Richardson Bay Shoreline Study Evaluation of Sea Level Rise Impacts and Adaptation Alternatives ***PUBLIC REVIEW DRAFT*** October 14, 2015*** This project was funded through the Marin County Watershed Program and was prepared by: Roger Leventhal, P.E. Senior Engineer Marin County Flood Control & Water Conservation District 3501 Civic Center Drive, Suite 304 San Rafael, CA 93913 (415) 473-3249 [email protected] with help from Sam Veloz and Nathan Eliot Point Blue Conservation Science 3820 Cypress Drive #11 Petaluma, CA 94954 Liz Lotz, Resource GIS Specialist County of Marin Lisa Owens-Viani, Technical Editor i CONTENTS 1.0 INTRODUCTION .................................................................................. 1 2.0 BACKGROUND AND SCOPE ................................................................. 3 2.1 GOALS OF THE STUDY .............................................................................. 5 2.2 RICHARDSON BAY .................................................................................... 6 3.0 ASSESSING IMPACTS OF DIRECT SHORELINE FLOODING FROM RICHARDSON BAY ............................................................................ 11 3.1 MAJOR EXISTING SHORELINE INFRASTRUCTURE .................................. 11 3.2 RICHARDSON BAY SHORELINE REACHES .............................................. 12 3.3 MAJOR ISSUES ASSOCIATED WITH SEA LEVEL RISE AND CLIMATE CHANGE .................................................................................................. 15 3.4 RATES OF SEA LEVEL RISE IN SAN FRANCISCO BAY.............................. 18 3.5 DEVELOPMENT OF SEA LEVEL RISE SCENARIOS FOR STUDY ANALYSIS ............................................................................................................... 20 3.6 APPROACHES TO MAPPING IMPACTS OF SEA LEVEL RISE ..................... 25 4.0 TOOLBOX OF Adaptation ALTERNATIVES ......................................... 27 4.1 WHAT IS A “REASONABLE AND POTENTIALLY EFFECTIVE” FLOOD PROTECTION ALTERNATIVE? .................................................................. 27 4.2 PERMITTING AND REGULATORY ISSUES ................................................ 28 4.3 FLOOD REDUCTION TOOLS FOR DIRECT BAY COASTAL (TIDAL) FLOODING .............................................................................................. 29 5.0 SHORELINE FLOODING INUNDATION UNDER CURRENT AND FUTURE SEA LEVEL RISE SCENARIOS ............................................................ 55 5.1 SEA LEVEL RISE SCENARIO RESULTS - INUNDATION EXTENT AND DEPTH .................................................................................................... 55 5.2 IMPACTS ASSESSMENT BY SHORELINE REACH ..................................... 65 6.0 DIRECT COASTAL FLOOD REDUCTION ALIGNMENTS UNDER SEA LEVEL RISE SCENARIOS ................................................................... 87 6.1 DECIDE WHERE TO “LIMIT THE TIDES” – THE LIMIT OF DIRECT COASTAL FLOODING (LDCF) ALIGNMENT ............................................................... 87 6.2 EVALUATE ADAPTATION OPTIONS .......................................................... 88 6.3 CONCEPTUAL COST ESTIMATE ASSUMPTIONS ....................................... 89 6.4 CONCEPT LEVEL COST ESTIMATES ...................................................... 143 6.5 SUMMARY OF COSTS ............................................................................ 162 7.0 CONCLUSION: PERSPECTIVE ON THE FUTURE OF FLOODING AND FLOOD PROTECTION ALONG THE SHORELINE ................................ 171 7.1 NEXT STEPS .......................................................................................... 171 8.0 REFERENCES ................................................................................. 175 TABLES Table 1. Values of Projected Sea Level Rise and Standard Deviation (From NRC 2012). ......................................................................................................... 21 Table 2. Proposed Sea Level Rise (SLR) Projection Scenarios For Inundation Assessments................................................................................................ 23 Table 3. Barrier Top Design Elevation Alternatives. ............................................. 32 Table 4. Summary of Flooded Areas by Sea Level Rise (SLR) Scenario Assuming No Adaptation/Mitigation Measures. ................................................................. 62 Table 5. Facilities Potentially Flooded Under Different Levels of Sea Level Rise (SLR), Assuming No Adaptation.................................................................... 64 Table 6. Estimated Value Of Properties And Buildings Impacted Under Different Levels Of Sea Level Rise Based On Tax Assessor Values. .............................. 65 Table 7. Reach 1 Alignment Lengths. .................................................................. 94 Table 8. Reach 2 Alignment Lengths. .................................................................. 96 Table 9. Reach 3 Alignment Lengths. .................................................................. 98 Table 10. Reach 4 Barrier Lengths. .................................................................. 100 Table 11. Reach 5 Barrier Lengths. .................................................................. 101 Table 12. Reach 6 Barrier Lengths. .................................................................. 102 Table 13. Richardson Bay Entrance Tide Barrier Lengths. ................................ 108 Table 14. Reference Costs for Large Tidal Barriers. ........................................... 109 Table 15. Reach 1 Barrier Lengths. .................................................................. 114 Table 16. Reach 1, Marine City to Coyote Creek (60 Inch Sea Level Rise). .......... 115 Table 17. Reach 2, Coyote Creek-Bothin Marsh Barrier Lengths (36 Inch Sea Level Rise). ......................................................................................................... 120 iii Table 18. Reach 2, Coyote Creek-Bothin Marsh (60 Inch Sea Level Rise). .......... 121 Table 19. Reach 3, Mill Valley West (36 Inch Sea Level Rise). ............................ 129 Table 20. Reach 3, Mill Valley West (60 Inch Sea Level Rise). ............................ 131 Table 21. Reach 4, Mill Valley East (36 Inch Sea Level Rise). ............................. 134 Table 22. Reach 4, Mill Valley East (60 Inch Sea Level Rise). ............................. 134 Table 23. Reach 5, Seminary Marsh (36 Inch Sea Level Rise). ........................... 135 Table 24. Reach 5, Seminary Marsh (60 Inch Sea Level Rise). ........................... 136 Table 25. Reach 6, Strawberry Peninsula (36 Inch Sea Level Rise). .................... 137 Table 26. Reach 6, Strawberry Peninsula Barrier Lengths. ................................ 138 Table 27. Reach 7, Strawberry Circle-Greenwood Cove (36 Inch Sea Level Rise). 142 Table 28. Strawberry Circle-Greenwood Cove Barrier Lengths. .......................... 143 Table 29. Summary of Potential Right Of Way Costs with 12 Inch Sea Level Rise. ................................................................................................................. 148 Table 30. Summary Of Potential Right Of Way Costs With 36 Inch Sea Level Rise. ................................................................................................................. 149 Table 31. Summary of Potential Right Of Way Costs With 60 Inch Sea Level Rise. ................................................................................................................. 150 Table 32. Estimated Design And Permitting Costs For Reaches 1-3. .................. 152 Table 33. Design And Permitting Cost Estimates For Reaches 4-7 With 12 Inch Sea Level Rise. ................................................................................................. 153 Table 34. Design And Permitting Costs for selected Alignments of Reaches 4-7 For 36 Inch Sea Level Rise. .............................................................................. 154 Table 35. Concept Level Construction Cost Estimates For Large Tide Gate Structures. ................................................................................................ 154 Table 36. Unit Capital Costs For 12 Inch Sea Level Rise Alternatives. ................ 156 Table 37. Unit Capital Costs For 36 Inch Sea Level Rise Alternatives. ................ 157 Table 38. Unit Capital Costs For 60 Inch Sea Level Rise Alternatives. ................ 158 Table 39. Summary of Concept Level Construction Cost Estimates For 12 Inch Sea Level Rise. ................................................................................................. 159 Table 40. Concept Level Construction Cost Estimates For 36 Inch Sea Level Rise. ................................................................................................................. 160 Table 41. Concept Level Construction Cost Estimates For 60 Inch Sea Level Rise. ................................................................................................................. 161 Figures Figure 1: Richardson Bay Reach Delineation Map. .............................................. 13 Figure 2: Projected Range Of Sea Level Rise by Year for Various Studies (From NRC 2012). ......................................................................................................... 20 Figure 3: Concrete Floodwall. ............................................................................. 33 Figure 4: Sheet Pile Wall. ..................................................................................