Defining flows to protect instream biota : a critique of the instream flow incremental methodology and the development of a hierarchical habitat-based approach, using the pennant-tailed catlet, Chiloglanis anoterus in the Marite River, South Africa

Doctoral Thesis


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University of Cape Town

This thesis focusses on two approaches to determining Instream Flow Requirements (IFR) for regulated rivers, specifically in the sub-tropical eastern region of South Afiica using a flow-sensitive fish species, the pennant-tailed catlett 07iloglanis anoterus. In response to the diminishing and altered flow regimes of rivers, and the ecological consequences, a range of methodologies has evolved that attempt to quantify IFRs for rivers. One group of methods that attempts to do this are known as habitat-assessment approaches. They focus specifically on understanding how changes in river flow affect the quantity of physical instream habitat. The most widely used of these is the Instream Flow Incremental Methodology (lAM) and it's associated computer packages, PHABSIM II. More recently, South Africa has also turned its attention of ways to defining IFRs. Given lAM's prominence internationally, it was considered as one potential methodology. Nonetheless, its applicability to local conditions required testing. At the same time, the easterly-flowing rivers were under increasing development pressure, providing a particular immediacy to find appropriate means to define IFRs. Thus, my research was designed to assess the downstream effects of the Injaka Dam on the physical habitat of a flow-sensitive fish species of the Marite River. Specifically, it aimed to test the local applicability of lAM, based on the microhabitat requirements of C anoterus, and to explore an alternative approach if it were found to be unsuitable. Microhabitat is described on the basis of three hydraulic variables: depth, velocity and Channel Index (substratum and cover).

Bibliography: leaves 249-279.