Groundwater In the Basin

Groundwater is mainly used in the Limpopo basin for irrigation and rural supplies (Barros 2009). It is noted that over 1 000 boreholes have been drilled in the Limpopo basin, however, very few of these have had continuous water levels measured and there is limited information on depth, geological characteristics, and location (LBPTC 2010). The existing aquifer in the medium lower Limpopo Valley has depths ranging from 80 to 200 m (Barros 2009). The map showing the number of boreholes in the basin is shown in the River Basin under the Groundwater Chapter.

Very little monitoring of groundwater conditions has been conducted throughout the basin and has only been completed where resources have been overexploited. The main need for groundwater data is due to the interconnected nature of groundwater and surface water interactions as discussed in SW/GW Interactions in the River Basin.

Transboundary Aquifers

Within the Limpopo River basin there are three transboundary aquifers along the northern border of South Africa with Botswana, Mozambique, and Zimbabwe (Cobbing et al. 2008):

• Ramotswa Dolomite
• Tuli Karoo
• Limpopo

The Limpopo aquifer underlies the Limpopo River which is a well-known sand river in southern Africa. It is also a transboundary aquifer with unconsolidated alluvial deposits which fill the river channel and build up the irregular adjoining floodplain. Sustainable utilisation of the aquifer is dependent up the management of surface water in the river (Cobbing et al. 2008). A mean saturated thickness is noted at 3.5 m with a hydraulic conductivity of 120 m/day (Cobbing et al. 2008). The aquifer is the broadest east of the Limpopo/Shashe confluence increasing to 500 to 700 m as it enters Mozambique, but narrows to 50 m near the Limpopo/Crocodile confluence.

Transmissivity, estimated from pump testing boreholes near the confluence of the Motlouse and Limpopo Rivers, is in the order of 2 700 m³/day (Alemaw 2008).

The following table estimated annual groundwater abstractions in the Limpopo River basin (Environmentek, CSIR 2003).

Estimated annual groundwater abstractions in the Limpopo River basin.

Source:Environmentek, CSIR 2003

As water scarcity is an issue previously discussed in the Climate and Weather Chapter, groundwater recharge, in general, is minimal in the Limpopo River basin. The figure below indicates recharge varies throughout the basin with the highest recharge in the southern portion of the basin in South Africa and lowest groundwater recharge occurring in the northern portion of the basin with portions in Botswana, South Africa, and Mozambique.

Botswana

About 80 % of the population of Botswana relies on groundwater as a source of drinking water. Most of the livestock and mining industry are dependent upon groundwater during the dry season (LBPTC 2010). In many rural areas groundwater may be the only source of water that is economical. Limitations to further groundwater development, in spite of its potential, has recharge rates that are very small to negligible. The current use is being done inefficiently therefore it does not have long-term sustainability.

The groundwater potential for Botswana from sand rivers in the Limpopo River basin is estimated at approximately 565 m³ per day per km of river (Alemaw 2008).

Mozambique

Within the basin in Mozambique groundwater has high salinity and low productivity therefore limited potential. Where salinity is high, for example in the interior of the Gaza province, groundwater is not suitable for consumption (Barros 2009). The water supply for the city of Xai-Xai in Mozambique is supplied via groundwater.

South Africa

The highest well yields, excluding the alluvium associated with the sand rivers, occur in the southern portion the Limpopo River basin in South Africa. In karst formations well yields can be up to 2 000 m³/day with generally good quality (Environmentek, CSIR 2003). In all other geological formations in the basin, well yields are typically 20 to 50 m³/day, with occasional yields of up to 150 m3/day.

The municipal water demand for the town of Musina in South Africa, located near the border with Zimbabwe, is met from groundwater as is the annual 4 Mm³ for the Venetia diamond mine (Cobbing et al. 2008). It is assumed this is met with water abstracted from the alluvial deposits within the Limpopo River.

Groundwater use varies in each national Water Management Area (WMA). In general, large portions of the rural population water requirements in each WMA are met with groundwater as it is often the only dependable source of water. Some of the larger centres such as Polokwane, Mokopane, and Makhado receive their water partly from local wellfields (DWAF 2003a,b,c,d).

Zimbabwe

Alluvial deposits are common in southern Zimbabwe, occurring as sand filled ephemeral rivers (Moyce et al. 2006). The Mzingwane River, a tributary of the Limpopo river, is a sand filled channel, with extensive alluvial aquifers distributed along its banks on the lower catchment. The Mzingwane river contributes approximately 25 % of the run-off in the Limpopo River as noted in the Hydrology Chapter in The River Basin.

These alluvial aquifers are currently being utilised with irrigation schemes and are considered to have potential to support significant additional irrigation development, using infiltration galleries and well point systems to exploit the resource (Moyce et al.2006).

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