Agricultural Groundwater Use in SSA

As shown in Table 5.3, national statistics on water use are not readily available for most countries. As such it is clear that one must consult multiple and often inconsistent data sources to paint even a rudimentary picture of its use at a continental scale. This approach is of course fraught with problems. For example, most use appears to be in small rural villages, where boreholes and wells have been installed by multiple agencies: government, individuals, non-governmental organizations (NGOs) and relief agencies. This use is scattered and individually quite small and therefore both difficult to measure and seemingly inconsequential. As a result, it frequently goes unreported (UNEP, 2003, p. 2), and total use tends to be underestimated. The cumulative impact of even small-scale uses of groundwater can be significant as the many scattered boreholes in Burkina Faso (Fig. 5.2) or the many shallow wells and deep tube wells in wadi systems (alluvial aquifers) in Djibouti (Jalludin and Razack, 2004) illustrate.

Examining the history of groundwater development in the region also highlights the difficulties in collecting meaningful statistics for groundwater use. For example, in southern Africa some of the literature relating to groundwater use is project-based or localized. Often, one has to consult multiple sources (government, consultants, NGOs and even individual water users) to construct a meaningful database relating to use. Here, an attempt is made at classifying groundwater use according to development objective and the agents responsible for installation of boreholes or wells (Table 5.4). One of the challenges arising from such a model of groundwater development is poor coordination of agents and the difficulty in trying to establish the actual extent of groundwater use or the number of boreholes drilled and used. In this scenario, it is also very difficult to capture the extent of groundwater use for livelihood and other purposes and its overall contribution to the economy.

Despite the problems associated with lack of data or incomplete data, some of the data available do present a picture that agricultural groundwater use is important at local scales in parts of SSA. For example, in the Limpopo province in northern South Africa there are reportedly more than 35,000 boreholes mostly used for domestic water and irrigation of small gardens, and Asian-style growth rates (see Wang et al., Chapter 3, and Sakthivadivel, Chapter 10, this volume) in development have been documented (Tewari, forthcoming). In semi-arid Botswana, water supply is largely groundwater-based (Brunner et al., 2004). Groundwater in Botswana is mostly used for rural, domestic and livestock purposes and this has steadily increased over the last 30 years, as shown by the number of registered boreholes in the country (Fig. 5.3). The increase in groundwater use in Botswana has been accompanied by overdraft as the abstraction is presumably greater than recharge (Kgathi, 1999). Such use of groundwater is mirrored in several other countries. Pockets of small-scale groundwater irrigation are found in Tanzania where reportedly 200 ha are irrigated using diesel and electric pumps; and in Malawi and Zimbabwe where collector wells are used to abstract water from weathered basement complex aquifers (FAO, 1997). In Cameroon, groundwater makes up only 2% of renewable water resources (Table 5.3). Yet, in the north of the country, where reservoirs are limited and precipitation is lower than the national average, groundwater is the most widely available water resource and is used for domestic, agricultural and industrial purposes (Njitchoua et al., 1997). Similarly, in Borno and Yobe of Nigeria's Lake Chad basin, groundwater is the predominant source of domestic

Discharge of wells (m3/h) Legend

Estimated discharge

10-50 m3/h

Discharge of wells (m3/h) Legend

Estimated discharge

10-50 m3/h

50 100 km

MAHRH/SG/DGIRH/P.GIRE - October 2003

Fig. 5.2. Wells across Burkina Faso. (From Obuobie and Barry, forthcoming.)

50 100 km

MAHRH/SG/DGIRH/P.GIRE - October 2003

O to

Fig. 5.2. Wells across Burkina Faso. (From Obuobie and Barry, forthcoming.)

Table 5.4. Types of groundwater use in SSA.

Type of groundwater use

Purpose

Responsible agent for borehole/well installation

Drought mitigation

Normal supply

Emergency relief

Social responsibility activities

Livestock watering Agriculture (crops)-bridging mechanism so that crops do not fail to mature Domestic water supply Domestic water Commercial irrigation

Domestic water during drought years Stock water

Boreholes installed as part of ongoing aid and development activities

Individuals Government

Individuals NGOs

Municipalities Government in the case of rural communities (both central and local)

NGOs CBOs

Governments Churches NGOs CBOs

Governments Churches

NGO - non-governmental organization. CBO - community-based organization.

1970

1980

1990

Year

Fig. 5.3. Number of boreholes drilled over time in Botswana. (From DWA, 2002.)

1970

1980

1990

Year

Fig. 5.3. Number of boreholes drilled over time in Botswana. (From DWA, 2002.)

water and for other non-irrigation uses, and more than 2000 boreholes are used in the two states alone (Bunu, 1999).

In addition to the numerous small-scale groundwater uses in SSA such as those mentioned above, large-scale commercial irrigation occupies the largest usage of groundwater, especially in South Africa in the Karst aquifer region of the upper Limpopo River basin in the north-west province where about 77 million cubic metres are abstracted annually for irrigation (IUCN, 2004), and in the wider Limpopo Water Management Area where about 850 million cubic metres are abstracted annually for irrigation (Basson et al., 1997). Also, the Karst aquifers in the Lomagundi area (central Zimbabwe) and the Nyamandhlovu aquifer (western Zimbabwe) are exploited for commercial irrigation (Masiyandima, forthcoming). Irrigation officials in Zimbabwe estimate that more than 17,000 ha are irrigated commercially using groundwater.

Combining aquastat figures with the results of a set of county surveys and some assumptions, Giordano (2006) estimated that there were perhaps 1 million hectares of groundwater irrigation in SSA. Although this is a rough estimate, it gives some indication of the possible direct role of groundwater in agricultural production in SSA. In an effort to measure the value of groundwater in other regions where use is more widespread and forms part of broader irrigated settings, irrigated area or the volume of water applied can be a reasonable measure of agricultural impact. By such measures, the value of groundwater in SSA is clearly small given the region's physical size and rural population. Yet groundwater is still considered the resource of choice in many, particularly rural, areas. The importance accorded to groundwater in parts of SSA is reflected by the number of site-specific studies on certain aspects of groundwater use such as recharge (Taylor and Howard, 1996; Njitchoua et al., 1997; Brunner et al., 2004). There have been many other groundwater recharge studies: in the Kalahari in Botswana (de Vries et al., 2000), Ghana (Asomaning, 1992), Kenya (Singh et al., 1984), Uganda (Howard and Karundu, 1992), Zambia (Houston, 1982) and Zimbabwe (Houston, 1990). Most studies try to quantify available groundwater resource from recharge.

Given the general belief that groundwater has been relatively undeveloped in SSA, it is not surprising that most studies focus on increased use. Yet, there are indications from a number of regions that the 'development' stage discussed by Shah and Kemper (respectively Chapter 2 and Chapter 8, this volume) has already been passed and overabstraction is now the issue. For example, farmers in the Dendron area in the Limpopo province of South Africa have experienced declining water levels over the last two decades in the aquifers that supply all of their irrigation (Masiyandima et al., 2001). Similar problems have been reported in the Nubian aquifer system (which is admittedly a fossil system with no recharge) in northern SSA (Ulf and Manfred, 2002) and in other arid and semi-arid environments such as in Botswana. Abstraction of groundwater from Botswana's aquifers generally exceeds annual recharge (Kgathi, 1999). This is manifested by the declining water levels in several well fields. According to the Department of Water Affairs (Botswana), in some well fields groundwater levels are declining by as much as 2.6 m/year. Clearly there is little scope of additional groundwater development in such areas.

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