Transboundary aquifers

 Another alternative to unsustainable diversion projects lies in responsible exploitation of groundwater. Taylor et al’s novel work maps groundwater storage estimates for Africa, estimating supplies 100* that of surface water[1]. Yet such stores are emitted from freshwater estimates despite potential to act as a ‘buffer’ for growing food insecurity[2]. Northern Africa alone is found to have  substantial borehole yield potential. However, the Orange riparians have aquifer potential supportive of small-scale irrigation of - 0.5–5 l s ^-1. , important in strengthening community level food security.

Similarly to surface waters, aquifers can be transboundary - between them the Orange riparians share five aquifers (figure 1). Figures 2- 4 explore the potential of the aquifers for the orange riparians. Likewise to transboundary surface waters, there exists guidance for sharing aquifers in the ‘Law of Transboundary Aquifers’.

Figure 1: Transboundary aquifers between the Senqu basin riparians.*

Figure 2: Groundwater potential of Orange basin riparians.

Lesotho ≈ 100* its annual renewable freshwater (RFW) in total groundwater storage (TGS).

Namibia ≈ 1000*.

South Africa ≈ 100*.

Botswana ≈ over 1000*.

Figure 3: Aquifer productivity and approximate depth to groundwater (DTG) (A) (top).

(A) shows predominantly low DTG with some in a deeper band across Botswana, Namibia and South Africa. Maximum DTG is 100m meaning affordable access cost suited to small-scale irrigation.

(B) shows moderate – low aquifer productivity for all riparians. 

Figure 4: Aquifer productivity in different geological environments.

Most common underlying geology is consolidated sedimentary rock allowing intermediate borehole yield (0.5–5 l s ^-1 ). Botswanas groundwater potential is greatest; beneficial as it’s main irrigation occurs away from the Senqu.

One may presume that because of the transboundary situation of some aquifers, there is potential for conflict between riparians. However, Cobbing et al’s study of South Africa’s transboundary aquifers states that preconceived notions that aquifers that are not managed holistically will be exploited to the detriment of another state are largely misplaced in this context [1]. With reference to four of the five transboundary aquifers below, Cobbing et al find that aquifer transmissivity is low and regional meaning that ‘transboundary impacts of groundwater abstraction are likely to be very small’[2]. Whilst highly transmissive aquifers need strong cooperative management, this study shows the need to recognise the heterogeneity of aquifers and necessary management. Conflict over transboundary aquifers for the Senqu riparians is very unlikely, however if exploited sustainably the rich underground water source can provide smaller scale security in what is likely to become an even more unpredictable water future.