Below the surface

Exploring groundwater as a significant sustainable water source. By Grethe Bestbier.

“One thing I can tell you,” said Prof. Eilon Adar, leading groundwater hydrologist and former director of the Zuckerberg Institute for Water Research at Ben-Gurion University of the Negev, “groundwater is a reliable and non-trivial source of water.” While most of South Africa relies on surface water, difficult climatic conditions and limited rainfall is forcing us to consider properly using other water sources. According to Adar, groundwater is the best way to bridge this water shortage.

Surface water’s limitations and Israel’s response

Although surface water sources are easily developed and relatively inexpensive to use, they depend on rainfall fluctuations and climate change. Groundwater is not influenced to the same extent. Compared to surface reservoirs, groundwater reservoirs are huge and can tolerate climatic variations much better.

“In Israel, until 2004 when massive seawater desalination began, the entire development of the modern water supply system was based on groundwater,” said Adar.

Israel secured sufficient and adequate water supplies, even in desert areas, by developing their groundwater resources.

“Without enough streams, we were looking for groundwater in Israel. Excluding the Jordan River, the only source of agricultural development throughout the history of Israel were aquifers,” said Adar.

Aquifers discharge groundwater through natural springs and seepage into the oceans. To add to its water supply, Israel constructed the National Water Carrier, completed in 1964. The system combines groundwater from the natural Yarkon springs and production wells with surface water from the Jordan River, and diverts it via pipelines to the Negev Desert.

Initially, they drilled relatively shallow wells into the coastal aquifer. When that was not enough, they dug deeper — sometimes more than a kilometre — into artesian aquifers.

“We knew that we had deep groundwater, because we had 3D-mapped the subsurface hydrological structure, in order to identify potential pockets of fresh and brackish water,” stated Adar.

Expensive? Yes. Worth the investment? According to Adar, a definite yes. “It provided most of the water needs for Israel until 2004 when additional desalinated water was introduced into the water supply system.”

A fragile source of water

“Whenever we interfere with Mother Nature, there can be problems. Our job is to mitigate this and ensure that we act in an environmental and appropriate way,” said Adar.

He emphasised that unless you have studied the hydrogeological structures, there is no way to know what is going on in these underground water stores. A lack of knowledge can lead to catastrophic mistakes.

Groundwater is stored within the saturated zone — where the space between mineral grains is saturated with water — and within an unsaturated zone — which also contains air. The natural recharge of the reservoir is from rainwater percolating through the unsaturated zone, which sieves away unwanted substances. Sometimes, to increase the natural recharge, water is directly injected into the saturated zone, bypassing this filtering system, with disastrous consequences.

Many other examples of the fragility of the groundwater system exist. Not knowing a spring’s storage capacity and the process of recharge, one might mistakenly think that you have an inexhaustible amount of groundwater when that is not the case. Inadequate groundwater abstraction might completely destroy the aquifer’s storage and water quality within months. But, as Adar rightfully asks, “Without adequate hydrogeological information, how can you know that?”

According to Adar, the Western Cape has much to learn about using groundwater, starting with its lack of hydrogeological data.

“In the Western Cape, I have seen that farmers hire a contractor, start to drill and have no idea what the target layer is,” said Adar.

There are no drilling records, no collection of soil and rock information, and no one knows what the subsurface three-dimensional hydrological structure is. Adar stressed the need to make observation boreholes in strategic locations for future groundwater abstraction, as a back-up system to surface water supply.

“I’m almost sure that in the future, because of climate variations, the surface water resources will not be sufficient to sustain increasing demands,” said Adar. “Groundwater is a reliable water source and sustainable water store. However, it is very fragile and unless studied in the most vigorous way, it can be a disaster. On the other hand, it can be a treasure as the best water savings account.”