Transboundary Aquifers Research Articles

Regional Groundwater Modeling of the Guarani Aquifer System

The Guarani Aquifer System (GAS) is a strategic transboundary aquifer system shared by Brazil, Argentina, Paraguay and Uruguay. This article presents a groundwater flow model to assess the GAS system in terms of regional flow patterns, water balance and overall recharge. Despite the continental dimension of GAS, groundwater recharge is restricted to narrow outcrop zones. An important part is discharged into local watersheds, whereas a minor amount reaches the confined part. A three-dimensional finite element groundwater-flow model of the entire GAS system was constructed to obtain a better understanding of the prevailing flow dynamics and more reliable estimates of groundwater recharge. Our results show that recharge rates effectively contributing to the regional GAS water balance are only approximately 0.6 km3/year (about 4.9 mm/year). These rates are much smaller than previous estimates, including of deep recharge approximations commonly used for water resources management. Higher recharge rates were also not compatible with known 81Kr groundwater age estimates, as well as with calculated residence times using a particle tracking algorithm.

An Enhanced Approach to the Spatial and Statistical Analysis of Factors Influencing Spring Distribution on a Transboundary Karst Aquifer

Karst aquifers are indispensable, yet vulnerable, resources; therefore, they require a comprehensive protection strategy. Since springs are the terminal points of the karst flow systems, knowledge of their distribution is a key element for the better understanding of groundwater flow, availability and vulnerability. The present study aims to introduce a data-driven analysis by the application of a spatial statistical technique (Weights of Evidence (WofE)) for the evaluation of factors influencing spring distribution in karst areas. A workflow was developed for investigating two questions: where will the springs locate, and where will the permanent springs evolve? This workflow has the potential for application to unconfined karst areas. This enhanced approach was applied to an unconfined transboundary aquifer, the Gömör–Torna Karst (HU and SK). The roles of five factors was statistically investigated: terrain elevation, distance to faults, distance of the carbonate–non-carbonate rock contact, distance to sinkholes, and precipitation distribution. The validation procedures confirmed the effectiveness of the approach. The resulting predictive maps are useful for decision-makers to delineate areas holding potential karst springs and to address water availability problems and protection measures. In addition, the WofE technique improved the comprehension of the geological conditions favourable for the formation of the springs.

Revision of the stygobiont gastropod genera Plagigeyeria Tomlin, 1930 and Travunijana Grego & Glöer, 2019 (Mollusca; Gastropoda; Moitessieriidae and Hydrobiidae) in Hercegovina and adjacent regions

The genus Plagigeyeria Tomlin, 1930 is one of the most typical elements representing the stygobiont fauna in the southern Dinaric Alps. In the current study I present the territory of Hercegovina (and its adjacent regions of Bjelašnica and the Dalmatian coast containing transboundary aquifers) as one of the two main biodiversity hotspots for distribution of the genus. It is comparable with the species radiation of Plagigeyeria in the Kotor Bay–Skadar Lake Basin area. My study of the karst springs and caves revealed, besides the presently known species, twelve new Plagigeyeria taxa detected in so-far uninvestigated karstic aquifers: Plagigeyeria erossi sp. nov., P. ljutaensis sp. nov., P. konjicensis sp. nov., P. pseudocostellina sp. nov., P. reischuetzorum sp. nov., P. olsavskyi sp. nov., P. listicaensis sp. nov., P. ozimeci sp. nov., P. jakabi sp. nov., P. angyaldorkae sp. nov., P. vriosticaensis sp. nov. and P. lewarnei sp. nov. Closer shell morphology investigation supported by the protoconch morphology revealed a presence of another genus within the former Plagigeyeria complex. The following taxa are transferred herein to Travunijana Glöer & Grego, 2019: Plagigeyeria robusta Schütt, 1959, P. robusta asculpta Schütt, 1972, P. ovalis Kuščer, 1933, P. edlaueri Schütt, 1961, P. klemmi Schütt, 1961, P. nitida Schütt, 1963, P. angelovi Schütt, 1972 and P. tribunicae Schütt, 1963, plus a new species, Travunijana gloeri sp. nov., is described for the genus. Distribution maps of both genera, Plagigeyeria and Travunijana, over the karst aquifers of Hercegovina and adjacent regions are presented with respect to the hydrogeological separation of the known spring karst conduits and aquifers.

Sustainable Use of Groundwater Resources in the Transboundary Aquifers of the Five Central Asian Countries: Challenges and Perspectives

Groundwater is critical for supporting socioeconomic development but has experienced gradual decreases in recent decades due to rapid population growth and economic development throughout the world. In recent years, the utilization of transboundary groundwater resources has received extensive attention globally. Because transboundary aquifers do not follow borders and are concealed, neighboring countries are prone to experiencing conflicts over the use of these transboundary groundwater resources. Therefore, an accurate and comprehensive assessment of the development potential of groundwater resources in these transboundary aquifers is necessary for the rational and fair use of those groundwater resources. Transboundary groundwater resources are an important water source for life, production, and ecological water use in Central Asia, which has a distinctive continental arid and semi-arid climate, and surface water resources in this region are relatively scarce. Considering the existing problems related to the utilization of groundwater resources in the transboundary aquifers in this region, we propose developing strategies for on-demand water abstraction, enhancing the ecological protection of transboundary aquifers, and strengthening international cooperation. This paper summarizes the distribution of 34 transboundary aquifers in Central Asia and analyzes the status and potential of groundwater resource uses in these transboundary aquifers.

Inaccurate Application of Isotope Hydrology Techniques to Nubian Sandstones Aquifer System in Sinai and North-Western Sahara Aquifers Systems

A comprehensive understanding of the groundwater dynamics of a transboundary aquifer system is highly needed for any successful transboundary cooperation policy. The present paper addresses the necessity of identifying specific cooperation problems which evolve out due to the improper handling and treatment of isotopic data of these hydro geological attributes and prevalent use patterns.

A methodology for assessing the pressures on transboundary groundwater quantity and quality – experiences from the Dinaric karst

A relatively novel and abridged methodology for assessing the quantity and quality status of groundwater bodies has been applied in the Dinaric karst of SE Europe. Validation of pressure on quantity is based on groundwater budgeting and the correlation of available groundwater reserves and projected water demands, while pressure on quality is estimated by GIS-created maps: vulnerability – hazard – risk. The results obtained from the studied groundwater bodies indicate mostly low pressure on water quantity, but increased risk from diffuse and point pollution sources. The application of methods is possible in many transboundary and inner aquifer systems even in geologically complex environments where there is insufficient monitoring dataon the groundwater regime.

Can reporting enhance transboundary water cooperation? Early insights from the Water Convention and the Sustainable Development Goals reporting exercise

AbstractA notable milestone in transboundary water cooperation has been the incorporation of reporting both under the Sustainable Development Goals (SDGs) framework and the Convention on the Protection and Use of Transboundary Watercourses and International Lakes. Much can be gained from reviewing the initial reporting exercise, which took place in 2017 and 2018. The first reporting exercise has demonstrated that, while progress has been made in the last decades, the need to strengthen cooperation over transboundary rivers, lakes and aquifers is clearly evident. Additionally, the experience of the first reporting exercise suggests that, although some adjustments might be made, reporting can play a valuable role in advancing transboundary water cooperation in the years to come.

Introduction

Introduction

The Transboundary Nature of the Allende–Piedras Negras Aquifer Using a Numerical Model Approach

AbstractThe Allende–Piedras Negras (APN) aquifer is located between the states of Texas (United States [U.S.]) and Coahuila (Mexico). The Rio Grande crosses the aquifer, acting as a natural and political divide between the countries. However, it remains unclear whether the APN aquifer can be considered a truly transboundary aquifer flow system, which would potentially require joint management by two different administrative jurisdictions. The main purpose of this study was to evaluate the transboundary nature of this aquifer. This was achieved by developing a detailed hydrogeological model to analyze the direction of volumetric fluxes within the APN aquifer using Visual MODFLOW. The model simulated a spatially averaged cumulative drawdown of 0.76 m for the entire aquifer over an 18‐year modeling period (2000–2017). The flow convergence zone, previously located below the Rio Grande, has shifted to the U.S. side in most locations, driven by higher pumping rates of the wells located near the river. This shift of the convergence zone from one country to the other means that groundwater recharge from one side flows underneath the river to the other side. This qualifies the APN aquifer as a “transboundary groundwater flow system.” The procedure followed in this study may be applied to other aquifers that straddle the U.S.–Mexico border and may motivate future modeling studies on other poorly studied transboundary aquifers around the world and thereby enable bi‐national aquifer management.

Reasonable Use?: The Challenges of Transboundary Groundwater Regulation in the Eastern United States

AbstractRegulating groundwater in the Eastern United States (U.S.), particularly transboundary aquifers between states, is a challenge given the patchwork quilt of common law, statutory frameworks, and agency rules. Such regulation is made more challenging by the need for better quantification of pumping and use. These dynamics are exemplified through several case studies, including the first ever U.S. Supreme Court case related to groundwater withdrawals (set in the Eastern U.S.). As dynamics such as expanded irrigation, population increases, and ecological considerations influence groundwater use across the Eastern U.S., water use will continue to be an important driver for economic activity and interaction within and between states. To effectively regulate transboundary aquifers, governance solutions must incorporate current science into decision making and be implemented at local, state, regional, and federal scales.

Synthesizing existing frameworks to identify the potential for Managed Aquifer Recharge in a karstic and semi-arid region using GIS Multi Criteria Decision Analysis

Imbalance between water supply and demand is increasing in many parts of the world. Lack of water security is attributed to climate change, population growth and unsustainable abstraction of groundwater. Managed Aquifer Recharge (MAR) can increase groundwater recharge, facilitate higher water availability and accessibility, and hence reduce water supply deficit. This paper investigates the potential of MAR in a karstic and semi-arid region with the use of GIS Multi Criteria Decision Analysis (GIS-MCDA). While previous studies have focused on MAR techniques and MAR suitably mapping separately, this paper combines technique selection and suitability mapping to emphasize the importance of considering both. The methodology was applied for a karstic and semi-arid region, using the Ramotswa Transboundary Aquifer Area (RTAA) as case study. MAR suitability mapping of the selected MAR technique was carried out with six thematic layers using Weighted Linear Combination (WLC) decision rule. The objective was to identify suitable areas for implementation of spreading methods and generate MAR suitability maps to guide decision-making in such implementation. The suitable areas were identified at the border between Botswana and South-Africa. The study develops a methodology for GIS-MCDA considering spreading method for a karstic aquifer, but more research is needed to assess the methodological transferability to other karstic and semi-arid regions.

Reassessing the Draft Articles on the Law of Transboundary Aquifers through the lens of reciprocity

ABSTRACT In spite of groundwater’s growing importance, the 2008 Draft Articles on the Law of Transboundary Aquifers have yet to be fully adopted by the international community. As states contemplate the future of the draft articles, this article aims to reassess them through the lens of the legal principle of reciprocity. To do so, this article provides a framework for the analysis of law via reciprocity, followed by its application to the draft articles. Although this article primarily finds that they follow a reciprocal structure, it also identifies areas to be revisited, including sovereignty and recharge zone states.

Geophysical prospecting as a tool for the hydrogeological characterization of the Ocotepeque-Citalá transboundary aquifer (ATOC), Trifinio Region, El Salvador-Honduras

La exploración geofísica, se dedica a estudiar las propiedades físicas del subsuelo; normalmente, es utilizada en la búsqueda de recursos naturales tales como: petróleo, agua subterránea, minerales metálicos, yacimientos geotérmicos, etc. En otras ocasiones se utiliza para investigaciones arqueológicas; determinación de estructuras de aguas residuales y tuberías de abastecimiento de agua potable (cuando no se tienen planos del diseño). Las aplicaciones son muy diversas y existen varios métodos aplicables, que utilizan diferentes propiedades físicas de la materia tales como: el electromagnetismo, resistividad eléctrica, propagación de ondas (sísmicas), atracción gravitacional (gravimetría). Dichas propiedades, están íntimamente relacionadas con las características del subsuelo y la naturaleza geológica de los materiales en profundidad. Ayudan a localizar y algunas veces determinar las dimensiones del recurso buscado. Esta investigación aborda el caso de los métodos geoeléctricos aplicados a la exploración hidrogeológica. Para realizar este tipo de exploración, se requiere de una fuente de corriente directa, que se pueda manipular la cantidad de corriente que se inyecta al subsuelo, y un voltímetro, capaz de detectar las diferencias de potencial que se generan al inyectar la corriente. Este, se conoce como el método de las cuatro puntas. A partir de los valores de corriente y diferencia de voltaje que se obtienen, se procede a calcular la resistividad eléctrica del subsuelo.

Effective Transboundary Aquifer Areas: An Approach for Transboundary Groundwater Management

AbstractThe natural complexity, heterogeneity, and extent of transboundary aquifers around the world, have led to controversy over which method or criteria should be used to identify and delineate their boundaries. Currently, there is no standard methodology that aquifer‐sharing countries can use to delineate the area of a transboundary aquifer. In the case of Mexico and Texas, Mexico uses administrative boundaries, whereas Texas uses geological boundaries. This paper proposes a method for delineation and prioritization of aquifers (or aquifer areas) called effective transboundary aquifer areas (ETAAs), which uses a combination of physical criteria (geological boundaries, topography, and hydrography) and the location and density of active water wells in the borderland between Mexico and Texas. This method identifies the area of priority (productivity area) in the aquifer using pumping patterns or hot spots regardless of the aquifer’s surficial geological limits, therefore offering a more effective, local and practical management option at the transboundary level. Different geological features or pumping patterns will have different sizes and locations of ETAAs within the same aquifer. In West Texas, which is dominated by bolsons, the method produces limited options for ETAAs, whereas in South Texas in the easternmost border the identified ETAAs are more significant.

Groundwater Management in the Borderlands of Mexico and Texas: The Beauty of the Unknown, the Negligence of the Present, and the Way Forward

AbstractOver the last decade, transboundary aquifers traversing the Mexico‐Texas border have generated growing interest of federal institutions on the Mexico side and state and federal institutions on the Texas side. Notwithstanding this, binational efforts to understand, assess, and manage shared groundwater resources remain limited and politically sensitive. On the Mexico side, long‐standing centralized groundwater governance structures have created institutional barriers at the local level to the expansion of knowledge and cooperation over these transboundary resources. On the Texas side, property rights related to groundwater resources limit the scope of options available for cooperative management of cross‐border aquifers. This paper examines stakeholders' perspectives on the borderland between Mexico and Texas through 44 surveys and personal interviews. Findings show that stakeholders appear to support a binational groundwater agreement as a means for assuring the sound long‐term management of transboundary groundwater resources in the border region; however, the majority of stakeholders also suggest that short‐term local or regional arrangements may be preferable over binational agreements as local/regional approaches may be more achievable or realistic. Second, participants identified leadership and individual personalities as key factors for success at the local level but noted that such influence had limited sustainability and limited regional‐systemic effects. Third, the stakeholders indicated that water quality, rather than water quantity, is the main driver of transboundary cooperation efforts in the region. Fourth, participants suggested that failures and successes in groundwater cooperation efforts are based more on fear and political lobbying than on understanding of scientific facts.

Krypton-81 dating of the deep Continental Intercalaire aquifer with implications for chlorine-36 dating

Deep groundwater samples from the Continental Intercalaire (CI) aquifer in the Northern Tunisian Sahara have been analyzed for noble gases 3He, 4He, Ne and 81Kr, and for 14C to better constrain the groundwater residence time of this large transboundary aquifer. Its significant radiogenic 4He content and background-level 14C both indicate water older than a few tens of thousands of years. Distinct helium concentrations and Ne/He ratios suggest different groundwater flow paths through the Tozeur and Kebili regions. 81Kr is applied for the first time on the CI aquifer, providing more direct evidence for the presence of old groundwater with 81Kr/Kr ratios at 63% – 15% of the atmospheric value, corresponding to residence times of 150 – 630 ka. These newly obtained 81Kr ages enable a re-evaluation of the previously reported data from the Tozeur region in order to better constrain the input values of 36Cl/Cl and Cl. The initial 36Cl/Cl ratio is found to be 4 – 6 times larger than previously assumed, and the initial Cl concentration 6 – 15 times smaller. The results of 81Kr dating and the recalibrated 36Cl dating define an eastward age progression across >500 km of flow path from the Algerian to Tunisian sections. This study exemplifies the utility of 81Kr not only as an independent and conservative chronometer, but also as a supplemental measurement to better calibrate the parameters required for other age tracers, including cosmogenic 36Cl and radiogenic 4He.

Hydrochemistry and multi-isotope study of the waters from Hanlé-Gaggadé grabens (Republic of Djibouti, East African Rift System): A low-enthalpy geothermal resource from a transboundary aquifer

Water from ten thermal springs, five drinking-water boreholes and one hand-dug well from Hanlé-Gaggadé grabens has been analyzed for major-minor hydrogeochemical parameters and multi-isotope composition: δ2H(H2O), δ18O(H2O), δ18O(SO42−), δ34S(SO42−), δ13C(DIC), 14C(DIC), and δ11B. The interaction of the thermal water with both silicic (basaltic) and sedimentary rocks and its low enthalpy (T ≤ 150 °C) regime make this area an optimal site for testing chemical and isotope geothermometers and optimizing them for similar difficult cases. In this study, the use of radiogenic carbon (14C) reveals that the age of the deep aquifer is between 12,500 and 8700 years ago (late Pleistocene/early-to-mid Holocene), which places it within the East African Humid Period. The oxygen and hydrogen stable isotope ratios of the water molecules, δ2H(H2O), δ18O(H2O), show common characteristics between the groundwater from this area and that of groundwater from nearby local lakes (Asal-Abhé) and palaeolakes (Sakalol-Hanlé-Gaggadé-Dobi), which were interconnected during that period to form the terminal Awash River Basin. The comparison of these aquifers within the transboundary aquifer located between northeast Ethiopia and Djibouti helps to reconstruct both the palaeoenvironmental history and the hydrogeochemical characteristics of this regional aquifer. At present, these data are poorly defined, but it is of fundamental importance for the constructive use of water resources in arid areas. Finally, a conceptual model was proposed for the Hanlé-Gaggadé low-enthalpy geothermal system on the basis of the geochemical and isotope data on the thermal and non-thermal groundwaters combined with geological and tectonic information and the results of recent geophysical studies.

Spatial Data Management and Numerical Modelling: Demonstrating the Application of the QGIS-Integrated FREEWAT Platform at 13 Case Studies for Tackling Groundwater Resource Management

Because of the spatial nature of groundwater-related data and their time component, effective groundwater management requires the application of methods pertaining to the Information and Communication Technologies sector, such as spatial data management and distributed numerical modelling. The objective of this paper is to demonstrate the effectiveness of the QGIS-integrated FREEWAT platform and an approach combining spatial data management and numerical models to target groundwater management issues. FREEWAT is a free and open source platform integrated in a Geographic Information System environment and embedding tools for pre- and post-processing of spatial data and integrating numerical codes for the simulation of the hydrological cycle, with a main focus on groundwater. To this aim, this paper briefly presents the FREEWAT platform, introduces the FREEWAT approach, and showcases 13 case studies in European and non-European countries where the FREEWAT platform was applied. Application of the FREEWAT platform to real-world case studies is presented for targeting management of coastal aquifers, ground- and surface-water interaction, climate change impacts, management of transboundary aquifers, rural water management and protection of groundwater-dependent ecosystems. In this sense, compared to other existing software suites, FREEWAT allows data analysis and visualization to accomplish each step of the modelling workflow, i.e., from data analytics, to conceptual model definition, to numerical modelling and reporting of results. The presented experiences demonstrate that improved access to data and the portability of models and models’ results can help to promote water sustainability from the local- to the basin-scale. Furthermore, FREEWAT may represent a valuable tool to target the objective of increasing the capabilities of public authorities and private companies to manage groundwater resources by means of up-to-date, robust, well-documented and reliable software, without entailing the need of costly licensing, nowadays seldom affordable by public water authorities. Based on the strengths highlighted, the FREEWAT platform is a powerful tool for groundwater resources management, and for data collection, sharing, implementation and comparison of scenarios, for supporting planning and decision-making.

Protection and Use of Transboundary Groundwater Resources under Public International Law—An Analysis of the UN International Law Commission’s Draft Articles on the Law of Transboundary Aquifers

Groundwater is one of the world’s most important water resources. Although it is highly susceptible for pollution and overexploitation, its extraction rate is predicted to increase over the next decades. Against this background, this article discusses the contribution of the UN International Law Commission’s Draft Articles on the Law of Transboundary Aquifers to the protection of this precious resource. It first provides some information on the characteristics of groundwater and aquifers, then describes briefly the existing international legal regimes addressing transboundary groundwater and the evolution of the Draft Articles, and finally analyses the main criticisms and positive aspects of the Draft Articles.

Global Assessment of Current and Future Groundwater Stress With a Focus on Transboundary Aquifers

AbstractWe quantified groundwater stress worldwide by applying the global water resources and water use model WaterGAP 2.2b (Water ‐ Global Assessment and Prognosis) for current conditions (1981–2010) as well as for the 2050s under the worst‐case greenhouse gas emissions scenario RCP8.5. To improve global‐scale groundwater stress assessments, we suggest three new water quantity‐related groundwater stress indicators as well as a new way for communicating projected future groundwater stress at the grid‐cell level (~55 × 55 km) and for larger spatial units such as transboundary aquifers (>20,000 km2). The new indicators encompass the ratio of net abstractions from groundwater to groundwater recharge, human‐induced changes in groundwater discharge, and human‐induced groundwater depletion. We compare them to four conventional indicators used in the Transboundary Waters Assessment Programme and show how they can add value to global‐scale studies or are even more suitable for indicating groundwater stress. We assess potentials and limitations of all indicators by addressing their level of process representation, data requirements, uncertainty, and the underlying different concepts of sustainable groundwater use. To support adaptation to climate change, we recommend showing both the ensemble mean and the worst‐case scenario of future groundwater stress that we derived from five climate and two irrigation scenarios. For characterizing groundwater stress in spatial units such as transboundary aquifers, areal fractions where a selected indicator threshold is exceeded should be considered. Finally, hot spots of future groundwater stress should be identified by combining relative changes from current conditions with absolute values of future groundwater stress.