Muskrat Falls Project - CE-13 (Public) Page 1 of 170 Muskrat Falls Project - CE-13 (Public) Page 2 of 170 Newfoundland and Labrador Hydro - Lower Churchill Project GI1140 - PMF Study Final Report - December 2007 Table of Contents Glossary of Abbreviations List of Tables List of Figures Executive Summary 1. Introduction ......................................................................................................................................... 1-1 1.1 Background................................................................................................................................. 1-1 1.2 Probable Maximum Flood Definition .......................................................................................... 1-1 1.3 Approach .................................................................................................................................... 1-2 1.3.1 Review of Previous Studies................................................................................................ 1-2 1.3.2 Analysis of Meteorological Data........................................................................................ 1-3 1.3.3 Development of the Hydrological Model of the Churchill River ........................................ 1-3 1.3.4 Review of Flood Handling Procedures for Upper Churchill ............................................... 1-3 1.3.5 Flood Routing to Establish the PMF for Gull Island and Muskrat Falls ................................ 1-4 2. Review of Previous Studies................................................................................................................... 2-1 2.1 Churchill Falls Power Project: Snowmelt and Frequency Studies for Design Floods, 1969........... 2-1 2.2 Gull Island Maximum Probable Flood Study, 1975 ..................................................................... 2-2 2.3 Flood Handling Study of the Churchill Falls Complex, 1989 ....................................................... 2-2 2.4 Churchill River Complex, PMF Review and Development Study, 1999....................................... 2-3 2.5 Summary..................................................................................................................................... 2-4 3. Lower Churchill Basin .......................................................................................................................... 3-1 3.1 Basin Description........................................................................................................................ 3-1 3.2 Climate ....................................................................................................................................... 3-1 3.3 Flow Regime............................................................................................................................... 3-2 4. Upper Churchill Basin.......................................................................................................................... 4-1 4.1 Basin Description........................................................................................................................ 4-1 4.2 Climate ....................................................................................................................................... 4-1 4.3 Flow Regime............................................................................................................................... 4-2 4.4 Flood Operation.......................................................................................................................... 4-2 5. Meteorology......................................................................................................................................... 5-1 5.1 General....................................................................................................................................... 5-1 5.2 Precipitation................................................................................................................................ 5-1 5.2.1 Spring PMP ....................................................................................................................... 5-2 5.2.2 All-Season PMP................................................................................................................. 5-3 5.2.3 Spring 100-year Rainfall .................................................................................................... 5-3 5.2.4 All-Season 100-year Rainfall.............................................................................................. 5-4 5.3 Temperatures .............................................................................................................................. 5-4 5.4 Snowpack ................................................................................................................................... 5-5 5.5 Climate Change .......................................................................................................................... 5-6 5.6 Comparison with Previous Studies .............................................................................................. 5-7 PRH-325967.10049 Rev. 0, Page i Muskrat Falls Project - CE-13 (Public) Page 3 of 170 Newfoundland and Labrador Hydro - Lower Churchill Project GI1140 - PMF Study Final Report - December 2007 6. Churchill River Basin Watershed Model............................................................................................... 6-1 6.1 The SSARR Model....................................................................................................................... 6-1 6.2 Model Configuration................................................................................................................... 6-1 6.2.1 The Smallwood Reservoir Basin ........................................................................................ 6-2 6.2.2 The Ossokmanuan/Gabbro Lake Basin .............................................................................. 6-3 6.2.3 The Lower Churchill Basin ................................................................................................ 6-4 6.3 Calibration .................................................................................................................................. 6-6 6.3.1 Calibration Criteria............................................................................................................6-6 6.3.2 Calibration Data................................................................................................................6-6 6.3.3 Calibration Adjustments .................................................................................................. 6-10 6.3.4 The Smallwood Reservoir Basin ...................................................................................... 6-10 6.3.5 The Ossokmanuan/Gabbro Lake Basin ............................................................................ 6-11 6.3.6 The Lower Churchill Basin .............................................................................................. 6-11 6.3.7 Commentary ................................................................................................................... 6-12 6.3.7.1 The Smallwood Reservoir Basin............................................................................. 6-12 6.3.7.2 The Ossokmanuan/Gabbro Lake Basin .................................................................. 6-13 6.3.7.3 The Lower Churchill Basin .................................................................................... 6-14 6.4 Verification ............................................................................................................................... 6-14 7. PMF Simulations................................................................................................................................... 7-1 7.1 General....................................................................................................................................... 7-1 7.2 Meteorological Input................................................................................................................... 7-2 7.2.1 Rainfall.............................................................................................................................. 7-2 7.2.2 Temperatures ....................................................................................................................7-2 7.2.3 Snowpack ......................................................................................................................... 7-3 7.3 PMF Cases .................................................................................................................................. 7-3 7.3.1 100-year Snowpack and Spring PMP ................................................................................. 7-4 7.3.2 PMSA and 100-year Spring Rainfall ................................................................................... 7-4 7.3.3 Summer/Autumn PMP Preceded by 100-year Rainfall ....................................................... 7-4 7.4 Results Summary......................................................................................................................... 7-5 7.5 Sensitivity Checks and Analysis................................................................................................... 7-5 7.6 Comparison with Previous Studies .............................................................................................. 7-8 7.7 Comparison with Historic