DELTA STEWARDSHIP COUNCIL A California State Agency DELTA ADAPTS: CREATING A CLIMATE RESILIENT FUTURE SACRAMENTO-SAN JOAQUIN RIVER DELTA CLIMATE CHANGE VULNERABILITY ASSESSMENT DRAFT FLOOD HAZARD ASSESSMENT TECHNICAL MEMO NOVEMBER 5, 2020 November 2020 1-1 Delta Adapts: Creating a Climate Resilient Future Chapter 1. Introduction CONTENTS CHAPTER 1. Introduction ........................................................................................... 1-1 1.1 Background ................................................................................................................1-1 1.2 Purpose ......................................................................................................................1-2 1.3 Open Science and Key Assumptions ........................................................................1-5 1.4 Overview of Approach ..............................................................................................1-6 CHAPTER 2. Tidal Datums Analysis .......................................................................... 2-2 2.1 DSM2 Model Runs .....................................................................................................2-2 2.2 Methods ....................................................................................................................2-5 2.3 Results ........................................................................................................................2-6 CHAPTER 3. Peak Water Level Analysis ................................................................... 3-1 3.1 Regression Equation Development ..........................................................................3-1 3.1.1 DSM2 Model Runs ........................................................................................3-1 3.1.2 Regression Equations ...................................................................................3-3 3.1.3 Regression Equation Validation ...................................................................3-5 3.2 Stage-Recurrence Curve Development ....................................................................3-8 3.2.1 Overview of Approach ..................................................................................3-8 3.2.2 Tide Distribution ...........................................................................................3-8 3.2.3 TDI Distributions ...........................................................................................3-9 3.2.4 Streamflow Partitioning Adjustments ...................................................... 3-12 3.2.5 Sea Level Rise Distributions....................................................................... 3-18 3.2.6 Storm Surge Analysis ................................................................................. 3-18 3.2.7 Monte Carlo Analysis ................................................................................. 3-20 CHAPTER 4. Flood Hazard Mapping ......................................................................... 4-1 4.1 Mapping Scenarios ....................................................................................................4-1 4.1.1 Overview .......................................................................................................4-1 4.1.2 Deterministic Scenarios ................................................................................4-1 4.1.3 Probabilistic Scenarios ..................................................................................4-3 4.2 Mapping Methods .....................................................................................................4-5 4.2.1 Levee Centerline Data ..................................................................................4-6 4.2.2 DSM2 Node Location Updates .....................................................................4-8 4.2.3 Levee Overtopping .................................................................................... 4-11 4.2.4 Flood Regions ............................................................................................. 4-12 4.2.5 Generating Flood Maps ............................................................................. 4-15 4.2.6 Delta Inflow Assumptions and Flood Mapping ........................................ 4-15 4.3 Flood Hazard Maps ................................................................................................ 4-17 4.3.1 Deterministic Scenarios ............................................................................. 4-18 4.3.2 Probabilistic Scenarios ............................................................................... 4-23 CHAPTER 5. Overall System Findings ...................................................................... 5-1 1-2 November 2020 DELTA STEWARDSHIP COUNCIL A California State Agency CHAPTER 6. References ............................................................................................ 6-2 CHAPTER 7. Supporting Appendices ....................................................................... 7-1 E.1 Products ...........................................................................................................................7-2 E.1.1 Attributes .........................................................................................................7-3 E.2 LiDAR DEM background ..................................................................................................7-3 E.3 Heads-up digitizing to adjust levee centerlines .............................................................7-4 E.4 Elevation attributes .........................................................................................................7-4 E.5 QAQC: External peer review ...........................................................................................7-4 E.5.1 Legal Delta ........................................................................................................7-4 E.5.2 Suisun Marsh ....................................................................................................7-6 E.6 Assumptions and Limitations ..........................................................................................7-6 E.7 Selection of source data layers: ......................................................................................7-7 E.7.1 Legal Delta ........................................................................................................7-7 E.7.2 Suisun Marsh ....................................................................................................7-9 November 2020 1-3 Delta Adapts: Creating a Climate Resilient Future Chapter 1. Introduction APPENDICES Appendix A Total Delta Inflow Distribution Appendix B Tide Distribution Appendix C Sea Level Rise Distribution Appendix D Regression Coefficients Appendix E Levee Dataset Metadata Appendix F Delta Adapts Inundation Polygon Identification Method Appendix G Flood Exposures by Tract FIGURES Figure 1-1. Delta areas mapped within the FEMA floodplain for existing conditions ....................1-4 Figure 1-2. Overview of flood hazard analysis approach .................................................................1-7 Figure 2-1. DSM2 model output locations ........................................................................................2-4 Figure 3-1. Root mean square error at each model node for validation dataset ...........................3-6 Figure 3-2. Max error at each model node for validation dataset ..................................................3-7 Figure 3-3. TDI distributions for Existing Conditions and Future Conditions at 2050 and 2085 ..................................................................................................................................... 3-12 Figure 3-4. CDF of daily water level exceedance for historical, 2030, 2050, and 2085 planning horizons ............................................................................................................... 3-20 Figure 4-1. Levees and Water Surface Elevation Index Points ........................................................4-7 Figure 4-2. 2009 DSM2 calibration documentation .........................................................................4-9 Figure 4-3. Relocated nodes and grid (black), old node locations (green), and updated channels form DWR (various colors) that were used to adjust the relocated nodes ..... 4-10 Figure 4-4. Flood regions used in Delta Adapts Flood Analysis .................................................... 4-13 Figure 4-5. Delta Adapts regions at selected levels of water surface elevations ........................ 4-14 Figure 4-6. Influence of channel inflow capping on peak water surface elevations in the Delta .................................................................................................................................... 4-17 Figure 4-7. Flood hazard map for Deterministic Scenario M-0 (Existing Conditions) ................. 4-18 Figure 4-8. Flood hazard map for Deterministic Scenario M-1 (2030 Conditions) ...................... 4-19 Figure 4-9. Flood hazard map for Deterministic Scenario M-2 (2050 Conditions) ...................... 4-20 Figure 4-10. Flood hazard map for Deterministic Scenario M-3 (2050 Conditions) .................... 4-21 Figure 4-11. Flood hazard map for Deterministic Scenario M-4 (2050+ Conditions).................. 4-22 Figure 4-12. Flood hazard map for Probabilistic Scenario M-0 (Existing Conditions) ................. 4-23 Figure 4-13. Flood hazard map for Probabilistic Scenario M-5 (2030 Conditions)