Journal of the Faculty of Environmental Science and Technology, Okayama University Vo1.9, No.I. pp.87-98. February 2004 Water Resources and Environmental Management in Ghana Kwabena KANKAM-YEBOAH*, Philip GYAU-BOAKYE**, Makoto NISHIGAKI*** and Mitsuru KOMATSU*** (Received December 3, 2003) Three principal river basins are found in Ghana and the Volta River Basin is the major one, covering about three-quarters of Ghana. The basin is shared with Mali, Burkina Faso, Cote d'lvoire, Togo and Benin. Water from the Volta River Basin is used for drinking water supply, generating hydro-electric power, irrigation, inland fisheries and lake transport. The sustainable management of the Volta River Basin is thus of great importance. Land use activities in the basin are thus closely monitored not only in Ghana, but also in the other riparian countries as well. This paper presents information and data on the water resources and environmental management of the Volta River Basin in Ghana. Key words: water resources, environmental management, Volta River Basin, Ghana, water utilization 1 INTRODUCTION both the forest and savannah zones since the early 1970s (Opoku-Ankomah and Amisigo, 1998; Paturel, et al. Ghana is covered by three main river basins. These 1997; Aka, et al. 1996). The mean annual temperatures are the Volta, South-Western and the Coastal Basins. The vary between 24.4 DC and 28.1 DC. Gyau-Boakye and Volta River Basin (Fig. 1) covers about 70 % of the total Tumbulto (2000) have observed that the mean annual surface area of the country and it is shared by six West temperature in the basin has increased by 1 DC between Africa countries, namely; Ghana, Mali, Burkina Faso, 1945 and 1993. Cote d'lvoire, Togo and Benin. In Ghana, the Volta River has been dammed at Akosombo for hydro-electric 1.2 Geology, soil and vegetation power, creating the largest man-made lake in the world. The Volta Basin in Ghana is mainly underlain by The generated electricity is also supplied to the consolidated sedimentary formation, consisting of neighbouring countries of Cote d'lvoire, Burkina Faso, sandstones, shale, arkose, mudstone, sandy and pebbly Togo and Benin. Water from the lake is used for water beds and limestones. These rocks cover 45 % of the supply (domestic and industrial) and irrigation. Also, the country (WARM, 1998; Kankam-Yeboah, et al. 2003). lake has become a major waterway for transport, linking Other formations found in the basin consist of granites the south of the country to the north. Due to its vast and associated granites. The soils of the basin are extent and national importance, the sustainable basically Savannah Ochrosols, groundwater laterites and management of the Volta Basin is of very great laterite-ochrosols and acid gleisols. The basin is importance in Ghana. It is for this reason that this basin principally located in the interior wooded savannah is used as a case for the study of the hydrology, water ecological zone. The predominant vegetation is grass resources and environmental management in Ghana. with trees such as baobab, dawadawa, nim and sheanut trees in the north and Acacia sp. and mangroves in the 1.1 Climate south. The climate in the Volta Basin is mainly Tropical Continental or Interior Savannah. The rainfall 2 WATER RESOURCES distribution is principally unimodal. The rainfall season occurs from May to October, followed by a prolonged 2.1 Surface Water Resources dry season between November and April. The mean 2.1.1 Coverage annual rainfall ranges from 1,000 to 1,300 mm. The The major tributaries of the Volta River (also called distributions of mean annual rainfall and the Volta lake) are the Black, White and Oti rivers. Into evapotranspiration in Ghana are shown in Fig. 2 and 3, these, minor rivers and streams empty their waters. The 2 respectively. Rainfall studies in West Africa show that Black Volta has a total drainage area of 149,015 km , 2 there has been a decline in the mean annual rainfalls for with only about a fifth (38,107 km ) of this lying wholly in Ghana (WARM, 1998; Kankam-Yeboah, 1997). The Black Volta is shared by Ghana, Burkina Faso and Cote • Graduate School of Natural Science and Technology, Okayama d'lvoire. The main tributaries of the Black Volta are University, Okayama, Japan ([email protected] ac.jp) •• Water Research Institute (CSIR), P.O. Box M.32, Accra, Ghana Benchi, Chuko, Laboni, Gbalon, Pale, Kamba and Tain ••• Faculty of Environmental Science and Technology, Okayama rivers. University, Okayama, Japan 87 88 MAL I N HI G E R F A S 0 J ! \....... .......... , ........ ...... I..... • lobo-O:oulasso BA $ IN ......, .\. '- ,..... ""1\ \.".-._. I UI 9 o > ... 0 .c z .~ . a 0 UI - Z 0 7 u t<IJmasi • LEGEND r_.-.- ~lernQlional Bdry. ___ Drainage .Area Bdry• • Town Sc ale. in. .Mile S o SO 100 e: p.- 1 ! J 5' ~ a f./ , UI F G 0 F 5' 4' t to 0° l' " Fig.! The Volta River Basin (Modified after WARM, 1998) 89 Kankarn-Yeboah et al. / Water Resources and Environmental Management in Ghana 11" 10" ' g" 8" 7" 6" Fig.2 Rainfall isohyets in Ghana (Modified after WARM, 1998) 90 j-'--------l.-------l---t""""=::::-L .J.. Fig.3 Potential evapotranspiration in Ghana (Modified after WARM, 1998) Kankam-Yeboah et al. / Water Resources and Environmental Management in Ghana 91 The White Volta Basin, which Ghana shares with graph paper to define station frequency curves. From Burkina Faso and Mali, covers an area of about these frequency curves, floods of return period 1.1, 1.5, 2 2 104,752krn with only 45,804 km lying in Ghana. The 5, 10, 25, 50 years (Qr) and the index flood, Qind (flood main tributaries of the White Volta are Mole, Kulpawn, of return period of 2.33 years) were obtained. The Sisili, Red Volta, Asibilika, Agrumatue, Nasia and corresponding regression equations derived for the Volta Nabogo rivers. Rivers System are as follows (Ontoyin, 1985): The Oti Basin is shared by Ghana, Burkina Faso, 2 Togo and Benin. It occupies an area of about 72,778 km QT/Qind = 0.97 + O.4y for Black and White Volta (2) 2 out of which only 16,213 krn lies in Ghana. The main QT/Qind = 1.00 + 0.94y for Oti (3) tributaries of Oti are Afram, Obosom, Sene, Pru, QT/Qind =1.00 + 0.66y for Lower Volta (4) Kulurakun, Daka, Asukawkaw and Mo rivers. Beside the above-mentioned tributaries and south of where, y =-In [-In(I-I!f)] and T = return period in years. Ghana is the Lower Volta River. It is shared between Ghana and Togo and it occupies an area of about 62,651 These derived equations for flood estimates in the krn2of which 59,414 krn2lies in Ghana. Volta River Basin ought to be used with caution and the results should be treated as provisional since they are 2.1.1 Runoff based mainly on limited data. Only very few hydro­ 3 The total annual runoff for Ghana is 54.45 billion m , stations have continuous records of 20 years and more, of which 38.3 billion m3 is accounted for by the Volta giving rise to many inter-station correlation estimates. River System (WARM, 1998). The total annual runoff 3 originating from Ghana alone is 39.4 billion m , which is 2.1.3 Surface water quality 68.6 % of the total annual runoff. The Volta Rivers The mean pH of the Volta Rivers System varies from System contributes 64.7 % of the actual runoff from 6.9 to 7.5 in the Oti River at Saboba and on the Black 3 Ghana, nearly, 25.5 billion m . Volta at Bamboi, respectively. The range is not very The Oti basin, though only about 18 % of the total wide and the waters appear mostly neutral (pH 7.0). The catchment of the Volta River System, contributes maximum level of dissolved salts, in terms of between 30 % and 40 % of the annual flow of the Volta conductivity, was 280.0 /-ls/cm in the Oti River at Saboba Rivers System (Moxon, 1968). The reason for this is that (WARM,1998). the catchment of the Oti River is the most hilly and The mean suspended solids concentrations are mountainous in the whole Volta basin. generally low, less than 200 mg/l; and the dissolved Opoku-Ankomah (1998) estimated the total annual oxygen concentrations generally indicate low levels of discharge of the White Volta basin to be 303.29 m3/s, pollution. The mean annual suspended yields in some of where the percentage of flow from outside the country to the rivers in the Volta Basin are as follows: the total flow is estimated to be 36.5 %. The mean annual flow of the Black Volta at Bamboi is 218.97 m3/s, out of Black Volta 19.97 tons/krn2/year which about 42.6% originate outside of Ghana. The total White Volta 21.09 tons/krn2/year annual flow from the Oti catchment was estimated to be Oti 53.58 tons/krn2/year 3 365.5 m /s with 89.1 m 3/S from within the country. In general, there is a great variability between the wet 2.2 Groundwater resources and dry season flows in the river basins in Ghana, the The Paleozoic sedimentary formations, locally Volta River Basin being no exception. referred to as the Voltaian Formation, which underlie the Volta Basin have little primary porosity. Groundwater 2.1.2 Floods occurrence is thus associated with the development of Periodic and temporary flooding occurs in many parts secondary porosity as a result of jointing, shearing, of the country, as a result of heavy rains and overflows fracturing and weathering (WARM, 1998).