Browsing by Author "Bennett, George"

Now showing 1 - 9 of 9
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    Analysis of methods used to validate remote sensing and GIS-based groundwater potential maps in the last two decades: A review
    (Elsevier BV, 2024) Bennett, George
    The integration of remote sensing data, machine learning and geographic information system in managing and analysing spatial data helps in generating maps showing groundwater potential. These maps are important tools for aiding stakeholders and decision-makers in groundwater resources to make informed decisions during groundwater development and management; to ensure the reliability of these maps, validation with the field data is conducted. This study analysed 125 scientific articles spanning the period from 2002 to 2023. The results show that around 85% of articles contain validated maps, indicating a significant number of researchers adhere to validate the remote sensing and GIS-based maps with field data, which is crucial in scientific research. However, 15% of articles contain non-validated maps. This is an alarming figure; therefore, journals should be strict in ensuring that validation is adhered to. In the reviewed articles, a total of 10 methods were used to validate groundwater potential maps using various parameters such as well yield, well/spring discharge rate, aquifer transmissivity, well specific capacity, and presence of wells/springs. This study will also add to the knowledge of selecting appropriate methods for validating remote sensing and GIS-based groundwater potential maps. The use of field data reflecting aquifer productivity is more appropriate for validation of groundwater potential maps.
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    Delineation of the aquifer structure and estimation of hydraulic properties on the flanks of Mount Meru, Northern Tanzania
    (Elsevier, 2022) Bennett, George; Camp, Marc Van; Shemsanga, Ceven; Kervyn, Matthieu; Walraevens, Kristine
    Understanding of the aquifer structure and its hydraulic properties provides comprehensive knowledge for proper groundwater utilisation and management. This study delineated the aquifer structure using litho-hydrostratigraphical cross-sections, and estimated the hydraulic parameters using single well pumping tests for various locations on and around Mount Meru. Results show that, the aquifer system on the flanks of Mount Meru is a sloping aquifer with sloping beds. On the far east of the eastern flank, the aquifer is composed of debris avalanche deposits, while on the north-eastern and west flanks the aquifer is composed of weathered fractured lava, whereas on the south-western flank, the aquifer is composed of different layers: pyroclastics on the top, weathered fractured lava, weathered pyroclastics, and weathered fractured lava at the bottom. The aquifer is semi-confined on the north-eastern and western flanks; on the north-eastern flank, the overlying debris avalanche deposits acting as an aquitard, while on the western flank, the overlying layers: pyroclastics and unweathered lava acting as an aquitard and aquiclude, respectively. The aquifer is unconfined on the far east of the eastern flank and south-western flank. The transmissivity of the aquifer on the north-eastern flank is substantially increasing with increasing depth, while variable, both at the shallow depth of hand-dug wells and the larger depth of boreholes, on the south-western flank; indicating aquifer heterogeneity. On the north-eastern flank, the topmost part of the aquifer, exploited by hand-dug wells, has a low transmissivity (T = 1.3 m2/d) and potential for smaller withdrawals for local water supply with limited consumption, while the upper part of the aquifer, captured by boreholes, has an intermediate transmissivity (T = 35 m2/d) and potential for local water supply, whereas the deeper part of the aquifer has a high transmissivity (T = 788 m2/d) with potential of somewhat regional importance. On the western flank, the aquifer has a very low transmissivity (T = 0.4 m2/d) and potential for local water supply with limited consumption. On the south-western flank, on average, the topmost part of the aquifer, exploited by hand-dug wells, has very low to intermediate transmissivity (range of T: 0.3–21 m2/d), leading to variable potential for smaller withdrawals for local water supply (private consumption), whereas the deeper part of the aquifer, captured by boreholes, has low to intermediate transmissivity (range of T: 9–43 m2/d) and potential for local water supply
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    Estimation of groundwater recharge from groundwater level fluctuations and baseflow rates around Mount Meru, Tanzania
    (Elsevier BV, 2024) Bennett, George; Shemsanga, Ceven; Kervyn, Matthieu; Walraevens, Kristine
    Estimating groundwater recharge, direct runoff and baseflow is essential for understanding groundwater resource availability and managing groundwater systems. This study estimates groundwater recharge, direct runoff and baseflow on two slopes of Mount Meru: the northern and southern slopes using the water-table fluctuation (WTF) method and baseflow separation technique. High-frequency groundwater level measurements in five shallow wells over three hydrological years from 2018 to 2021 were analysed, while streamflow data in four gauging stations over nine hydrological years from 2010 to 2019 were used. The results of the WTF method show that the aquifer undergoes an average recharge of 544 mm/year and 90 mm/year on the south-western and north-eastern slopes, respectively. On average, this recharge is about 53% and 13% of the annual rainfall on each slope. The baseflow results show that the aquifer on the south-eastern and north-western slopes recharges an average of 88 mm/year and 54 mm/year, respectively, which is on average about 12% and 7% of annual rainfall, respectively. In general, the high recharge on the south-western slope is attributed to the high rainfall, and the high hydraulic conductivity and high hydraulic diffusivity of the pyroclastic deposits compared to the debris avalanche deposits on the north-eastern slope. In addition, debris avalanche deposits show homogeneous recharge conditions, while pyroclastic deposits show heterogeneous recharge conditions. The WTF method can be useful to identify areas of preferential recharge so that preferential groundwater flow paths can be mapped for focused recharge of surface runoff during the rainy season.
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    Geogenic groundwater pollution in volcanic rock aquifer systems on the eastern, western and northern flanks of Mount Meru, Tanzania–special reference to fluoride
    (Vrije Universiteit Brussel, 2019) Bennett, George; Rombaut, Stefanie; Van Reybrouck, Jill; Shemsanga, Ceven; Kisaka, Mary; Tomašek, Ines; Fontijn, Karen; Kervyn, Matthieu; Walraevens, Kristine
    No abstract
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    Hydrochemical characterisation of high-fluoride groundwater and development of a conceptual groundwater flow model using a combined hydrogeological and hydrochemical approach on an active volcano: Mount Meru, Northern Tanzania
    (MPDI, 2021) Bennett, George; Reybrouck, Jill Van; Shemsanga, Ceven; Kisaka, Mary; Tomašek, Ines; Fontijn, Karen; Kervyn, Matthieu; Walraevens, Kristine
    This study characterises high-fluoride groundwater in the aquifer system on the flanks of Mount Meru, focusing on parts of the flanks that were only partially or not at all covered by previous research. Additionally, we analyse the impact of rainwater recharge on groundwater chemistry by monitoring spring discharges during water sampling. The results show that the main groundwater type in the study area is NaHCO3 alkaline groundwater (average pH = 7.8). High F− values were recorded: in 175 groundwater samples, the concentrations range from 0.15 to 301 mg/L (mean: 21.89 mg/L, median: 9.67 mg/L), with 91% of the samples containing F− values above the WHO health-based guideline for drinking water (1.5 mg/L), whereas 39% of the samples have Na+ concentrations above the WHO taste-based guideline of 200 mg/L. The temporal variability in F− concentrations between different seasons is due to the impact of the local groundwater recharge. We recommend that a detailed ecohydrological study should be carried out for the low-fluoride springs from the high-altitude recharge areas on the eastern and northwestern flanks of Mount Meru inside Arusha National Park. These springs are extracted for drinking purposes. An ecohydrological study is required for the management of these springs and their potential enhanced exploitation to ensure the sustainability of this water extraction practice. Another strategy for obtaining safe drinking water could be to use a large-scale filtering system to remove F− from the groundwater.
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    Hydrogeochemical characteristics of shallow groundwater in volcanic rock aquifer systems in the western and northern flanks of Mount Meru, Tanzania
    (Ghent University, 2018) Bennett, George; Walraevens, Kristine; Van Reybrouck, Jill; Segers, Laura; Shemsanga, Ceven; Kisaka, Mary; Kervyn, Matthieu; Fontijn, Karen
    .No abstract
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    Hydrogeochemical characterization of the groundwater in northern and eastern areas of Kilwa district and Songosongo Island in, Tanzania
    (Wiley, 2024) Mlay, Asantael Herman; Shemsanga, Ceven; Bennett, George; Ntalikwa, Justin
    This study aimed to investigate the hydrochemical and hydrogeochemical facies and mechanisms controlling groundwater quality from the northern and eastern parts of Kilwa district and Songosongo Island in Tanzania. Multifaceted methods were used to analyze the hydrochemical properties of water in relation to local geology and proximity to the Indian Ocean. The pH of the groundwater ranged from 5.18 to 7.56 with an average value of 6.64 which is slightly acidic. Electrical Conductivity (EC) ranged from 354 to 1429.50 μS/cm with an average value of 1652.6 μS/cm while Total Dissolved Solids (TDS) values varied from 170 to 1825 mg/L with an average value of 918.8 mg/L. The average values for Ca2+, Mg2+, Na+, and K+ were 36.9, 21.4, 152.5, and 13.31 mg/L, while for NO3−, Cl−, HCO3−, and SO42- were 2.1, 256.3, 156.6, and 45.8, respectively. The study found that groundwater closest to the ocean had elevated values of TDS, Na+, and Cl− and were more affected by seawater intrusion compared to those further inland. The dominant groundwater type was established to be Na-Cl mostly nearest to the ocean while Ca-Mg-Cl was more encountered towards the inland. The groundwater in the northern and eastern parts of Kilwa is mainly controlled by seawater intrusion and recharge water. The Neogene formations consisting of clay, silts, coastal sands, and alluvium had lower Na+, Cl−, EC, and TDS values than the Paleogene which is more influenced by marine sediments. Thus, these findings call for improved groundwater monitoring to track changes in water quality since several parameters including sodium, magnesium, chlorides, TDS, EC, and pH were higher than recommended values for drinking purposes. However, the majority of the water samples were suitable for human consumption.
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    Identification of low fluoride areas using conceptual groundwater flow model and hydrogeochemical system analysis in the aquifer system on the flanks of an active volcano: Mount Meru, Northern Tanzania
    (Elsevier, 2022) Bennett, George; Reybrouck, Jill Van; Shemsanga, Ceven; Kisaka, Mary; Tomašek, Ines; Fontijn, Karen; Kervyn, Matthieu; Walraevens, Kristine
    This study investigates the localities of low and high F− groundwaters in the aquifer system on the flanks of Mount Meru to come up with guidelines to provide groundwater that can be used for drinking water supply without health impacts on the population. Our study focuses on parts of the flanks which were only partially or not at all covered by previous research. Results show that the groundwater chemistry of F−-rich NaHCO3 alkaline groundwater in the area is controlled by dissolution of weathering aluminosilicate minerals, dissolution of F−-bearing minerals, the precipitation of carbonate minerals as secondary products and the dissolution of magmatic gases. The low F− groundwaters which can be used for drinking water supply without health impacts under the WHO limit (1.5 mg/L) are the low-fluoride springs from the high altitude recharge areas on the eastern and north-western flanks of Mount Meru inside Arusha National Park, whereas on the western flank the groundwater meets the Tanzanian limit (4.0 mg/L). On the south-western flank, the shallow aquifer composed of alluvium deposits at lower elevations, shows F− values that meet the Tanzanian limit. One of the three investigated deep boreholes on this flank also meets the Tanzanian limit, suggesting a possibility of finding relatively low F− groundwaters in the deep aquifer. Yet, in general, the deposits at lower elevations are found to contain high to very high F− values, whereas the deposits at high elevations contain groundwater of low F− values. Thus, the internal texture and grain size of geological formations, the burial depth of these formations and the water residence times are the factors determining the groundwater mineralisation and F− concentrations in the area. The study identified that the deep hydrothermal system has influence on the high F− groundwaters on the eastern and north-eastern flanks of Mount Meru.
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    Naturally occurring potentially toxic elements in groundwater from the volcanic landscape around Mount Meru, Arusha, Tanzania and their potential health hazard
    (Elsevier, 2021) Tomašek, Ines; Mouri, Hassina; Dille, Antoine; Bennett, George; Bhattacharya, Prosun; Brion, Natacha; Elskens, Marc; Fontijn, Karen; Gao, Yue; Gevera, Patrick Kirita; Ijumulana, Julian; Kisaka, Mary; Leermakers, Martine; Shemsanga, Ceven; Walraevens, Kristine; Wragg, Joanna; Kervyn, Matthieu
    The population of the semi-arid areas of the countries in the East African Rift Valley (EARV) is faced with serious problems associated with the availability and the quality of the drinking water. In these areas, the drinking water supply largely relies on groundwater characterised by elevated fluoride concentration (> 1.5 mg/L), resulting from interactions with the surrounding alkaline volcanic rocks. This geochemical anomaly is often associated with the presence of other naturally occurring potentially toxic elements (PTEs), such as As, Mo, U, V, which are known to cause adverse effects on human health. This study reports on the occurrence of such PTEs in the groundwater on the populated flanks of Mt. Meru, an active volcano situated in the EARV. Our results show that the majority of analysed PTEs (Al, As, Ba, Cd, Cr, Cu, Fe, Mn, Ni, Se, Sr, Pb, and Zn) are within the acceptable limits for drinking purpose in samples collected from wells, springs and tap systems, suggesting that there is no immediate health risk associated with these PTEs. However, some of the samples were found to exceed the WHO tolerance limit for U (> 30 μg/L) and Mo (> 70 μg/L). The sample analysis also revealed that in some of the collected samples, the concentrations of total dissolved solids, Na+ and K+ exceed the permissible limits. The concerning levels of major parameters and PTEs were found to be associated with areas covered with debris avalanche deposits on the northeast flank, and volcanic ash and alluvial deposits on the southwest flanks of the volcano. The study highlights the need to extend the range of elements monitored in the regional groundwater and make a more routine measurement of PTEs to ensure drinking water safety and effective water management measures