The development of principles and procedures for the establishment of water quality objectives for aquatic systems and their application on the Jukskei River System, Gauteng

D.Phil.Water quality management in South Africa changed drastically over the last 20 years, from focussing on effluent control to managing the water resource itself. This resulted in the promulgation of the National Water Act (Act 36 of 1998) which introduced amongst others the classification of water resources and the Reserve. The implementation of the Act is currently in process, and this requires the development of a number of "tools". One such a need is to develop a protocol to set water quality objectives for water resources that takes cognisance of both the classification and the Reserve. The move to manage water resources has also taken place in other countries such as the United Kingdom, the United States of America, The Netherlands and Australia. However, most of these countries do not have the same circumstances or the same approach to water quality management as South Africa. In most cases those countries have adopted single value water quality objectives that lead to an on/off assessment of the success of management actions that does not take full cognisance of the natural variability of water quality such as is experienced in South Africa. Water quality is not static and the effect on a user is a function of dose and exposure. In most cases users can recover from short term exposures to undesirable conditions, as long as these effects are still chronic and not acute. Water quality can therefore not be assessed by making use of a single value, but must be based on a description of the central tendency as well as extreme values. This assessment (ideal, acceptable, tolerable, unacceptable) of water quality should also be linked to management actions so that managers of water resources know where to focus the limited resources at their disposal. In this thesis a protocol is developed that can be used to determine water quality objectives that take into account the class of the water resource, as well as the Reserve. Together with this an assessment system is offered that allows managers to prioritise their actions. The protocol was applied to the Jukskei River Catchment, using data that was collected over a six year period. The protocol was found to be robust and yielded water quality objectives that can be used to focus attention on the most pressing problems.Prof. G.J. Steyn Dr. H. H. du Pree