Written by: Izak Smit (Scientific Services, Kruger National Park) with inputs from: Willem du Toit and Ernest Bertram (Department of water affairs and forestry, Pretoria), Wouter Jordaan (Conservation Services, Sanparks), and Ben du Plessis (Technical Services, Sanparks)
For many people groundwater equates to boreholes making "unavailable and unused" water available for humans, animals and irrigation. On the surface, this may also seem to be the case in the Kruger National Park (KNP) where all of the bush-, concession- and trails camps, as well as picnic sites and ranger posts and some rest camps (Punda Maria and Orpen) depend entirely on groundwater for their daily water requirements.
Satara rest camp utilises boreholes for irrigation of their gardens, and every visitor to Kruger is familiar with the borehole-associated waterholes dotted across the landscape. However, what many people are not aware of is that even under natural, un-impacted conditions groundwater plays a vital role in Kruger. Groundwater forms an integral part of the hydrological (water) cycle and plays important functional roles in the ecosystem.
Ever wondered why rivers keep flowing in the dry season when it hasn't rained for months? "Invisible" groundwater is largely responsible for the "visible" flow (base flow) of rivers and the maintenance of surface water in pools, pans and wetlands. Throughout the year, but much more visibly during the dry season, the water stored in the subsurface is slowly released into these low-lying surface water bodies.
If the groundwater level drops to below the level of the river during extended droughts, surface water, which is well known to support a wide range of biodiversity, is negatively affected. However, it is not only extended droughts that could influence the groundwater levels.
If not properly managed, artificial impacts such as over-pumping from boreholes could also jeopardise the contribution of groundwater to the ecological functioning of a system. Furthermore, although groundwater is defined as subsurface water, it does not mean that vegetation does not have access to it. Groundwater-dependent ecosystems are ecosystems that have access to subsurface water on which they depend for their survival.
The alluvial floodplains, especially around the Limpopo, Levuvhu and, to a lesser extent, Shingwedzi rivers, are good examples of such systems in Kruger. The Greefswald forest in the Mapungubwe National Park is another famous groundwaterdependent ecosystem under the protection of Sanparks.
If the groundwater level drops, these unique ecosystems become stressed and may be threatened. In line with a "nature evolving" management strategy, the water-for-game programme in Kruger was revised in 1997, which resulted in the closure of many supply boreholes.
This network of unused boreholes has remained intact and provides a unique opportunity to monitor the natural fluctuation of the rest water levels inside these boreholes. The information collected from these boreholes is especially useful as reference sites against which current operational boreholes can be benchmarked and the impacts quantified.
Consequently, the water levels in many of these unused boreholes are now measured bi-annually by the different rangers in Kruger, building up a record of groundwater level behaviour over time (see graph). This monitoring programme, which entails measurements of the water levels at the end of the dry and wet season respectively, has been running since 2001.
The intention is to establish it as a longterm monitoring programme. The dataset will grow in value as long-term trends emerge. However, six years after inception valuable information has already been forthcoming from this monitoring programme.
In general, the groundwater level appears to be shallower on the eastern basaltic landscapes than on the western granitic landscapes of the park. Furthermore, over time the trends in water level reflect annual rainfall patterns.
The good rainfall received in large parts of Kruger in the most recent climatic year has, like the good rainfall of the 2003/2004 season, resulted in a rise of the median groundwater level measured in more than 120 boreholes across Kruger (see map). This illustrates the dynamic fluctuation of groundwater and most importantly, the dependence thereof on rainfall for recharge.
The groundwatermonitoring programme, coordinated by Kruger's Conservation Services and archived and analysed by the GIS Lab at Scientific Services, is providing valuable information on the status of Kruger's aquifers, as well as the linkages that exists between groundwater, climate and vegetation.
The department of water affairs and forestry (Dwaf) who has also noticed the value of this extensive network of non-operational boreholes and expressed an interest to extend their national groundwater monitoring programme into a relatively pristine area such as Kruger.
The possibility of installing electronic data loggers in some of these unused boreholes is currently being discussed with Dwaf. It is believed that Kruger can play an important role in understanding groundwater dynamics and the interaction between surface water, groundwater, climate and vegetation in a largely un-impacted area.
Next time you sit alongside a flowing river during the dry winter months or you park your car under the beautifully green and lush riparian vegetation flanking an apparently dry riverbed, remind yourself that you are in fact experiencing a "visible" expression of an "invisible" resource - groundwater!