Detection and Delineation of Contaminant Migration using the Terrain Conductivity Technique outside the Perimeters of the Dompoase Landfill Facility in Kumasi – Ghana.

Electromagnetic conductivity survey was conducted outside the perimeters of an active municipal landfill facility located at Dompase, a suburb of Kumasi, Ghana. The study was undertaken to identify potential conductive layers probably connected with leachate communication from the landfill. The Geonics EM 34-3 terrain conductivity equipment was used as the geophysical tool for the survey. Operating in the low induction number regime, three intercoil separations of 10, 20 and 40 m were used in both the horizontal and vertical dipole configurations. The specific area of interest was the two sides of a discharge stream which carries treated effluent from the treatment ponds. Data were acquired at 10 m meter interval along sixteen east–west profiles, each of length 100 m, running approximately perpendicular to the discharge stream. There were seven and nine profiles respectively on the right and left sides of the discharge stream. The high conductivity found within the depths 30 to 60 m close to the southern boundary of the landfill might suggest leachate communication from the landfill. The linear pattern of the contour lines in that anomalous zone probably indicate the presence of zones of weakness trending approximately perpendicular to the direction of flow of the discharge stream. This weak zone could account for the lateral spread of leachate within those depths, where leachate plume has so far migrated. Keywords: Aquifer, Contamination, Leachate, Electromagnetic conductivity, Geonics EM-34-3, Horizontal dipole, Landfill, Monitoring well, Vertical dipole

2D Electrical Resistivity Tomography (ERT) Survey using the Multi-Electrode Gradient Array at the Bosumtwi Impact Crater, Ghana

The 10.5 km diameter Bosuntwi impact crater in Ghana is occupied by a lake of about 8.5 km in diameter. The multi-electrode gradient array has been used to carry out 2D electrical resistivity tomography (ERT) survey at different locations around the crater. The 2 m take-out cable of the ABEM LUND Resistivity Imaging System was modified to function as a 5 m take-out. 2D electrical resistivity survey was carried out along six (6) radial profiles running from the shore of the lake towards the crater rim. The least-square inversion technique was used to invert the topographically corrected data. The area extending from the lake shore towards the crater rim contains essentially three formations: the low resistivity regions from the shore of the lake towards uphill with resistivities < 64 W.m representing the lake sediments; the moderately high resistivity regions with values between 128 and 200 W.m interpreted as impact related breccias such as dikes, allochthonous or parautochthonous depending on their geometries; lastly, the model clearly differentiates the resistive basement metamorphic rocks of resistivities > 128 W.m from the lake sediments and the breccias due to their geometry and lateral extent. The ERT models allowed us to locate faults and fractures and also the thickness of the post impact lake sediments and the breccias. The results showed that the cables take-outs of the multi-core cable can be modified to suit the requirements of a particular survey thus highlighting the utility of this technique in impact cratering studies and geo-electrical imaging studies in general. Keywords: impact crater, target rock, electrical resistivity tomography (ERT), multi-electrode gradient array, roll-along techniqu

Groundwater Exploration using 1D and 2D Electrical Resistivity Methods

Integrated geophysical techniques involving 2D electrical resistivity imaging (ERI) and vertical electrical sounding (VES) were used to delineate groundwater potential zones for borehole siting in the Pru District of the Brong Ahafo Region of Ghana. The ABEM Terrameter LS was employed in the survey. A total of fifteen (15) 400 m - ERT profiles and thirty-one (31) VES points were investigated using the Schlumberger protocol. The Res1DINV and Res2DINV inversion software were used for data analysis. The 2D ERI images showed a lot of fractures within the subsurface of the study area. The results of the VES generally revealed either three or four subsurface geological layers at the selected points. The second and third layers were found to possess relatively low-to-moderate resistivity values indicative of potential aquifer zones. The resistivity of the fourth layer indicated the presence of slightly-fractured to fresh bedrock. The borehole logs depict four sequences: brownish or lateritic sandy clay overlying highly weathered sandstone which is underlain by moderately weathered sandstone and highly fractured sandstone basement. Keywords: Electrical resistivity tomography, vertical electrical sounding, groundwater, aquifer, geological layer and hydrogeology

West Africa's moist convective environment as observed by the Atmospheric Infrared Sounder (AIRS)

Knowledge of the seasonal positioning of the Intertropical Discontinuity (ITD) is critical to understanding seasonal moist convective processes and associated rainfall over West Africa. This study constitutes a new analysis of the seasonality of moist convection over West Africa, relative to the ITD, based on NASA's Atmospheric Infrared Sounder (AIRS) measurements from 2003 to 2018. Results show that AIRS resolves the seasonal march of the ITD, including its inherent diurnal-scale variations. AIRS captures the north–south daytime skin temperature dipole around the ITD, with greater relative temperatures to the north, especially during March–August. In the vicinity of the nighttime ITD, AIRS profiles indicate increased instability that is characteristic of nocturnal thunderstorm propagation. For seven Ghana weather stations, we show that AIRS positive moisture and equivalent potential temperature anomalies coincide with observed thunderstorm days. On these thunderstorm days, the mean latitude of the AIRS-derived ITD is displaced 3°, 0.2°, and 2° north of its DJF, MAM, and SON climatological positions, respectively, and 1.2° south in JJA. Among four common thunderstorm initiation indices considered, the K-index is determined to be most skillful. The findings of this study contribute to the Global Challenges Research Fund, African Science for Weather Information and Forecasting Techniques project's mission to build local tropical weather forecasting capacity and capabilities in West Africa

Verification of satellite and model products against a dense rain gauge network for a severe flooding event in Kumasi, Ghana

Floods as a result of severe storms cause significant impacts on lives and properties. Therefore, timely and accurate forecasts of the storms will reduce the associated risks. In this study, we look at the characteristics of a storm on 28 June, 2018 in Kumasi from a rain gauge network and satellite data, and reanalysis data. The storm claimed at least 8 lives and displaced 293 people in Kumasi, Ghana. The ability of satellite and reanalysis data to capture the temporal variations of the storm was assessed using a high temporal resolution (accumulation per minute) rain gauge data. We employed the observation data from the Dynamics–Aerosol–Chemistry–Cloud Interactions in West Africa (DACCIWA) rain gauges to assess the storm's onset, duration, and cessation. Subsequently, the performance of the ERA5 reanalysis and Global Precipitation Measurement (GPM) satellite precipitation estimates in capturing the rainfall is assessed. Both GPM and the ERA5 had difficulty reproducing the hourly pattern of the rain. However, the GPM produced variability that is similar to the observed. Generally, the region of maximum rainfall was located in the southern parts of the study domain in ERA5, while GPM placed it in the northern parts. The study contributes a verification measure to improve weather forecasting in Ghana as part of the objectives of the GCRF African Science for Weather Information and Forecasting Techniques (SWIFT) project

Advancing human nutrition without degrading land resources through modeling cropping systems in the Ethiopian highlands

Food shortage in sub-Saharan Africa is generally considered a function of limited access to food, with little thought to nutritional quality. Analyzing household production of nutrients across farming systems could be valuable in guiding the improvement of those systems. An optimization model was employed to analyze the scenario of human nutrition and cropland allocation in enset (Enset ventricosum)/root crop-based and cereal-based systems of the Ethiopian Highlands. The type and amount of nutrients produced in each system were analyzed, and an optimization model was used to analyze which cropping strategies might improve the nutritional quality of the household using existing resources. Both production systems were in food deficit, in terms of quantity and quality of nutrients, except for iron. The energy supply of resource-poor households in the enset/root crop-based system was only 75% of the recommended daily dietary allowance (RDA) of the World Health Organization (WHO), whereas resource-rich farmers were able to meet their energy, protein, zinc, and thiamine demands. Extremely high deficiency was found in zinc, calcium, vitamin A, and vitamin C, which provided only 26.5%, 34%, 1.78%, and 12%, of the RDA, respectively. The RDA could be satisfied if the land area occupied by enset, kale, and beans were expanded by about 20%, 10%, and 40%, respectively, at the expense of maize and sweet potato. The cereal-based system also had critical nutrient deficits in calcium, vitamin A, and vitamin C, which provided 30%, 2.5%, and 2% of the RDA, respectively. In the cereal system, the RDA could be fully satisfied by reducing cropland allocated to barley by about 50% and expanding the land area occupied by faba beans, kale, and enset. A shift from the cereal/root crop-dominated system to a perennial-enset dominated system would decrease soil erosion by improving the crop factor by about 45%. This shift would also have a very strong positive impact on soil fertility management. However, any policy suggestions for change in cropland allocation should be done through negotiations with households, communities, and district stakeholders

L'impact du cratère du lac Bosumtwi (l'utilisation de la tomographie de la résistivité électrique (TRE) pour tracer la carte géométrique de la paroi internet du cr&tère et de l'impact associé à la structure)

Des mesures de résistivité électrique et des campagnes d observations géologiques ont été menées pour cartographier le contact sédiment/roche basale ainsi que les structures d impact associées au cratère d impact Bosumtwi datant de 1,07 millions d années. Le cratère de 10,5 km de diamètre s est formé dans des roches métamorphiques du Précambrien (2,1 à 2,2 milliard d années), d origine sédimentaire et volcanique. Il est actuellement rempli par le lac Bosumtwi de 8,5 km de diamètre. Ce cratère est la source des tektites et microtektites dispersées jusqu en Côte d Ivoire et au large des côtes ouest africaine. La campagne de mesures éophysiques consiste en 16 tomographies de résistivité électrique effectuées radialement des rives du lac vers les bords du cratère d impact. Chaque profil utilise un système d acquisition multi électrodes avec une distance minimum entre les électrodes de 5 m. Les données ont été corrigées des effets topographiques et inversées en utilisant le programme commercial d inversion Res2DInv, avec la norme L1 considérée plus robuste. La zone comprise entre les rives du lac et le bord externe du cratère de divise en trois formations géologiques principales. Les régions de faibles résistivités ( 128 .m) représentent les roches métamorphiques sous-jacentes, d origine volcanique ou sédimentaire. Les profils de résistivités permettent de retrouver la géométrie et l extension latérale de ces trois types de roches. Une correspondance directe entre la lithologie observée en surface et les structures mises en évidence par les mesures de résistivité électrique dans le sous-sol est observée à Dwamam au Sud-Est dulac. À Dwamam, les sédiments sont environ à 200 m de la rive du lac et s étendent environ sur 400 m vers les les bords du cratère, à la différence des autres zones où ont pu être cartographiés les sédiments. La topographie du contact sédiment/roche basale présente une direction particulière NE-SO avec un pendage variant entre 16 degrés au NE et 36 degrés au SO. Une majorité de fractures ont été remarquées dans le SO, remplies par des clasts et des brèches d impacts. Les failles sont surtout présentent à l Ouest du lac. En moyenne elles présentent un pendage variant entre 60o à l Est et 80 degrés à l Ouest du cratère. Des analyses statistiques ont été effectuées sur les directions et les pendages des failles selon les loi de von Mises et Fisher. Elles démontrent que les failles s alignent préférentiellement le long de deux directions principales. L analyse cumulée de la surface de contact sédiment/roche, des failles et de la localisation du champ de dispersion des tektites indique que le bolide d environ 0,8 à 1 km de diamètre responsable du cratère est arrivé du NE. Les résultats démontrent que les panneaux de résistivité électrique fournissent des informations utiles pour l étude des cratères d impact.Electrical resistivity tomography (ERT) and geological field surveys have been used to map the sediment/bedrock contact and impact related structures of the 1.07 Myr old Bosumtwi impact crater. The 10.5 km complex crater excavated in 2.1 2.2 Gyr Precambrian metasedimentary and metavolcanic rocks is filled by the 8.5 km Lake Bosumtwi. It is the source crater of the tektites and microtektites of the Ivory Coast strewn field. Electrical resistivity survey was carried out sixteen (16) profiles running from the shore of the lake towards the rim of the crater. The multi-electrode gradient array method with minimum electrode separation of 5 m was used. The data were corrected for topography and inverted using the L1 norm (robust inversion) techniqueof the Res2DInv software. The area extending from the lake shore towards the crater rim contains essentially three formations. The low resistivity regions ( 128 .m) fromthe lake sediments and the breccias due to their geometry and lateral extent. Also observed was a direct correspondence between the lithology on the surface and the subsurface resistivity structures at Dwamam in the southeast section of the lake. At Dwamam, the sediments were about 200 m away from the shore and stretch about 400 m towards the crater rim unlike in other areas where the sediments were mapped from the shore. The gradient of the sediments/bedrock contact showsa symmetry in the NE SW direction and dips between the lowest of 16 degrees in the NE to the highest 36 degrees in the SW. Majority of the fractures marked were in the southwest and were filled with clasts or impact breccia matrix. The faults were mostly delineated in the west. Averagely, the dips of the faults are about 60 degrees and 80 degrees for the east and west sections of the crater respectively. The dips of the faults were statistically treated using the von Mises and Fisher statistics, it was found that the faults have a preferred direction and it is possible to determine at least two different orientations. Theanalysis of the results of the sediments/bedrock surface and the faults combined with the location of the tektite strewn field indicate that the about 0.8 1 km bolide that created the complex crater came from the NE. The findings have shown that the ERT is efficient and a useful tool in impact cratering science research.PARIS11-SCD-Bib. électronique (914719901) / SudocSudocFranceF

Underrepresentation of Local Researchers in Geophysical Studies at the Bosumtwi Impact Crater: Insights from A Systematic Review

Impact cratering is an important aspect of planetary evolution. Geophysics plays a complementary role in identifying impact craters on Earth given the non-unique geological characteristics associated with such craters. The Bosumtwi impact crater in Ghana represents one of the world's most well-preserved and young mid-sized impact craters, and this study aims to evaluate the current state of geophysical research conducted in this area. The Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) technique was employed for data collection and analysis, which involved identifying and screening relevant sources of data. Results indicated that the maximum number of publications (14) on the Bosumtwi impact crater was recorded in 2007, with 15% of these articles being affiliated with Ghanaian institutions. Furthermore, only two articles reported funding from Ghana. The major geophysical methods applied in studies of the Bosumtwi impact crater include various techniques that have confirmed the presence of shock-metamorphosed rocks. Although geophysical methods cannot provide unambiguous evidence for an impact origin of the Bosumtwi crater, they did provide additional constraints in establishing its impact origin. This study highlights the lack of local financial support for research in Ghana and African countries in general, with the underrepresentation of Ghanaian geophysical researchers being a concerning outcome. The absence of hazard studies such as the creation of unstable cliffs and the long-term effects of the meteorite impact on inhabitants of the Bosumtwi impact crater is particularly significant. Further research is necessary to fully understand the implications of this underrepresentation. Moreover, this study highlights the importance of research at the Bosumtwi impact crater for achieving the UN Sustainable Development Goals