2016 City of Imperial Beach Sea Level Rise Assessment September 2016 Submitted to the City of Imperial Beach By Revell Coastal, LLC 125 Pearl Street, Santa Cruz, CA 95060 [email protected] 831.854.7873 This Page Intentionally Left Blank Contents Contents .............................................................................................................................................i Figures…………………………………………………………………………………………………………………………………………….…iv Tables…………… ................................................................................................................................... v Photographs ..................................................................................................................................... vi Acronyms/Abbreviations ................................................................................................................. vii Executive Summary ............................................................................................................................ 1 1. Planning Background .......................................................................................................... 1-1 Introduction ..................................................................................................................... 1-1 Location............................................................................................................................ 1-1 California Coastal Commission Sea Level Rise Policy Guidance & Local Coastal Programs .......................................................................................................................... 1-3 The Planning Process ....................................................................................................... 1-4 San Diego Regional Context ............................................................................................. 1-5 Definitions ........................................................................................................................ 1-6 2. Physical Setting ................................................................................................................... 2-1 Geology and Historic Geomorphology and Ecology ........................................................ 2-1 Coastal Processes ............................................................................................................. 2-3 Littoral Cell ....................................................................................................................... 2-4 Geomorphology ............................................................................................................... 2-5 Shoreline Change Rates ................................................................................................... 2-6 Human Alterations to the Shoreline ................................................................................ 2-2 3. Climate Science ................................................................................................................... 3-1 Climate Cycles .................................................................................................................. 3-1 Climate Change ................................................................................................................ 3-1 Future Climate Projections: Scientific Overview ............................................................. 3-2 Uncertainty ...................................................................................................................... 3-4 Other Regional Scientific Initiatives ................................................................................. 3-5 4. Existing Conditions and Vulnerability Assessment ................................................................ 4-1 Introduction ..................................................................................................................... 4-1 Existing Conditions - Overview ........................................................................................ 4-2 Existing Conditions - Key Findings .................................................................................... 4-4 Vulnerability Assessment Methodology .......................................................................... 4-5 City of Imperial Beach Sea Level Rise Assessment i September 2016 Contents Nuisance and Stormwater Flooding................................................................................. 4-6 Economic Analysis Methodology ..................................................................................... 4-9 5. Adaptation ......................................................................................................................... 5-1 Introduction ..................................................................................................................... 5-1 Adaptation Planning ........................................................................................................ 5-1 Maladaptation ................................................................................................................. 5-2 Challenges ........................................................................................................................ 5-2 Protect, Accommodate, and Retreat ............................................................................... 5-4 Secondary Impacts ........................................................................................................... 5-5 6. Analysis of Select Adaptation Strategies .............................................................................. 6-1 Methodology and Assumptions ....................................................................................... 6-1 6.1.1 Physical Methods ............................................................................................................. 6-1 6.1.2 Economic Methods .......................................................................................................... 6-2 Armoring ........................................................................................................................ 6-10 6.2.1 Physical Results .............................................................................................................. 6-13 Managed Retreat ........................................................................................................... 6-13 6.3.1 Physical Results .............................................................................................................. 6-15 Nourishment .................................................................................................................. 6-15 6.4.1 Physical Results .............................................................................................................. 6-17 Hybrid Dune Approach .................................................................................................. 6-17 6.5.1 Physical Results .............................................................................................................. 6-19 Groins ............................................................................................................................. 6-19 6.6.1 Physical Results .............................................................................................................. 6-21 Results of Economic Analysis of Adaptation .................................................................. 6-21 Sensitivity Analysis ......................................................................................................... 6-26 Tax Revenue Impacts to the City ................................................................................... 6-28 7. Conclusion .......................................................................................................................... 7-1 8. Discussion – What’s next? ................................................................................................... 8-1 Policies, Plans, & Programs .............................................................................................. 8-2 Policy Implementation ..................................................................................................... 8-5 Projects: Protect, Accommodate, or Relocate ................................................................. 8-7 nancingFi Implementation ............................................................................................... 8-2 9. Preparers ............................................................................................................................ 9-2 10. Acknowledgments ............................................................................................................ 10-1 11. References ........................................................................................................................ 11-1 City of Imperial Beach Sea Level Rise Assessment ii September 2016 Contents Appendix A. Sector Profile Results…………………………………………………………………………………………………..A-1 Appendix B. Physical Processes Technical Appendix…………………………………………………………….…………B-1 Appendix C. Economic Analyses Technical Appendix………………………………………………………………..…….C-1 Appendix D. Recommendations by Revell Coastal, LLC ……………………………………………………...............D-1 City of Imperial Beach Sea Level Rise Assessment iii September 2016 Figures Page Figure 1-1 Imperial Beach Overview ..........................................................................................................................