Sustainable Use Of Groundwater Research Articles

Integrating remote sensing, GIS-based, and AHP techniques to delineate groundwater potential zones in the Moulouya Basin, North-East Morocco

Groundwater is a valuable shared resource in the Moulouya Basin, but it has been in decline due to recent years of low rainfall and rapid population growth. To support socio-economic development, there is increased demand for this precious resource. This paper presents a standard methodology for delimiting potential groundwater zones using geographic information systems (GIS), an integrated analytical hierarchy process (AHP), and remote sensing techniques. Seven parameters that monitor the presence and mobility of groundwater, including drainage density, lithology, slope, precipitation, land use/land cover, distance to river, and lineament density, were incorporated into a raster data model using ArcGIS software. AHP-based expert knowledge was used to prepare a groundwater potential index and assign weights to the thematic layers. The study classified the area into five zones of varying groundwater potential: very high (26%), high (51%), moderate (13%), poor (9%), and very poor (1%). The accuracy of the model was validated by comparing the Groundwater Potential Zones map with data from 96 wells and boreholes across the basin. The validity of the results was confirmed by comparing them with the specific yield of the aquifer in the study area, yielding a high correlation coefficient (R2) of 0.79. The analysis revealed that 89.5% of the boreholes were situated in the high and very high potential zones, demonstrating the reliability and robustness of the employed approach. These findings can aid decision-making and planning for sustainable groundwater use in the water-stressed region.

Hydrogeochemical characteristics of groundwater contamination in Guwahati city, Assam, India: Tracing the elemental Threads

Groundwater serves as an important resource for drinking and agriculture in many countries, including India. Assessing the quality of groundwater is essential for understanding its chemical characteristics and suitability for consumption. This study aims to explore the factors affecting the hydrogeochemical changes in groundwater within Guwahati City, Assam, India. Groundwater samples were collected and analyzed for major and trace elements, as well as anion concentrations. Concentrations of As, Al, Ba, Cu, F−, Fe, Mn, and Pb exceeded the permissible limits set by both World Health Organization (WHO) and Bureau of Indian Standards (BIS), indicating serious health concerns for the local inhabitants. The distribution pattern of trace elements exceeding the guideline values is intricate, suggesting widespread contamination of groundwater throughout the study area. The Heavy Metal Pollution Index (HPI) and Water Quality Index (WQI) revealed that, except for the central zone, groundwater across the entire study area requires intervention. Piper plot illustrated that the groundwater is predominantly of Ca–HCO3 type, indicating the dominance of alkaline earth and weak acids. Groundwater hydrogeochemistry is mainly controlled by rock-water interaction and evolves through silicate weathering, carbonate weathering, and cation exchange processes. Multivariate statistical analysis identified distinct groups of groundwater based on chemical characteristics, emphasizing the role of both natural processes and anthropogenic activities in influencing groundwater quality. Regular monitoring, management, and intervention of groundwater sources throughout the study area are crucial for long-term use. The findings of this study will assist stakeholders, regulators, and policymakers in formulating strategies for the sustainable use of groundwater.

Correction: Evolution and sustainability of groundwater use from the Ica aquifers for the most profitable agriculture in Peru

Correction: Evolution and sustainability of groundwater use from the Ica aquifers for the most profitable agriculture in Peru

Polycentric Groundwater Governance: Insights from the Kavango-Zambezi Transfrontier Conservation Area

This paper analyses groundwater governance within a transfrontier conservation landscape. Given the current heightened interest in groundwater development, it is imperative that more thought be given to how groundwater resources can best be managed in different contexts for multiple uses and users. Transfrontier conservation areas are areas of vast biological diversity whose functioning and ecosystem integrity depends on the availability of water to sustain ecosystems and subsequently derive economic benefit. Further, climate vulnerable rural communities depend on and form an important part of this landscape. The work highlighted in this paper is based on a study conducted in parts of the Kavango-Zambezi Transfrontier Conservation Area (TFCA), the largest TFCA in the world. Climate induced challenges such as droughts and general poor land use planning have resulted in threats to long term sustainability of freshwater ecosystems and increased incidences of human-wildlife conflicts over limited water resources. Effective groundwater governance can potentially provide pathways for alleviating these challenges. Building on the theoretical fundamentals of polycentric governance, this paper analyses the case of the KAZA TFCA in which multiple levels of governance exist. The paper discusses how to achieve coordination and accountability within a shared landscape to foster sustainable use and management of groundwater. Groundwater within a TFCA context has the potential to alleviate human-wildlife conflict over freshwater, support groundwater dependant ecosystems and sustain smallholder agriculture for the rural communities. Understanding this role of groundwater adds to the framing of freshwater governance and conservation efforts within a TFCA and the identification and development of platforms for the integrated management of groundwater. Bringing together freshwater and conservation institutions in a multi-country context towards integrated water resource management is an initial and novel attempt which forms the foundation for achieving optimal governance approaches in the commons.

Water Governance in Tanzania – A Synthesis of Legal and Institutional Frameworks for Groundwater Management in the Upper Great Ruaha River Catchment

The importance of groundwater resources in buffering the effects of climate change on water scarcity and security is highly acknowledged worldwide. However, groundwater development and use can only be sustainable with a more robust policy and institutional arrangements related to water governance. The purpose of this study was to analyse the legal framework of water resource development and management in order to contribute in identifying policy constraints to sustainable groundwater resource development and management in Tanzania. The paper used information from literature reviews and data collected through qualitative methods using a case study of Usangu Plains in the Upper Great Ruaha River Catchment in Tanzania. The findings reveal that water governance institutional frameworks are well structured to provide guidelines on how water as a basic human resource can be utilised and properly managed, but most importantly, these institutional arrangements place disproportionate emphasis on groundwater. Attaining sustainable groundwater development and use requires new disclosures and narratives in water policy and law, integrating both surface and groundwater resources. The weaknesses identified in groundwater governance need to be taken on Board once, the existing water institutional frameworks open to perfection for sustainable utilisation of groundwater resources

A Study on Groundwater Irrigation Expansion in Bihar, India

Water use has increased by more than twice the rate of population growth over the past century. Although, there is worldwide water scarcity, an increasing number of areas are chronically short of water. There has been a substantial increase in irrigated areas in the last thirty -five years. The Net Irrigated Area (NIA) in Bihar has increased from 2808 thousand hectares in 1985 to 3083 thousand hectares in 2021. The total annual replenishable groundwater potential of Bihar has been estimated as 33.15 billion cubic meters (bcm) with an annual extraction of 13.50 bcm. The share of surface water is declining while groundwater is increasingly being used in crop production. A total of 11754 thousand hectares have been estimated as the ultimate irrigation potential in the state, including major, medium and minor irrigation schemes, utilizing both surface and groundwater. If the available potential is fully exploited, it can cover more than the total cultivated area of the state. Considering the interests of both present and future generations attention needs to be directed towards the sustainable use of groundwater and promoting various sources of surface water.

Estimation of shallow groundwater recharge in central Qinghai-Tibet Plateau by combining unsaturated zone simulation and improved water table fluctuation method

Accurate estimation of groundwater recharge (GR) is crucial for sustainable groundwater use, particularly in alpine regions that are sensitive to climate change response. However, quantifying the amount of GR in these areas is challenging due to the absence of measurement data and an unclear understanding of the GR mechanism. In this paper, we proposed a new method (HS-IWTF) for estimating GR in the central Qinghai-Tibet Plateau. The method utilized Hydrus-1D to create an unsaturated zone soil water transport model, which provides a reference value for specific yield (Sy). Additionally, the method incorporated the impact of groundwater potential decline at various freeze–thaw stages to improve recharge estimation. The results showed that HS-IWTF method can be better applied for estimating GR in alpine regions. The simulated recharge of groundwater though vertical infiltration ranged from 191.7 to 217.8 mm/yr, primarily from precipitation infiltration. The total GR ranged from 312.1 to 405.0 mm/yr, with significant recharge contributed by snow and ice thaw and lateral runoff. The HS-IWTF method is more precise and reliable than simulated infiltration and traditional water table fluctuation (WTF) method in reflecting recharge changes at various monitoring sites during each freeze–thaw period. The thawing process period (0.95 mm/d, 11 %) and the complete thawing period (1.07 mm/d, 61 %) contributed more recharge at higher recharge rates due to improved recharge sources and conditions. The air temperature rise promoted the degradation of the cryosphere and raised the ratio of recharge precipitation (GR/PT), particularly in regions with high altitude and proximity to permafrost and glaciers where recharge was significantly high during the freezing period. This study provides valuable information on the measurement of GR in alpine regions and the crucial role of freeze–thaw processes in GR.

Tourism-Related Pressure on the Freshwater Lens of the Small Coral Island Gili Air, Indonesia

Tourism on Gili Air, a small coral island in Indonesia, has increased significantly. Groundwater is the primary water source on the island. This study aims to estimate the sustainability of groundwater use on this small coral island. It conducts an initial assessment of the freshwater lens system using cost-effective methods to evaluate the available freshwater volume and sustainability of water withdrawals related to tourism. The results and methods can be transferred to other low-lying islands. The results show that Gili Air has a well-developed freshwater lens, estimated to contain 2 million cubic meters of water, with an annual recharge rate four times higher than the water demand of the island’s inhabitants. However, our findings suggest that the rapid increase in tourism resulted in unsustainable water withdrawals between 2016 and 2019. Without proper groundwater monitoring and management, this could lead to seawater intrusion into the aquifer.

Delineation of groundwater potential zone using geospatial tools and analytical hierarchy process (AHP) in the state of Uttarakhand, India

Groundwater plays a vital role in global climate change and substantial human needs. However, the groundwater potential zone (GWPZ) delineation is essential for fulfilling livelihood needs. In recent years, studies based on geographic information systems (GIS) have acquired much attention in groundwater exploration. Thus, in order to determine the groundwater potential zone in the state of Uttarakhand, we employ a multi-criteria decision analysis (MCDA) based analytical hierarchy process (AHP) model with overlay weighted linear combination approach in this study. For groundwater potential zone demarcation, nine thematic layers such as geology, geomorphology, LULC, drainage density, slope, rainfall, soil, TWI, and curvature were created using remote sensing (RS) images and conventional data for a geographic information system (GIS). Furthermore, the weight of the parameters has been determined using AHP technique and overlay analysis was determined using GIS tools. A thematic map was categorized as “very poor,” “poor,” “moderate,” “good,” “very good,” and “excellent” in order to determine the groundwater potential zone. According to the results, the area covered by the 'very poor' categories is 187.43 km2 (0.16 %) followed by 'poor' 2109.66 km2 (3.99 %), 'moderate' 29024.06 km2 (54.78 %), 'good' 15151.13 km2 (28.67 %), 'very good' 6537.19 km2 (12.37 %), and 'excellent' 814.84 km2 (1.55 %) with the accuracy of 89.9 %. The 'very poor' and 'moderate' groundwater potential zones were observed as 0.16 % and 54.78 %, respectively, and the possibility for GPZ gradually increased from the northeast to the southwest. The findings of this study have implications for future research on sustainable groundwater use, basin management of agriculture, and the link between groundwater and climate change.

Environmental Tracers Tritium 3H and SF6 Used to Improve Knowledge of Groundwater Sustainability of a Crystalline Rock Island Aquifer of Tobago, West Indies

Understanding the residence time, flow velocities, and storage volumes in fractured rock aquifers is essential for assessing the sustainable use of groundwater in island aquifer systems. Environmental tracers such as tritium (3H) and sulfur hexafluoride (SF6) that enter the aquifer systems through natural hydrological processes are effectively used to quantify the “apparent age” of young groundwater (<60 years) to calculate these aquifer characteristics. The island of Tobago is predominantly a fractured rock aquifer system that contains groundwater sub-basins that produce 100–1000% more than their calculated recharge. In this study, we analyzed ten samples from groundwater wells throughout the island for environmental tracers to establish the “apparent age” of the groundwater. We then estimated the active flux and storage volume of the aquifer. The 3H results of ten wells throughout the island range between 0.02 and 0.60 TU. The groundwater samples to the south of the island possess more pre-modern groundwater ages (older ages) than samples in the north of the island. These tritium values reveal age ranges between 18 and 60–plus years. This finding suggests that fractures create flow paths oriented towards the southern parts of the basin that enable the transport of groundwater across significant topographic boundaries and watershed divides. Additionally, the data may support that southern wells are connected to isolated old sources of groundwater. SF6 values range between 0.91 and 7.97 (part per trillion volume) with an interpreted age range between 18 and 39 years. Both tracers support the original hypothesis that longer residence time waters are located south of the island except for three SF6 samples which are believed to be affected by “excess air”.

DAMPAK EKSPLOITASI AIR TANAH SECARA BERLEBIHAN TERHADAP PEMENUHAN KEBUTUHAN AIR PENDUDUK DI DESA RAENYALE, KECAMATAN SABU BARAT KABUPATEN SABU RAIJUA

This study aims to determine (1) the impact of excessive exploitation of groundwater on the fulfillment of groundwater for residents in Raenyale Village (2) Strategies for overcoming the impact of excessive exploitation of groundwater on meeting the water needs of residents in Raenyale Village.The method used in this study is a quantitative descriptive research method to test hypotheses using statistical data tests. In this study there were 103 people who became the research sample consisting of people who used drilled wells, people who used dug wells and the head of Raenyale Village. Data collection methods used are questionnaires, interviews, observation and documentation. The results showed that (1). The impact of groundwater exploitation in Raenyale Village is that there are 17 dug wells which are experiencing drought due to excessive use of drilled wells which means that the community is forced to incur additional expenses by buying tanked water to meet the population's water needs. (2). The strategy for overcoming the impact of groundwater exploitation is that there are 13 people who make infiltration wells, plant trees around the well area and with community awareness and understanding of the importance of sustainable development and use of groundwater.

O- and H-isotope record of Cape Town rainfall from 1996 to 2022: the effect of increasing temperature, and the ‘water crisis’ of 2015 to 2018

Abstract The O- and H-isotope composition of rainfall collected monthly at the University of Cape Town (UCT) between 2009 and 2022 has been added to a previously published data set from 1996 to 2008 to make a continuous 27 year record. Monthly rainfall over the 27 year period has a range in δD and δ18O values from -57 to +21‰ and -8.1 to +3.5‰, respectively, and shows limited but discernible temperature and amount effects. The 27 year rainfall record defines a Local Meteoric Water Line (LMWL) whose equation is δD = 5.96*δ18O + 7.00 (r = 0.88), a slight change from the LMWL of 1996 to 2009 (6.41*δ18O + 8.89). Annual rainfall at UCT has varied from ~992 mm (2017) to 1996 mm (2013), with no systematic change in annual rainfall amount (r = −0.16). However, from 2015 to 2022, the average annual rainfall of 1 145 mm has been below the 27 year average of 1 313 mm. Mean monthly temperature has increased from 1996 to 2022 (r = 0.53), and the weighted mean annual δD and δ18O values have increased by ~4‰ (r = 0.53) and ~0.5‰ (r = 0.64), respectively, over the 27 years. The UCT data and the data for 1961 to 1974 from Cape Town International Airport plot around the same LMWL, with an average deuterium excess (d-excess) of 13.78 and 12.95, respectively. Natural springs in the area plot close to the LMWL with an average d-excess of 14.15, whereas local well-point and borehole water samples generally plot below the LMWL with an average d-excess of 10.65. These differences can be explained by relatively rapid recharge of springs and slower recharge of groundwater, with the latter containing an additional component, that could either be rainwater that fell during a period of hotter drier climate or, more probably, municipal mains water. Long-term monitoring of groundwater and spring water as well as rainwater would be of great help in assessing the sustainability of groundwater use, among other important questions.

Addressing the challenges of climate scenario-based impact studies in modelling groundwater recharge on small barrier islands at the German North Sea coast

Study RegionBarrier island at the German North Sea coast Study FocusDrinking water supply on small barrier islands strongly depends on extractions from their freshwater lens below the island when no pipeline to the mainland exists. The shape and extend of the lens is influenced by sea level change, abstraction and groundwater recharge, while groundwater recharge is the only inflow of freshwater into the system. To ensure sustainable use of groundwater in the future within changing climate conditions, knowledge in long-term groundwater recharge is required which can be obtained by climate scenario-based simulations. However, hydrological modelling on small barrier islands faces challenges, such as the lack of calibration and validation data. In addition, the historical long-term mean of main climate variables, such as precipitation and temperature, is represented inadequately in available regional climate models. In order to quantify previously mentioned topics, a water balance model was set up for the small barrier island Norderney. Subsequently, climate change impact on groundwater recharge was simulated.New hydrological insights for the region: The applied methodology increases plausibility and confidence in impact assessments compared to a-priori model applications. Future long-term development of groundwater recharge is highly dependent on the underlying climate model and emission scenario, but also affected by large uncertainties throughout the model chain, e.g. by the approach used for bias-correction. The scenario results can be directly used as forcing data for three-dimensional groundwater models.

Chemical Characteristics-Based Evolution of Groundwater in Tailan River Basin, Xinjiang, China

Groundwater plays an important role in ecological environment protection in arid and semi-arid areas. Therefore, understanding the characteristics of hydrochemical evolution is of great significance for the sustainable use of groundwater in the area of the Tailan River Basin. The Tailan River Basin is located in an arid, ecologically sensitive area in western China. In this study, we collected 42 groups of representative water samples from the Tailan River Basin and analyzed the chemical distribution in the groundwater using mathematical statistics, Piper and Gibbs diagrams, ion ratio analysis, and hydrogeochemical simulation methods. We also discussed the water–rock interactions in the groundwater hydrochemical evolutionary process. The results were as follows: (1) The chemical types of groundwater changed from HCO3·SO4-Ca·Na to SO4·Cl-Na·Ca, Cl·SO4-Na, and Cl-Na, and the total dissolved solids content increased from less than 1 g/L to more than 40 g/L from the gravel plain to the fine soil plain. (2) The Gibbs diagram, the ion ratio analysis, and the saturation index showed that the groundwater chemical characteristics in the study area were mainly controlled by water–rock interactions, as well as evaporation and concentration. Along the runoff of groundwater, halite and gypsum were dissolved. Nevertheless, dolomite and calcite precipitated. The relationship between the chlor-alkali index and [(Na+ + K+)-Cl−] and [(Ca2+ + Mg2+)-(HCO3− + SO42−)] indicated that cation exchange also affects the chemical composition of groundwater in the area. (3) Through reverse hydrogeochemical simulation, the main water–rock effect of the groundwater runoff process revealed by qualitative analysis was quantitatively verified.

Identification of groundwater potential zones in data-scarce mountainous region using explainable machine learning

Groundwater is a critical resource, yet its detailed assessment in mountainous regions is challenged by varying topography, complex hydrogeological characteristics and limited data. In this study, machine learning approaches were used to analyze the groundwater potential in five different watersheds in Nepal. Explainable machine learning models (EBM and GAMI-net) were used to identify zones with different groundwater potentials and controlling factors. The models were validated with k-fold cross-validation using the area under the receiver operating characteristics curve for the two groundwater potential models with unseen validation dataset of 0.87 and 0.88 respectively. We found that precipitation, elevation, soil bulk density, slope and lineaments primarily controls the groundwater potential in the study regions. The expected impact of each of the factors on groundwater potential was complex and multimodal. The results of this study can be used to improve water resource management and ensure sustainable groundwater use in the region.

Sustainable Water in Mining? The Importance of Traditional Owner Involvement in Commercial Water Use and Management in the Pilbara Region of Western Australia

AbstractThe mining industry is a significant water user, an issue that gains a particular prominence in arid zone mining regions, such as the Pilbara region in Western Australia (WA). Mining companies extract vast amounts of water from the groundwater aquifers to access orebodies and to dewater the mine pits. Much of this water is dumped in creeks, injected back into the aquifer downstream or used in mining processing. There is increased awareness from community members for sustainable water use in mining beyond life of mine, and the emergence of Environmental, Social and Governance (ESG) principles in the mining and metals sector signals a shift towards recognizing the importance of water stewardship. Much of the land subject to dewatering in the Pilbara is also subject to native title determinations. For Traditional Owners, important cultural values are associated with water. However, water is not adequately covered in native title, especially in relation to commercial use. We argue that Traditional Owner involvement in design and management of the use of excess water from a mining proponent's water licence (dewatering) can assist in sustainable use of groundwater, as well as provide opportunities in social and economic enterprises. As a provocation style piece, this paper is based on secondary literature, rather than ethnographic data. It explores the political and regulatory landscape of mine dewatering and outlines the limitations that have existed historically and currently and which inhibit Traditional Owners to participate in water management or commercial water interests. We also provide a high‐level analysis of several mining proponents' public policy commitments to water stewardship to assess the sustainable use of water which involves stakeholders such as Traditional Owners in water decision‐making. Finally, we identify possible opportunities and provide some recommendations, for water futures in this dry region where iron ore mining and gas extraction, already massive, are expanding further.

Coastal Groundwater-Dependent Ecosystems are Falling Through Policy Gaps.

Coastal groundwater-dependent ecosystems (GDEs), such as wetlands, estuaries and nearshore marine habitats,are biodiversity hotspots that provide valuable ecosystem services to society. However, coastal groundwater and associated ecosystems are under threat from groundwater exploitation and depletion, as well as climate change impacts from sea-level rise and extreme flood and drought events. Despite many well-intentioned policies focused on sustainable groundwater use and species protection, coastal GDEs are falling through gaps generated by siloed policies and as a result, are declining in extent and ecological function. This study summarized then examined policies related to the management of coastal groundwater and connected ecosystems in two key case study areas: Queensland (Australia) and California (USA). Despite both areas being regarded as having progressive groundwater policy, our analysis revealed three universal policy gaps, including (1) a lack of recognition of the underlying groundwater system, (2) fragmented policies and complex governance structures that limit coordination, and (3) inadequate guidance for coastal GDE management. Overall, our analysis revealed that coastal GDE conservation relied heavily on inclusion within protected areas or was motivated by species recovery, meaning supporting groundwater systems remained underprotected and outside the remit of conservation efforts. To close these gaps, we consider the adoption of ecosystem-based management principles to foster integrated governance between disparate agencies and consider management tools that bridge traditional conservation realms. Our findings advocate for comprehensive policy frameworks that holistically address the complexities of coastal GDEs across the land-sea continuum to foster their long-term sustainability and conservation.

Hydro-chemometrics of the Nubian Aquifer in Sudan: an integration of groundwater quality index, multivariate statistics, and human health risk assessment

This research employed the groundwater quality index (GWQI), multivariate statistical methods, and human health risk assessment model to investigate the suitability of groundwater for domestic uses in northern Khartoum state, Sudan. The groundwater samples were analyzed for eleven physiochemical parameters, including pH, EC, TDS, TH, Cl−, SO42−, NO3−, Ca2+, Mg2+, Na+, HCO3− and the primary investigation indicated the deviation of these parameters from World Health Organization (WHO) standards. The hydrochemical analysis revealed different groundwater facies with the dominance of Ca–Mg–HCO3 water type. Consequently, the groundwater samples were classified, based on GWQI, into three categories as 76.4% of the samples fall in the excellent water class, 17.6% are projected in the good water class, and 5.9% of groundwater samples are considered unsuitable for human consumption. The multivariate statistical methods were applied, including Pearson’s correlation analysis, principal component analyses (PCA), and hierarchical cluster analysis (HCA). Three principal components (PCs) explaining 86.07% of total variances are extracted. These PCs indicated that rock-water interactions and agricultural practices influence groundwater quality in the study area. Additionally, HCA is used to categorize groundwater samples based on the concentration of the physiochemical parameters. Consequently, three types of groundwater were identified as low, medium, and highly mineralized. In the final stage, the non-carcinogenic human health risk was assessed based on the concentration of NO3− using the United States Environmental Protection Agency (USEPA) models. The obtained hazard quotient for children indicated that 64.7% of groundwater samples are beyond the permissible limit (1 <), and the use of these samples may result in health consequences. Therefore, remedial measures are suggested for the sustainable use of groundwater.

Hydrochemical and isotopic characteristics of the Lodwar Alluvial Aquifer System (LAAS) in Northwestern Kenya and implications for sustainable groundwater use in dryland urban areas

Groundwater is a crucial resource for dryland regions such as this, where surface water resources are limited and unreliable. This paper presents a study of the Lodwar Alluvial Aquifer System (LAAS) in northwestern Kenya and its hydrochemical and isotopic characteristics, with the goal of understanding how to sustainably manage the groundwater system. As a result, the paper focuses on elucidating the hydrogeochemical and river-groundwater interaction (using environmental isotopes and major ion chemistry) of an aquifer that is located in the north-western dryland of Kenya. The study utilised environmental isotopes of oxygen-18 (18O), deuterium (2H), and tritium (3H) as tracers for establishing recharge sources and origin of groundwater. A sampling campaign involving 112 water samples was conducted to establish isotopic compositions of rain, spring, surface water (rivers, scoop holes, dams and lake) and groundwater at the peak of the wet season in May 2018. The tritium values in the study area ranged from 1.1 to 2.4 TU. Considering the median values of δ18O and δ2H in surface water and groundwater samples, four clusters emerge based on the degree of enrichment; Cluster 1 comprises the lake water (δ18O = +6.01, δ2H = +41.9); Cluster 2 is the Turkwel and Kawalase river water with slightly positive relative to VSMOW and with different δ2H values (+7.6‰ versus −9.8‰). The third cluster is the groundwater of the Shallow Alluvial Aquifer (SAA) and the Deep Aquifer (DA) (δ18O = −0.96‰ and −0.70‰; and δ2H = +0.4‰ and +0.6‰, respectively). The last cluster comprises the most isotope-depleted waters of water pans, scoop holes, Intermediate Aquifer (IA) and Turkana Grit Shall Aquifer (TGSA) with median values ranging from −2.87‰ to −2.48‰ for δ18O and −8.6‰ and −16.4‰ for δ2H. While the SAA is mainly recharge by the Turkwel River, a relationship is observed between the values deuterium in the Kawalase (−9.6‰ VSMOW) and IA (−8.6‰ VSMOW). Understanding recharge sources and aquifer vulnerability of similar strategic aquifers helps scientists appropriately advise policymakers and the water community who develop sustainable water use, aquifer protection and conservation strategies. In addition, the study contributes scientific evidence of isotopic compositions of groundwater in the Horn of Africa. Furthermore, the evidence of surface water-groundwater interaction presents a case of a fragile dryland ecosystem. Future work will involve the installation of piezometers in strategic aquifer zones to monitor groundwater levels in relation to river gauging data to quantify the amount of recharge and establish the impacts of rainfall variability in the upstream catchment.

Bridging the data gap: using remote sensing and open-access data for assessing sustainable groundwater use in Kumasi, Ghana

Abstract Groundwater use has significantly increased in the rapidly urbanising city of Kumasi, Ghana. But there is a lack of understanding of whether the groundwater system can sustain the growing demand in the future amidst climate change and rapid urbanisation. Using remote sensing datasets and a water balance approach, this study estimated the groundwater recharge and assessed how urbanisation has affected its groundwater sustainability. Sustainability is investigated by comparing multi-annual groundwater withdrawals to long-term average annual replenishment. Results show that while groundwater recharge has decreased by 80% from 1986 to 2020, mainly due to substantial (63%) loss of permeable land, groundwater consumption has seen a six-fold increase. Groundwater consumption in 2020 exceeded the long-term average groundwater recharge by 2.2Mm3, suggesting that the current groundwater use trends are unsustainable for future groundwater availability. Under a ‘business-as-usual’ scenario, a four-fold increase in groundwater consumption is predicted by 2050 while climate change and land-cover changes may reduce groundwater recharge by 10% and 55% respectively. Practical measures such as promoting artificial groundwater replenishment approaches, adopting low-impact development and instituting demand management measures must be implemented in the Metropolis. This should be informed by further studies to ascertain the exact condition of the groundwater.