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Report No 678-F-001 METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT Table 10.1 Reach-specific summary of the combined biophysical consequences for each scenario with Phase 1 dams in place. In general terms the level of impacts are coded as follows: blue – negligible; green – low; yellow – moderate; purple – severe; red – critically severe. Reach Minimum Degradation Design Limitation Fourth Treaty 1 M S S S 2 7 Proximal to dam or weir M L S S S S CS S 3 L M M S 4 5 6 Distant from dam or weir L N N L L N L L N L L N 8 N L L M The Minimum Degradation scenario serves as a baseline comparison. Removal by Phase 1 structures of 30-40% of the MAR in the form of large inter-year floods as well as a significant proportion of small intra-year floods and reduction of dry season base flows by a small proportion would lead to only slight or negligible biophysical changes in most downstream reaches. Moderate biophysical changes would likely be measured in the reaches downstream of Katse and Mohale dams and Matsoku Weir; these would largely be comprised of geomorphological changes and impacts to local fish populations caused by the structures themselves. At the other end of the spectrum, critically severe biophysical changes are expected under the Treaty Scenario, and are being observed in the reaches downstream of Katse Dam where > 95% of the MAR has been diverted. The intermediate Design Limitation and Fourth Scenarios are intermediate as well in terms of biophysical changes. An important observation is that the most severe changes would be expected in the proximal river reaches, with considerably lower impacts in the more distant reaches. A comparison of the levels of severity of biophysical impact at each IFR site and the percentage of MAR hypothesised for each site (Figure 10.1) confirms the general positive correlation between the two variables, indicates that biophysical impact in distant reaches is much less per proportion of MAR diverted than in proximal reaches. 10.4. SOCIAL IMPACTS Table 10.2 summarises the severity of social impacts, in the absence of any specific mitigation and compensation programmes, predicted for the various river reaches. These are correlated with the biophysical impacts but display a different pattern of distribution, perhaps influenced by the distribution of communities in relation to the various reaches and the local geomorphology, which influences the distribution and abundance of important resources such as fish, trees and herbs, and the extent to which communities gather and utilize these resources. The Treaty Scenario leads to critically severe social impacts through resource depletion in the reaches immediately downstream of Katse and Mohale dams (2 and 7). The table demonstrates that, whatever the scenario, the social impacts are low for all sites located at least two reaches away from a dam or weir (4, 5 and 6). This factor is discussed further in Section 11. 52
% MAR released 70 60 50 40 30 20 10 0 Report No 678-F-001 METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT N L M S CS Severity of biophysical impacts Severity of biophysical impacts 0 1 2 3 4 5 6 Proximal reaches Distant reaches Figure 10.1 Comparison of % MAR diverted with the severity of biophysical changes in various reaches. Table 10.2 Reach-specific summary of the combined socio-economic consequences for each scenario with Phase 1 dams in place. In general terms the level of impacts are coded as follows: blue – negligible; green – low; yellow – moderate; purple – severe; red – critically severe. Reach Minimum Degradation Design Limitation Fourth Treaty 1 Proximal L M M M 2 to dam or L S S CS 7 weir L M S CS 3 L S S S 4 Distant L L L L 5 from dam L L L L 6 or weir L L L L 8 N M M M 53
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