Assessment Of Groundwater Recharge Research Articles

Application of decision support system/remote sensing/GIS techniques in groundwater recharge assessment

ABSTRACT Managing water resources and storing water through the identification of groundwater recharge zones (GWRZs) are critical to water security in Egypt. Decision-support systems (DSSs), remote sensing, and GIS techniques have yielded significant data for water resources modeling. The geologic, geomorphic, climatic, and hydrologic features of the Toshka area, Western Lake Nasser, Egypt, have been generated by data from Shuttle Radar Topography Mission, Climatic Research Unit gridded Time Series, Sentinel 2 time series, and Landsat-8 OLI. Fifteen GIS thematic maps have been ranked and normalized using five DSS techniques: Analytical Hierarchy Process (AHP), Fuzzy Analytical Hierarchy process (FAHP), Frequency Ratio (FR), Shannon Entropy (SE), and Multi-Influencing Factor (MIF). To ensure the computational usefulness of these models, GWRZs have been extracted and compared. The outcomes showed that 83, 87.5, 99.1, 99.1, and 87.5% of the existing wells are in high to extreme GWRZs for AHP, FAHP, FR, SE, and MIF, respectively. The receiver operating characteristic curve (ROC) was used to assess the effectiveness of these models. It was found that the SE model had the highest predictive performance rates, as its ROC accuracy value was 91.1%, while the FR, AHP, FAHP, and MIF approaches had values of 91, 84.4, 81.9, and 89.9%, respectively.

Groundwater Recharge Assessment in Central Benin: The Case of the Collines Region (West Africa)

The objective of this study was to assess groundwater recharge in the hard-rock central region of Benin so as to compare it with the water needs of the local population. To reach this objective, we applied the Water Table Fluctuation (WTF) method, which requires long-term monitoring of groundwater level fluctuations. Groundwater level time series were used in combination with other data (including time series of surface water discharge and rainfall) to estimate groundwater recharge but also to shed further light on the relationship between surface water and groundwater. The results demonstrated that the minimum inter-annual groundwater recharge amount is about 1.09 × 109 m3, which is enough to cover the basic water needs of the local population. It should be highlighted that in sub-regions where the density of the population is high, water shortage can still occur with the above estimated groundwater recharge amount. This study has also illustrated that when applying the WTF method, sites with a highly uncertain specific yield can be detected.

Uncertainties in physical and tracer methods in actual groundwater recharge estimation in the thick loess deposits of China

Groundwater recharge (GR) can be estimated with physical, tracer techniques and numerical modelling; however, the uncertainties in these methods have not been fully interpreted. This study selected six methods for actual GR estimation in the saturated zones with different data requirements and method assumptions, including two physical methods (i.e., water table fluctuation WTF and Darcy's law DL) and four tracer techniques (i.e., chloride mass balance CMB, tritium renewal rate TRR, chlorofluorocarbons CFC and 14C dating method CBD). Taking the loess tablelands of China as an example study area, we first analyzed the uncertainties in these methods and then recommended the appropriate methods for GR estimation in regions with thick vadose zones. Overall, the recharge rates from WTF, CMB and CFC (88 ± 24, 98 ± 33 and 53 ± 9 mm/year) were much greater than those from DL, TRR and CBD (10 ± 3, 14 ± 3 and 7 ± 5 mm/year). The differences in estimated GR are closely related to the method parameters, assumptions and temporal scales. Specifically, the model parameters (e.g., specific yield, hydraulic conductivity) exhibit large ranges due to spatiotemporal heterogeneity, and the physical methods are more sensitive to hydrogeological parameters compared with the tracer techniques. The uncertainties related to model assumptions originate from the simplified water/solute movement processes. The lag effect of the thick vadose zone largely limits WTF and TRR, but contributes to CMB. Ignoring the mixing and dispersion effect may overestimate recharge by 36–48 % for CFC, and the heterogeneity of the aquifer reduces the potential of CBD for recharge estimation. Overall, CMB is considered as the most optimal method for estimating GR in the thick loess deposits. This study deepens the understanding of the uncertainties in GR assessment methods in regions with thick vadose zones.

Groundwater dynamics on small carbonate islands: Insights from radiocarbon and stable isotopes in Kikai Island, Southwest Japan

Groundwater, the world's largest freshwater resource, faces significant challenges due to the overexploitation and depletion of aquifers in the 21st century. Small island groundwater aquifers are particularly valuable, and a scientific understanding of the behavior of subsurface water systems is vital. A comprehensive study using radiocarbon, stable oxygen isotopes, stable hydrogen isotopes, and hardness analysis (Δ14C, δ18O, δD, Ca, Mg) of groundwater was conducted in Kikai Island, a southern island in the Amami archipelago, Japan. The geological features and small size of the island make it an ideal location for assessing groundwater recharge and discharge relationships. Groundwater dynamics were investigated using samples collected seasonally from 15 points around the island (wells, springs, and an underground dam). Δ14C results indicated that despite considerable differences in precipitation, spatial variations were more prominent than seasonal variations, suggesting the presence of a large groundwater reservoir. The stable isotopes and hardness values, commonly used to detect groundwater dynamics, did not provide clear evidence to support this trend for the study site, a low-lying small island. However, the combination of deuterium excess (d-excess) values with radiocarbon analysis has the potential to provide a better understanding of groundwater flow. This study further illustrates that a combined approach utilizing Δ14C, δ18O, δD, and hardness levels can yield invaluable insights into groundwater dynamics. Considering geomorphic and geological features, groundwater in Kikai Island was categorized into five groups, providing insights into spatial groundwater flow. Results of this study indicate that the use of 14C allows the detection of groundwater movement with a high dynamic range and increased sensitivity, deepening our understanding of the diverse carbon sources that influence the groundwater system. Insights from this study are especially important for the efficient water management in comparable small carbonate islands and for tackling issues associated to overexploitation, pollution, and water scarcity.

Aquifers Recharge Potentiality Evaluation using Bivariate and Multivariate Statistical Analysis: A Case Study in Malwathu Oya River Basin

An aquifer is a body of porous rock or sediment saturated with groundwater that plays a vital role in the hydrological cycle. Due to rapid population growth and urbanization, these valuable resources face threats like climate changes, pollution, and over-exploitation. Overdraft, where extraction exceeds recharge, can lead to groundwater depletion. Although Sri Lanka is not considered a water- scarce country, it faces rising water demands due to rapid population growth. Especially in dry zones, groundwater is crucial for drinking and agriculture; unauthorized agro-wells exacerbate groundwater issues. Therefore, this research aims to assess groundwater recharge potential zones in Malwathu Oya river basin using Bivariate and Multivariate statistical analysis. Comparing these techniques will lead to the precise identification of potential recharge areas. And this study primarily focuses on the implementation of GIS to find solutions for this kind of challenge without performing field investigations. Therefore, eight conditioning factors; water level, electrical conductivity, lithology, soil, slope, lineament density, drainage density and land use were selected as groundwater recharge influencing factors. The well inventory database consisted of 380 well locations and, out of these, 70% was considered as the training dataset, and the remaining 30% was taken as the testing data set. Groundwater recharge potential maps (GRP) were developed in ArcGIS 10.8, based on the results obtained from Frequency Ratio (FR), Logistic Regression (LR) and their ensemble method. For testing the accuracy of the FR model, test well locations were cross tabulated with the GRP map, and the highest well percentage was achieved in high groundwater recharge potential zone (37.39%). In the LR model, cross-tabulation results showed that 62.61% of testing wells were in the very high potential zones. The ensemble method of FR and LR revealed that 53.04% of test wells fall into the very high potential class. Hence, it can be assumed that LR predictions are more reliable than the FR model. To further validate the LR model and ensemble model, Receiver Operating Characteristics curve method was used. The Area Under the Curve (AUC) values for Success rate curve (SRC) and prediction rate curve (PRC) in LR method were 63% and 57% respectively. In ensemble method, the AUC values for SRC and PRC were 89% and 75%. These results indicate that the LR model is relatively poor estimator, whereas FR and LR ensemble method is relatively good estimator to evaluate groundwater recharge potential in Mulwathu Oya river basin.
 
 Keywords: Area under curve, Frequency ratio, GIS, Groundwater recharge, Logistic regression

Sensitivity of Groundwater Recharge Assessment to Input Data in Arid Areas

Natural groundwater recharge (GR) assessment depends on several hydrogeological and climatic inputs, where uncertainty is inevitable. Assessing how inputs’ uncertainty affects GR estimation is important; however, it remains unclear in arid areas. This study assesses inputs’ uncertainty by examining the changes in GR simulations resulting from modifications in climatic, land use, and soil inputs. A physical-based hydrological model was built to estimate GR from 18 different GR scenarios across Qatar. Scenarios S1–S7 were created from different climatic inputs but identical land use and soil maps. Scenarios S8–S14 were created from different land use maps (analyzed from historical Landsat satellite images) but similar climatic and soil inputs. In S15–S18, the soil parameters were changed while the climatic and land use maps were kept the same. The results show that climatic inputs are key factors controlling the GR in arid areas, followed by land use inputs and soil classification. A strong correlation was observed between the GR values and precipitation, while moderate (non-significant) correlations were observed between the GR values and potential evapotranspiration and wind speed. Soil changes affected the GR simulations but inconsiderably compared with climatic and land use inputs. Since GR estimation is fundamental but uncertain in arid areas, the study findings contribute to narrowing the uncertainty in GR estimation.

Assessing Groundwater Recharge in the Wabe River Catchment, Central Ethiopia, through a GIS-Based Distributed Water Balance Model

The utilization of groundwater has emerged as an indispensable asset in facilitating economic advancement, preserving ecological integrity, and responding to the challenges posed by climate change, especially in regions characterized by aridity and semi-aridity. The sustainable management of water resources requires an assessment of the geographical and temporal patterns of groundwater recharge. The present study employed the GIS-based WetSpass-M model to model the water balance components by utilizing hydro-meteorological and biophysical data from the Wabe catchment, which spans an area of 1840 km2 in central Ethiopia, for a long time. The objective of this study was to assess the long-term average annual and seasonal groundwater recharge for the catchment area utilizing the WetSpass-M model. The input data were collected through remote sensing data and surveys in the field. The model was employed to gain insights into the process of groundwater recharge in a particular region and to facilitate effective management, prudent utilization, and sustainable planning of water resources in the long run. Water balance components were estimated using seasonal fluctuations in evapotranspiration, surface runoff, and groundwater recharge. The Wabe catchment’s summer, winter, and mean long-term yearly groundwater recharge were determined to be 125.5 mm, 78.98 mm, and 204.51 mm, respectively. The model indicates that summer seasons account for 86.5% of the mean annual precipitation, while winter seasons account for 13.5%. On the other hand, the groundwater system percolates 14.8% of the total annual rainfall (1374.26 mm). While evapotranspiration accounts for 51% of total precipitation and surface runoff accounts for 34.1%, the Wabe catchment’s mean annual evapotranspiration and surface runoff values are simulated at 701.11 mm and 485.58 mm, respectively. The findings suggest the use of the WetSpass-M model to precisely calculate the water balance components within the Wabe catchment.

Assessment of Groundwater Recharge and Groundwater Quality in The Upstream of Tondano Watershed, North Sulawesi, Indonesia

Raw water need increases along with the development of a region. In terms of quantity and quality, surface water tends to decrease, which causes an increase in groundwater exploitation. For groundwater in the Tondano watershed to be sustainable and meet the required quality standards, it is necessary to know about groundwater recharge and groundwater quality. This study’s objectives are to calculate groundwater recharge using a simplified groundwater balance and to evaluate groundwater quality using physico-chemical parameters. The method used in this study is to estimate groundwater recharge by calculating groundwater balance using data on annual rainfall, annual evapotranspiration, and annual runoff. Meanwhile, for groundwater quality, Physico-chemical properties were measured, including pH, TDS, EC, and temperature, at 21 measurement points, including springs, dug wells, and drilled wells. The results indicate that groundwater recharge calculation shows a positive value of 318.34 mm/year. The measurement of Physico-chemical parameters in the field suggests that the pH value is in the range of 6.1-7.9, the TDS range is 50-200 mg/L, the EC range is 110-400 μs/cm, and the temperature range is 23.4-35.6 °C. The analysis using World Health Organization standards and Ministry of Health standards show that the groundwater quality is suitable for use.

Multi-Station Hydrological Modelling to Assess Groundwater Recharge of a Vast Semi-Arid Basin Considering the Problem of Lack of Data: A Case Study in Seybouse Basin, Algeria

Water resource management scenarios have become more crucial for arid to semi-arid regions. Their application prerequisites rigorous hydrological modelling approaches since data are usually exposed to uncertainties and inaccuracies. In this work, Soil Water Assessment Tool (SWAT), an open source semi-distributed, continuous-time, process-based physical hydrological model is used to model hydrological processes and eventually calculate groundwater recharge estimations in Seybouse basin, Northeast Algeria. The model uses estimated rainfall to calibrate the model with observed discharge from hydrometric stations. Model calibration and validation are performed over four hydrometric stations located in the basin. Uncertainty analysis and sensitivity analysis supported the calibration period. SUFI-2 algorithm is used for uncertainty estimations along with a global sensitivity analysis prior to calibration simulations. Simulated flood hydrographs showed generally good accuracy with few misfits on the peaks. The model obtained satisfactory and consistent calibration and validation results for which the Nash score varied from 0.5 to 0.7 for calibration and from −0.1 to 0.6 for validation and R2 from 0.6 to 0.7 for calibration and 0.03 to 0.8 for validation. Moreover, estimated water budget values show strong similarities with the observed values found in the literature. The present work shows that the rigorously calibrated and validated SWAT model can simulate hydrological processes as well as major high and low flows using estimated rainfall data.

Assessment of Groundwater Recharge Using WetSpass and MODFLOW Coupling in Jedeb Watershed, Upper Blue Nile Basin, Ethiopia

Assessment of Groundwater Recharge Using WetSpass and MODFLOW Coupling in Jedeb Watershed, Upper Blue Nile Basin, Ethiopia

WaterpyBal: A comprehensive open-source python library for groundwater recharge assessment and water balance modeling

Water balance modeling is an essential aspect of water management projects. This study presents WaterpyBal, a tool that generates spatial–temporal water balance models, focused on diffused precipitation and recharge modeling. WaterpyBal has flexible input data and modeling time intervals and integrates different stages of the water balance assessment, such as data interpolation and evapotranspiration and infiltration calculations, while taking into account soil characteristics and urban water cycle. WaterpyBal calculates water budget parameters such as recharge, deficit, and runoff and can be used to create maps, datasheets, and raster archives. WaterpyBal has a modular design that ensures its further development. This Python library is accompanied by the WaterpyBal Studio, a graphic user interface that facilitates the usage of WaterpyBal in water management projects. The functionality of WaterpyBal is demonstrated using a synthetic example. In essence, WaterpyBal supports sustainable groundwater management projects and ensures reproducible research results in these environmental fields.

Assessment of Under Ground Water Resources through RS and GIS Techniques

Water resource management is of utmost importance due to climate change and increased water demand. With 98% of the world’s freshwater being ground water, monitoring its distribution is crucial. These modern-day tools aid in assessing changing land use patterns, mapping water resources, and analyzing hydrogeological data. This paper explores the role of RS and GIS applications in exploring and assessing groundwater resources, estimating natural recharge distribution, analyzing hydrogeological data, and monitoring processes. The study area is situated in the Jodhpur district of Rajasthan, India, characterized by a dry region with sand dunes, alluvial areas, and scattered hillocks. To analyze groundwater potential zones, various spatial datasets such as rainfall, land use, land cover, soil type, and slope were prepared using topographic maps and satellite imagery through integrated RS and GIS techniques. The Soil and Water Assessment Tool (SWAT) integrated with ArcGIS software was used to estimate run off and groundwater recharge through water balance ratios. The research findings demonstrate that GIS and RS layers were analyzed, including factors such as watershed, land use, slope, soil type, temperature, solar radiation, and rainfall data. The water balance ratio was found to be a driving force impacting soil erosion, plant growth, and sediment movement. Overall, this study highlights the effectiveness of RS and GIS techniques for assessing groundwater recharge. The results obtained through these tools provide valuable insights for decision-makers in managing water resources and understanding the potential impacts of human activities on groundwater quality.

Assessment of groundwater recharge and connectivity with surface water in a mountainous watershed using natural tracers in Daejeon, Korea

The water supply from headwater streams in mountainous regions is considered an important source for sustaining both water quality and quantity in lowland areas. The Korean terrain is characterized by mountainous regions, the hydrological environment is significantly impacted by seasonal weather conditions. This study focused on investigating the hydrochemistry and isotopic composition of groundwater and surface water to identify hydrological connectivity within a mountainous watershed area in Daejeon, Korea. The estimated recharge rate using water budget methods suggests that approximately 20% of the total precipitation contributes to groundwater recharge in this site. The δ18O–δ2H values of the water samples indicate a meteoric water source for groundwater recharge, while the isotope composition of surface water reveals altitude effects, implying that groundwater recharges at a higher altitude region. Additionally, water revealed altitude effects suggesting that the groundwater was inferred to recharge at a higher altitude region. The hydrochemical conservative components (87Sr/86Sr ratio and Cl−) indicate that this watershed undergoes temporary similar water–rock interactions along its flow path, but it is also impacted by anthropogenic contaminants from the surrounding public area. The results of the three-component endmember mixing analysis demonstrate that groundwater is predominantly influenced by surface water, indicating a close interrelationship among various water bodies in mountain hydrology. These findings provide a comprehensive approach to water resource management by combining recharge rate estimation and the assessment of water body connectivity using natural tracers.

Modelling groundwater recharge, actual evaporation, and transpiration in semi-arid sites of the Lake Chad basin: the role of soil and vegetation in groundwater recharge

Abstract. The Lake Chad basin, located in the centre of northern Africa, is characterized by strong climate seasonality with a pronounced short annual precipitation period and high potential evapotranspiration. Groundwater is an essential source for drinking-water supply, as well as for agriculture and groundwater-related ecosystems. Thus, assessment of groundwater recharge is very important although also difficult because of the strong effects of evaporation and transpiration, as well as the limited available data. A simple, generalized approach, which requires only limited field data, freely available remote sensing data, and well-established concepts and models, is tested for assessing groundwater recharge in the southern part of the basin. This work uses the FAO dual-Kc concept to estimate E and T coefficients at six locations that differ in soil texture, climate, and vegetation conditions. Measured values of soil water content and chloride concentrations along vertical soil profiles together with different scenarios for E and T partitioning and a Bayesian calibration approach are used to numerically simulate water flow and chloride transport using Hydrus-1D. Average groundwater recharge rates and the associated model uncertainty at the six locations are assessed for the 2003–2016 time period. Annual groundwater recharge varies between 6 and 93 mm and depends strongly on soil texture and related water retention and on vegetation. Interannual variability of groundwater recharge is generally greater than the uncertainty of the simulated groundwater recharge.

Vadose zone water stable isotope profiles for assessing groundwater recharge: Sensitivity to seasonal soil sampling

Groundwater recharge is widely recognized as being the most important parameter for the sustainable management of water resources. In semiarid environments, groundwater recharge can be quantified using the piston displacement method (PDM). From a single soil sampling campaign, the PDM relies on linking the deeper vadose zone soil pore water stable isotope composition (δ2HH2O and δ18OH2O) to the local meteoric water line (LMWL). However, the isotopic composition of precipitation changes seasonally, influencing the water isotope composition of the vadose zone over time. Thus, it is important to test whether the PDM is sensitive to seasonal soil sampling and whether the assessed recharge rate is independent of the time of sampling. This study investigates the effect of seasonal soil sampling on the distribution of vadose zone stable isotope composition to determine whether the sampling time influences the estimate of recharge rate from PDM. Soil samples were obtained along vertical profiles through the vadose zone in a semiarid region during the spring, summer, and autumn seasons. Specifically, the δ2HH2O and δ18OH2O of the soil pore water were determined along vertical profiles, and the PDM was applied to quantify the annual recharge. The δ2HH2O and δ18OH2O values range from −7.3 to −3.5 ‰ and from −54.4 to +7.41 ‰, respectively, and plot along a continuum with a slope less than the LMWL. Samples from deeper in the vadose zone profile had distinct ranges in isotopic composition between the three soil sampling campaigns, with isotopic composition of spring sampling dominated by lower values and those from autumn with higher values. Despite these differences, the resulting annual recharge rates from the different sampling campaigns are comparable (1.5 to 2 % of annual precipitation). Even though the pore water isotopic composition changed over time, the shift between the deeper vadose zone isotopic compositions and the LMWL remained relatively constant, leading to a similar recharge estimate over time. Therefore, the PDM-based recharge assessment in the tested semiarid environment is independent of the sampling time, which indicates that sampling for assessing groundwater recharge can be undertaken during any season.

Groundwater recharge assessment using GIS approach in Chiang Mai basin

The geographic information system (GIS) techniques were used to groundwater recharge estimation and groundwater recharge potential map in Chiang Mai Basin. The groundwater recharge estimation use slope, rainfall and infiltration factor for calculation. Amount of groundwater recharge are 597.20 – 896.19 m3/year. The study used lithology, land use, lineaments, drainage and slope gradient as influence factors to the groundwater recharge potential. The groundwater potentiality was integrated from thematic maps and derived from the sum of the weighted factor using weight overlay method in the GIS system. Almost of the study area is classified as the high groundwater recharge potential zone. The moderate groundwater recharge potential zone is located in the western part of study area and along with the Ping River.

Hydrological modeling of the Silala River basin. 1. Model development and long‐term groundwater recharge assessment

AbstractThe Silala is a small river, originating in the Andean Altiplano, which flows from Bolivia into Chile. Prior to a legal dispute between Chile and Bolivia over the status and use of the waters of the Silala, few hydrological studies had been performed in the basin. Further insights were required to better understand the surface‐water and groundwater discharges from Bolivia to Chile, and the effects of historical channelization of the Bolivian wetlands on these flows. A semi‐distributed hydrological model was therefore developed to estimate the discharges from the basin and provide recharge inputs to a groundwater model used to investigate the effects of channelization. Long‐term temperature and precipitation data were available for 1969–1992, while more detailed data were available for 2018–2019. 1969–1992 was selected as a suitable length of record for long‐term groundwater recharge estimation, and the recent data were reserved for model validation, reported in a companion paper. Prior model parameter ranges were identified based on field observations and scientific literature, and sampling of both input and parameter uncertainty allowed determination of representative, lower and upper groundwater recharge scenarios. Results show strong inter‐annual and seasonal variability, the largest groundwater recharge being observed during the Austral summer. A representative groundwater recharge rate of 39.5 mm/year was obtained for the basin to the international border, with feasible lower and upper bounds of 34.9 and 50.2 mm/year, respectively. This lies within the range of 21–51 mm/year estimated by Bolivia for 1969–2017, albeit higher than their best estimate (24 mm/year).This article is categorized under: Science of Water > Hydrological Processes

Groundwater Recharge Assessment for Small Karstic Catchment Basins with Different Extents of Anthropogenic Development

Climate change and anthropogenic development considerably influence groundwater resource distribution and conditions. Catchment basin groundwater recharge—discharge computation reliability is needed for effective groundwater management policy formulation and implementation and also for resolving environmental challenges in such a watershed. This paper compares groundwater recharge patterns between urbanized and nearly natural small catchment basins of Israel’s Western Mountain Aquifer (WMA). The correlation between precipitation volumes and surface runoff shows that surface runoff volume constitutes 3–4% of the precipitation volume in the Natuf catchment and 1–2% in the Te’enim catchment. These assessments reflect the differences in the land use, outcrop lithology, topography and hydrodynamic properties of the WMA within the model basins. A groundwater recharge assessment based on water balance and water table fluctuation methods was performed for the mountainous karstic Te’enim and Natuf catchment basins for all the available data from 2000 to 2020. The water balance method provided reliable estimates. The groundwater recharge assessment considered land use classification and climate changes during this period. The average multiannual groundwater recharge values for the 2000–2021 period varied from 17.6 × 106–24.8 × 106 m3 to 24.5–29.2 × 106 m3 for the Te’enim and Natuf catchment basins, respectively. For the relatively dry period of the 2013/2014–2017/2018 hydrological years when detailed measurements of the surface runoff were available, the corresponding groundwater recharge volumes were 17.6 × 106 m3 and 24.5 × 106 m3. The corresponding local groundwater recharge coefficients constitute 0.46–0.57 for the mostly agricultural Te’enim basin and 0.29–0.32 for the urbanized Natuf basin. A significant difference in the groundwater recharge coefficients between the studied catchments is caused mostly by the differences in land use. It is suggested that applying such a groundwater recharge estimation for small hydrological sub-basins can improve one’s understanding of the groundwater recharge distribution within a major basin, enabling the application of an accurate regional hydrogeological model that may be extrapolated to other similar regions.

Limpopo National Park (Mozambico): groundwater assessment as a tool for a sustainable management of the area

This paper deals with updated results coming from hydrogeological studies carried on the framework of the SECOSUD Phase II, called “Conservation and equitable use of biological diversity in the SADC region (Southern African Development Community), a project supported by the Italian Ministry of Foreign Affairs in the SADC, whose focus area includes South Africa Development Countries. The main goal of the SECOSUD Phase II Project is the definition and implementation of scenarios for sustainable development, aimed at an equitable conservation of biodiversity resources and, as a consequence of this target, the hydrogeological characterization, with the groundwater recharge assessment, of this area and its buffer zone. Limpopo National Park is one of the jewels in the crown of Mozambique’s protected areas. As a matter of fact, sustaining the conservation of biodiversity, due to its complexity and multiple drivers, which stress it, is on first a matter of water environment assessment, as most ecosystems are highly dependent on the hydrological cycle and groundwater availability. After gathering regional and local geological data, which let us set up a detailed geological map of the area under study, pointing out the main outcropping geological units, with their main hydrogeological properties, the methodological approach adopted has been to assess the potential infiltration, applying the Inverse Hydrogeological Budget Technique, performed for the focus area. Because of the lack of meteorological data referred to Limpopo National Park, it has been applied a spatial distribution of precipitation measurements, collected in many gauge stations, located in the Kruger National Park during the last 54 years, which represent an interesting rainfall historical series. The target of the study has been to assess a trend of meteorological data with the aim of understanding how precipitations could affect groundwater recharge, and their influence on groundwater availability. The estimation of groundwater recharge is the tool for suggesting better water management in the area, aimed to preserve as much biodiversity as people living in the buffer zone.

Groundwater recharge processes in the Lake Chad Basin based on isotopic and chemical data

The Lake Chad Basin is Africa’s largest endorheic basin. Because water supply for the rural population and most of the urban population depends on groundwater, assessment of groundwater recharge is crucial. Recharge sources for the upper Quaternary aquifer are precipitation, rivers, and swamps. Using water chemistry, and environmental (18O, 2H, 3H) and carbon (14C) isotopes, recharge processes can be assessed and groundwater ages roughly estimated. For this purpose, more than 1,000 samples from groundwater, surface water and precipitation were analysed for hydrochemistry and environmental stable isotopes. Furthermore, 3H measurements and 14C values of dissolved inorganic carbon for groundwater from the northeastern part of the Basin are included in the evaluation. The environmental isotope distribution shows recent recharge from precipitation north of Lake Chad (Kanem Region), where very low 3H values indicate occurrence before the 1960s bomb peak. Focused recharge from fresh river water is typical for Salamat Region in south Chad and the Komadugu Yobe wetlands between Nigeria and Niger. Slightly high δ-values in water occur in the Waza Logone area between Chad and Cameroon. Groundwater along the Lake Chad shore and the Bahr el Ghazal corridor show high δ-values (δ18O –0.78 to 7.45‰, δ2H –13.6 to 30.8‰). Recharge is caused by surface water that undergoes evaporative processes before percolation. Groundwater ages of 600–4,150 years, estimated from 14C analyses combined with high SO4 concentrations, along the Bahr el Ghazal indicate that recharge was caused by residuals of the Mega Lake before it dried out completely.