Characterization of groundwater availability and groundwater use within the main Hortgro production areas, including recharge and run-off assessments

South Africa is a semi-arid country with highly variable weather patterns (Botai et al., 2018). Climate change projections suggest that extreme weather events are likely to increase, leading to higher temperatures and reduced freshwater flows, ultimately affecting both the quality and quantity of water (Cullis et al., 2019). The Western Cape, characterised by a Mediterranean climate, is known for winter rainfall and warm, dry summers (The Fynbos Guy, 2023). Consequently, groundwater becomes especially crucial during the summer months when crops require extensive irrigation and rainfall is at its lowest.

Given the Western Cape’s complex yet favourable geological features, it’s crucial to comprehend groundwater in the South African context, particularly within the Western Cape, as the agricultural industry heavily depends on it.

For this reason,  Hortgro requested that GEOSS South Africa Pty (Ltd) compile a geohydrological assessment to highlight the importance of groundwater within their main pome and stone fruit production areas (Map 1) in the Western Cape. The study aims to describe the hydrogeological setting for each growing area, focusing on the climate, geology, and aquifer regime, as well as what water uses are registered for these areas and the expected vertical recharge.

The main objectives of this project are to:

• Describe the geohydrological setting for each of the twelve (12) growing areas in terms of

:- General Setting

– Climate

– Regional Hydrogeology (aquifer type and yield, groundwater quality and vulnerability)

– Regional Geology

• Complete a water balance for each production area utilizing:

– Existing registered groundwater users

– Vertical recharge expected (aquifer firm yield)

– The volume of groundwater available within the aquifer

• Provide clear guidance on groundwater monitoring, management and authorisation of groundwater.

The methodological approach followed for this project focused on already available data and did not rely on any field work. A desktop study was conducted for each growing area to provide a comprehensive overview of the hydrogeological setting. The regional hydrogeology, aquifer vulnerability and geology was assessed using published sources. To assess what the current groundwater use for these areas are, the Water use Authorization & Registration Management System (WARMS) and National Groundwater Archive (NGA) was used. Vertical recharge was then assessed and a groundwater balance could then be calculated using the water use figures from WARMS and the calculated recharge to assess if a area is potensially being over abstracted.

When looking at the volumes of groundwater abstraction that has been registered together with the expected yield (only taking into account vertical recharge) for each growing area, it was observed that 8 out of the 12 growing areas noted positive water balances, and 4 noted negative water balances. For the 4 growing areas that displayed negative water balances, it must be noted that these areas have been noted as having a lateral recharge component.

The Piketberg growing area is located on a mountain range that host Southeast-Northwest trending faults that act as groundwater conduits and allows groundwater to flow between different catchments. Lateral recharge is thus expected for this production area that could not be accounted for with the AFY model. Because the average water level in very deep, over abstraction is a valid risk for this area and care should be taken to monitor abstraction to ensure sustainability.

The other three areas that noted negative water balances are the Breede Valley, Wolseley -Tulbagh and Ceres production areas. All these production areas are located within valleys surrounded by mountains that would drain into the valley. Lateral recharge is thus also expected to play a role in these areas. The mountains have a higher rainfall than the valleys below and are dominated by the sandstone rich TMG formations that are known to have high recharge rates. Although the average water level is relatively shallow, the NGA datapoints are spaced far apart. Because of these data gaps, over abstraction cannot be ruled out for these areas, but it should also not be assumed based only on this data that over-abstraction is occurring.

In conclusion, the risk of over abstraction of groundwater in areas that have a negative water balance is higher, but additional data would be needed to confirm if the current abstraction is unsustainable and should be curtailed.

As the data for this assessment was obtained through regional datasets, it is highly

recommended that groundwater monitoring take place within the growing areas. A general Groundwater Management guideline is outlined in the final main report as well as the groundwater management brochures.

While groundwater presents a sustainable and cost-effective solution to many of South Africa’s water supply challenges, the success of groundwater projects typically hinges on thorough planning and discussions before borehole drilling. These discussions should include what the required vs expected yield and qualities are, outlining the complete operational process. In essence, this involves geohydrological site selection, well-informed drilling practices, scientific yield and quality testing, obtaining the necessary licenses from authorities, equipping guided by yield testing, and informed management through monitoring, including potential treatment and storage. Each of these steps can either lead to the successful implementation of groundwater as a viable solution to a water supply problem or result in an expensive and misinformed failure. Although these steps are closely interconnected, most companies and contractors tend to specialize in only one to three of these aspects. Therefore, it is advisable to organize smaller meetings among the different parties involved to ensure clear communication and collaboration.

The various steps that need to be taken are outlined below and include parties that should be involved:

• Borehole Siting – Geohydrologist (along with geophysicist and geologist).
• Drilling – Drilling contractor and geohydrologist (possibly environmentalist as well, depending on the area and scale of the project).
• Yield and Quality Testing – Yield testing contractor, geohydrologist and water chemistry laboratory (potentially environmentalist as well, depending on the area and scale of the project).
• Authorisation – Geohydrologist and Department of Water and Sanitation
• Equipping – Local/regional supplier of borehole pumps (who will require the drilling log/report and the yield and quality report), with monitoring infrastructure and equipment.
• Treatment and Storage – Water treatment specialist (who will require the yield and quality report, as well as the specifications of the equipment to be installed).
• Long-term management to ensure sustainable use – Geohydrologist and the water user.

Depending on the size of the project some of these steps may be simple and quick to address, often leading groundwater users to overlook them entirely. Whether simple or complicated it is highly advisable to thoroughly discuss each of these steps before proceeding with the project. Groundwater is a valuable resource that should be treated with respect and protected accordingly by all. Borehole drilling is not a simple once-off exercise. Users need to remember that boreholes require on-going care and maintenance.