This documentation is designed to be read by users who are reasonably familiar with the basic concepts underlying the quantification of instream flow requirements (IFRs) and the methods used within South Africa. It also assumes some familiarity with the concepts of the 'Ecological Reserve' and the role that it plays in the new legislation relating to management of water resources in South Africa. Readers unfamiliar with these concepts are recommended to the reference section of the document where there are listed a number of recent publications that are referred to in this document.  During the late 1980s and 1990s, the IFR for rivers in South Africa were quantified using the 'Building Block Methodology' (BBM) which is summarised in King and Louw (1998) and fully described by King, et al., (1999) and Tharme and King (1998)) and which will be briefly summarised later in this document. As the new South African Water Act was developed during 1997 and 1998 in preparation for its implementation starting in 1999, it became apparent that more rapid methods of assessment were required. This led to the concepts of the 'Planning Estimate' and the 'Preliminary Reserve'. These are now referred to as the 'Desktop estimat' and the 'Intermediate determination', while the most detailed type of study is called a 'Comprehensive determination'.