Edgerly Island and Ingersoll Tract Flood Management Plan and Adaptation Study 8/30/2018
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EDGERLY ISLAND AND INGERSOLL TRACT FLOOD MANAGEMENT PLAN AND ADAPTATION STUDY 8/30/2018 August 30, 2018 Prepared for Napa River Reclamation District Napa County Flood Control & Water Conservation District EDGERLY ISLAND AND INGERSOLL TRACT FLOOD MANAGEMENT PLAN AND ADAPTATION STUDY August 30, 2018 Prepared for Napa River Reclamation District Napa County Flood Control & Water Conservation District 550 Kearny Street Suite 800 San Francisco, CA 94108 415.896.5900 www.esassoc.com Irvine Sacramento Los Angeles San Diego Oakland San Francisco Orlando Santa Monica Pasadena Seattle Petaluma Tampa Portland Woodland Hills TABLE OF CONTENTS Page Executive Summary ................................................................................................................. 1 ES-1. Introduction ............................................................................................................. 1 ES-2. Existing Flood Hazard and Management ............................................................... 1 ES-3. Flood Management Plans ....................................................................................... 2 ES-4. Next Steps ............................................................................................................... 5 1. Introduction..................................................................................................................... 6 1.1 Plan Development Process..................................................................................... 6 1.2 Report Organization ................................................................................................ 7 2. Existing Flood Hazard and Management ..................................................................... 8 2.1 Vertical Datums ....................................................................................................... 9 2.2 Historic Flood Events .............................................................................................. 9 2.3 Flood Water Levels and Frequency ...................................................................... 10 2.4 Sea-level Rise ....................................................................................................... 13 2.5 Geotechnical Considerations ................................................................................ 15 2.5.1 Settlement .................................................................................................. 15 2.5.2 Seepage ..................................................................................................... 15 2.5.3 Slope Stability ............................................................................................ 16 2.5.4 Earthquakes ............................................................................................... 16 2.5.5 Breaches .................................................................................................... 17 i ESA / D160787 August 30, 2018 Table of Contents Page 2.6 Community Infrastructure ...................................................................................... 17 2.7 Existing Flood Management ................................................................................. 18 2.7.1 County Code Building Requirements ......................................................... 20 3. Flood Management Plans ............................................................................................ 22 3.1 Evaluation Criteria ................................................................................................. 22 3.2 Flood Management Strategies .............................................................................. 25 3.3 Flood Management Measures .............................................................................. 27 3.3.1 Flood Barriers ............................................................................................. 27 3.3.2 Floodproofing ............................................................................................. 30 3.3.3 Flood Preparedness and Planning ............................................................ 33 3.3.4 Residual Risk ............................................................................................. 34 3.4 Flood Management Plans ..................................................................................... 34 3.4.1 Plan 1: Flood Preparedness and Planning ................................................ 35 3.4.2 Plan 2: Vinyl Sheet Pile Floodwalls to 12.5 ft NAVD ................................. 41 3.4.3 Plan 3: Steel Sheet Pile Floodwalls to 15.5 ft NAVD ................................. 46 3.5 Comparison Between Plans .................................................................................. 51 4. Suggested Next Steps ................................................................................................. 54 4.1 Integration with Regional Planning ....................................................................... 54 4.2 Engineering Data and Analyses ........................................................................... 54 4.3 Environmental Review and Permitting .................................................................. 55 4.4 Funding ................................................................................................................. 56 5. References .................................................................................................................... 58 6. List of Preparers ........................................................................................................... 60 ii ESA /D160787 August 30, 2018 Table of Contents Page 7. Figures ........................................................................................................................... 61 APPENDIX A: HISTORIC FLOODING APPENDIX B: ELEVATION SURVEY DATA APPENDIX C: HYDRAULIC ANALYSES APPENDIX D: GEOTECHNICAL AND STRUCTURAL ENGINEERING ANALYSES APPENDIX E: COST ESTIMATES APPENDIX F: CONCEPTUAL ECONOMIC ASSESSMENT Edgerly Island and Ingersoll Tract Flood Management and Adaptation Study iii Table of Contents Page List of Figures Figure 1. Project Area .............................................................................................................. 62 Figure 2. Vertical Datums ........................................................................................................ 63 Figure 3. 1973 Flood Event ..................................................................................................... 64 Figure 4. February 2017 Flood Event ...................................................................................... 65 Figure 5. FEMA Special Flood Hazard Areas ......................................................................... 66 Figure 6. Edgerly Island Cross Section & Flood Water Levels, Existing Conditions .............. 67 Figure 7. Sea-Level Rise Projections ...................................................................................... 68 Figure 8. Edgerly Island Cross Section & Flood Water Levels, 1 ft and 2 ft Sea-Level Rise ....................................................................................................................... 69 Figure 9. Edgerly Island Cross Section & Flood Water Levels, 3 ft and 5 ft Sea-Level Rise ....................................................................................................................... 70 Figure 10. Levee Failure Modes .............................................................................................. 71 Figure 11. Elevations of Community Infrastructure ................................................................. 72 Figure 12. Sheet Pile Wall, Oblique View ................................................................................ 73 Figure 13. Plan 1: Flood Preparedness and Planning – Map ................................................. 74 Figure 14. Plan 1: Flood Preparedness and Planning – Schedule ......................................... 75 Figure 15. Plan 2: Vinyl Sheet Pile to 12.5 ft NAVD – Map .................................................... 76 Figure 16. Plan 2: Vinyl Sheet Pile to 12.5 ft NAVD – Implementation Sequence ................. 77 Figure 17. Plan 2: Vinyl Sheet Pile to 12.5 ft NAVD – Schedule ............................................ 78 Figure 18. Plan 3: Steel Sheet Pile to 15.5 ft NAVD – Map .................................................... 79 Figure 19. Plan 3: Steel Sheet Pile to 15.5 ft NAVD – Implementation Sequence ................. 80 Figure 20. Plan 3: Steel Sheet Pile to 15.5 ft NAVD – Schedule ............................................ 81 Figure 21. Comparison of Plan Approaches to Flood Risk Reduction .................................... 82 iv ESA /D160787 August 30, 2018 Table of Contents Page Figure 22. Comparison of Plan Barriers Design Flood Elevations and Flood Event Elevations .............................................................................................................. 83 Figure 23. Comparison of Community Coordination ............................................................... 84 List of Tables Table 1 Comparison of 100-year water level estimates for the Napa River adjacent to EIIT .................................................................................................................... 12 Table 2 Water levels for the Napa River adjacent to EIIT .................................................... 13 Table 3 Levee eyebolt marker elevation changes, 1984-2017 ...........................................