groundwater shared between two or more countries. Approximately 5,116 km of land border and seven aquifers is shared between South Africa and Namibia, Botswana, Zimbabwe, Mozambique, Swaziland and Lesotho as shown in Figure 4-11 [2]. The seven transboundary aquifers shared with South Africa have been identified for further investigation with only one of the seven consisting of only shallow and local aquifers [110].
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Figure 4-11 – Map of seven transboundary aquifer systems shared with South Africa [110]
Whilst this is encouraging from an electrical perspective through the development of UGPHES schemes and cross boundary wheeling of electricity, the actual management of transboundary groundwater may be a challenge. Further consideration needs to be given to the nature of the aquifer itself in terms of its hydraulic properties which includes transmissivity.
4.4.1 Limpopo river a lluvial aqu ife r
The northern border between Botswana, Mozambique, Zimbabwe and South Africa is created by the Limpopo River as shown in Figure 4-11. The irregular adjoining floodplain
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resulting from unconsolidated alluvial deposits that fill the river channel constitutes an international transboundary aquifer [2, 111]. The aquifer is currently tapped by using wellpoint systems, hand-dug wells, infiltration galleries and boreholes generally located on the river bank [112]. The town of Musina meets its municipal water demand by tapping off the Limpopo river through the use of boreholes and wellpoints while agricultural use by neighboring countries from this aquifer is negligible. Resource-poor farmers consider this aquifer as a valuable source of water that allows during dry periods for meeting and sustaining irrigation demands [2].
It must be noted that there is no evidence of the potential of this aquifer being fully explored. Deeper exploratory wells need to be drilled in an effort to understand the full extent of the aquifer and its potential to be adapted for use in a UGPHES scheme.
4.4.2 Lesotho/Easte rn Free State Ka roo aquifer
The boundaries between western Lesotho and south-eastern South Africa are created by the Caledon, Senqu, Mohokare/Clarens and Makhaleng rivers. The aquifer characteristics for this area comprise of the Burgersdorp Formation, Molteno Formation and the Elliot Formation [2].
The Burgersdorp Formation is a semi-confined to confined aquifer able to support borehole yields <0.5 l/s and with a mean transmissivity of 20 m2/d [113, 105]. Many boreholes have been dug in this formation and used for the supply of water to small rural communities and farms [2].
The Molteno Formation is classified as a semi-confined aquifer with an average transmissivity of 20 m2/d and is regarded as the best aquifer in this region. The borehole yields from the Molteno Formation are >3 l/s while there is also spring discharges as high as 0.5l/s [113, 105].
The Elliot Formation is an aquifer that is classified as poor due to its compact nature. The underlying Molteno Formation and aquifer are often in hydraulic continuity. The borehole yields are only 0.9 l/s and transmissivity is 5 m2/d [113, 105].
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The low borehole yields and low transmissivities of the transboundary aquifers between Lesotho and South Africa makes this area unfavorable for the application of UGPHES technology. It must be noted as with the Limpopo River Alluvial Aquifer, that there is no evidence of the potential of this aquifer being fully explored with the drilling of deeper exploratory wells [2]. Deeper drilling could yield aquifers with improved transmissivities and well yields suitable for implementation in a UGPHES scheme.
4.4.3 Mozamb ique/Zululand Coastal a quife r
The Zululand coastal plain extends approximately 250 km south of the Mozambique and South Africa border along the northeast coast of South Africa, and approximately 1,000 km north towards and into Mozambique. Groundwater recharge figures for this area ranges between 5% and 18% across the plain [114]. Land use for this area which is sparsely populated, is limited to subsistence farming, nature conservation, irrigation farming using surface water and limited commercial forestry. The South African side of the boundary has a confirmed north-south groundwater divide which continues north towards and into Mozambique with the flow separated towards the coast (east) and the Pongola River (west) [2].
A primary aquifer with shallow groundwater levels underlies the entire plain giving rise to fresh water lakes which are used to support the water requirements of the majority of the local population. The aquifer capacity is estimated to be able to support a population
>500,000 with the Uloa Formation being the most productive aquifer with transmissivity
>1,000 m2/d and borehole yields up to 30 l/s [2]. Limited information is available for the aquifer on the Mozambique side of the border however it is expected to be similar to that on the South African side [2].
It is envisaged that the demand for groundwater from this aquifer is unlikely to be significantly expanded in the future with little to no risk of competition for water between South Africa and Mozambique thereby negatively impacting the available water resources [110].
The vastness of this aquifer and excellent transmissivity presents a very promising opportunity for the development of a UGPHES scheme that could greatly contribute towards the dire need for generating capacity in South Africa. There are however many
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parameters that will first need to be investigated to ascertain the viability of such a scheme in this area. One such parameter is the head height which is directly proportional to the power output. Due to the shallow groundwater levels, this could prove to be an obstacle.