Volta Basin Research Articles

Lithostratigraphy, sedimentation and evolution of the Volta Basin in Ghana

We present a revised lithostratigraphy for the Voltaian Supergroup of Ghana, based on a review of existing literature, interpretations of remotely sensed data and reconnaissance field survey of the Volta Basin. These strata thicken eastwards, to a maximum of between 5 and 6 km adjacent to the Pan-African Dahomeyide orogen. They began to accumulate some time after about 1000 Ma, along the margin of an epicontinental sea. Initial sedimentation, comprising the age-equivalent Kwahu and Bombouaka Groups, shows a cyclical mode of deposition controlled by eustatic changes in sea-level that produced a range of nearshore marine, littoral and terrestrial environments. A major erosional interval was followed by deposition of the 3–4 km thick Oti-Pendjari Group. Basal tillites and associated sandy diamictons are correlated with the Marinoan (end-Cryogenian) glaciation, indicating a maximum depositional age of about 635 Ma. The overlying cap carbonates and tuffs were deposited within a shallow epeiric sea bordered by a volcanically active rift system. The main part of the group records the transition from a rifted passive margin to a fully developed foreland basin receiving marine flysch in the form of argillaceous strata interbedded with highly immature wacke-type sandstones and conglomerates. Maximum accommodation space was developed within a foredeep adjacent to the Dahomeyide belt. Towards the end of the orogenic phase, the foredeep succession became partially inverted and then was buried under coarse terrestrial, red-bed molasse of the Obosum Group.

Palaeomagnetism of neoproterozoic formations in the volta basin

The Volta basin lies on the southern part of the West African craton, more precisely on the Leo (or Man) craton. The Dahomeyides chain is thrust onto its eastern fringe. The Volta basin is filled with Neoproterozoic to Cambro- Ordovician sediments. From bottom to top they are: the Boumbouaka Supergroup made of sandstone, micro-conglomerates, siltstones, shales and limestone lenses; the Pendjari or Oti Supergroup composed of a triad made of a diamictite, a cap carbonate and a silexitic complex that passes upwards to siltstones and shales; the Tamale Supergroup representing the molasse of the Dahomeyides chain. The three supergroups were sampled for palaeomagnetic study. The magnetic mineralogical study shows magnetite and hematite as carriers of magnetization. Mean palaeomagnetic directions are calculated on the high temperature components and yield a mean palaeopole, Plon=349.3°, Plat=44.1°, dp=26.6°, dm=33.7°, for formations with ages between 993±62 Ma and 660±9 Ma and a mean palaeopole, Plon=119.5°, Plat=71.2°, dp=19.8°, dm=38.1°, for sites dated between 635 Ma and 600 Ma which are, respectively, the ages of the marinoan glaciations in Volta basin and the Pan-African deformation, responsible of the Dahomeyides chain. The palaeolatitudes of the older formations about 44.9° S and that of the younger sites about 9.1° S show a migration of the West African craton from medium to low latitude during the Neoproterozoic, in conformity with the Snowball Earth hypothesis. KEYWORDS: West African craton, Volta basin, Virtual Geomagnetic Pole, Palaeolatitude, Snowball Earth

Climate Change Impact on Water Resources at the Transboundary Level in West Africa: The Cases of the Senegal, Niger and Volta Basins

The series of droughts of the past three decades that affected the Sudano-Sahelian zone of West Africa, particu- larly Niger, Volta and Senegal basins impacted the water resources, ecosystems and the fragile economies of at least 13 of the 16 countries of the region. Declining rainfall, highly variable in time and space has resulted in more than proportionate decrease in river discharges, and declining level of freshwater bodies. This situation translated into falling groundwater levels and accelerated desertification process, hence major crises of food insecurity and massive migration, which often leads to conflicts. The challenges and uncertainties associated with the impacts of future climate changes on water re- sources in West Africa are further compounded by many other factors, including regional demographic factors, non- existing or inadequate water policies, inefficient management strategies and lack of reliable and adequate data. This paper synthesizes the state of art research regarding climate change impact on water resources in West Africa economies of Senegal, Niger and Volta Basins while also making prescriptions on what can be done in terms of adaptation strategies, rather than mitigation, to reduce the severity of the expected impacts on the already stressed and poverty-stricken econo- mies of West Africa,

Laser Raman micro-spectroscopy of Proterozoic and Palaeozoic organic-walled microfossils (acritarchs and prasinophytes) from the Ghadamis Basin, Libya and Volta Basin, Ghana

Laser Raman microspectroscopy was used as a microchemical analysis technique to characterize the wall chemistry of organic-walled microfossils (acritarchs and prasinophytes) extracted from Proterozoic (Tonian: ca. 900 Myr) and early Palaeozoic (Silurian: ca. 420 Myr) marine sediments in the Volta Basin of Ghana, and the Ghadamis Basin of Libya, respectively. Raman spectra of Proterozoic acritarchs show spectral features characteristic of kerogenous compounds at ~1350 and ~1600 cm−1, consistently with previously published reports. In addition, spectra from prasinophyte algae from the Silurian sample also show an interesting spectral feature at ~1707 cm−1indicative of carbonyl moieties.Broadly speaking, shape and position of Raman bands appear to depend on the nature of the specimen considered, suggesting that laser micro-Raman analysis can potentially be used to establish phylogenetic relationships (high-rank taxonomy) among the main groups of pre-Cambrian to Palaeozoic palynomorphs.

Laser Raman micro-spectroscopy of Proterozoic and Palaeozoic organic-walled microfossils (acritarchs and prasinophytes) from the Ghadamis Basin, Libya and Volta Basin, Ghana

Laser Raman microspectroscopy was used as a microchemical analysis technique to characterize the wall chem- istry of organic-walled microfossils (acritarchs and prasinophytes) extracted from Proterozoic (Tonian: ca. 900 Myr) and early Palaeozoic (Silurian: ca. 420 Myr) marine sediments in the Volta Basin of Ghana, and the Ghadamis Basin of Libya, re- spectively. Raman spectra of Proterozoic acritarchs show spectral features characteristic of kerogenous compounds at ∼1350 and ∼1600 cm −1 , consistently with previously published reports. In addition, spectra from prasinophyte algae from the Silurian sample also show an interesting spectral feature at ∼1707 cm −1 indicative of carbonyl moieties. Broadly speaking, shape and position of Raman bands appear to depend on the nature of the specimen considered, suggesting that laser micro-Raman analysis can potentially be used to establish phylogenetic relationships (high-rank taxonomy) among the main groups of pre-Cambrian to Palaeozoic palynomorphs.

Productivity of irrigation technologies in the White Volta basin

Parts of the White Volta basin in northern Ghana and southern Burkina Faso have witnessed a spectacular rise of irrigated agriculture since about 2000, largely without government support, and seems to have been triggered by a strong and growing demand for vegetables, notably tomatoes in the urban centres of southern Ghana. It is interesting to note the variety of different irrigation technologies that individual and groups of smallholder farmers adopted, adapted and implemented. Some technologies are well-known, such as those associated with conventional sources of water like small and large reservoirs; others have been rarely described in literature, such as temporal shallow wells and alluvial dugouts. This paper describes and characterises these different irrigation technologies and conducts a comparative analysis of their productivities, in terms of crop yield, water use and financial returns. The study was conducted in three neighbouring and transboundary watersheds (Anayari, Atankwidi and Yarigatanga) located in the Upper East Region of Ghana and southern Burkina Faso. For the study, 90 tomato farmers with different irrigation technologies were surveyed during one crop season (2007/2008). The results show that adequate fertilizer application is the major contributor to irrigation productivity. Technologies characterised by relatively small farm sizes are better managed by the surveyed farmers because they are able to provide adequate water and crop nutrients thus resulting in higher productivity, and high profit margins. Apart from technologies that depend on reservoirs, all other technologies surveyed in the paper are farmer driven and required no government support. This ongoing type of endogenous irrigation development provides a strong backing that the way forward in sub-Saharan Africa is for governments to create policies that facilitate poor farmers becoming irrigation entrepreneurs. Such policies should aim to enhance the reliability of markets (both input and output) as the driving force, and facilitate people’s access to land and water.

Drought frequency in the Volta Basin of West Africa

According to various reports, climate change is responsible for the change in rainfall amount and pattern accompanied by the various degrees of extreme events in Sahelian West Africa in recent years. Other reports also suggest that there has been a “recovery” of the rainy season (Nicholson 2005). In this study, temporal characteristics of meteorological droughts in the Volta basin, a semi-arid region in West Africa, are investigated in order to provide a guide for sustainable water resource management. For this purpose, drought intensity, areal extent and recurrence frequency is analysed using the standardised precipitation index (SPI) for a time series between 1961 and 2005 from 52 meteorology stations across the Volta basin. Using this analysis the severity of the historical droughts of 1961, 1970, 1983, 1992 and 2001 that occurred in the region are assessed and their intensity, areal extent and return periods are obtained. The drought intensity is lower than −2.0 over nearly 75% of the region, meaning that a major part of the region was under extreme drought conditions during this year. The drought of 1983/1984 has a probability of occurrence of up to 0.1 from records spanning 44 years. The areal extent of extreme drought conditions is about 90% during this drought period.

Geochemistry of Precambrian sedimentary rocks used to solve stratigraphical problems: An example from the Neoproterozoic Volta basin, Ghana

The Neoproterozoic Volta basin of Ghana (∼115,000 km 2; depth up to 5–7 km) consists of flat-lying sedimentary rocks, mainly sandstones that unconformably overlie the crystalline basement of the West-African craton. The stratigraphical column has been subdivided into three main units, in upward succession the Bombouaka, Oti and Obosum Groups, but poor exposure has resulted in major disagreements on stratigraphical correlations and on the areal extents of these units. Geochemical data (major and trace element concentrations as well as Rb–Sr, Pb and Sm–Nd isotope data) on siltstones and mudstones, intercalated with the sandstones from the different units, were used in an attempt to solve some of these problems. Siltstones and mudstones from the Bombouaka Group can be unequivocally distinguished from similar rocks from the Oti and Obosum Groups by higher K 2O and Rb, larger Eu anamalies, higher 87Sr/ 86Sr, and more negative ɛ Nd values. Geochemical distinction between samples from the Oti and Obosum Groups is ambiguous because published geological maps differ with respect to the relative extents of the Oti and Obosum Groups. Rb–Sr isotope data, combined with high degrees of correlation between the concentrations of K and Rb, and Ca and Sr, indicate that mobility of these elements did not significantly change their concentrations during surface weathering. The clear geochemical distinction between mudstones and siltstones from the Bombouaka Group and similar rocks from the Oti and Obosum Groups is used to solve one of the outstanding controversies regarding the stratigraphy of the Volta basin.

HIV testing in community based research: a case study of female genital schistosomiasis and HIV in the Volta Basin of Ghana

HIV testing is a major issue of concern in developing countries. This paper aims at documenting field experiences in regard to testing for HIV in a community- based research. Detailed protocol was followed and participation in the study was on voluntary basis. Focus group discussionswere held in study community. The study objectives were deliberated on and participants were informed of the procedures to be undertaken. Those who gave consent were then recruited for the study. A total of 331 volunteered to undergo further screening for genital schistosomiasis.Vaginal swabs, cervical biopsy and blood was collected and tested for genital schistosomiasis, some common sexually transmitted infections and HIV. Female genital schistosomiasis prevalence found was 10.3%, Trichomonas vaginalis, 2.1%, Candida albicans, 9.6%, Gardnerellavaginalis, 11.8% and HIV 6.6%. The study also showed that, the location of Voluntary Counseling and Testing (VCT) services in rural communities in the Volta Basin were unavailable. The use of trained counselors from the governmental health facilities for field work was a challenge due to their heavy work load. It was also observed that the problem of fear and stigmatization still had a negative influence on opting for HIV testing. The authors recommend the scaling up of VCT services in rural communities through the Community-based Health Planning and Services (CHPS) initiative and NHIS scheme using the Maternal and Child Health service providers. The training of community leaders on HIV issues is also recommended as they occupy positions of influence and can impact positively on community-based HIV-related activities

Virtual water trade: a realistic policy option for the countries of the Volta Basin in West Africa?

Trade in virtual water, the substitution of the use of scarce water resources for agricultural production by importing food from water-rich countries has been said to be a potential solution to water crises and water conflicts throughout water-stressed regions worldwide. While trade in foodstuffs may have helped to alleviate water stress in parts of the Middle East and Northern Africa and provides an efficient response to the periodic drought occurrences, it has to be doubted whether virtual water trade is a water governance option that can be applied in many countries of the South. As examples from the West African Volta River Basin suggest, cultural values focussing on agricultural and livestock production, socio-economic factors such as a low level of education and a strong dependency of livelihoods on subsistence agriculture, weak governments that are unable to trigger and finance large-scale reform processes, as well as dysfunctional and unfair market systems, largely limit the widespread application of virtual water trade.

Computing the net primary productivity for a Savanna- Dominated ecosystem using stable isotopes: A case study of the Volta River Basin

The hydrologic systems and the terrestrial ecosystem of the Volta river basin in West Africa, play important role in the carbon cycle. This is so because of the coupling of water vapour release and CO2 uptake during photosynthesis, expressed as water use efficiency or transpiration ratio. Hydrologic and land-cover data, together with stable isotope ratio measurements of d18O and dD, and data from the global network of isotopes in precipitation (GNIP) are used to determine the net primary productivity (NPP) of the savanna-dominated ecosystem. The d18O and dD values in the Volta rivers range from -4.72 to 2.37 mm-l and from -35.28 to 9.30 mm-1 SMOW, respectively. The results indicate that the vegetation is supported by 380 km3 of rainfall, out of which 50% is returned to the atmosphere via plant transpiration. Associated with annual transpiration is the NPP of 0.170 × 1015gCyr–1 or 428 gCm-2 from the terrestrial ecosystem. Modelled estimates of heterotrophic soil respiration in this study slightly exceeded the NPP estimates, implying a small source of CO2 to the atmosphere. This condition does not favour the postulated existence of a major sink of atmospheric CO2 in the Volta basin.

Physico-chemical properties of three salt-affected soils in the Lower Volta Basin and management strategies for their sustainable utilization

Differences in physical and chemical properties of three salt-affected soils, designated as pedons 1, 2 and 3, in the Lower Volta basin ofGhana were evaluated. Pedons 1 and 2 were located at Mokordzie in the South Tongu District while Pedon 3 was at Salo in the Ketu Districtof the Volta Region of Ghana. The soil properties determined included texture, pH, organic carbon, available P and K, exchangeable basesand acidity. The texture of the soils varied from clay to silty clay. The low pH of the soils, attributed to the presence of pyrite, ranged frommoderately acidic to extremely acidic and vary in the order Pedon 1 > Pedon 3 > Pedon 2. The electrical conductivity of all the three pedonswere more than 4 dS/m, thus, their rating as moderately saline. Organic C content in the A-horizon of pedons 1 and 2 were comparativelyhigher than Pedon 3. Total N contents of the three pedons was generally low. Available K, on the other hand, was very low within all thehorizons of Pedon 2; medium in Pedon 3 and ranged from very low to medium in Pedon 1. The CEC of the A-horizon of Pedon 1 is mediumbut the B-horizon is between low to high. Those of pedons 2 and 3 were between medium to very high in both horizons. The CEC is generallyin the decreasing order Pedon 1 > Pedon 2 > Pedon 3. Exchangeable sodium percentage (ESP) of all the three pedons were lower than 15,hence, the soils were rated saline. Based upon these data, pedons 1, 2, and 3 were classified as Gleyic Solonetz, Endogypsi-Gleyic Solonchakand Gleyic Solonchak, respectively. Suggested management practices to improve upon the productivity of these soils are ridges/mounds,application of lime (gypsum or oyster shells), organic manures and residues, planting of salt-tolerant crops, agroforestry, leaching anddrainage

The Volta Basin Water Allocation System: assessing the impact of small-scale reservoir development on the water resources of the Volta basin, West Africa

Abstract. In the Volta Basin, infrastructure watershed development with respect to the impact of climate conditions is hotly debated due to the lack of adequate tools to model the consequences of such development. There is an ongoing debate on the impact of further development of small and medium scale reservoirs on the water level of Lake Volta, which is essential for hydropower generation at the Akosombo power plant. The GLOWA Volta Project (GVP) has developed a Volta Basin Water Allocation System (VB-WAS), a decision support tool that allows assessing the impact of infrastructure development in the basin on the availability of current and future water resources, given the current or future climate conditions. The simulated historic and future discharge time series of the joint climate-hydrological modeling approach (MM5/WaSiM-ETH) serve as input data for a river basin management model (MIKE BASIN). MIKE BASIN uses a network approach, and allows fast simulations of water allocation and of the consequences of different development scenarios on the available water resources. The impact of the expansion of small and medium scale reservoirs on the stored volume of Lake Volta has been quantified and assessed in comparison with the impact of climate variability on the water resources of the basin.

Surface/groundwater interactions in the Bani and Nakambe rivers, tributaries of the Niger and Volta basins, West Africa

The upper Niger and Volta rivers exhibit a great and highly contrasting variability of inter-annual runoff. The Bani River, the largest tributary to the Niger River in Mali, shows a dramatic decrease in runoff after the 1970s, with the result that many boreholes in the region have dried up since the drought began. In contrast, the Nakambe River (Upper Volta basin, in Burkina Faso) shows an increase in runoff for the same period, leading to unexpected flood peaks that damaged infrastructures. The contribution that the groundwater and its variability make to surface runoff variability is assessed in this study by comparing the data of the national groundwater monitoring networks of Mali and Burkina Faso to surface runoff. Several variables are compared at the basin scale: the date of the maximum level of the water table, the annual rainfall, discharge, low flows and depletion coefficients. Variability in the low flows of the Bani River is well correlated to a decrease in the water table. Since 1970, the greater decrease in runoff in comparison to the rainfall decrease is due to a reduction in the baseflow, related to the cumulated rainfall deficit. Concerning the Nakambe River, the runoff increase is not supported by a water table increase, but is due to the increase in runoff coefficient related to land degradation.

Yields and water productivity of rainfed grain crops in the Volta Basin, West Africa

The observed water productivity (WP, kilograms of crop per cubic metre of rain) of cereals is very low in the Volta Basin: mean WP barely reaches 0.15 kg/m3 for maize (±0.05), with a mean yield of 1.25 t/ha (±0.58). We sought to explain these observations by using simulation modelling to develop a frequency analysis along a 9° transect on the meridian of Ouagadougou, that is about the whole gradient of rainfall in the basin. At both plot and basin scale, the model indicated that fertilizers would allow much higher yields and thus better WP.

Farmer–herder conflicts and water governance in a semi-arid region of Africa

Sedentary farmers in the Volta Basin are endangering the activity of transhumant herders relying on grazing ranges between 9° and 11°N. Despite mutual benefits, farmers try to deny them access to water and thereby the possibility to graze their stock on crop residues. This new behaviour is changing the geographical distribution of traditional activities and risks endangering herding activity, a leading economic resource in these regions. Meeting livestock watering requirements is thus a matter of local conflict resolution and good governance. Countries should be encouraged to adopt legislation to maintain or even promote the mobility of herding activities.

A decision-support tool for water allocation in the Volta Basin

The first version of a decision-support tool (DST) for the management of the transboundary water resource of the Volta Basin is presented in this article. The DST coupled a hydrologic model with the Water Evaluation and Planning (WEAP) water‐allocation model. It was calibrated and validated by reproducing observed river flows and water stored in the hydropower reservoirs, respectively. It considered the impact of possible future climate changes (potentially critical) and the development of upstream small reservoirs (leading to upstream–downstream trade-offs) on the Akosombo hydropower scheme. This DST may foster transboundary dialogue for the integrated management of the basin's water resources.

Modelling daily precipitation features in the Volta Basin of West Africa

AbstractThe combination of a conventional Markov chain model (zero and first order) and a gamma distribution model are found to be applicable to derive meaningful agricultural features from precipitation in the Volta Basin (West Africa). Since the analysis of the monthly or annual precipitation amount does not provide any adequate information on rainfall timing and sufficiency of crop water requirement, rainfall modelling was performed on a daily time scale for 29 rainfall stations. The modelled rainfall features follow distinct spatial patterns, which will be presented as maps of(1) rainfall occurrence probabilities and (2) recommendations of optimal planting dates. In addition, the effective drought index (EDI) working on daily time scales is calculated in order to assess drought properties of five different rainfall regions within the Volta Basin. Apart from the common way of separately modelling the duration and intensity due to their different distributions, a copula approach is chosen in this study to construct a bivariate drought distribution. Application of the measures derived to agricultural decision support will be discussed briefly. Copyright © 2009 Royal Meteorological Society

Changing paradigms in volta basin water management: customary, national and transboundary

This paper examines water management policies and institutions in the Ghanaian and Burkinabe portions of the Volta basin of West Africa. The paper begins with a brief historical overview of political, cultural and environmental developments in the basin since the late 19th century. Customary approaches to water management in the Volta are described next, followed by colonial and post-colonial water management developments in Ghana and Burkina Faso. The interplay between customary and national water management institutions in the watershed is then analysed so as to understand how conditions changed as a result of national-level developments. The paper also examines transboundary developments in the Volta basin, and concludes with a discussion of some of the strengths and weaknesses of the different management approaches.

Characterization and appraisal of facets influencing geochemistry of groundwater in the Kulpawn sub-basin of the White Volta Basin, Ghana

Groundwater composition in the Kulpawn basin is largely controlled by aluminosilicates dissolution and cation exchange resulting in mainly Ca-Mg-HCO3 and NaHCO3 water types. Principal component analysis, Piper graphical classification, and stable isotope (18O and 2H) of groundwater and surface-water samples were used to delineate geochemical processes and groundwater facies. The groundwater is mildly acid to neutral and low in conductivity. Chemical constituents except HCO3− and SiO2 have low concentration. No cation shows clear majority, however, the order of relative abundance is Na+ > Ca2+ > Mg2+ > K+. HCO3− is the predominant anion and the order of abundance is HCO3− > NO3− > SO42− > Cl−. SiO2 concentration is high compared with the major cations. Dissolution of plagioclase, pyroxene and biotite and cation exchange are responsible for groundwater composition. Isotopic data suggest integrative, smooth and rapid recharge from meteoric origin. The groundwater quality is generally good for domestic usage; however, 18 and 47% of boreholes respectively have NO3− and F− levels outside WHO recommended limits suggesting potential physiological problems in some localities. The groundwater has low sodium absorption ratio and low to moderate salinity hazard but significant magnesium hazard partially limiting its use for irrigation.