DRAFT Final Report Environmental Flows Assessment Upper Trishuli-1 Hydropower Project Appendix E: Final Report Environmental Flows Assessment Upper Trishuli-1 Hydropower Project, Nepal Prepared for: APPENDIX E Environmental Flows Assessment Upper Trishuli-1 Hydropower Project Appendix E: Environmental Flows Assessment Prepared for: Supplemental ESIA- Nepal Water and Energy Development Company Upper Trishuli-1 Hydropower Project, Nepal & the International November 2014 Finance Corporation (IFC) Cover Photo: Trishuli River downstream from the proposed powerhouse site, facing upstream. October, 2013. [Photo: P. de la Cueva] © 2014 ESSA Technologies Ltd. ESSA Technologies Ltd. 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Table of Contents List of Figures ............................................................................................................................................ iii List of Tables ............................................................................................................................................... v 1 Overview ................................................................................................................................................ 6 2 Hydrology and Water Resources Use in the Project Area ............................................................... 9 2.1 Hydrological analysis .................................................................................................................... 9 2.2 Water and river users ................................................................................................................. 11 3 Impact Hypotheses and Linkages to Habitat ................................................................................... 14 3.1 Introduction ................................................................................................................................. 14 3.2 Upstream Hypotheses ................................................................................................................ 15 3.3 Diversion Reach Hypotheses ..................................................................................................... 16 3.4 Downstream Hypothesis ............................................................................................................. 16 3.5 Impacts of the Project ................................................................................................................. 17 4 Aquatic Ecology of the Project Area ................................................................................................ 18 4.1 Literature Synthesis: Fisheries in the Gandaki River System and the Trishuli Watershed ........ 18 4.2 Summary of Aquatic Surveys in the Project Area ....................................................................... 25 4.3 Indicator Species for Environmental Flows ................................................................................ 31 5 Environmental Flow Assessment ..................................................................................................... 35 5.1 Introduction ................................................................................................................................. 35 5.2 Design Flow Scenario ................................................................................................................. 36 5.3 Alternative Environmental Flow Scenarios ................................................................................. 41 5.4 Assessment with IHA Metrics ..................................................................................................... 45 5.5 Power under Design & Environmental Flow Scenarios .............................................................. 46 6 Summary and Recommendations..................................................................................................... 49 6.1 Summary ..................................................................................................................................... 49 6.2 Recommendations ...................................................................................................................... 50 7 Terms of Reference: Environmental Flows Management Plan ...................................................... 52 7.1 Goals of the EFMP...................................................................................................................... 52 7.2 Approach and methodology ........................................................................................................ 52 7.3 Complementary Aquatic Baseline ............................................................................................... 53 7.4 Definition of Environmental Flow Rules ...................................................................................... 55 7.5 Mitigation measures .................................................................................................................... 55 7.6 Operations Monitoring Program .................................................................................................. 59 7.7 Organization and Capacity ......................................................................................................... 60 7.8 Stakeholders Consultation Plan .................................................................................................. 61 7.9 Regional Collaboration ............................................................................................................... 61 7.10 Reporting ................................................................................................................................... 61 7.11 Schedule of implementation ...................................................................................................... 61 8 References and Further Reading ...................................................................................................... 62 Annex 1: Taxonomy of Fish Species in the Upper Trishuli .................................................................. 52 Annex 2: Summary of IHA metrics .......................................................................................................... 53 i | Annex 3: Power Generation Model .......................................................................................................... 56 Annex 4: Synopsis of Adaptive Management ........................................................................................ 59 ii| APPENDIX E Environmental Flows Assessment- Upper Trishuli-1 Hydropower Project List of Figures Figure 2-1: Unimpaired average annual discharge for the Trishuli River at the UT-1 intake weir based on scaled Betrawati gauge data for 1967–2010. Representative low-flow (1970) and high-flow (2000) years are highlighted with red symbols. The water year period is based on the interval from March 1 to the last day of February in the following calendar year. ......................................................................................................... 10 Figure 2-2: Daily flow hydrographs for representative low-flow (1970) and high-flow (2000) years in linear (upper) and logarithmic (lower) scales. .................................................................... 10 Figure 2-3: River uses in the diversion reach of the Project. .................................................................... 11 Figure 2-4: Fishing activity registered by NESS field team through the aquatic survey period .................. 12 Figure 2-5: Hydropower development (existing and under planning) in the Trishuli Watershed ................ 13 Figure 3-1: Schematic representation of a run-of-river facility showing the three distinct sections: upstream, diversion and downstream. ................................................................................... 14 Figure 4-1: Major sub-basins of the Gandaki River system. The five sub-basins shown in color have been surveyed in the historical fish inventories summarized in Table 4-1. ................... 18 Figure 4-2: Five fish sampling locations of the DOFD (2008) survey are marked with green triangles. The UT-1 Project area is indicated by the red rectangle. ....................................... 19 Figure 4-3: Location of monitoring sites for the monthly aquatic habitat and water quality surveys .......... 25 Figure 4-4: Wetted width at the five monitoring locations ........................................................................... 26 Figure 4-5: Relationship between wetted width and the different habitat types through the year .............. 27 Figure 4-6: Evolution of periphyton density and total suspended solids concentration .............................. 27 Figure 4-7: Evolution of macro-invertebrates density and total suspended solids concentration ............... 28 Figure 4-8: Species diversity (presence) throughout the fish survey monitoring period ............................. 28 Figure 4-9: Evolution of S. richarsonii catch during the monitoring period (August 2013- September 2014) in the five river monitoring stretches ......................................................... 29 Figure 4-10: Results of catch per unit method for the two sampling methods (cast