Volta Basin Research Articles

Pan-African Paleostresses and Reactivation of the Eburnean Basement Complex in Southeast Ghana (West Africa)

This faulting tectonics analysis concerns the southernmost segment of the Dahomeyide Orogen and the West-African craton eastern margin in southeast Ghana. The analysis of strike-slip faults in the frontal units of the Dahomeyide Belt indicates that four distinct compressive events (NE-SW, ENE-WSW to E-W, ESE-WNW to SE-NW and SE-NW to SSE-NNW) originated the juxtaposition of the Pan-African Mobile Zone and the West-African craton. These paleostress systems define a clockwise rotation of the compressional axis during the structuring of the Dahomeyide Orogen (650–550 Ma). The SE-NW and SSE-NNW to N-S compressional axes in the cratonic domain and its cover (Volta Basin) suggest that the reactivation of the eastern edge of the West African craton is coeval with the last stages of the Pan-African tectogenesis in southeast Ghana. An extensional episode expressed as late normal faulting is also recorded in this study. This E-W to SE-NW extension, which is particular to the southernmost part of the Dahomeyide Belt, appears to be post-Pan-African. This extension probably contributed to the formation of a major Jurassic rifting zone that originated the Central Atlantic and the Benue Trough.

Groundwater level monitoring and recharge estimation in the White Volta River basin of Ghana

Recharge quantification is an important pre-requisite for effectively managing groundwater resources as recharge estimates are needed to determine sustainable yields of groundwater aquifers for rational and sustainable exploitation of the resource. In this study, the water table fluctuation method has been applied in the White Volta River basin of Ghana (approx. 46,000km2) to estimate seasonal fluctuations in groundwater levels in the basin and subsequently to estimate recharge to the groundwater for the 2006 and 2007 water years. Results show high seasonal and spatial variability in the water level, with a range of 1240–5000mm in 2006, and 1600–6800mm in 2007. Seasonal rainfall was found to be the main source of recharge to the aquifers in the basin as water level rise occurred only in the rainfall season. Recharge to groundwater in the White Volta basin was estimated to vary between 2.5% and 16.5% of the mean annual rainfall, with a mean recharge of 7–8%.

Joint climate–hydrology modeling: an impact study for the data-sparse environment of the Volta Basin in West Africa

The Volta Basin in West Africa is a region sensitive to water shortage. Future climate conditions therefore may put additional stress on the competition for the scarce water resources between industry, agriculture, and households. For an investigation of the sensitivity of the hydrological regime to global climate change in the data-sparse and poorly gauged region of the Volta Basin, joint regional climate–hydrology simulations were performed. MM5 was used as a regional climate model to downscale two time slices of a global ECHAM4 simulation to a resolution of 9 km. These regional climate simulations were used to drive a physically based, distributed hydrological model at 1 km resolution. The performance of the model components and the joint model system was evaluated for different historical periods. Results show that discharge in the Volta Basin reacts highly sensitively to precipitation differences. The pronounced rainfall decrease at the beginning of the rainy season is not transferred to discharge changes. During the rainy season most of the surplus rainfall evaporates due to a strong increase in evaporation as a consequence of higher near-surface air temperatures. The average change signal in precipitation, as well as surface and subsurface hydrology variables, lies in most variables within the range of inter-annual variability, but regionally stronger signals are also observed.

Multi-pronged assessment of land degradation in West Africa to assess the importance of atmospheric fertilization in masking the processes involved

Separating human-induced land degradation from that caused by natural processes in the world of global climate and atmospheric change is a challenging task, but important for developing mitigation strategies. Current remote-sensing data and spatio-temporal analyses allow the distinction of climate and human-induced land degradation on a sub-continental scale, but the underlying processes cannot be discerned at this scale. This study is conducted at a river-basin scale to (1) identify land degradation hotspots in a basin or sub-basin, and (2) assess the correspondence and divergence of land degradation assessed by NDVI shifts with and without accounting for atmospheric fertilization with that based on soil erosion assessment at a sub-basin scale. Long-term remote sensing (NDVI) and rainfall data were used to identify human-induced land degradation hotspot areas in the Volta basin. The results were compared with the critical zone of soil loss in the White Volta sub-basin derived from a spatially distributed soil erosion model, validated by field-measured data. A spatial comparison of the above studies revealed that the biomass productivity (NDVI)-based land degradation assessment grossly underestimated the extent to which soil is being lost, unless a correction was included to account for atmospheric fertilization. Based on inter-annual NDVI signals land degradation was evident in about 8% of the Volta basin's landmass, but when accounting for atmospheric fertilization, as much as 65% of the land is losing some of its vital attributes such as soil quality or vegetation productivity. The study demonstrates the need for using a multi-pronged assessment strategy in land degradation assessment that offers an insight of the processes involved in land degradation.

Cooperation in Transboundary Water Sharing with Issue Linkage: Game-Theoretical Case Study in the Volta Basin

AbstractThis paper investigates issue linkage of water and energy in transboundary water sharing agreements and evaluates how such issue linkages can enhance the scope of cooperation between upstream and downstream countries. In a case study on transboundary water sharing between Burkina Faso and Ghana, the main upstream and downstream riparians in the Volta Basin, the paper evaluates both the scope and sustainability of such cooperation based on issue linkage. In the framework of a static Stackelberg game with numerical analysis, it is found that the interdependency of countries can lead to efficient and effective solutions regarding water sharing. In the cooperation phase, Ghana has the opportunity to increase its water consumption for agriculture, which is currently restricted, while Burkina Faso benefits from discounted hydropower as a compensation for restricting its water consumption. In such a case, the cooperation is mutually beneficial and stable. However, such interdependency may not be sustaina...

Imams of Gonja

AbstractThe Kamaghate lineage which claims to belong to the Diakhanke tradition of Haji Salim Souaré and the Soninke clerical lineage of Diaby-Gassama has held the imamate in Begho and expanded with the Gonja into the Western Volta basin. Its roots can be followed to centres of Islamic diaspora such as Djenne, Odienne, Samatiguila, Tiemé, Kong, Bouna and Bondoukou. It forms part of an Eastern Diakhanke branch which has introduced Islam into the Volta Basin, the Kamaghate being the principal actors in the western half, while the Baghayogho have established themselves more in the eastern half, among the Mole-Dagbane speakers. Islamic missionary efforts can thus be shown to be well organized by African muslims, in establishing specialist “maraboutic” lineages and attributing them exclusive spheres for the purpose of converting the non-Moslem populations of the Sahel and savannah regions, and even gaining influence as court advisors in the kingdoms of the forest zone. Thus the Kamaghate also hold the imamate for all Muslims at the Ashanti capital, while a special karamoko serves the court alone.

The 2007 flood in the Sahel: causes, characteristics and its presentation in the media and FEWS NET

Abstract. During the rainy season in 2007, reports about exceptional rains and floodings in the Sahel were published in the media, especially in August and September. Institutions and organizations like the World Food Programme (WFP) and FEWS NET put the events on the agenda and released alerts and requested help. The partly controversial picture was that most of the Sahel faced a crisis caused by widespread floodings. Our study shows that the rainy season in 2007 was exceptional with regard to rainfall amount and return periods. In many areas the event had a return period between 1 and 50 yr with high spatial heterogeneity, with the exception of the Upper Volta basin, which yielded return periods of up to 1200 yr. Despite the strong rainfall, the interpretation of satellite images show that the floods were mainly confined to lakes and river beds. However, the study also proves the difficulties in assessing the meteorological processes and the demarcation of flooded areas in satellite images without ground truthing. These facts and the somewhat vague and controversial reports in the media and FEWS NET demonstrate that it is crucial to thoroughly analyze such events at a regional and local scale involving the local population.

Geochronology of granitoid and metasedimentary rocks from Togo and Benin, West Africa: Comparisons with NE Brazil

The westernmost part of the Pan-African (c. 600Ma) Dahomeyide orogen in Togo and Benin consists of a complex stack of thrust sheets, mainly composed of Palaeoproterozoic (‘Eburnean’, c. 2000Ma) granitoid rocks and younger volcanic and metasedimentary successions. This thrust stack comprises the suture between the West-African craton and the Benino-Nigerian province to the east. This eastern province consists largely of migmatites, supracrustals and granitoid rocks. Rb–Sr and Sm–Nd isotope data for four granites from the western domain confirm the Palaeoproterozoic age of these rocks found by earlier studies. One of these granites yielded a zircon U–Pb age of c. 2060Ma. Twenty samples from the eastern region yield Rb–Sr and Sm–Nd data indicating that both migmatites and granitoid rocks are of Neoproterozoic (Pan-African) age. Zircon U–Pb data on six of these samples yielded ages ranging from c. 650 to c. 550Ma. Suggestions that parts of the migmatites might be of Eburnean age could not be confirmed. The Neoproterozoic granitoid rocks may represent a Pan-African arc overlying an eastward dipping subduction zone, and Sm–Nd data indicate that they contain significant proportions of older crustal material. Age probability diagrams for detrital zircons from three metasedimentary rocks (one from Nigeria) and one S-type quartz diorite from the eastern region show prominent peaks at c. 1900Ma and 2400–2200Ma. A provenance of the zircons from sources in the Borborema province in NE Brazil or lateral equivalents thereof is suggested. A few Neoproterozoic zircons are present in three of the samples. On the basis of Th/U ratios a distinction can be made between Neoproterozoic zircons of metamorphic and detrital origin. The zircon age probability diagram of a quartzite from northern Benin exhibits one peak, at c.1900Ma, different from the other metasedimentary samples. This quartzite might be correlated with sedimentary strata of the Volta basin that overlie the Eburnean basement in Ghana, Togo and Burkina Faso. Correlation of the rocks in the study area with those in the Borborema province is discussed.

Analysis of some hydrological parameters of the Nasia River Catchment in the Northern Region of Ghana for its socio-economic development

The Nasia River is the drainage basin of the left bank tributary of the White Volta located in the Northern Region of Ghana. Most years, rivers in the White Volta basin flow only three or four months, causing seasonal deficits across the region. This research therefore studies the hydrology of the Nasia River Basin and the catchment’s conditions so as to determine the potentials for irrigation development. Thirty years of daily river flows and climatic data for Nasia River were obtained from Hydrological Services Department and the Regional Meteorological Agency at Tamale. Soils and geological information about the basin were obtained, whilst topographic maps with scale of 1:50,000 were acquired from the Regional Survey Department at Tamale for the determination of the catchment characteristics. The results obtained in the study suggested that the Nasia river basin has enough surface water resources which could be harnessed for irrigation and other socio-economic development of the area. The seasonal variation in the runoff yield is influenced by the catchment’s physical characteristics. Optimum flow parameters for hydrological design purposes indicate that the guaranteed yield which is exceeded 95% of the time is 0.0438 m3/s, whilst the characteristic drought at 63% exceedance is 0.40 m3/s. Key words: Catchment, hydrology, Nasia River, water balance.

Meteorological characteristics and potential causes of the 2007 flood in sub‐Saharan Africa

AbstractIn August and September 2007 media and aid organizations reported on a severe flood in large parts of sub‐Saharan Africa caused by a sequence of extreme rain events. However, the reporting was partly controversial and much was speculated about how unusual the flood event was. Here, we analyse various observational data sets in order to assess and to compare the spatio‐temporal characteristics and intensity of the flood and the associated rain events. The return times are estimated from daily precipitation time series at fine spatial resolution, and the potential causes are disclosed in a global and regional context.Satellite data reveal that the flood was not large scale but confined to the main river basins in sub‐Saharan West Africa. Nonetheless, abundant rainfall prevailed over large parts of Western Africa extending north into the Western Sahara, particularly during the second half of August and the beginning of September 2007. In detail, various precipitation data sets differ considerably in terms of the monthly anomalies, demonstrating the difficulty to delineate meteorological extreme events even at a sub‐continental scale and during the most recent past. Return times typically range between 1 and 50 years with high spatial heterogeneity but amount to 1200 years in the regional mean over the Upper Volta Basin. Among the potential causes we identify a La Niña event in the tropical Pacific, anomalous heating in the tropical Atlantic coming along with a greater depth of the monsoonal westerlies, and enhanced activity of African easterly waves, both evident in 2–6 day zonal wind and outgoing longwave radiation variance anomalies. Copyright © 2010 Royal Meteorological Society

A survey of female genital schistosomiasis of the lower reproductive tract in the volta basin of Ghana

To determine the prevalence of female genital schistosomiasis in riparian communities in the Volta basin of Ghana, The study was a cross-sectional study conducted among women 15-49 years in the Volta Basin. Urinary schistosomiasis prevalence was determined using microscopy. A structured questionnaire was also administered to collect information on the demography, obstetric history and reproductive health experiences. Cervical punch biopsy was collected from women who consented to be screened for FGS. Descriptive statistics was used to determine frequency of occurrence, chi squared and logistic regression to identify associated variables Urinary schistosomiasis prevalence among the women was 24.8% while 10.6% of them diagnosed with FGS. More FGS diagnosed women (57.7%, p value =0.04%) were observed to report copious discharge, vaginal itch (80.8%, p=0.042) and lower abdominal pain (66.7%, p= 0.041) compared to FGS negative women. The predominant abnormal observation of the lower genital tract made was erythematous cervix (18.8%). The study confirms the reproductive health symptoms associated with FGS and recommends awareness creation on FGS among women in endemic communities to facilitate early treatment.

CLIMATE CHANGE AND COOPERATION IN TRANSBOUNDARY WATER SHARING: AN APPLICATION OF STOCHASTIC STACKELBERG DIFFERENTIAL GAMES IN VOLTA RIVER BASIN

Abstract As multiple countries share a river, the likelihood of conflicts over distributing water resources increases, particularly under the effects of climate change. In this paper, we demonstrate how countries can cooperate in sustainable transboundary water sharing under such conditions. We examine the case of water distribution in the Volta Basin of West Africa between the upstream country, Burkina Faso, and the downstream country, Ghana. The latter faces an additional tradeoff between the production of hydropower in the south, close to the outlet of the basin, and agricultural water use in the reservoir’s catchment area in the north. In the framework of a stochastic Stackelberg differential game, we show how sustainable water‐sharing agreements can be achieved by linking transboundary flows to hydropower exports. Our results indicate that, through cooperation, Ghana will have an opportunity to increase its water abstraction for agriculture, which has remained largely restricted. We also find that the equilibrium strategies for the long‐run distribution are stable even with increasing variances of water flow.

Validation of TRMM Data in the Black Volta Basin of Ghana

AbstractThis study was conducted in the Black Volta basin, Ghana, to determine how Tropical Rainfall Measuring Mission (TRMM) satellite-derived rainfall compares with ground-measured values and the possibility of using it to complement ground-measured rainfall. Bilinear interpolation was used to resample 0.25°×0.25° TRMM 3B42V6 monthly rainfall grids to determine site-specific rainfall of the basin based on rain gauge locations and analyzed statistically. The study showed that the correlation between the monthly datasets ranged from 0.73 to 0.88. A plot of the average monthly data of all the stations gave a correlation coefficient (R) of 0.94. The overall catchment rainfall was well represented by TRMM data. However, the annual station rainfalls were either underestimated or overestimated. The underestimations and overestimations were mostly below 20% and 10%, respectively, of the raingauge measurements. Although the TRMM rainfall data did not perfectly match with the ground measurements, it can still be ...

Earth and shadow: substance, medicine and mobility in the history of Ghana's Tongnaab shrines

Shrines associated with the deity Tongnaab in the Talensi region of northern Ghana formed the centre of a precolonial regional cult that encompassed a variety of peoples in the savannas of the Volta basin. Despite attempts by the British colonial state to destroy the shrines and to suppress ritual activity in the Tong Hills, by the 1920s the cult was spreading beyond its heartland into the Akan forest and the Gold Coast to the south. There it became known as Nana Tongo, one of a wave of anti-witchcraft healing movements. This paper examines the material culture and the mechanics of this history of ritual mobility and metamorphosis. It reflects upon the connection between the metaphysical concept of ‘shadow’ and the physical substance of earth, both of which were transported in a portable shrine called a bo’artyii and used to empower satellite medicine shrines. As these items traversed cultural frontiers they were subject to local reinterpretation and transformation.

New sedimentological and biostratigraphic data in the Kwahu Group (Meso- to Neo-Proterozoic), southern margin of the Volta Basin, Ghana: Stratigraphic constraints and implications on regional lithostratigraphic correlations

Since several decades, geologists disagree about the lithostratigraphic subdivision of the Volta Basin sedimentary infilling. Correlations at the scale of the Volta Basin were up to now largely limited by the discontinuity of outcrops along the basin margin and by the scarcity of stratigraphic constraints within the sedimentary succession. Even if a subdivision of the Volta Basin infilling into three main groups (Bombouaka, Oti, and Obosum Groups) is now generally accepted, there is no agreement for lithostratigraphic subdivision at the formation scale. The Bombouaka Group, which represents first deposits of the Volta Basin sedimentary infilling, is particularly concerned. During mapping project in Ghana, authors proceeded to a sedimentological study of the Kwahu Group deposits on the Kwahu Plateau area. Some samples collected during field mapping were analyzed on a palynological point of view and revealed several layers rich in palynomorphs (acritarchs). Siliciclastic sediments composing the Kwahu Group are distinguished in 12 main facies associations, which are interpreted to be representative of both marine and continental environments. Sedimentological study of these facies associations leads to identify a cyclic vertical evolution of depositional settings at different scales, which are interpreted as sequences. The Kwahu Group is thus composed of three distinct macrosequences (about 300–500 m thick) interpreted as deltaic progradational sequences. Each macrosequence has been used to define formations for mapping, sequence stratigraphy key surfaces being considered as limits for cartographic units. The acritarch content of the analyzed samples allows rather coarse but nonetheless useful biostratigraphic constraints which, in association with data from sedimentological and sequential analysis, are used to improve correlations into the Bombouaka and Kwahu Groups at the scale of the Volta basin. The present data complemented with the few recently published studies on Voltaian deposits, lead to a new regional lithostratigraphic synthesis of the Bombouaka and Kwahu Groups, based on stratigraphic constrains and sequence stratigraphy.

Poverty in small-scale fisheries

Using a new framework combining vulnerability and exclusion as two central dimensions of poverty, this article revisits some of the long-standing beliefs about poverty in small-scale fisheries. We argue that the issue of poverty in fish-dependent communities cannot be reduced to a simple correlation between income poverty and fishery dependence. A more thorough analysis is required that must account for the diversity of fishing-related livelihoods and the complexity of causes of poverty, both inside and outside the sector. The article highlights how poverty in fishing communities often relates to a wide range of socio-institutional factors other than income, including landownership, debt, access to health, education and financial capital, and marginalisation from political decision making. The empirical examples used in this article refer to inland capture fisheries from the Volta and Mekong basins but, arguably, the analysis applies to other fisheries (inland and coastal) in developing countries.

Levels of Total Mercury in Different Fish Species and Sediments from the Upper Volta Basin at Yeji in Ghana

In this study, total mercury concentrations were determined in sediments and seven different fish species from the Upper Volta Basin area of Yeji in Ghana. Mercury concentrations found ranged from 44.17 to 85.88ng/g wet weight for Synodontis gambiesis, from 11.25 to 79.73ng/g wet weight for Synodontis membranaceus, from 13.11 to 38.64ng/g wet weight for Synodontis ocellifer, from 16.39 to 25.82ng/g wet weight for Distishodus rotratus, from 40.80 to 90.30ng/g wet weight for Bagrus docmac, from 10.48 to 61.90ng/g wet weight for Chrysichthys nigrodigitatus and from 12.33 to 24.18ng/g wet weight for Gnathoneus senegalensis. These values are below the 500ng/g guideline recommended by the WHO/FAO, implying that fish from the Upper Volta Basin area of Yeji are safe for human consumption. Good correlation was observed between mercury concentration and fresh weight (R(2)=0.6067) and total length (R(2)=0.8754) for Gnathonemus senegalensis. However, poor correlations were observed between mercury concentration and fresh weight and total length for the other six species. Mercury in sediments ranged from 11.87 to 70.25ng/g dry weights with a mean of 41.60ng/g dry weight being below the IAEA threshold of 810ng/g.. These values show that sections of the Upper Volta River remain relatively clean in spite of substantial loadings of mercury into the river's basin from gold mining activities.

Spatial and temporal variation in population genetic structure of wild Nile tilapia (Oreochromis niloticus) across Africa

BackgroundReconstructing the evolutionary history of a species is challenging. It often depends not only on the past biogeographic and climatic events but also the contemporary and ecological factors, such as current connectivity and habitat heterogeneity. In fact, these factors might interact with each other and shape the current species distribution. However, to what extent the current population genetic structure reflects the past and the contemporary factors is largely unknown. Here we investigated spatio-temporal genetic structures of Nile tilapia (Oreochromis niloticus) populations, across their natural distribution in Africa. While its large biogeographic distribution can cause genetic differentiation at the paleo-biogeographic scales, its restricted dispersal capacity might induce a strong genetic structure at micro-geographic scales.ResultsUsing nine microsatellite loci and 350 samples from ten natural populations, we found the highest genetic differentiation among the three ichthyofaunal provinces and regions (Ethiopian, Nilotic and Sudano-Sahelian) (RST = 0.38 - 0.69). This result suggests the predominant effect of paleo-geographic events at macro-geographic scale. In addition, intermediate divergences were found between rivers and lakes within the regions, presumably reflecting relatively recent interruptions of gene flow between hydrographic basins (RST = 0.24 - 0.32). The lowest differentiations were observed among connected populations within a basin (RST = 0.015 in the Volta basin). Comparison of temporal sample series revealed subtle changes in the gene pools in a few generations (F = 0 - 0.053). The estimated effective population sizes were 23 - 143 and the estimated migration rate was moderate (m ~ 0.094 - 0.097) in the Volta populations.ConclusionsThis study revealed clear hierarchical patterns of the population genetic structuring of O. niloticus in Africa. The effects of paleo-geographic and climatic events were predominant at macro-geographic scale, and the significant effect of geographic connectivity was detected at micro-geographic scale. The estimated effective population size, the moderate level of dispersal and the rapid temporal change in genetic composition might reflect a potential effect of life history strategy on population dynamics. This hypothesis deserves further investigation. The dynamic pattern revealed at micro-geographic and temporal scales appears important from a genetic resource management as well as from a biodiversity conservation point of view.

Farming systems and food production in the Volta Basin

The predominantly rural population in the Volta Basin depends on rainfed crops, a practice which becomes increasingly risky as the rainfall decreases from south to north and rural poverty increases. Yields are low throughout because of drought and dry spells within the growing season, infertile soils, low inputs, poor infrastructure, and low labour productivity. Water-related diseases are widespread and half of all rural households depend on low-quality water. Fertilizer and small-scale irrigation can improve the yields of rainfed crops and alleviate poverty, but the duality between the legal state and the traditional hierarchy complicates land tenure by hindering investment. Small-scale irrigation has little effect on hydropower dams downstream.

Optimal Allocation of Flows (Water) Within the Volta Basin System of Ghana

In this paper, a hypothetical network is proposed for the Volta Basin System (V.B.S) using the optimization technique for obtaining corresponding optimal allocation of flows from runoffs in the sub-basins (source) to the sink (Akosombo reservoir). Maximum flow paths and their capacities with consumptive and non-consumptive flows were identified. We are able to determine the optimal withdrawals on these flows for either consumptive or non-consumptive use.Keywords: Network, sub-basins, sources and sinks, consumptive and non-consumptive flows, optimal allocation