Daily Maverick
Dailymaverick logo

South Africa

South Africa, World, Our Burning Planet

As water resources dwindle, managed aquifer recharge offers hope for a resilient future

As water resources dwindle, managed aquifer recharge offers hope for a resilient future
Roger Parsons
By Roger Parsons
20 May 2025
Facebook
1
Water scarcity is escalating globally, driven by a growing population and climate change. The reuse of water and wastewater is an imperative, but faces major social challenges.

I recently spent three inspirational days at Ismar12 – an international symposium on managed aquifer recharge. At various stages in the past, it has also been referred to as artificial recharge, enhanced recharge and water banking. The symposium was attended by 180 delegates from 30 countries, including most of the leading experts in the field.

Managed aquifer recharge – or MAR – involves deliberately introducing water into aquifers using various techniques, including infiltration basins and boreholes, injection boreholes and riverbank filtration. It is mostly intended that the recharged water be recovered later, but other strategic objectives, such as environmental management, also exist.

MAR helps mitigate the effects of over-extraction, prevents land subsidence, enhances water quality by promoting natural filtration and is used to control the migration of contaminated groundwater and ecological management and mitigation. Crucially, it will play an increasingly important role in adapting to climate change by providing a reliable water source, particularly during droughts.

MAR is nothing new and has been practised for centuries. The initial prototype of MAR can be dated back to 475 BC to 221 BC in China, where channels were dug to facilitate the infiltration of surface water into the ground to raise the groundwater level for agricultural irrigation.

Since the arrival of the 20th century, MAR has gained much traction and is now used around the world. Orange County, California, is well known for its water woes and has included MAR in its water supply mix since the 1940s. Both Australia and Israel have used MAR for decades. A presentation at the symposium described how the Israelis inject air below their recharged basins to improve infiltration rates and prevent clogging, two critical factors in the MAR process.

It is not only arid and semi-arid countries that form part of the MAR family. MAR is used in Basel, Switzerland, to protect their groundwater supplies from various sources of urban contamination.

About 70% of Sweden’s water supply is derived from the subsurface, and MAR is actively used to ensure sustainability. In the Netherlands, MAR is used to protect freshwater supplies from seawater intrusion, again ensuring sustainable drinking water sources.

Southern African examples


Research into the feasibility of adopting MAR on the Cape Flats Aquifer was undertaken in the 1970s by pioneers Dr MR Henzen and Dr G Tredoux of the CSIR. However, the concept was never taken up by the then Cape Town municipality.

Nonetheless, southern Africa has two long-standing, good examples of large-scale MAR. MAR has been part of the water supply mix since groundwater was first developed in 1976 to supply water to Atlantis on the Cape West Coast. Here, stormwater run-off and treated effluent are used to improve sustainability and prevent saline intrusion as the primary aquifer is used to supply water to the industrial township.

In Windhoek, Namibia, after much research and a dire need to meet the growing water demand of the city, it took a leap of faith to inject treated surface water from their dams into specially designed boreholes for a period of three years. The objective was to prevent high evaporation losses from the dams and store water below ground in aquifers where such losses do not occur.

The cost of the injected water and the expected recovery rate were just two of the concerns at that time. These were put to rest when the next drought rolled along – as they do in semi-arid environments. The artificially recharged water proved to be a lifesaver, and without it, Windhoek would have been up the creek without a paddle, so to speak.

Challenges


Applying MAR comes with several challenges that must be carefully addressed for successful implementation. MAR schemes require scientific hydrogeological exploration, numerical modelling, engineering design, environmental assessment and regulatory approval. This has to be supported by field trials and monitoring.  

With support from the Department of Water and Sanitation (DWS) and the Water Research Commission (WRC), a blueprint was prepared in 2007 for the implementation of MAR schemes. Our recent droughts pushed this option to the forefront and a nationwide strategy is in place to adopt MAR – where feasible and when needed.

Dr Ricky Murray, who led the DWS/WRC projects, identified 10 MAR success criteria, now widely adopted in the intentional literature. The priority criterion – at least for me – is whether MAR is actually needed. If we oversell the concept, it will lead to failures.

Cape Town groundwater


Detailed monitoring across Cape Town during the past eight years showed that the groundwater levels have not been affected by either the drought or over-abstraction. Essentially, the aquifers have remained full, with no capacity to accept more recharge. Regular winter flooding on the Cape Flats confirms this.

However, some 20 million cubic metres of water are pumped each year in the Philippi Horticultural Area (PHA) to produce 70% of the fresh produce sold in Cape Town. At the same time – and in response to the Day Zero drought of 2015-2017 – the City of Cape Town is implementing plans to pump groundwater from the Cape Flats Aquifer to bolster domestic water supplies.

In this situation, MAR will play a crucial role in increasing the yield of the aquifer system, promoting the sustainability of both the domestic and agricultural water sources and ensuring that the abstraction does not induce saline intrusion.

Treated sewage effluent, stormwater and desalination


An interesting feature of the Cape Flats MAR scheme is that treated sewage effluent will be used to recharge the system. A highly sophisticated treatment plant is being built to ensure that the effluent is fit for human consumption, and the movement through the aquifer will further polish the water.

Almost all sewage effluent generated in California’s Orange County is now treated and recharged back into the aquifers. This has been going on since the 1960s. The use of impaired quality water as a source water for MAR has long been shown to be a safe and technically feasible option.

One of Dr Murray’s success criteria is understanding what source water for MAR is available, including volumes and when it is available. I have already discussed the use of treated impaired quality water, but water can also be sourced from rivers and dams when plentiful, from stormwater run-off and desalination. It can even be pumped from one part of an aquifer to another.

Climate change models suggest that in these parts, rainfall might increase, but will come in short, sharp bursts with longer dry periods in between. This will result in much shorter periods of river run-off, as already exists in the Karoo.

Over the past decade, the Department of Water and Sanitation embarked on a series of experimental projects in the western Karoo to help mitigate the prolonged drought.

For example, low-cost and easy-to-maintain structures were built in a normally dry riverbed near Calvinia to retain or retard the flow of flood water. Infiltration boreholes were drilled and trenches dug to promote subsurface infiltration of these waters.

Similar efforts at Vanwyksvlei and Brandvlei have also proven to be successful. Sand dams have been particularly effective in dealing with the high sedimentation load of floodwater.

By learning from the experiences of the international community and persevering with the research, the viability and success of MAR schemes can only improve. DWS is currently in the process of formulating legislation to authorise some of these small schemes to enhance the recharge of groundwater in drought-stricken areas.

Range of projects


One of the things that struck me at the symposium was the range of scale of MAR projects, ranging from massive projects to macro efforts. Mexico City has a population of some eight million people, and 70% of its water supply is derived from underlying aquifers. MAR is used to supplement natural recharge and combat land subsidence in the central part of the basin.

In contrast, Unicef established a MAR scheme at Dollow, Somalia on the border with Ethiopia to capture flood waters. Using simple technologies with low maintenance requirements, the captured water is stored underground and later abstracted from shallow wells to supply water to a growing number of war-displaced refugees. Previously, the intermittent flooding of the Dawa River was considered a hazard, but now is a critical tool for survival and combating climate change.

Rainwater harvesting is often punted for promoting water resilience. However, the problem with this approach is that usually there is little rain to harvest during droughts, and the volume of rain that can be harvested is small.

Rhodes University plans to overcome these constraints. In response to Makhanda’s well-documented inability to regularly and reliably supply water to the city, Rhodes is developing groundwater to keep the university functional. Further to a desktop study and numerical modelling, Phase 1 of the project entails routine exploration, and drilling and testing of the Witteberg Aquifer. This will also include the design and implementation of water treatment and reticulation systems.

The second phase will entail capturing rooftop water and recharging it into the ground. The objectives of the second phase are to promote sustainability and prevent affecting other groundwater users.

One of the keynote speakers, Dr Peter Dillon from Australia, observed that there was a growing awareness of the potential role of MAR in water resources and, globally, the implementation of MAR has accelerated at a rate of 5% per year during the past few decades. It has demonstrated itself to be technically feasible and less costly when compared with dams and desalination, for example.

With the science and engineering in place, it now becomes an issue of political and social licence. DM

Dr Roger Parsons is a hydrogeologist with almost 40 years’ experience. He is in private practice and former Western Cape branch chair of the Ground Water Division. He was awarded the Ground Water Medal by the Ground Water Division of the Geological Society of Southern Africa for outstanding service and dedication to furthering the science and technology of groundwater.

Categories:

Tags: