The White Volta Basin
Location and Geography
The larger White Volta River Basin (9o10’00’ N, 1o15’00” W) has a total area of about 107,417 Km2 and drains Ghana, Burkina Faso, and Togo with an approximate length of 885km. The part of the White Volta Basin in Ghana comprises the entire Upper East Region, about 70% of the Upper West Region, and 50% of the Northern Region. The portion in Ghana covers an area of about 47, 000 Km2 which is approximately 20% of the total landmass of Ghana and 44% of the area of coverage of the larger White Volta Basin.
The basin is drained by tributaries of the White Volta which traverse the basin in rural settings providing permanent and ephemeral streams. It begins as the Nakambe River in Burkina Faso. The Red Volta and Sissili are tributaries of the White Volta and draw their source in Burkina Faso. Riverine systems and streams of the White Volta provide surface water resources that are very important in the water economies of most communities within and outside the basin. They serve as sources of irrigation water resources for communities living in their immediate neighborhood. The apparently complex network of streams in the area are more prominent in the rainy seasons, as most of the ephemeral stream channels dry out during the dry season.
There are stream gauges placed at representative locations within the basin to provide periodic readings of stream flow throughout the year. Surface water resources in the basin consist of flows generated inside Burkina Faso as well as flows from within Ghana. The mean annual flow of the White Volta is about 300 m3/s of which about 36.5% is generated in Burkina Faso (Barry et al., 2005). These estimated flows from Burkina Faso are measured from gauging stations at the borders with Burkina Faso. These include the gauging station at Nangodi in the Red Volta and Yarugu. These stations respectively measure average flows of 30 m3/s and 80 m3/s (Opoku-Ankomah and Amissigo, 1997). The White Volta basin flows contribute 25% of the annual total flows into the Volta Lake.
From the perspectives of the surface hydrology, the basin has been divided into nine (9) sub-catchments or sub-basins (Figure 1). The rainfall pattern in the area is of the typical savannah type with two main seasons: the rainy and dry seasons. Throughout the basin, there is a single rainy season in the year.
Figure 1. A sub-catchment map of the White Volta Basin, Ghana.
Geology and Hydrogeology of the White Volta
The hydrogeology of the White Volta is still under development. The unique hydro-stratigraphy has not yet been fully developed to assist in decision making regarding groundwater resources of the basin. The effective development of the local hydrogeology of the White Volta Basin would be very critical in developing groundwater resources for climate resilient water related projects in the basin. Groundwater resources of the basin have not been sufficiently quantified.
The area is underlain by two main geological formations (Figure 2): rocks of the Birimian Super Group comprising of meta-volcanics, meta-sediments, and granitic intrusions; and the Voltaian Super Group, comprising partially metamorphosed sedimentary rocks in the south of the basin. Hydrogeological properties and groundwater fortunes of rocks of both formations depend on the presence and degree of interconnectivities of secondary permeabilities created in the wake of fracturing and/or weathering. Aquifers of the Birimian are amongst the most prolific in Ghana and are very important in the water economies of most communities in the extreme north of the White Volta.
Aquifer transmissivities are quite variable in space in both geological terrains (Banoeng-Yakubo et al., 2010). The hydrogeological conditions of parts of the Voltaian have been discussed in previous researches of Acheampong and Hess (1998), and Yidana et al (2008). Yidana et al. (2008) report aquifer transmissivity and specific capacity values in the southern parts of the Voltaian to, respectively, fall in the range of 0.18 – 197.7 m2/d, and 0.5 – 148.6 m3/d/m. Later on, using a numerical groundwater flow model, Yidana (2011) estimated aquifer hydraulic conductivity values to range between 1.19 m/d and 6.3 m/d. The model estimated groundwater recharge in the range of 0.9 – 6% of annual precipitation. Using a soil moisture balance model, Carrier et al (2008) suggested groundwater recharge in the range of 12 mm/yr and 268 mm/yr, representing 1.1% and 28.2% of the total annual precipitation in the basin. Several other estimates of groundwater recharge using natural tracers and models suggest promising rates of groundwater recharge in the basin.
Figure 2. Geological Map of the White Volta Basin
Water Resources and livelihoods in the White Volta Basin
The water resource is not equally abundant everywhere for abstraction to meet immediate water resources needs. Current surface water uses in the basin are estimated at about 0.11m3/s for domestic and about 2 m3/s for many small irrigation projects in the watersheds (Barry et al., 2005). The White Volta Basin underlies some of the vulnerable communities where sustainable domestic water supply is a key requirement for sustainable socio-economic development and the general wellbeing of communities within its catchment area. Moreover, there appears to be a deficit in the domestic water supply situation.
Demand for potable water in much of the basin appears to have outstripped the supply, although the potential appears to be high. In much of the basin, groundwater is being abstracted at relatively shallow depths through boreholes to meet domestic water needs. The current dispensation mandates the Community Water and Sanitation Agency, CWSA, to coordinate, supervise, and oversee the development of water schemes based on groundwater resources for small towns and rural areas where surface water resources are either not available or too far from the communities. In the bigger towns and urban areas close to surface water, piped systems are used based on these surface water sources. Through the coordination of the CWSA, several boreholes have been drilled in the White Volta basin. Some of them have dried out especially within the parts of the basin underlain by rocks of the Voltaian. Historically, several factors have been blamed for high failure rates. However, the main cause of well failure is the inadequate information on the hydrogeological conditions of the rocks in the area. Other factors such as poor borehole development, incompatible completion materials and pumps amongst other factors have also played major roles in areas where poor supervision coupled with incompetence of contractors lead to poor development and consequently, high borehole failure rates. Frequent borehole failure in much of the area, and rising populations at the national rate of about 2.5% per annum suggest that the demand for increased expenditure on water resources development/infrastructure in the area to meet basic needs.
Farming is the main source of employment and has generally been rain-fed over the past years. Erratic rainfall patterns attending climate change/variability in recent times, have adversely affected the general livelihoods as the rain-fed agricultural practice does not appear to be effective coupled with the late onset of the rainy season (Kuntsmann and Jung, 2005) and the heavier late rains leading to colossal crop failures. Food cropping and animal rearing are the most practiced agricultural activities in the region. There are some irrigation schemes which depend largely on surface flows in the basin. The predominant ones are the Tono irrigation facility in Navrongo in the Kasena-Nankana District with an irrigable area of about 2,500 ha, the VEA irrigation system in Bongo, which has an irrigable area of about 1000 ha. There is also the Bontanga irrigation facility in the Northern Region with an irrigable area of 500 ha and a total annual water requirements of 11 Mm3. The Integrated Tamale Fruit factory in the Savelugu District has an irrigable area of about 1,000 ha and total annual water requirement of 4 Mm3. All these systems are based on surface water bodies which are predominantly the tributaries of the White Volta river system. There are other small scale irrigation schemes practiced all over the basin. The Tono and VEA irrigation projects respectively have annual water requirements of 40 Mm3 and 8 Mm3 (WRC, 2008). In parts of the basin, there are groundwater based small scale irrigation activities which run predominantly on groundwater from dugouts and shallow wells in the basin.
The utility of groundwater from shallow aquifer systems for dry season irrigation has been reported to be increasing in the basin. Among other things, Laube et al. (2008) cite the apparent unreliability of rains in recent times and the improved infrastructure such as the road network that links the north to the south of the country to convey food crops as the factors responsible for the growing interests in dry season irrigation in parts of the White Volta Basin especially within the Upper East Region. Increasing awareness of the local farmers through knowledge sharing has apparently contributed to the notable increase in the number of small scale farmers using shallow groundwater for irrigation in the basin. Barry et al (2010) observed that this practice is not only widespread within the basin, but has also been an important source of sustenance for most families in the basin especially during the dry season months. As agriculture employs a large percentage of the population within the basin, the most effective adaptation strategy that can buffer farmers in the area against the impacts of climate change/variability is the development of an irrigation system that is resilient to the impacts of climate change and can also withstand pressures from rising populations and competing interests. Several workers have bemoaned the absence of the requisite data to guide the sustainable abstraction of groundwater resources for such commercial abstractions, especially as the practice becomes widespread and is gaining popularity as an effective buffer against the impacts of climate variability.
The main industrial establishments in the basin are agro-based and thrive on agric-based products and/or services. These include the Northern Tomato Factory in Pwalugu which thrives on tomatoes produced from irrigation schemes in Tono, VEA and other schemes; the Meat Factory in Bolgatanga; the Ghana Cotton Company in Tamale and Bolgatanga; the Integrated Tamale Fruit Company in Savelugu, and the Shear-butter processing facilities in several parts of the White Volta Basin. Other sources of employment in the basin include carpentry, auto servicing, shoe making, soap making amongst others.
Harvesting of fuel wood and charcoal burning are also important income generation ventures in the basin (WRC, 2008). However, these activities have led to the destruction of large portions of the savannah vegetation and have contributed to the dwindling of the vegetative cover of the basin. In the entire basin, 10 – 15% of the population is employed in the formal sector (GSS, 2010), but 65 – 80% are largely engaged in agricultural related employment and businesses.
Currently, the surface water resources at Tono and VEA irrigation dams are under significant stress due to low inflows from Burkina Faso. At the time of this project the Tono facility had been temporarily shut down due to low water levels. The implication of this on the local economy, which depends so much on irrigation of vegetables and rice, is very dire. Also, there has been reduced contribution of the inflows from the White Volta into the Akosombo hydroelectric dam, leading to significant reductions in the power generation capacity of the dam in recent times.
The water resources base of the White Volta and the larger Volta Basin are very sensitive to climate change/variability (Kasei, 2009) especially the surface flows. Kunstmann and Jung (2005), suggest variable climate conditions within the larger Volta Basin. Their model show a slight increase in rainfall by about 5% during the 2030 – 2039 period, compared to data for the 1991 - 2000, although there are significant variations in both space and time throughout the period. A significant decrease in precipitation by up to 70% is predicted for the month of April but this is expected to be offset by increases in precipitation during the months of June, July and August. The net effect is that the rainy season is shortened with intense rains. McCartney et al (2012), predict an increase in the frequency of low return flows based on historical evaluation of monitored stream flows and climate change trends.
Annual temperatures have also been predicted to increase by 1°C in the dry season and 2°C during the rainy season (Kunstmann and Jung, 2005). Evapotranspiration rates have been projected to increase by up to 10% in the southern parts of the basin. Surface runoff has also been projected to increase by up to 18%, reflecting a nonlinear response of surface runoff to precipitation patterns. These projections will have an impact on the usual agricultural practice in the area due to the predominantly rain-fed nature.
The implication is that the overreliance on the surface water based facilities for irrigation and other economic activities may not be the best buffer against erratic rainfall patterns attending climate change/variability. Therefore, water resources development will have to take into account, the impacts of climate change/variability on surface precipitation and surface flows, and the spatial distribution and availability of such water resources within the basin.
The current project will examine the feasibility of abstracting groundwater under climate change conditions to support groundwater based livelihood support systems in the basin.
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