Know Your Water: sustainable groundwater research

Know Your Water - Crowdfunding Campaign

As drought grips large parts of South Africa, the importance of groundwater as a secure source of water for domestic and agricultural needs has become clear. However, whilst many people think of groundwater as an unlimited resource, groundwater does have a finite limit and needs to be managed sustainably to ensure future supply. Help contribute to a nationwide citizen science project to predict our groundwater's sustainability by determining how much of our groundwater is dependent on rainfall.

 

Determining the sustainability of South Africa’s groundwater resources

The Idea

The purpose of this campaign is to accumulate the funds necessary to collect as many rainfall and groundwater samples across the country as possible. The aim is to develop a model that determines distribution of renewable groundwater resources in South Africa. Renewable groundwater reserves are those that have been recharged by rainfall in the last 50 years. Climate change will directly impact the amount of recharge and hence the model will also be able to predict vulnerability to climate change. It will be developed by the combined efforts of Stellenbosch University students as well as the public as a citizen science initiative. This sampling will begin at the end of this funding campaign on the 19th of March 2017.

The Science

The primary objective is to model the distribution of modern groundwater across South Africa. Modern groundwater is defined in this project as groundwater that has been replenished by rainfall sometime in the last 50 years. In order to work this out, an isotope tracer, tritium (the radioactive isotope of hydrogen), will be measured in rainfall and groundwater samples. 

Tritium is naturally produced in the stratosphere and is incorporated into the water molecule and then transported to land via precipitation (which is rain, but also fog, dew and mist). So long as it is in contact with the atmosphere we assume that it has a concentration that is in equilibrium with the atmosphere. But, once it enters the groundwater system, it’s no longer in contact with the atmosphere, and the concentration starts to reduce because of radioactive decay.  Therefore, the longer groundwater is isolated from the atmosphere, the lower the tritium concentration in groundwater will be (see Figure 1). 

By knowing the concentration of tritium in rainfall and the concentration in a groundwater reservoir we can predict how regularly the reservoir is being replenished by precipitation that contains atmospheric tritium. Once we know this, we can model how renewable the resource is as well as how vulnerable it is to variations in climatic conditions e.g. a reduction in rainfall.

The recharge pattern of Tritium enriched rainfall, its groundwater flow path and subsequent decay. Adapted from Alley et al, 1998.

The recharge pattern of Tritium enriched rainfall, its groundwater flow path and subsequent decay. Adapted from Alley et al, 1998.

The Method

The sampling trip will involve the collection of groundwater samples from pre-determined boreholes where we can measure the depth to water as well as setting up rainfall collection stations. Citizen scientists who have received their sampling kits via post will sample their groundwater from boreholes/springs, post the samples back to us and we will send them, along with rainfall samples sent to us, off for determination of the tritium activity. We then use modelling software that incorporates tritium activities along with depth to water levels to determine the distribution of modern groundwater. Our initial plan is to make one field trip in March 2017. However, if we raise enough funds we will also try to sample again after the winter rains.

The "Know Your Water" team are a group of postgraduate students at Stellenbosch University. The project is the brainchild of Jared van Rooyen and forms the basis of his MSc. Yaa Agyare-Dwomah and Zita Harilall are working on their honours theses and will work on the precipitation model that feeds into Jared’s groundwater model. The project is supervised by Dr. Jodie Miller who works on the application of isotopes to solving water problems.