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METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT c. assess the ecological impacts of the four release scenarios using the biophysical database that is compiled during the IFR study; d. assess the social impacts resulting from flow reduction for four scenarios; e. assess the economic impact on the Population at Risk using the ecological and social impacts. Thereafter, the Consultant will: check the computations for the yield assessment of the Phase 1 against the revised impact assessments, combined with existing assessments IFR Sites 1, 2, 3, 7 and 8; produce qualitative and quantitative ecological, social and economic impact reports for all eight IFR sites. TASK 2: REGIONAL CONTEXT OF IMPACT SIGNIFICANCE a. The IFR will be set in regional context where possible. b. The Phase 1 summary report (see Task 4) will be structured to incorporate the appropriate material. TASK 3: OPTIMIZATION OF THE FLOWS AVAILABLE UNDER THE TREATY SCENARIO a. The DRIFT database for the IFR reaches, including all relevant hydrological data, previous assumptions on flows under the Treaty scenario, biophysical impacts and estimated resource losses, will be retrieved and reviewed. b. Based on the assumed maximum use of the flow release capabilities of Katse Dam, Mohale Dam and Matsoku Weir, the historic variations in annual and seasonal flows, and the biophysical and seasonal sensitivities of the various river reaches, an initial flow release schedule for each structure will be recommended which will minimize ecological and social impacts. c. The proposed release programmes will be reviewed with LHDA Operations to confirm their practicality. d. The resultant reductions in the previously predicted social and economic impacts are not expected to be substantial and these aspects will not be revisited. TASK 4: PREPARATION OF NEW SUMMARY REPORT f. An additional Summary Report will be prepared, based on the format of the existing Final Report: Summary of Main Findings (Report LHDA 648-F-02), which will present findings for Phase 1 structures for the four studied scenarios. Relevant text from the existing summary and other reports will be used wherever possible. New sets of tables and figures showing only Phase 1 structures and affected rivers will be prepared. The Project Manager will attend, on invitation, all meetings of the LHDA IFR Steering Committee to present report revisions, answer queries and deal with other relevant management and contractual issues. Report No. 678-F-001 B-4
METSI CONSULTANTS: SUMMARY OF MAIN FINDINGS FOR PHASE 1 DEVELOPMENT ANNEX C. SUMMARY DESCRIPTION OF THE DRIFT METHOD DRIFT (Downstream Response to Imposed Flow Transformations) is explained in detail in Report No 648-F-03. Its major steps, as used in LHDA Contract 648, are outlined below. BIOPHYSICAL COMPONENTS OF THE PROCESS Preparing the Hydrological Data Step 1: For each IFR site, a representative 20-year data set of both present-day and historical daily flows were examined and the low and high flows separated by visual inspection. Step 2: In each data set, wet and dry low flow seasons were delineated. Step 3: Summary data were produced to describe the range of low flows in each of the seasons. Step 4: Annex C - High flows were allocated to size classes and summary statistics produced for each class. Linking the Hydrological Statistics to River Features Step 5: Low flow ranges were marked on cross-sectional diagrams at each site. These diagrams also showed information such as the location of zones of riparian vegetation and kinds of substrata. (see Figure C.1). Step 6: The highest level of each class of high flow was also marked on the graphics of the surveyed crosssections. Reducing Flow Levels and Recording the Biophysical Consequences Step 7: The reductions that could be made to the top end of the low flows with only minimal biophysical degradation of the ecosystem were described. Step 8: The predicted biophysical consequences of a further structured series of reductions to the top end of the low flows were described. Step 9: The contribution to river condition made by the high flows in each class was described. Step 10: Numbers of high flows in each class that could be harvested with minimal degradation to the ecosystem were identified. Step 11: The biophysical consequences of further reductions in high flow events were described. Step 12: All the consequences, each linked to its flow-reduction level, were entered into a database (Table C.1). Report No. 678-F-001 C-1
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