*3.1.1 Spatial changes in groundwater resources of the KSTA*

The KSTA is the largest transboundary aquifer that South Africa shares with a neighbouring state. Thus, changes in groundwater storage will not be uniform throughout the entire surface area of the aquifer. During a given period, some areas of the aquifer may experience increased recharges, whereas other areas of the same aquifer experience a discharge. **Figure 9** shows the spatial variation in groundwater storage depth of the KSTA.

**Figure 9** shows how the depth of groundwater in the aquifer changed over time. Areas that increased in depth as well as areas where depth was reduced are depicted across the aquifer. The figure shows that large parts of the aquifer experienced a decline in groundwater storage depth between 1978 and 2007. The figure also shows that recharge and discharge is not uniform throughout the surface of the aquifer. Moreover, even though there was some form of discharge of groundwater from the aquifer between 1948 and 1967, at that time discharge occurred in small areas. Furthermore, between 1948 and 1957, large discharge of groundwater occurred in parts of the Free State, the Eastern Cape, as well as small areas around the border of the Northern Cape Province (refer to **Figure 4** showing the location of the aquifer), as revealed by the negative changes in groundwater depth.

**Figure 7.** *Average groundwater volume in the KSTA, 1948–2020.*

**Figure 8.** *Groundwater volume in the KSTA, 1948–2020.*

In the same decade, positive changes in depth were observed throughout the entire surface of the aquifer; however, increased recharge occurred largely in Lesotho. In the next decade, it can be seen from **Figure 9** that areas of discharge covered the north-eastern parts of the aquifer and became more pronounced in Lesotho, spreading to neighbouring parts of the Eastern Cape as well as Kwa-Zulu Natal, whereas recharge was observed throughout the remaining area of the aquifer. This changed again between 1968 and 1977, with the decade experiencing the

*Groundwater Dynamics in Transboundary Aquifers of Southern Africa DOI: http://dx.doi.org/10.5772/intechopen.109906*

**Figure 9.** *Spatial changes in groundwater storage of the Karoo Sedimentary TBA.*

highest recharge (largest positive changes in groundwater depth) recorded in the study. Although the decade (1968–1977) was dominated by higher recharge and low to almost non-existent discharge, this was short-lived. The rate of discharge (shown by the decreasing depth of water in the aquifer) increased and eventually became higher than the rate of recharge (which is represented by increasing depth) in the subsequent years from 1978 to 2007. Areas of recharge currently account for less than 10% of the total surface area of the Karoo transboundary aquifer. The graph also shows that the largest discharge of groundwater from the Karoo aquifer occurs in Lesotho. Similar conclusions were reached in previous studies in California [41, 42], China [43, 44], India [45–50], Iran [51], the Indus Basin transboundary aquifer [52], Kenya [53] and the North-Western Sahara Aquifer System (NWSAS) [54], where groundwater storage was found to be declining over time.

#### **3.2 The Stampriet Transboundary Aquifer System (STAS)**

Groundwater storage within the area of the Stampriet aquifer is depicted in **Figure 10**. The volume of groundwater in the area is presented over a period of 72 years, from 1 January, 1948 to 31 December, 2020.

The volume of groundwater fluctuated between 30 and 37 km3 , with some years (1950–1951, 1954–1955,1957–1958, 2000–2001, and 2005–2006) depicting volumes above 37 km3 . The volume of groundwater in the aquifer fluctuated throughout the study period, showing periods of declines and increases in volume. The aquifer's largest increase in volume was recorded between 1970 and 1980, and the largest decrease was recorded between 1980 and 1990. Moreover, the largest volumes of groundwater were recorded between 1975 and 1978, where values were above 45 and 47 km3 , respectively. The monthly fluctuations in groundwater volume are depicted in **Figure 11**.

Groundwater volumes were higher between January and July where average volumes are 33 km3 or above, with a slight decline in average volumes recorded between August and December each year.

**Figure 10.** *Average groundwater volume in the STAS, 1948–2020.*

**Figure 11.** *Groundwater volume in the STAS, 1948–2020.*
