The Densu basin (Figure 1.4) is a coastal river catchment in southern Ghana of approximately 2564 km2 which lies in a region with a mean daily temperature ranging between 24oC and 31oC. Even though the Densu river is a relatively small river compared to others in the country, with a mean annual flow volume of about 499x106 m3, from mean annual rainfall of 1190mm and mean annual potential evapotranspiration of 1095-1460mm per annum (WARM, 1998), the
Figure 1.4 Map of Ghana (Adapted from: http://www.volu.org/map.html) showing the position of Densu Basin and its hydrological map.
Densu is considered to be one of the most important rivers in the country with respect to its social and economic importance as a water supply source to communities along its route (WARM, 1998, WRC, 2000). In addition, it is also the main source of the drinking water supply for the western part of the capital city of Accra because it flows into the Weija Reservoir, which is a major source of potable water for south western Accra. The cost of treating water from the Densu River is about ten times that from the Volta River at Kpong (which is well managed by the Volta River Authority because of the Akosombo hydroelectric project scheme on the River Volta), but because it is supplied by gravity it makes it more economical than the water from the Volta which must be pumped to Accra.
Nsawam Koforidua
ACCRA Gulf of Guinea
Manhia
Weija Dam N
0 14km
Densu Basin
However, like many other watersheds in Ghana and West Africa, it faces conflicting water uses, i.e. providing public water supply at Koforidua and Weija (Figure 1.4) with water for agricultural, tourism and recreational uses, whilst maintaining the quality of water for water supply. However, various human activities within the Densu Basin have resulted in serious ecological problems which risk the environmental degradation of the river basin (WARM, 1998 and WRC, 2000).
• Erosion due to farming within the catchment with attendant siltation causes occasional serious flooding;
• Extensive deforestation particularly along the river banks as a result of lumbering, fuel wood extraction and clearing of land for farming;
• High levels of air pollution due to poor domestic and industrial waste disposal;
• Nutrient contamination of surface waters from inefficient use of fertilizers;
• Growth of aquatic weeds in the river and downstream in the impoundment at Weija reservoir, due to unapproved use of chemicals for fishing, and the human introduction of exotic alien water plant species e.g. Water Hycinth;
and
• General loss of biological diversity has been observed in certain parts of the basin.
The human-induced problems described above are exacerbated by:
1. Lack of institutional capacity for water management at both Government and water providers’ level and
2. Water shortages due to low flows and drying-up of streams upstream in the basin with attendant reduction in water levels of reservoirs downstream are observed annually.
Water shortages are experienced frequently in the whole basin but especially in the uppermost section in the dry season when 1) demand for drinking water cannot be met from the intake weir at Koforidua due to low water levels and 2)
poor water delivery structures which have, over the years, been producing below their installed capacities due to worn out mechanical plants (WRC, 2000).
The resultant effects of these environmental problems within the basin culminated in a public outcry over the quality and quantity of water supplied from the Weija Reservoir within the basin, resulting in a ban on farming along the Densu river by the government (e.g. Daily Graphic, Friday 14/09/2001) and a call to use water resources judiciously (Daily Graphic, Thursday 18/09/2001) as shown in Figure 1.5.
As a result of the growing public concern, the government of Ghana signed a Memorandum of Understanding (MOU) in 1999 with the United Nations Centre for Human Settlements-Habitat (UNCHS) to collaborate in a project on
“Managing Water for African Cities”. The project was meant to find solutions to the increasing water demand in the fast growing African cities of which Accra, and subsequently the Densu basin, featured. The resulting report by Nii Consult (2001), concluded:
“the Densu River Basin is being degraded by intensified agriculture involving the use of agrochemicals, timber logging, fuel-wood extraction, urban wastes (excreta, garbage, and liquid). This is threatening the livelihood and also the natural resources on which the majority (farmers) depend. In addition the survival of the terrestrial bio-diversity is at risk”.
Nii Consult (2001) also recommended the formation of a Densu River Basin Management Board (DRBMB) with the objective to facilitate the co-ordination and integration of the plans and programmes of the different institutions at the district level. The DRBMB was inaugurated in Accra on March 22 2004 comprising of 17 Board members who come from (Ghanaweb, 2004) five out of the eight districts within the basin; government ministries (i.e. Environmental Protection Agency (EPA); Ministry of Food and Agriculture (MOFA); Ministry of Health (MOH); Ghana Water Company Limited (GWCL)); religious bodies, non-governmental organizations, the National Council on Women and Development (NCWD), traditional rulers, the Water Research Institute (WRI) of the Council for
Figure 1.5 Newspaper reports on the Densu Basin (Source: Daily graphic 14/09/2001 & 18/09/2001)
Scientific and Industrial research (CSIR); National Development Planning Committee (NDPC) and Lands Commission. They are mandated to evolve plans for the conservation, development and utilization of water resources in the basin. The activities of the DRBMB are to create awareness and mobilize political will; ban farming in buffer zones; introduce environmental and farmer friendly systems of agricultural production (crops and livestock); desilt drains;
improve hydrological data collection; and to control clay and sand extraction and the quarrying of stone. Other activities include to enforce mandatory preparation of Environmental Impact Assessments (EIAs) for development projects; monitor and assess the state of natural resources, and to implement the community small towns and urban towns’ water supply system rehabilitation in the districts. Finally, the DRBMB is to tackle other issues not mentioned but necessary at the local level within the basin to improve effective river basin management that will help to reverse the degradation of the basin and restore it to good health, in order to enable the basin to provide the necessary services required of it.
The Densu river basin, following from the problems enumerated earlier shows that there is a need for a basin–wide planning approach because of its scale (2564km2) and this (basin wide planning approach) is also seen from some of the activities granted to the DRBMB which includes involving stakeholder participation, awareness raising, public meetings, capacity building and training is in order. As part of the DRBMB activity to “monitor and assess the state of natural resources”, the Government of Ghana and the Council for Scientific and Industrial Research (CSIR) commissioned this PhD study to provide 1) an analysis of environmental and hydrological interactions within the basin to facilitate knowledge and understanding of the hydrological regime through hydrological modelling 2) to assess the impact of land use on the future water resources of the basin and 3) to provide recommendations based on the outcome of (1) above that would facilitate improved water resources management of the basin.