thank the French National Program (ANR)” Investment for Future - Excellency Equipment” project EQUIPEX CRITEX (grant # ANR-11-EQPX-0011) for providing MRS equipment. The Geological Survey of Ireland (GSI) provided financial support for the fieldwork in the framework of the Geoscience Research Program (2016).Peer reviewedPostprin

Observed controls on resilience of groundwater to climate variability in sub-Saharan Africa

Groundwater in sub-Saharan Africa supports livelihoods and poverty alleviation1,2, maintains vital ecosystems, and strongly influences terrestrial water and energy budgets. Yet the hydrological processes that govern groundwater recharge and sustainability—and their sensitivity to climatic variability—are poorly constrained4. Given the absence of firm observational constraints, it remains to be seen whether model-based projections of decreased water resources in dry parts of the region4 are justified. Here we show, through analysis of multidecadal groundwater hydrographs across sub-Saharan Africa, that levels of aridity dictate the predominant recharge processes, whereas local hydrogeology influences the type and sensitivity of precipitation–recharge relationships. Recharge in some humid locations varies by as little as five per cent (by coefficient of variation) across a wide range of annual precipitation values. Other regions, by contrast, show roughly linear precipitation–recharge relationships, with precipitation thresholds (of roughly ten millimetres or less per day) governing the initiation of recharge. These thresholds tend to rise as aridity increases, and recharge in drylands is more episodic and increasingly dominated by focused recharge through losses from ephemeral overland flows. Extreme annual recharge is commonly associated with intense rainfall and flooding events, themselves often driven by large-scale climate controls. Intense precipitation, even during years of lower overall precipitation, produces some of the largest years of recharge in some dry subtropical locations. Our results therefore challenge the ‘high certainty’ consensus regarding decreasing water resources in such regions of sub-Saharan Africa. The potential resilience of groundwater to climate variability in many areas that is revealed by these precipitation–recharge relationships is essential for informing reliable predictions of climate-change impacts and adaptation strategies

Implementing borehole in Cambodia: geophysical contribution

To drill successful boreholes, hydrogeologists have to answer fundamental questions, i.e. where is the groundwater? what will be the yield of a borehole ? what is the water quality? Geophysics is very attractive to complete the standard hydrogeological approach to answer these questions, but conventional methods provide information which is not always directly related to groundwater. A new method, called Surface Nuclear Magnetic Resonance (SNMR), is supposed to detect groundwater directly at various depths. A geophysical study was implemented in Cambodia with conventional and SNMR methods to measure the geophysics contribution to a drilling programme. This paper presents the main technical and financial analyses of this operation

La caractérisation des aquifères par une méthode non invasive (les sondages par résonance magnétique protonique)

Disposer d'eau de qualité en quantité suffisante est un besoin vital qui n'est pas encore satisfait pour un grand nombre d'individus. Qu'il s'agisse de la recherche de nouveaux gisements ou de la gestion rationnelle d'aquifères en exploitation, différents outils sont utilisés pour améliorer la connaissance de systèmes parfois complexes. La géophysique est un de ces outils, et la méthode des sondages par Résonance Magnétique Protonique (RMP) est une méthode unique car elle mesure un signal émis par des noyaux de la molécule d'eau. Cette thèse a pour objectif de préciser les informations hydrogéologiques qui peuvent être obtenues au travers des sondages RMP. Les résultats de sondages sont d'abord comparés aux données issues de forages et de pompages d'essai, puis la capacité des sondages RMP à caractériser les aquifères est mesurée au travers de l'utilisation conjointe de différentes méthodes géophysiques. Trois contextes hydrogéologiques sont retenus: les milieux poreux continus, les aquifères de socles et les roches carbonatées. Ce travail montre que la méthode des sondages RMP est opérationnelle pour décrire en une dimension la géométrie des réservoirs, et estimer l'emmagasinement et la transmissivité des aquifères. Cette estimation est quantitative lorsque les sondages sont étalonnés sur des valeurs de références généralement définies par des pompages d'essai. La caractérisation des aquifères est améliorée lorsque les sondages RMP sont mis en œuvre conjointement avec des méthodes traditionnelles. L'interprétation de paramètres complémentaires permet alors de décrire les structures géologiques, les paramètres hydrauliques et la conductivité électrique de l'eau. Les taux de succès de forages implantés sur la base de cette étude ont été améliorés, et une modélisation hydrodynamique réalisée à l'échelle d'un bassin versant en s'appuyant sur la géométrie et les paramètres hydrauliques estimés par la géophysique a été validée par les observations.Provide sufficient quantity of water is an important task, not yet satisfied for a grand number of individuals. Complex tools are often required both for prospecting of new resources and for rational use of exploited aquifers. Geophysics is one of these tools, Magnetic Resonance Sounding (MRS) method has an particular value as it uses a signal provided directly by water molecules. This thesis aims to determine hydrogeological information, which can be obtained by MRS. The sounding results are first compared with direct data from wells and test pumping and then the validity of MRS results for estimation of reservoir parameters is verified by different geophysical methods. Three geological settings were used for this study: continuous porous medium, basement aquifers and calcareous rocks. It is shown that MRS method is valid for one dimension measurement of reservoir geometry and for estimating of stockage capacity and transmisivity of aquifers. These estimations are quantitative if soundings are calibrated on the reference values usually defined by test pumping. The characterisation of aquifers is improved by the joint use of MRS and traditional geophysical methods. Additional parameters thug obtained allow the description of geological structure, hydraulic parameters and electric conductivity of water. Rate of success in water drilling was improved by using methods developed in this study and the hydrodynamic model of catchment area based on hydraulic geometry estimated by geophysics was verified by observation.AVIGNON-Bibl. de géologie (840072202) / SudocORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF