Instream flow assessments for regulated rivers in South Africa using the Building Block Methodology

Abstract The demand for water from South Africa's growing population is creating an ever-increasing pressure on the country's rivers. The urgent need to provide more water services often conflicts with the desire to maintain or improve the ecological condition of the rivers. To provide guidance on the sustainable use of a river's water-resources, the Building Block Methodology (BBM) has been developed for assessing the instream flow requirement for any river. Development has been done jointly over the last five years by the national Department of Water Affairs and Forestry (DWAF) and river scientists, and the accent is on identifying a complex of different magnitude flows for maintenance of entire river ecosystems. The BBM caters for the almost universal reality in South Africa of having rapidly to provide scientific guidance on such flows for a river in cases where biological data and understanding of the functioning of the river are limited. However, the methodology works equally well in data-rich situa...