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6.4. ECONOMIC IMPACTS Report No 678-F-001 METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT The annual resource losses for the predicted reduction in riverine resources and the costs of mitigation of healthrelated impacts are shown in Table 6.3. 6.5. WATER YIELD The Phase 1 system yield (using an annual reliability of 98%) associated with the Treaty Scenario is 26.8 m 3 s -1 . Table 6.3 Annual social losses and costs associated with the Treaty Scenario. Cost Type Component Resource losses* 1 Mitigation Costs* 3 Monetary Value (Maloti) Fish* 2 1,738,683 Forage 79,357 Medicinal plants 83,223 Wild vegetables 658,913 Trees & shrubs 5,092,358 Sub-Totals 7,652,534 Public health 229,695 Animal health 151,807 Sub-Totals 381,502 Totals 8,034,036 * 1 Based on local trade values * 2 Total loss of resource use assumed for Reach 1 (Matsoku), proportional losses for other reaches * 3 Costs of avoiding health impacts 36
7.1. HYDROLOGY Report No 678-F-001 METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT SECTION 7. DESIGN LIMITATION SCENARIO This scenario describes the consequences of imposing design-limited releases from the Phase 1 dams on the downstream river reaches. The effects of the physical dimensions of the LHWP structures (Annex E) are translated into hydrological parameters in two ways: average annual releases from the dams are limited to 30-40% of the MAR as measured at the dam sites; instantaneous flow limitations are imposed by features of the relevant structures; outflows from Matsoku Weir are geared for the best seasonal distribution of low-flow releases, together with short-duration flushes, and it is assumed that it is possible to release any proportion of the inflow from the weir if the outlet tunnel gates from Matsoku Weir to Katse Dam are kept closed. It is further assumed that: floods of 10 and 20 years return period would spill over all dams, except Katse Dam, where only to the flood of 20 years return period would spill; floods of 2 to 5 years return period would not be released from the dams. The hydrological computations applied to the Design Limitation Scenario are as follows: − the flow regimes at the IFR Sites immediately downstream of the dams and weir (IFR Sites 1, 2 and 7) are determined first according to the limitations described above; − thereafter, the flow regimes at IFR Sites further downstream are estimated using the continuity of flow and historical data. Within the limits set by the criteria, high and low flows could be combined in many ways to create modified flow regimes for the rivers. In an iterative process, combinations of high and low flows that are deemed to be leastdamaging to the rivers are selected. In general, the Design-Limitation flow regimes are reduced from those described for the Minimum Degradation Scenario in two ways. The range of low flows is reduced to a level between the Minimum Degradation and Treaty Scenarios. For instance, the present-day range of wet-season low flows at IFR Site 1 is 0.02-6.75 m 3 s -1 . The top of the range is reduced to 6.00 m 3 s -1 in the Minimum Degradation Scenario, and to 3.00 m 3 s -1 in this scenario. Similarly the present-day, dry-season range of low flows is set at 0.00-4.03 m 3 s -1 . The top of the range is reduced from 4.00 m 3 s -1 to 1.00 m 3 s -1 in this scenario. The numbers of floods of all four classes of within-year floods are reduced, most to the level of only one or no occurrence per annum. The 1:2 and 1:5 year floods are eradicated, but the 1:10 and 1:20 year floods remained. The lowest percentages (33-35%) of the present-day MAR (Table 7.1) are immediately downstream of the three major dams, and the values increased down the rivers to the highest percentage (65%) at IFR Site 6. Details of the calculations are given in the Specialist Report (No 678-002) and the Hydrology Report for 648 (No 648-F-13). The actual releases from the dams, should this scenario be adopted, would have to be based on the capping levels for low flows and the flood volumes provided in the Report No 678-002. 37
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