A prototype decision support system for streambank rehabilitation.

Abstract

The condition of a stream is often judged by the state of its banks. This, the lack of adequate advice for streambank rehabilitation, and the drive by legislation, particularly the National Water Act, 1998 (RSA Act no. 36 of 1998) and the National Environmental Management Act, 1998 (RSA Act no. 107 of 1998), to restore South African riparian areas, created a need for more information into such systems. Identifying a gap in what we know about rehabilitating degraded streambanks led to the development of a decision support system for the selection of streambank rehabilitation techniques. The Streambank Rehabilitation Decision Support System, or SR-DSS, aims to provide riparian managers with advice on choice of technique at degraded streambank locations along a river system. Techniques were sought from the scientific literature and organised to recommend appropriate techniques for combating certain erosive processes. Rutherford et al. (1999) conclude that placing priority on sites of lower importance may be an inefficient manner of spending the resources at hand. Foreseeing this likelihood, a priority setting system was developed and based on the principles of Rutherfurd et al. (1999). These principles aim to prioritise human interests without compromising ecological interests. Along a given stream, the areas of degradation that compromise property will nearly always have the highest priority. Once these have been addressed, sites of ecological value are taken into consideration followed by sites that require substantial effort to restore. It is argued that sites taking substantial effort to restore have the least to 'loose' should they degrade further. To enable the use of these principles a site scoring system was developed, so that sites could be prioritised. This was based on the value and threat rating tables developed by Heron et al. (1999). It was soon realised that a framework was needed within which the above could be set. For this purpose, Kapitzke's (1999) planning and design procedure was adapted to form an eleven-step framework which would guide the rehabilitation venture from priority setting, to the treatment outcome. The rehabilitation approach was tested in the case of the Foxhill Spruit. The small size of the catchment allowed the different segments of the approach (framework, priority setting model, field assessment sheet and SR-DSS) to be tested in real world conditions. The approach was found to have a number of strengths. The framework brought to the attention of the user, the dominant forces at play at each site, and was useful in determining the recommendation given by SR-DSS. The priority setting model allowed sites to be arranged in order of priority, that, according to Rutherfurd et al. (1999), would be the most efficient in terms of ecological value maintained, and resources saved. The field assessment sheet was consistent in rating the degree of intervention required, and in each case directed the user to the appropriate sections in SR-DSS. SR-DSS recommended appropriate techniques that would match the erosive forces occurring at each site. Comparing the technique chosen by SR-DSS to techniques that may have been recommended instead substantiated this finding. The techniques chosen by SR-DSS were found to be superior. This approach considers all aspects of sound streambank rehabilitation and may be used to gain advice on small streams in South Africa.