Groundwater in South Africa has great potential to supplement our country’s water demands. Currently, studies show that less than 10% by volume of the Average Groundwater Exploitation Potential is abstracted on an annual basis. The 2017 drought has aided in creating awareness of the importance of this resource towards building water resilience. If managed correctly, groundwater is commonly viewed as a sustainable source. Oftentimes, the ‘sustainability’ of a groundwater resource is an ‘open-ended’ definition based on the hydrogeologist’s interpretation of aquifer pumping test data alone. This approach often discounts the cumulative impact of environmental factors (including drought and climate change) and other users on groundwater. The use of numerical groundwater models to support and inform the conceptual models provides the mechanism to bridge this gap.
This paper discusses various approaches and examples of where numerical modelling plays a key role in supporting groundwater usage in a sustainable and informed manner. In particular, this includes:
•Inclusion of impact from other anthropogenic activities and groundwater users, with model scenarios that show the potential impact of each on the other, as well as the combined result to groundwater (levels and water quality)
•Consideration of extreme climatic events (e.g. 1 in 100-year drought and/or flood), including the use of uncertainty analysis and consideration of dynamic groundwater management, such as the possible varying of sustainable pumping rates to suit the prevailing conditions
•Identification of groundwater receptors and appropriate assessment of potential impacts to those receptors from groundwater usage, including “target-audience” thinking in the post-processing and reporting of numerical model results, so as to convey clear messages to the interested and effected parties and stakeholders
•Use of multiple methods and technologies to calculate and model surface water / groundwater interaction and recharge, including uncertainty analysis, and intelligent challenging of traditional methods of estimating groundwater recharge