The application of a hydraulic biotope matrix to the assessment of available habitat: Potential application to IFRs and river health monitoring

In an attempt to meet the requirement of the new South African Water law a number of initiatives are under way to determine the flow requirements for our rivers. An essential component of this initiative is the determination of the influence of changing flows on instream habitat. Two components need to be assessed: change in the aerial extent of habitat and change in habitat diversity. This paper presents a technique that aims to address qualitative and quantitative changes in instream habitat in response to changing flow discharge. A hydraulic biotope classification based on a matrix of substrate and flow type has been developed by the authors in collaboration with stream ecologists. Hydraulic biotope diversity was studied in the Buffalo River, Eastern Cape province, and results show how the composition of hydraulic biotopes depends on both the channel morphology and the discharge. These findings complement parallel studies carried out by Padmore and Newson in the United Kingdom. The classification system promises to provide a useful way to describe discharge-related changes in habitat. Early research by Wadeson and Rowntree was based on point surveys and ignored the spatial distribution and aerial extent of hydraulic biotopes. King and Schael have developed a mapping technique to describe the distribution of hydraulic biotopes, but its application is limited by time and manpower requirements. This paper demonstrates a relatively simple field technique, which is under development, based on overhead photography. The technique allows a quantitative assessment of the changes in the aerial distribution of hydraulic biotopes in response to changes in discharge. The potential application of this technique to both IFR assessments and the River Health Programme is discussed. Keywords: habitat mapping; environmental flows; geomorphology (Afr J Aqua Sci: 2001 26(1): 67-73