Characteristics of a crystalline granitic aquifer in north-western Ghana

The groundwater potential of north-western Ghana has been assessed in terms oftransmissivity and specific capacities of the basement aquifers. Data from short-term and constant-discharge pumping tests on 14 boreholes were analysed. The Cooper-Jacob straight line analytical methodwas used to determine the aquifer characteristics. The computed  transmissivity values of the aquifers varied significantly from 0.37 to 44.5m2 d-1 ; with their specific capacity values ranging from 1.04 to 56.7 m3 d-1m-1 • The storage coefficient from four observation boreholes  indicated that the aquifers were under confined conditions with values in the order of 10-5• Total head losses of the boreholes anributed to laminar and turbulent flows ranged from 28 per cent to 84 per cent. The aquifer characteristics confirm that groundwater occurrence is localised, confinedand controlled by the development of secondary porosity. Therefore, to obtain adequate water for sustainable use, groundwater abstraction in the study area should be preceded by extensive geophysical investigations using integrated methods

Sustainable Groundwater Exploitation under Natural Conditions in Southwest Ghana

Groundwater has been recognised as the most cost-effective option of safe water supply to rural communities in Ghana. The demand for potable water has led to the drilling of a large number of boreholes in many parts of the country. To establish the threshold of groundwater development from storage in a major river catchment (Pra River) in South-West Ghana, studies on recharge to the weathered aquifer and statistical evaluations of specific capacity and potential yield have been carried out. The SACSMA conceptual hydrological modelling system was used for the recharge estimate. With recharge rate of 50 mm/yr, the natural groundwater resources in the basin was estimated to support a maximum withdrawal of 12 l/s for a 10 hour per day pumping. The groundwater resources potential of 1.6 l/sｋ㎡ could be considered the threshold of groundwater exploitation in similar river basins in South-West Ghana. A study into the relation between permeability and recharge under different conditions and scenarios is required to define their limiting role in groundwater resources development

Impacts of Climate Change on Stream Inflows into the Volta Lake

The study examined the impact of climate change on future water availability in the Volta Lake from climate downscaled data using ensemble projections of two Global Climate Models (MPEH5 and HADCM3) and two emission scenarios (A1B and A2) used in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. The SWAT hydrological model was calibrated and validated and then used with the downscaled climate change data to assess the impacts of climate change on the inflows to the Lake. Results from the impact assessment showed that future mean annual streamflow into the Volta Lake could increase by about 17 and 16 percent under the A1B and A2 scenarios, respectively. However, streamflow from Geoere, Boromo and Dapola in the Black Volta basin and Nawuni in the White Volta basin could decrease. The projected increase in total annual streamflow in the basin is consistent with the increase in annual rainfall in the basin under both the A1B and A2 scenarios of between 2.0 and 8.0 percent obtained in a separate climate downscaling study. Since streamflow in some of the sub-basins were found to decrease under the climate change scenarios investigated, integrated and prudent management of the basin's water resources would be necessary to ensure sustainability in water use

Suspended sediment transport into a water supply reservoir in southern Ghana

Weija reservoir on the Densu river serves as a source of water supply to parts of Greater Accra and Central regions of Ghana. The Densu river basin is characterised by accelerated land degradation. A number of Integrated Water Resources Management (IWRM) interventions have been implemented in the basin. Reports suggest there has been an improvement of physicochemical parameters of the water resources. However, there is no recent study on fluvial sediment transport in the basin. This paper assessed sediment transport into the Weija reservoir via the Densu River. Weekly suspended sediment concentration and river discharge were monitored over a 1 year period to quantify sediment yield into the reservoir. The results indicated that total annual suspended sediment yield, and annual specific suspended sediment yield were 5375 t yr-1 and 2.0 t km-2 yr-1, respectively. These were relatively low compared to results obtained by past studies on the Densu basin at upstream Mangoase (6146 t yr-1 and 2.49 t km-2 yr-1) and other river basins in Ghana. Parameters established from a yield rating curve indicated that parts of the basin were degraded and sediment transport in the basin was largely due to the availability of sediment in the catchment and not just due to high river discharges. The relatively low sediment transport at Weija may be indicative of the success of the IWRM interventions. It is recommended that these be sustained and/or intensified

Determination of water requirements for producing irrigated rice and other crops in the Afram river valley bottom at Aframso, Ghana

No Abstract Available Ghana J. Sci, Vol.40 2000: 15-2

Water users' associations and integrated water resources management in Ghana

Water Users' Associations (WU As), are important component of  participatory governance arrangement for sustainable management of water resources in Ghana. At present, WUAs' are not organised in their respective sectors to function effectively. However, a number of the groups exist, evidenced by their governance structure, membership status, experience and knowledge in various sectors of the economy that are relied upon by public institutions especially in times of crisis. Although they offer a number of opportunities that are acquiescent for use in water governance. WUAs are besieged by a myriad of weaknesses and threats that need to be minimised to achieve their objectives. The current legal and institutional framework does not provide clear roles and or  responsibilities with regards to integrated water resources management(I WRM) for WU As. Thus. the WU As in Ghana do not seek to promote the IWRM as they seek to promote the socio-economic interests of their membership.It is recommended that the formation of WUAs be  encouraged and supported to play key roles expected of WUAs in IWRM inGhana

Flood pulse alterations of some river basins in Ghana

Flood analysis is crucial for designing drainage, managing water quality, assessing the impact on lives and properties among others. The objective of the study was to determine the trends, occurrences and magnitude of floods in Ghana using hydrological data. The study looked at flood phenomenon in Ghana, because flooding has been observed recently as the most common natural hazard in the country. Specifically, the rainfall amounts from selected gauging stations in Ghana and river discharges from the three main river systems namely, Volta (at Bamboi), south western (at Twifu Praso) and the coastal (at Okyereko) river systems in Ghana were considered. Peak streamflows from the selected river systems were also analysed. Flood frequencies were derived using the flow duration curve (FDC), and the high flow frequency (return period) determined to support the analysis. The threshold values above which streamflows are peak flow were estimated from the FDC at 90 per cent probability of non-exceedance for the selected rivers. The results of the analysis showed that increases in the number of occurrence of high streamflows with declining trends of monthly rainfall in the last decade (2000-2010) have been prevalent. This means that rainfall amount is not necessarily the major cause of recent high streamflows (or flood), though there are evidences of direct runoff during rainy season in Ghana. It is, therefore, recommended that as a country, there is the need to improve the drainage systems in the cities, and also provide adequate storage for floods during the rainy seasons. It is further recommended that flood pulse analysis be carried out on a continuous basis as and when new meteorological and hydrological data is available