This case study focuses on the water resource situation in arid countries like Namibia, which are approaching or have reached the end of their conventional water resources. In these cases, there is no option but to use and enhance local groundwater resources. Hard-rock aquifers (a feature of the hydrogeology of Africa) and their associated MAR issues provide a further focus. A summary of the Windhoek system is provided in Table 7.

Table 7 – Windhoek MAR Scheme.

Namibia is located along the arid south-west coast of Africa. The capital, Windhoek (population 326,000 in 2011), is situated in a semiarid region of the country’s central highlands (Figure 25). The average annual rainfall in Windhoek is 360 mm and the average evaporation is 2170 mm/year. River systems originating in the Auas and Eros Mountain ranges are draining away from the city in all directions. As a result, local surface water resources are very limited and most of the city’s water supply is obtained from surface impoundments located tens to hundreds of kilometers from the city. Large fluctuations in annual rainfall aggravate the situation (Kirchner and van Wyk, 2001; Murray, 2017).

Figure 25 – Windhoek central city and mountains in background (Pixabay).

Windhoek owes its existence to the presence of springs, which provided an ample supply of water when the area was first settled around 1840. The mostly thermal springs emerged from deep-seated faults in quartzites that form the main aquifer. The town continued to rely on groundwater and in 1911 a wellfield development was initiated. In 1933 a small surface storage dam was added. As a result of overuse of the aquifer, another surface storage dam, located further away, was added in 1957. In the years from 1966 to 1969, use of the aquifer had grown to 2.5 times the estimated average natural recharge of 1.7 Mm³/year, so development of supplementary water sources became urgent (Murray, 2017; Kirchner and van Wyk, 2001).

Augmentation Options in a Water-Scarce Country

By 1974 a new water master plan included an Eastern National Water Carrier to supply water to the central areas from the Okavango River some 750 kilometers to the north. Construction of the carrier began in the late 1970s in several phases. First, a 94-kilometer pipeline was built from the Von-Bach Dam at Okahandja to the Omatako Dam. From there an open water canal was constructed for approximately 300 km to Grootfontein and groundwater from the Berg Aukas mine was pumped into the canal. The last phase of the Eastern National Water Carrier, connecting Grootfontein to the Okavango River near Rundu, was never built. However, the latest information indicates that due to the current drought, a pipeline from Rundu to Grootfontein is being considered again to augment the water supply for the central areas of Namibia (Weidlich, 2019).

By 2000, the water demand stood at 20 Mm³/year and most of the city’s water was coming from the surface water supply scheme consisting of three interconnected dams as discussed in Section 3 “The Source Water”. The wellfield contribution was about 10 percent of the city’s total water supply and another 10 percent was coming from the wastewater reclamation.

In 1968, headlines in South African papers read: “Windhoek drinks sewage water.” Following pilot studies from the early 1960s regarding direct reclamation of sewage water, a full plant was built in 1968. In 2001, the New Goreangab Reclamation Plant was built with a capacity of 7.7 Mm³/year, which was one of the largest of its kind in the world at the time. Windhoek had become one of the first cities in the world to introduce direct recycling of effluent for drinking purposes (du Pisanie, 2006).

An important water demand management measure has been the use of wastewater for the restricted irrigation of sports fields, parks and cemeteries within the city. Since 2002, the New Goreangab Reclamation Plant supplies a better quality of water for unrestricted irrigation. Approximately 1.4 Mm³ was produced for irrigation in 2002 and the supply from this system is expected to increase further (van Rensburg, 2006).

Still, Windhoek was fast outgrowing the available water resources and attention turned to MAR. From 1997 to 1998, four borehole injection tests were conducted in the Windhoek Aquifer and an economic feasibility study by the city indicated that artificial recharge was the most viable water supply augmentation option available. In 2002, construction of the first stage of the scheme took place. It included six injection boreholes with a combined recharge capacity of 10,000 m³/day (Murray et al., 2018).

Actual injection started in 2006 and continued until 2012 when the targeted recharge area could not receive any more water. The scheme’s success led to two expansion phases with a third planned for 2017. This included the drilling of new deep boreholes of up to 500 m depth for abstraction purposes. The aim is to utilize as much of the aquifer’s storage as practically possible (as a water bank), as this will significantly enhance the city’s water supply security (Murray, 2017; Murray et al., 2018).

The cost of the entire MAR scheme (from 2016 onwards) is estimated to be US$ 52.4 million, including borehole siting, drilling and testing, borehole pump installations, bulk supply pump stations, pipelines and power supply infrastructure. The City of Windhoek has already spent over US$ 8.4 million on the scheme, and is looking to fund an additional US$ 9.6 million which they will have to source externally (Murray, 2017).

The MAR Opportunity

A 2013 cost comparison by the Windhoek city engineer (Figure 26) shows the available alternatives – the Tsumeb aquifer (450 km north) and the Okavango River pipeline (700 km north) – to be 1.9 and 2.7 times more expensive than the MAR option. MAR is 1.8 times more expensive than reclaiming Windhoek’s sewage water to drinking water quality. The city engineer closed a presentation about the Windhoek Managed Aquifer Recharge with a quotation (Peters, 2014):

“We are faced with a series of great opportunities brilliantly disguised as impossible situations” (adapted from Charles Swindoll).

Figure 26 – Windhoek water supply locations and a more recent cost comparison (Peters, 2014).