Cuvelai-Etosha Basin Research Articles

Ecotoxicological evaluation of surface waters in Northern Namibia

The increasing pressure on freshwater systems due to intensive anthropogenic use is a big challenge in central-northern Namibia and its catchment areas, the Kunene and the Kavango Rivers, and the Cuvelai-Etosha Basin, that provide water for more than 1 million people. So far, there is no comprehensive knowledge about the ecological status and only few knowledge about the water quality. Therefore, it is crucial to learn about the state of the ecosystem and the ecological effects of pollutants to ensure the safe use of these resources. The surface waters of the three systems were sampled, and three bioassays were applied on three trophic levels: algae, daphnia, and zebrafish embryos. Additionally, in vitro assays were performed to analyze mutagenicity (Ames fluctuation), dioxin-like potential (micro-EROD), and estrogenicity (YES) by mechanism-specific effects. The results show that acute toxicity to fish embryos and daphnia has mainly been detected at all sites in the three catchment areas. The systems differ significantly from each other, with the sites in the Iishana system showing the highest acute toxicity. At the cellular level, only weak effects were identified, although these were stronger in the Iishana system than in the two perennial systems. Algae growth was not inhibited, and no cytotoxic effects could be detected in any of the samples. Mutagenic effects and an estrogenic potential were detected at three sites in the Iishana system. These findings are critical in water resource management as the effects can adversely impact the health of aquatic ecosystems and the organisms within them.

New insights into the flow dynamics of a deep freshwater aquifer in the semi-arid and saline Cuvelai-Etosha Basin, Northern Namibia: Results of a multi-environmental tracer study

Study regionA paleo-megafan system of the Cubango River in the northern parts of the semi-arid Cuvelai-Etosha Basin, shared by Angola and Namibia. It hosts a deep freshwater aquifer, the so-called Kalahari-Ohangwena 2 (KOH-2), with the potential to resolve the imminent regional water supply shortages. Study focusHydrogeochemical and multi-environmental tracer studies incorporating the use of age tracers 14C, 36Cl, 81Kr and 4He to determine the age of groundwater and provide insights into the flow dynamics of the KOH-2. New hydrological insights for the regionStable water isotopes and noble gas thermometry show that in a period with higher rainfall and recharge, temperatures were at least 3 – 4 °C lower than today. Several arguments led to the conclusion that younger groundwater, possibly of an age of 35,000 years, is mixed with ancient saline pore water. These include: 1) the correlation of measured 36Cl and 81Kr ratios, as well as 4He concentrations, using a binary mixing model, and 2) the substantial variation in 81Kr ages, ranging from 40,000 to 170,000 years, over relatively short distances—a phenomenon challenging to explain by advective groundwater flow equations. Consequently, the ages derived from 81Kr measurements serve as indicators of the extent of freshening and therefore describe mixing ages rather than absolute travel times.

Efundja as a risk driver and change agent for the Cuvelai-Etosha basin rural communities.

Despite the presence of a national disaster risk management strategy, the national disaster response mechanism rather reactively responds to the hazard as opposed to being proactive. Results indicates that the strategy is not fully implemented and the parts that are implemented functions as a top-down approach. Respondents reported a wide range of impacts and a general inability to effectively cope with Efundja, coupled with an absence of their voices in deliberations about risk reduction matters. Additions to the current disaster risk management strategy is proposed and several recommendations derived from the research results concludes the article. Should these recommendations be implemented into the Namibian disaster risk management strategy, Efundja as risk driver will also become an agent of change.

3D electrical structure definition of aquifer systems in the Kalahari basin in Southern Angola based on legacy data reprocessing

The Kalahari-Ohangwena transboundary aquifer system, recently identified in Northern Namibia, comprises 3 major aquifers with very different characteristics. The shallowest is discontinuous and with limited reserves, but it has local importance in water supply for the population, since it is easy to reach, and often presents good hydrochemical quality. An intermediate deeper aquifer is characterized by high salinity while the deepest aquifer, also mostly saline, can present zones with fresh water. However, the latter is located at considerable depths and is shaped by the bottom of the basin basement. There hasn't been a systematic hydrogeological data acquisition for decades in this area of Angola, but legacy electrical resistivity data reprocessing from geophysical surveys conducted >50 years ago in the Cunene Province allowed the construction of a quasi-3D geoelectrical model for the Angolan side of KOH aquifer system in the Cuvelai-Etosha basin. This model is based on 482 vertical electrical soundings carried out in 1966–67, using the Schlumberger array, that contribute to confirming the presence of the Kalahari-Ohangwena aquifer system in Angola. The obtained quasi-3D model highlights the geoelectrical features of hard bedrock and is validated with other hydrogeological and geophysical information. The quasi-3D electrical resistivity data is interpreted using selected boreholes and two time-domain electromagnetics transects carried out in Namibia, in the 2000s. Although both geophysical data acquisitions were >40 years apart, the results show a very good correlation between the deeper aquifer and the aquitard separating the intermediate aquifer from the deeper aquifer either with the results from Namibia or the borehole data. This is a direct result of the lack of alteration in the hydraulic conditions over these decades, without significant anthropogenic activity and negligible extraction from deep wells. Based on this analysis, the original dataset was considered a reliable source and this quasi-3D model was validated. Furthermore, the model can be considered in the future as an important tool for groundwater resources management, as well as a good starting point for further hydrogeological research in the province of Cunene.

Spatio-temporal characterization of surface water dynamics with Landsat in endorheic Cuvelai-Etosha Basin (1990–2021)

Socio-economic damages caused by extreme floods have been increasing rapidly in recent years, mainly driven by changes in the climate and modulated by increasing human population in deltic areas and floodplains. The Cuvelai-Etosha Basin (CEB) in southern Africa, covering southern Angola and northern Namibia, experiences socially and economically devastating extreme floods. Yet, accurate information on past and current surface water changes and dynamics is lacking. Here, we estimate and map the surface water extents in the CEB and its surroundings (CEB + S) for 32 years (1990–2021) from Landsat data using random forest models to provide long-term baseline information on surface water changes and dynamics. Based on the reference data, a total of 15,677 ± 1080 km2 have been inundated by surface water in the CEB + S during 1990–2021. This extent was accurately mapped by our local water extent product (mapped area = 16,273 km2, user’s accuracy = 91.5 ± 2.5%, producer’s accuracy = 91.1 ± 6%). With user’s and producer’s accuracy of 91%, our overall water extent provides the first most accurate long-term baseline information on surface water inundation in CEB + S necessary for local spatial planning processes to minimise future negative impacts of floods in the basin. Interannual variability of surface water extent is, however, high, with water extent ranging from 520.8 ± 375.7 km2 to 12372.3 ± 1154.7 km2 during the 1990–2021 period. The largest annual water extents (>10,000 km2) were recorded in 2006, 2008, 2009, 2011, and 2017, whereas the smallest extents (<1000 km2) were recorded in 1992 and 2019. We found that over 40% of the area inundated in the CEB + S during 1990–2021 was inundated less than 9 times. With human population increasing rapidly in the CEB + S, rarely inundated areas with short water residence could become a prime target for human settlements, which may lead to huge socio-economic damages during extreme floods if no preventive measures are put in place. Globally available surface water maps from the Global Land Analysis and Discovery (GLAD) and European Commission’s Joint Research Centre (JRC) did not provide realistic surface water extent for CEB + S, especially during years with extreme floods. Therefore, locally adopted product for operational monitoring of surface water in the CEB + S is needed to provide accurate information for informing spatial planning processes and surface water resource management strategies in this endorheic basin and help minimise future negative impacts of floods.

Community responses to the annual flooding (efundja) in the Cuvelai-Etosha basin, Northern Namibia

The efundja is the annual flooding experienced in the Cuvelai-Etosha basin of northern Namibia. This recurring flooding varies in intensity and impact the lives of the inhabitants of the basin in disparate ways. The rural population of the basin is especially vulnerable to the impacts associated with these floods.The governmental response to the efundja is mostly reactive, and the voices of the rural community are lacking in the development and execution of the disaster response strategy for the area. Limited studies exist to include the voices of rural communities in the narrative about the efundja and its impact and mitigation.This study used focus group discussions to investigate the experiences of heads of households in the affected rural communities in the study area to address this hiatus in the research. The results of the study can also aid in addressing the deficiencies in the governmental response strategy used to deal with the floods.Rural communities in the study area articulated the impacts of the efundja on their lives well and indicated that the impacts are pervasive and affect their entire way of life. They reported that the nature and duration of the efundja have changed over time, with a longer duration, more severe impacts, pollution, and poor water quality associated with recent efundja events. They attribute this mainly to climate change, an increase in the population of the basin, inappropriate human behavior and bad spatial planning. Although the rural communities reported various practical methods to alleviate the adverse impacts of the flooding, they expressed a general lack of capacity to deal with the flooding effectively. Empowerment through education and training on how to mitigate effects and participation in disaster response planning and execution were affirmed needs in the communities surveyed.The research and its results can be used to inform a better disaster response strategy for northern Namibia. The study can also be emulated in other areas of the Global South. The results of such studies can be compared with that of the present study to expand the disaster response narrative. Adding the voices of vulnerable rural communities can be a particularly valuable addition to the disaster response narrative since their views are sometimes excluded in disaster response studies.

Evaporation loss along the Calueque-Oshakati Canal in the Cuvelai-Etosha Basin (Northern Namibia): evidence from stable isotopes and hydrochemistry

ABSTRACT Since 1973, Kunene River water has been carried from the Calueque reservoir in Angola along a 160 km open concrete canal to the town of Oshakati in the central part of the Cuvelai-Etosha Basin and has been supplying drinking water to the most densely populated rural area of Namibia. Despite its importance for the region, intra-seasonal water quality and the technical condition of the canal are not routinely checked. Water samples were collected during four field campaigns right before the onset of the rainy season (November 2013 and 2014), and after the rainy season (June 2014 and May 2015), at 16 sites along the canal for stable water isotopes (deuterium, oxygen-17 and oxygen-18) and hydrochemical analyses. The isotope patterns and chemical composition of the canal water is discussed in comparison to local rain, Kunene source water, surface water and groundwater. Clear isotope enrichment indicates evaporative loss of water. A Craig–Gordon model was used to estimate water loss. The loss increases with distance from the source with a maximum of up to 10 %, depending on the season. The results are discussed in context of water availability, vulnerability and water resources management in this water-scarce area.

The role of local perched aquifers in regional groundwater recharge in semi-arid environments: evidence from the Cuvelai-Etosha Basin, Namibia

The influence of local perched aquifers on groundwater recharge in semi-arid areas at a regional scale remains inadequately studied, especially in southern Africa where data scarcity limits the understanding of recharge and groundwater flow processes. The objective of this study was to understand the interaction between localized perched aquifers and an underlying regional aquifer in the Cuvelai-Etosha Basin in Namibia. The connection between the perched and regional aquifers was assessed based on an extensive dataset of hydrochemical and isotope (δ18O and δ2H) measurements for groundwater from both shallow and deep hand-dug wells as well as boreholes. Ephemeral rivers and pans/depression landforms were analyzed separately. Recharge was calculated using the chloride mass balance method. It was found that groundwater originates from precipitation that undergoes strong evapotranspiration and water–rock interaction, especially carbonate dissolution. Overlapping chemical and isotopic compositions suggest a common or similar origin of groundwater in the perched and regional aquifers in the pan/depression hydrotope. No such similarity was established for the ephemeral river hydrotope, suggesting that ephemeral rivers contribute negligibly to regional groundwater recharge. This has important implications for groundwater management and helps to understand recharge processes in similar semi-arid environments.

Metagenomics Reveals Seasonality of Human Pathogenic Bacteria from Hand-Dug Well Water in the Cuvelai Etosha Basin of Namibia

Namibia is a large country with a population slightly above 2 million of which 73% live in rural areas. It is the driest country in sub-Saharan Africa with unpredictable rainfall patterns which occur between October and May. The Cuvelai Etosha Basin is a rural setting in which most people depend on groundwater to circumvent water scarcity by the construction of hand-dug wells. Communities consume hand-dug well water throughout the year without; knowledge of its safety, and treatment prior to use. Hence, this study aimed at evaluating the seasonal safety and quality of hand-dug well water for human consumption. A 16S rRNA metagenomics study was conducted to explore the influence of season on the human pathogenic bacterial species richness, diversity, evenness and abundance in the hand-dug wells. Bacterial pathogens were identified and analysis revealed no significant difference in species richness and diversity, and a significant difference in species evenness and abundance between the wet and dry seasons. Hence, seasonality had an influence on human bacterial pathogens evenness and abundance but had no influence on species richness and diversity. In addition, the water in hand-dug wells of the Cuvelai Etosha Basin is not safe for consumption and domestic use unless sanitized. It is recommended that efforts should be made to treat the water prior to use, and hand-dug wells should be properly constructed to reduce contamination.

Radon, Salinity and Elemental Concentrations of Water Sources within the Kuiseb and Cuvelai-Etosha Basin, Namibia

The absence of baseline information on radon measurements and concerns about possible consequences of long term exposure to high radon (Rn-222) concentrations and its progenies necessitated for the evaluation of radon concentrations in boreholes and households. This study thus investigated the levels of Radon gas (Rn-222), salinity and elemental composition of different water sources (tap-water, boreholesand surface water) within the Kuiseb and Cuvelai-Etosha basin, in order to address the lack of scientific correlational studies on radon levels and toxic trace elements in drinking water. Radon concentrations were measured using an AlphaGRAUD PQ2000 PRO system, and the elemental composition was determined using a NexION 350D Inductively Coupled Plasma Mass Spectrometer. The findings of this study showed high (2.71 Bq/m3) Rn-222concentrations in the Kuiseb (possibly caused by natural uranium ore deposits in the Erongo Region) compared to the 0.43 Bq/m3average in the Cuvelai-Etosha Basin. The study also measured high salinity (63 0/00) concentrations (linked to high Total Dissolved Solids of 25.46 g/L) in the Cuvelai waters compared to the (37 0/00) salinity (with low TDS of 3.8 g/L) in the Kuiseb, thus pointing to the geological and meteorological make up of Cuvelai i.e. Kalahari sedimentary rocks, runoff sediments, high temperature and evaporation rates, as well as alternating floods and drought (rainfall variations). The elements observed in significantly high concentrations include Ba, K, Sb, As, Cd, Cr, Cu, Mo, Ni, V, Zn and Bi in the Kuiseb, and Ca, Cl, Mg, Na, Al, Be, Br, Ce, Cs, Fe, Pb, Mn, Se, Ti in the Cuvelai-Etosha Basin. Further, the Cuvelai-Etosha proved to have more anthropogenic activities (including burning of vegetation) influencing the elemental composition, and causing deterioration of the water quality.

Isotopic Composition of Water Bodies in the Kuiseb and Cuvelai-Etosha Basin, Namibia

This study aimed to investigate the isotopic composition of different water bodies in two basins. Water samples collected from open and undefined water sources such as the Etaka and Ruacana waterfall and an artificial spring in the Cuvelai-Etosha Basin; aswell as the boreholes, Atlantic Ocean and fog from the Kuiseb Basin were analysed for stable isotopes namely, Deuterium (δ2H) and oxygen 18 (δ18O)) and elemental composition. Stable isotope ratios were measured using the Picarro L2120–i Analyser (Cavity Ring-Down Spectrometry method) and trace elemental composition was assessed using the Inductively Coupled Plasma Mass Spectroscopy (ICP-MS). Open water bodies of the Cuvelai-Etosha Basin were found to be enriched with heavy isotopes, and also plotted along the evaporation line (below and away from the Global Meteoric Water Line (GMWL)), which is indicative of the high evaporation rates within the basin. Kuiseb boreholes were depleted of heavy isotopes and plotted along the Global and Local Meteoric Water Line, indicating direct recharge from precipitation and minimal, if any, evaporation effects. Trace elemental analyses indicated possible contamination of water bodies with high concentrations of Al and Fe, confirming the effect of sediment input in the floodprone basin (Cuvelai), and continual erosion/hard crust in the Kuiseb. Positive correlations with r2greater than 0.5, confirming increase in δ18O and δ2H with increase in trace elements including Strontium and Lithium in the Kuiseb Basin, and Molybdenum (Mo) and Manganese (Mn) in the Cuvelai-Etosha Basin were also observed.

Sources of fish in the ephemeral western iishana region of the Cuvelai–Etosha Basin in Angola and Namibia

The triangle between the Kavango and Kunene rivers is drained by the Cuvelai, an ephemeral and deltaic drainage system covering more than 100 000 km2. In good rainfall years, the area becomes populated by fish communities dominated by five species migrating southward towards the endorheic Etosha Pan, the basin’s terminal sump. When water dries up, fish subsequently die-off and their sudden appearance in rainy years has captivated scientists for decades. The current study was prompted by hitherto untapped indigenous knowledge through narratives of opportunistic fish harvesting of migrating fish at temporary connections between the Kunene River and the Cuvelai- Etosha Basin. A reconnaissance fish survey in 2017 was complemented by digital satellite images and elevation data analyses. Results support the presence of at least three major ephemeral fish migration routes. The dominant fish genera migrating upstream in Kunene tributaries comprise Enteromius, Oreochromis and Clarias, all eurytopic and known to undertake upstream, lateral and downstream migrations on floodplains. Although other notable fish refugia in the Cuvelai–Etosha Basin are yet to be identified, there is a necessity for the protection and management of these migration routes in tandem with studies on the nature and extent of this inter-basin fish migration under climate change and variability.

Stable isotope signatures of meteoric water in the Cuvelai-Etosha Basin, Namibia: Seasonal characteristics, trends and relations to southern African patterns

ABSTRACTThe study area is the Namibian part of the Cuvelai-Etosha Basin (CEB), located in central northern Namibia. The CEB is home to 40 % of Namibia’s population, and most of the people live in rural areas. These people depend on both surface and groundwater resources which are limited in this dryland (mean annual rainfall ranging from 250 to 550 mm/a). The isotopic signatures of δ18O and δ2H from water samples (n = 61) collected over a course of 9 years from various research projects and existing (but mainly unpublished) data of meteoric water of the CEB (10 sites) were evaluated and local meteoric water lines (LMWLs) developed. Further, the data is discussed in the context of seasonal characteristics and trends and compared to available data from the Global Network of Isotopes in Precipitation (GNIP) for the southern African region. Our results extend the portfolio of previously published LMWLs for southern Africa and provide a more precise baseline for any isotope-based study in that region. The slope of the LMWL from the GNIP stations correlates with latitude. This correlation cannot be found within the CEB. The dominant control on the isotopic signature of the CEB of precipitation is seasonal.

Isotopic composition and elemental concentrations in groundwater in the Kuiseb Basin and the Cuvelai-Etosha Basin, Namibia

Abstract. We assessed environmental tracers in groundwater in two contrasting basins in Namibia; the Kuiseb Basin, which is a predominantly dry area and the Cuvelai-Etosha Basin, which is prone to alternating floods and droughts. We aimed to determine why the quality of groundwater was different in these two basins which occur in an arid environment. We analysed groundwater and surface water for the stable isotope ratios of hydrogen (δ2H) and oxygen (δ18O) by cavity ring-down spectroscopy and metals by inductively coupled plasma mass spectrometry. The δ2H and δ18O of surface water in the Cuvelai-Etosha Basin plot on an evaporation trend below the global meteoric water line (GMWL) and the local meteoric water line (LMWL). The δ2H and δ18O of some groundwater samples in the Cuvelai-Etosha Basin also plot on the evaporation trend, indicating recharge by evaporated rain or evaporated surface water. In contrast, the δ2H and δ18O of groundwater samples in the Kuiseb Basin plot mostly along the GMWL and the LMWL, indicating direct recharge from unevaporated rain or unevaporated surface water. Fifty percent of groundwater samples in the Cuvelai-Etosha Basin was potable (salinity &lt; 1 ppt) compared to 79 % in the Kuiseb Basin. The high salinity in the groundwater of the Cuvelai-Etosha Basin does not appear to be caused by evaporation of water (evapo-concentration) on surface prior to groundwater recharge, but rather by the weathering of the Kalahari sediments. The low salinity in the Kuiseb Basin derives from rapid recharge of groundwater by unevaporated rain and limited weathering of the crystalline rocks. The order of abundance of cations in the Kuiseb Basin is Na &gt; K &gt; Ca &gt; Mg vs. Na &gt; Mg &gt; Ca &gt; K for the Cuvelai-Etosha Basin. For metals in the Kuiseb Basin the order of abundance is Fe &gt; Al &gt; V &gt; As &gt; Zn vs. Al &gt; Fe &gt; V&gt; As &gt; Zn for the Cuvelai-Etosha Basin. The relative abundance of cations and metals are attributed to the differences in geology of the basins and the extent of water-rock interaction. Our results show that the quality of groundwater in Cuvelai-Etosha Basin and Kuiseb Basin which vary in the extent of aridity, is controlled by the extent of water-rock interaction at the surface and in the groundwater aquifer.

Spatio-temporal variations of hydrochemical and isotopic patterns of groundwater in hand-dug wells: the Cuvelai-Etosha Basin, Namibia

Abstract. The rural population in parts of the Cuvelai-Etosha Basin (CEB) in Namibia depends on groundwater as a source for drinking and livestock watering. The aim of this study is to investigate spatial-temporal patterns for understanding water origins and recharge processes of perched aquifers in the CEB. The study uses hydrochemical data and water stable isotope signatures (18O and 2H) of samples collected during (10) ten field campaigns over a three-year period (from 2014 to 2016) originating from two regions within the basin (Ohangwena and Omusati). A clear distinction between the shallow groundwater in the Omusati and Ohangwena regions documented by TDS values, hydrochemical water types as well as the isotopic compositions of water. These differences are influenced mainly by their location in the landscape, depth to water table, the type of well infrastructure and aquifer material. Spatial and temporal variations indicate that even though these perched aquifers are both within the same basin, they are chemically different because of the rock materials in which their flow. Therefore, these differences in the water hydrochemical composition as well as the processes governing perched aquifers must be taken into account when planning groundwater management in the basin.

The long road to sustainability: integrated water quality and quantity assessments in the Cuvelai-Etosha Basin, Namibia

Many arid and semi-arid regions of Southern Africa experience pressure on water resources as a result of limited rainfall, droughts, high population growth, and poor infrastructure. To satisfy domestic, agricultural, and livestock demands, multiple water sources are used, but the scientifi c and local knowledge on both the quality and quantity of these is limited for the study area. As part of SASSCAL Tasks 007, 010 and 014, numerous fi eld campaigns (2013–2017) were carried out in the transboundary Cuvelai-Etosha Basin (CEB) with the aim of providing a comprehensive description of surface and groundwater resources. The investigations reveal that sound management and coordinated use of water resources in the CEB need to be introduced. This could include, for example, adding further responsibilities to water point committees and developing management strategies based on a thorough understanding of hydrologically relevant processes. Suffi cient water exists, but its quality and quantity are highly variable. Simple actions at a local scale (e.g., rainwater harvesting, fencing off wells, use of perched aquifers) could improve the situation substantially.

Water resources in the Cuvelai-Etosha Basin

Water resources in the Cuvelai-Etosha Basin

Detection of &amp;lt;i&amp;gt;Escherichia coli&amp;lt;/i&amp;gt; and Harmful Enteric Bacterial Pathogens in Domestic Hand-Dug Wells in the Cuvelai Etosha Basin of Namibia

The Cuvelai Etosha Basin of Namibia is characterised by complex aquifer systems with multi-layered aquifers and various water qualities. Some parts of the basin have been covered with a pipeline system that supplies purified surface water from the Kunene River. Locations that lack a pipeline system utilise hand-dug wells as a source of drinking water. These wells draw water from shallow perched aquifers and are not protected from surface contamination nor is the water quality monitored. Sanitised water supply is relevant for the growth and development of societies and is a priority of the United Nations Millennium Development Goals. A bacteriological water quality study aimed at investigating the presence and seasonal variation of; Citrobacter, Escherichia, Klebsiella, Enterobacter, Proteus, Salmonella, Shigella, and Pseudomonas species was conducted on 44 hand-dug wells in the Ohangwena and Omusati regions of the Cuvelai Etosha Basin. Samples were collected from both the wet and dry seasons. Results disclosed the presence of Salmonella, Shigella, Citrobacter, Escherichia, Klebsiella, Enterobacter, Proteus, and Pseudomonas species. Chi-square confirmed a significant seasonal variation in Salmonella (P Shigella (P Citrobacter (P > 0.05), Escherichia (P > 0.05), Klebsiella (P > 0.05), Entero-bacter (P > 0.05), Proteus (P > 0.05) and Pseudomonas (P > 0.05) species. Water from these hand-dug wells is not safe for drinking unless it is subjected to appropriate treatment. It is recommended that hand-dug wells should be properly constructed at safe distances from contaminating structures such as pit latrines and routinely assessed for pathogens, and the water should be sanitized prior to consumption.

Groundwater quality and associated hydrogeochemical processes in Northwest Namibia

Namibia is one of the driest countries in southern Africa. Groundwater has played an important role in the development of Namibia. However, like those at some other places in Namibia, groundwater is unsuitable for drinking in parts of the Northwest of Namibia because of its poor quality. It is significant to assess groundwater quality and understand the hydrogeochemical processes for the management and utilization of groundwater resource in this water-short region. In this paper, we report the investigation and assessment of groundwater quality and associated hydrogeochemical processes in the Cuvelai-Etosha Basin and Kaokoveld region, northwestern Namibia. A total of 24 samples were collected for chemistry and stable hydrogen and oxygen isotopes analysis. The groundwater quality was evaluated by single factor index method. Hydrochemical and isotopic (δD and δ18O) data were used to study the hydrogeochemical processes of groundwater in the areas. The results show that most of the groundwater that originated from precipitation was unacceptable in appearance and tastes, but may be safe for human consumption. The salinity and concentrations of As, U and F− in some of groundwater samples exceeded of the WHO standards. The salinity increase of the groundwater is primarily due to minerals dissolution rather than evaporation. A number of the samples located in the Cuvelai-Etosha Basin and Kaokoveld region are low in TDS. The salinity of them mainly derives from the dissolution of carbonate. Some of the samples located in the west of the Cuvelai-Etosha Basin and Kaokoveld region have medium TDS. The salinity of them originates mainly from the dissolution of carbonate and the oxidation of pyrite. The highest Fe concentration in these samples is up to 13mg/L. The samples located to the east of Etosha Pan have high TDS. Halite and carbonate dissolution with strong cation exchange are the major source of the high salinity. The low Ca2+ concentrations in groundwater and rich fluorine sediments in Cuvelai-Etosha Basin favor the formation of high F− groundwater. The weak alkaline environment and high HCO3− contents are significant to the higher As and U contents. Insight from this study may be helpful to enhance the understanding of distributions and transfers of major ions and trace elements in groundwater and to improve the management and utilization of groundwater resources in the region and other similar areas.

Inverse modeling and uncertainty analysis of potential groundwater recharge to the confined semi-fossil Ohangwena II Aquifer, Namibia

The identification of potential recharge areas and estimation of recharge rates to the confined semi-fossil Ohangwena II Aquifer (KOH-2) is crucial for its future sustainable use. The KOH-2 is located within the endorheic transboundary Cuvelai-Etosha-Basin (CEB), shared by Angola and Namibia. The main objective was the development of a strategy to tackle the problem of data scarcity, which is a well-known problem in semi-arid regions. In a first step, conceptual geological cross sections were created to illustrate the possible geological setting of the system. Furthermore, groundwater travel times were estimated by simple hydraulic calculations. A two-dimensional numerical groundwater model was set up to analyze flow patterns and potential recharge zones. The model was optimized against local observations of hydraulic heads and groundwater age. The sensitivity of the model against different boundary conditions and internal structures was tested. Parameter uncertainty and recharge rates were estimated. Results indicate that groundwater recharge to the KOH-2 mainly occurs from the Angolan Highlands in the northeastern part of the CEB. The sensitivity of the groundwater model to different internal structures is relatively small in comparison to changing boundary conditions in the form of influent or effluent streams. Uncertainty analysis underlined previous results, indicating groundwater recharge originating from the Angolan Highlands. The estimated recharge rates are less than 1% of mean yearly precipitation, which are reasonable for semi-arid regions.