Groundwater - surface water interactions on deeply weathered surfaces of low relief in the Upper Nile Basin of Uganda

Little is known of the interactions between groundwater and surface water on the deeply weathered surfaces of low relief in the Great Lakes Region of Africa (GLRA). The role of groundwater in sustaining water levels in lakes, rivers and wetlands during periods of absent rainfall is also unclear. Indeed, groundwater is commonly excluded from estimations of the surface water balances. Piezometer nests constructed on the shores of Lakes Victoria (Jinja, Entebbe) and Kyoga (Bugondo) through this study, provide the first evidence of the lithologic interface and dynamic interactions between groundwater and surface water in the GLRA. Evidence is drawn from lithological analyses (texture, lithostratigraphy), geophysical surveys (resistivity mapping, VES), hydraulic tests, borehole hydrographs and hydrochemical (major ions, \delta^2H, \delta^1^8O) data. Groundwater interacts with surface waters primarily via preferential pathways within the coarse horizons towards the base of thick saprolite underlying relatively thin (<5 m) fluviallacustrine sands. Hydrological observations and hydrochemical data indicate that groundwater flows primarily into lakes; this interaction is dynamic varying by season and proximity to lake. Interactions between groundwater and Lakes Victoria and Kyoga are also influenced by changing drainage base (lake) levels that are controlled, in part, by regional, rather than local climatology and dam releases from Lake Victoria (Jinja). Groundwater levels are strongly influenced by rainfall-fed recharge that depend more upon heavy rainfall events (10 mm\cdot d^-^1) during the monsoons than the total volume of rainfall; mean vertical velocities in the unsaturated zone are ~1 m\cdot d^-^1. Layered heterogeneity in aquifer properties (hydraulic conductivity, storage) indicate deeply weathered rocks formed under prolonged in situ weathering (etchplanation) of lowrelief surfaces. This layered heterogeneity in the saprolite aquifer gives rise to a twocomponent recession in borehole hydrographs following recharge events. A firstapproximation of the proportion of the Lake Victoria’s water balance supplied by groundwater is derived from new observations in this study and is in the order of 1 %

Hydrogeochemical processes in groundwater in Uganda: a national-scale analysis

Groundwater represents a vital source of freshwater to meet distributed, rapidly rising demands for safe drinking water, irrigation and industry in low-income countries across the tropics. The hydrochemistry of groundwater within deeply weathered crystalline rock aquifer systems that predominate at low latitudes, is determined primarily by long-term biogeochemical weathering of the parent bedrock. Here, we evaluate geochemical footprints and baseline chemical quality of groundwater that have developed from water-rock interactions across a range of geological environments in Uganda using a national database of hydrochemical and hydrogeological records from 3271 locations. Sampled groundwaters are mostly shallow (69% of samples from depths of <20 m below ground level), fresh at time of drilling (Electrical Conductivity <1000 μS cm−1 in 96% of samples), and of good quality (<8% of samples exceed WHO (2011) guidelines values for chemical parameters in drinking water). Unpalatably high concentrations of total soluble and suspended Fe are, however, common (21%) in meta-igneous, granitic and metamorphic formations. The dominant (95%) anionic facies of groundwater is bicarbonate (HCO3−), indicative of localized flow systems (i.e. discontinuous aquifers) in which chemical evolution of groundwater (e.g. as per Chebotarev sequence) is minimal. Low well yields (82% < 3.6 m3 h−1) and specific capacities (84% < 5 m2 d−1) support this inference; low aquifer transmissivities and storage serve to regulate naturally groundwater withdrawals (i.e. impacts of over-abstraction are localized). Overall, the results attest to the intrinsic high quality of groundwater that occurs in deeply weathered crystalline rock environments in Uganda, which may be expected across tropical Africa

Physical factors contributing to rural water supply functionality performance in Uganda

This report communicates the findings generated from one of the project surveys – deconstruction and forensic analysis of 50 individual water points in Uganda. The report presents the new data generated to Uganda’s groundwater resource potential; the nature and condition of hand-pump borehole installations; and the significance of both of these factors to service performance. Based on the evidence collected, the main physical factors affecting functionality performance within Uganda are the poor condition of handpump components, and the complex aquifer resource. The impact of these factors can be mitigated through appropriate material choice for handpump components (non GI), increased investment in borehole siting and testing, and adequate accessibility to repairs and maintenance capacity with breakdowns. These factors should not be considered to be the only driving forces of functionality outcomes in these regions of Uganda, however, and the results of this survey need to be examined alongside the wider project findings. Wider institutional arrangements, resources and dynamics, are likely to play a significant role in the implementation of appropriate borehole construction, siting and design; procurement processes; and the management capacity available for water points at national to local levels

Permeability of the crystalline basement in Uganda : evidence from 665 pumping tests and implications for solar pumping

Crystalline basement rocks of Precambrian age underlie nearly three quarters of Uganda, providing groundwater supplies to meet ever increasing demand from rural areas and urban growth centres. Development of groundwater sources is commonly based on several factors including physical and socio-economic considerations that have a bearing on their functionality and long term reliability. Here we present new transmissivity data from 665 boreholes across basement aquifers in Uganda calculated from previously unanalyzed pumping test data. Other data are available to help interpret the transmissvity values, including borehole lithological logs, weathering thickness, well design and depth to groundwater. Spatial and depth comparisons are made to relate aquifer permeability to lithology and weathering, and also to relate borehole yields to well design. The data provide an improved understanding of the physical permeability of weathered crystalline basement rock aquifers across Uganda, complimenting earlier studies of vertical permeability profiles in focused areas. The analysis helps inform the physical capacity of the aquifer to supply the borehole yields to meet increasing demands, and application the potential for higher abstraction technologies, such as solar pumps

Vorkommen von Spurenelementen in Flusssedimenten und Grund- und Oberflächenwasser in der Bergbauregion von Gatumba, Ruanda

Aufgrund der intensiven Landnutzung durch Bergbau und Landwirtschaft sind die Gewässer im Gatumba Mining District durch Stoffaustrag aus Abraumhalden und Erosion stark geprägt. Untersuchungen während einer Trocken- und Regenzeit hinsichtlich der Konzentration von Spurenelemente haben gezeigt, dass von einer Gesundheitsgefährdung der lokalen Bevölkerung derzeit nicht ausgegangen werden kann. In der Regel weisen die Wasserproben der Trockenzeit gegenüber denen der Regenzeit tendenziell höhere Konzentrationen auf. Die Konzentrationen der Sedimente zeigen keinen entsprechenden Trend

HLA polymorphisms and detection of kaposi sarcoma-associated herpesvirus DNA in saliva and peripheral blood among children and their mothers in the uganda sickle cell anemia KSHV Study

Kaposi sarcoma-associated herpesvirus (KSHV, also called Human herpesvirus 8 or HHV8) is a γ-2 herpesvirus that causes Kaposi sarcoma. KSHV seroprevalence rates vary geographically with variable rates recorded in different sub Sahara African countries, suggesting that effects of genetic and/or environmental factors may influence the risk of infection. One study conducted in South Africa, where KSHV seroprevalence is relatively low, found that carriage of human leukocyte antigen (HLA) alleles HLA-A*6801, HLA-A*30, HLA-A*4301, and HLA-DRB1*04 was associated with increased shedding of KSHV DNA in saliva. Confirmation of those results would strengthen the hypothesis that genetic factors may influence KSHV distribution by modulating KSHV shedding in saliva. To explore these associations in another setting, we used high resolution HLA-A, B, and DRB1 typing on residual samples from the Uganda Sickle Cell Anemia KSHV study, conducted in a high KSHV seroprevalence region, to investigate associations between HLA and KSHV shedding in saliva or peripheral blood among 233 children and their mothers. HLA-A and HLA-DRB1 alleles were not associated with KSHV shedding in our study, but our study was small and was not adequately powered to exclude small associations. In exploratory analyses, we found marginal association of KSHV DNA shedding in saliva but not in peripheral blood among children carrying HLA- B*4415 and marginal association of KSHV DNA shedding in peripheral blood but not in saliva among children carrying HLA- B*0801 alleles. The contribution of individual HLA polymorphisms to KSHV shedding is important but it may vary in different populations. Larger population-based studies are needed to estimate the magnitude and direction of association of HLA with KSHV shedding and viral control

In-situ fluorescence spectroscopy is a more rapid and resilient indicator of faecal contamination risk in drinking water than faecal indicator organisms

Faecal indicator organisms (FIOs) are limited in their ability to protect public health from the microbial contamination of drinking water because of their transience and time required to deliver a result. We evaluated alternative rapid, and potentially more resilient, approaches against a benchmark FIO of thermotolerant coliforms (TTCs) to characterise faecal contamination over 14 months at 40 groundwater sources in a Ugandan town. Rapid approaches included: in-situ tryptophan-like fluorescence (TLF), humic-like fluorescence (HLF), turbidity; sanitary inspections; and total bacterial cells by flow cytometry. TTCs varied widely in six sampling visits: a third of sources tested both positive and negative, 50% of sources had a range of at least 720 cfu/100 mL, and a two-day heavy rainfall event increased median TTCs five-fold. Using source medians, TLF was the best predictor in logistic regression models of TTCs ≥10 cfu/100 mL (AUC 0.88) and best correlated to TTC enumeration (ρs 0.81), with HLF performing similarly. Relationships between TLF or HLF and TTCs were stronger in the wet season than the dry season, when TLF and HLF were instead more associated with total bacterial cells. Source rank-order between sampling rounds was considerably more consistent, according to cross-correlations, using TLF or HLF (min ρs 0.81) than TTCs (min ρs 0.34). Furthermore, dry season TLF and HLF cross-correlated more strongly (ρs 0.68) than dry season TTCs (ρs 0.50) with wet season TTCs, when TTCs were elevated. In-situ TLF or HLF are more rapid and resilient indicators of faecal contamination risk than TTCs

Permeability of the weathered bedrock aquifers in Uganda: evidence from a large pumping test dataset and its implications for rural water supply

Weathered crystalline-rock aquifers underlie around 40% of sub-Saharan Africa providing water supplies for half of its rural population; they are also prevalent across the tropics. The hydrogeology of these aquifers is complex and better understanding of the controls to aquifer transmissivity, alongside accurate borehole siting and appropriate design, is pivotal to the long-term performance and sustainability of water services in many countries. This study examines a substantial new dataset (n = 655) of aquifer transmissivity values across Uganda derived from previously unanalyzed pumping-test data. These data provide important new insights: weathered crystalline-rock aquifers are distinguished by pervasively low transmissivities (median <2 m2/d) in comparison to other areas in the tropics; highest transmissivities are observed in boreholes <50 m deep, implying that drilling deeper boreholes does not typically improve supply success or sustainability in Uganda; and increased groundwater abstraction through the use of higher-yielding pump technologies will prove challenging in most areas of Uganda and limit their use for piped water supplies. This study highlights the scientific value of data held in drillers’ records, which remain unanalyzed in many countries but may provide useful insight and understanding of aquifer characteristics

Drinking water quality from rural handpump-boreholes in Africa

Groundwater provides a vital source of drinking water for rural communities in many parts of Africa, particularly in the dry season when there are few safe alternative sources. This paper summarises results from a study (n = 428) assessing dry season water quality, both microbiological and inorganic chemistry, in handpump equipped boreholes (HPBs) across the Ethiopia Highlands (n = 142), Malawi (n = 162) and Uganda (n = 124) using a stratified, randomised sampling design. This study seeks to examine general water quality by randomly sampling rural groundwater supplies across larger areas with different geology and climate. The majority, 72%, of HPBs surveyed provide good quality dry season drinking water as defined by WHO drinking water quality criteria. Within this overall picture, the most notable constraints were from thermotolerant coliforms (TTCs), which exceeded the WHO drinking water guideline of zero colony forming units (cfu/100 ml) in 21% of sites (range 0–626 cfu/100 ml). TTC contamination was found to have a significant and positive correlation with annual average rainfall (ρ = 0.2, p = 0.00003). Across all three countries, WHO health based chemical drinking water quality values were exceeded at 9% of sites and were found for manganese (4%), fluoride (2.6%) and nitrate (2.5%); arsenic concentrations were below the guideline value of 10 μg l−1 (range 400 μg l−1) found in drinking water sources in Uganda challenges the decision by WHO not to formalise a health-based guideline for Mn. While the overall level of microbiological contamination from HPBs is low, results from this study strongly suggest that at a national and regional level, microbiological contamination rather than chemical contamination will provide a greater barrier to achieving targets set for improved drinking water quality under the UN-SDG 6. Efforts should be made to ensure that boreholes are properly sited and constructed effectively to reduce pathogen contamination

Characteristics of high-intensity groundwater abstractions from weathered crystalline bedrock aquifers in East Africa

Weathered crystalline bedrock aquifers sustain water supplies across the tropics, including East Africa. Although well yields are commonly <1 L s−1, more intensive abstraction occurs and provides vital urban and agricultural water supplies. The hydrogeological conditions that sustain such high abstraction from crystalline bedrock aquifers remain, however, poorly characterised. Five sites of intensive groundwater abstraction (multiple boreholes yielding several L s−1 or more) were investigated in Uganda and Tanzania. Analysis of aquifer properties data indicates that the sites have transmissivities of 10–1,000 m2 day−1, which is higher than generally observed in deeply weathered crystalline bedrock aquifers. At four of the five sites, weathered bedrock (saprolite) is overlain by younger superficial sediments, which provide additional storage and raise the water table within the underlying aquifer. Residence-time indicators suggest that: (1) abstracted water derives, in part, from modern recharge (within the last 10–60 years); and (2) intensive abstraction is sustained by recharge occurring over several decades. This range of encountered residence times indicates a degree of resilience to contemporary climate variability (e.g. short-term droughts), although the long-term sustainability of intensive abstractions remains uncertain. Evidence from one site in Tanzania (Makutapora) highlights the value of multi-decadal groundwater-level records in establishing the long-term viability of intensive groundwater abstraction, and demonstrates the influence of intra-decadal climate variability in determining the magnitude and frequency of recharge