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4.1.3 Design Limitation Report No 678-F-001 METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT This is a scenario based on the practical limitations of flow releases imposed by the designs of the Phase 1 structures (Annex E). In terms of volumes of water releases, it is intermediate between the above two scenarios. A full description appears in Report No. 678-002. 4.1.4 Fourth Scenario This scenario was selected to fall midway between the Treaty and design limitation scenarios and to provide a reference point between the former (legally defined and highest water yield but most severe environmental and socio-economic impacts) and the latter (possible within engineering constraints but likely to have high impacts on water yield and overall costs). A full description appears in Report No. 678-002. 4.2. DESIGNATION OF SEVERITY RATINGS USED FOR BIOPHYSICAL CONSEQUENCES 4.2.1 Individual Component Responses to Specific Flow Releases For each biophysical component at each flow reduction, the level of severity of the consequences for each of its sub-components was assessed relative to the present day condition of the river according to the scales shown in Table 4.1. Table 4.1. Percentage scales of change in biophysical components (abundance, function or composition) used in assigning severity ratings in the IFA. Severity Rating Geomorphology, Sedimentation, Water Quality, Vegetation, Macroinvertebrates Fish Herpetofauna; Mammals & Birds 0 0-5 0 – 5
Report No 678-F-001 METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT 4.2.2 Ecosystem Responses to Overall Reduced Flow Releases Biophysical consequences and explanations linked to each flow reduction level within a scenario were assessed in combination to create a single description of an overall ecosystem response for each river reach within each scenario. These are summarized further in Sections 5 to 8. The levels of impact can be interpreted as changes in the river from present-day (near natural) conditions, or for IFR Site 2 (immediately downstream of Katse Dam) an estimated near-natural condition, as follows: None: The river will stay in approximately the same condition as at present. Negligible: 0-10% change, either in most subcomponents or most important subcomponents, of the riverine ecosystem. Low: 10-20% change. Moderate: 20-40% change. Severe: 40-80% change. Critically severe: 80-100% change. 4.3. DESIGNATION OF SEVERITY RATINGS USED FOR SOCIO-ECONOMIC CONSEQUENCES Social impacts were assessed on a scenario-specific basis, i.e., the method required the identification of a comprehensive modified flow regime and assessment of its biophysical consequences before social impacts could be determined. 4.3.1 Cultural and Subsistence Use of River Resources Impacts on cultural and subsistence use of river resources were assessed using the predicted biophysical changes, the critical nature of the usage (i.e., the importance of the resource for the livelihoods of the affected populations), the number of households harvesting the resource, the frequency of usage, and the availability of alternative resources. The resulting social impact was then ranked for each resource on a four-point scale, using expert opinion, as follows: None: No appreciable change expected. Low: The resource is not important or, if important, its quantity is predicted to change by < 20%. Moderate: The resource is important, and its quantity is predicted to change by 20-50%. Severe: The predicted biophysical change is > 50% and the resource is considered to be essential for the livelihoods of the affected populations. 4.3.2 Public and Animal Health The impacts on public and animal health were assessed on the basis of biophysical changes that could influence people’s health, the wide range of factors influencing health and data, and on the extent of river use by members of the PAR and their livestock. Most of the diseases considered already occur in Lesotho and there is a risk of contracting them even in the absence of the LHWP. Thus, for health assessment, both a baseline probability and a future probability of contracting a disease or facing a health risk were considered. The predicted future probability was inclusive of the baseline probability of contracting the disease. Further, if the dams are expected to make a difference to health risk, this difference is reflected by adding the extra probability to the baseline probability. For each type of impact, a baseline probability (i.e., the present-day probability that someone in the community or a domestic animal would contract the disease or face the health risk), and a future probability were identified using the following scale: 19
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