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Report No 678-F-001
METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT
SECTION 13. IFR ASSESSMENT IN SOUTHERN AFRICA
The IFR assessment undertaken for the LHWP is, in many respects, the most detailed and advanced flow
assessment yet undertaken in southern Africa, and indeed anywhere in Africa. Key features have been the
comprehensive and integrated hydrological, biophysical and social approach, and the specific inclusion of
subsistence users into the assessment. Overall, the lessons learnt during the LHWP study are of great interest
and value to the rest of the world, and the expertise gained by both scientists and managers could and should be
exported to the rest of Africa and further. However, as noted below, IFA is not unique to Lesotho and
environmental flows are currently a subject of concern in eight southern African countries and in five other African
nations.
13.1. METHODS FOR ENVIRONMENTAL FLOW ASSESSMENT
The methods used in the LHWP to address the use of environmental flows for river management area comprise
the most advanced within four categories used in southern Africa 1 .
Reconnaissance-level assessments rely on historical hydrological records for setting flow targets; the
methods involve the least investment of time and effort, but there is the lowest confidence in their
predictions; they do not necessarily have any ecological relevance; their best use is in large-scale
regional planning of water resources.
Hydraulic methods require site measurements of the river, and are used in conjunction with hydrological
analysis to assess flows that occur often and are deemed to provide ‘good habitat’; links to the river
ecosystem are tentative or absent, and ‘good habitat’ is largely a value judgement.
Habitat-simulation methodologies link site-specific physical and hydraulic data for a range of discharges
to favoured habitat of selected species and provide a more structured assessment of discharges and the
related ‘good habitat’. These approaches have been used predominantly by Northern Hemisphere
countries where decades of research have provided sufficient data for high-resolution descriptions of the
flow requirements of selected plant and animal species. The methods focus on single species, usually
fish of important recreational or economic value, and largely ignore the other parts of the ecosystem
(e.g., aquatic invertebrates, water birds, riparian trees, marginal vegetation, algae), which are also flow
dependent and which will influence the fish populations in some way. They focused mainly on the lowflow
regime of the rivers in question.
Holistic approaches address all parts of the ecosystem and all parts of the flow regime, and include the
Building Block Methodology (BBM) used in South Africa, the Holistic Approach developed in Australia,
and now the DRIFT (Downstream Response to Imposed Flow Transformations) approach used in the
LHWP-affected rivers and described earlier in this report. A further development is the Flow Restoration
Method used in Australia to address river rehabilitation. Holistic approaches are increasingly being
recognized globally as the most appropriate way to do IFA as they allow a comprehensive assessment
of the likely ecological and subsistence implications of a range of possible flow manipulations, thus
placing before the decision-maker new information to supplement traditional engineering and economic
information upon which water-resource decisions have been made in the past.
1 Details and references are given in Paxton, B., C.B. Brown and J.M. King. 2002. A review of activities linked to
environmental flows in Africa. Unpubl. ms.
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