Report No 969/1/02

November 2002



Water of acceptable quality is both necessary for the improvement of the quality of life and essential in the maintenance of all forms of life. The semi-arid and arid regions of South Africa form approximately 66% of the country. Most of these regions do not have surface water resources. Groundwater is therefore becoming an important component of the water supply for many South African rural communities in these regions. It also offers a cost-effective solution for rapidly developing settlements, which lack the necessary infrastructure normally associated with water supply. The availability of water for various uses is directly related to the management of water quantity, quality and/or the elimination of diseases.

This report presents the findings of research conducted by the Institute for Groundwater Studies on the development of a risk-based decision tool (DT) to manage and protect groundwater resources. A risk can be defined broadly as the probability that an adverse event will occur in specified circumstances. Effective decision-making involves the management of risks: the identification, evaluation, selection and implementation of actions to reduce risk. Risk assessment is a technique that provides such information to the manager, thereby facilitating the complex and integrated decisions required.


The objectives of the project discussed in this document are summarised as:

The aim of this research is to develop a DT to aid groundwater resource managers in the task of optimising the utilisation of groundwater. The DT will include:


In this study, a tool that uses fuzzy logic based risk assessments to make decisions influencing groundwater management in South Africa is discussed. As a process of evaluating the potential for adverse impacts, risk assessment provides managers and the public with the means to surpass observations about relationships between events and their effects and, by so doing, to answer questions about what is safe and what is unsafe. However, the priority in performing any risk assessment is clarifying the factual and scientific basis of the risks posed. As such, both qualitative and quantitative evidence regarding the nature of the effects, their severity, and their reversibility or preventability must be examined.

In order to obtain accurate results from the risk assessment process, accurate data must be used. This report sets aside a chapter to discuss both aquifer and contaminant parameters and methods to obtain both sets of parameters.

The DT is divided into three tiers namely a rapid, intermediate and comprehensive assessment. For each of the tiers the following risk assessments can be performed:

Once the desired risk assessments have been completed, cost-benefit-risk analyses can be used to aid in decision-making regarding the management of a groundwater resource. A cost-benefit-risk analysis is defined as a set of procedures used for defining, comparing and measuring benefits and costs, which originate from either an investment or the operation of an activity.

Since the early 1980's geohydrologists and engineers have developed a number of techniques for protecting groundwater. Protection is divided into two categories: measures to prevent failure and pollution of water resources, and measures to remedy the effects of polluted water resources.

On completion of the different aspects of the DT a report will be generated including the input data and the results of the risk assessments and cost-benefit-risk analysis. Depending on the user, prevention measures can be included. Unfortunately no in-depth study has been completed on remediation options, but the user will be able to browse through the various options.


All the objectives of this project were met. There are many risk assessment methodologies available, however after consulting with Prof George Pinder of Princeton University it was decided to follow a fuzzy logic approach which incorporates the knowledge of professionals in both groundwater and risk assessment fields. Professionals who were consulted are:

Based on discussions with the above-mentioned experts and extensive literature surveys a risk based DT was developed uniquely for South African conditions.


Included in the DT are methodologies to characterise fractured rock aquifers: There is ongoing research concerning these aquifers and as new methodologies are developed it is important to include them in the DT.
This DT has been developed over a period of three years and even though it has been tested and calibrated by experts, it is important to note that in order to obtain more accurate results, it must be validated over a period of many years.

In addition the database of the DT has been populated with information; it can be expanded and more detail can be added.

The ecological risk assessment is limited to a few indicators to determine the risks for aquatic ecosystems. This assessment can be developed to include aspects such as flow conditions in rivers and fish species. In addition the impacts of groundwater on terrestrial ecosystems need to be considered and included in the ecological risk assessment. Accommodating these factors complicates ecological risk assessments.

The cost-benefit-risk analysis is crude and this can be developed into more comprehensive computations.

Even though uncertainty has indirectly been included in the DT, further development of the DT should include a comprehensive uncertainty analysis. The uncertainty analysis should include aspects such as the quality of data, the relationships between potential hazards and effects of concern and, the methods used to calculate risks. The uncertainty analysis thereby highlights the limitations of the risk assessment allowing decisions to be made in a more transparent fashion.

The DT developed in this report relies heavily on the expertise of geohydrologists, assumptions and approximations of real world conditions. Together with the heterogeneities present in groundwater systems it is impossible to guarantee the accuracy of the methodologies and the reader must take this into consideration. However as Hurst (1957) stated: It is usually better to do something which is 95% effective immediately, rather than to wait several years to improve the solution by 4%.

The DT can be a useful tool for a groundwater manager to use in order to obtain an understanding of the groundwater situation in a particular area and the impacts thereof.

In addition the DT can be used to rank groundwater related problems, thereby making groundwater management and protection an achievable task.