SOCIAL AND ECONOMIC WELL-BEING Decision Support Tool for the San Francisco Bay- Delta Levees Investment Strategy Documentation and Use David G. Groves, Nidhi Kalra, James Syme, Hollie Ellis, Charles L. Gardiner, Lawrence H. Roth Sponsored by the Delta Stewardship Council For more information on this publication, visit www.rand.org/t/RR2139 Published by the RAND Corporation, Santa Monica, Calif. © Copyright 2019 Delta Stewardship Council R® is a registered trademark. The RAND Corporation is a research organization that develops solutions to public policy challenges to help make communities throughout the world safer and more secure, healthier and more prosperous. RAND is nonprofit, nonpartisan, and committed to the public interest. RAND’s publications do not necessarily reflect the opinions of its research clients and sponsors. Support RAND Make a tax-deductible charitable contribution at www.rand.org/giving/contribute www.rand.org Preface The Delta Stewardship Council (Council) initiated the Delta Levees Investment Strategy (DLIS) project to develop a transparent strategy for prioritizing State-funded levee investments in the Delta. This project is in support of the requirements of California Water Code § 85305(a), which states: The Delta Plan shall attempt to reduce risks to people, property, and state interests in the Delta by promoting effective emergency preparedness, appropriate land uses, and strategic levee investments. 85306. The Council, in consultation with the Central Valley Flood Protection Board, shall recommend in the Delta Plan priorities for state investments in levee operation, maintenance, and improvements in the Delta, including both levees that are a part of the State Plan of Flood Control and nonproject levees. The DLIS project supported this Council charge by (1) developing an analytical framework to evaluate flood risk to each Delta tract or island with current maintenance and with additional levee upgrades; (2) creating a decision support tool (DST) to enable the Council and stakeholders to explore flood risk results for each island across different time frames and future scenarios; and (3) using the DST with the Council to develop a prioritized list of islands for levee investment, which informed a revision to the policy on “Prioritization of State Investments in Delta Levees and Risk Reduction,” as described in a March 2017 draft update of Chapter Seven of the Delta Plan (Delta Stewardship Council, 2013). This report describes use of the DST, along with its methodological basis. This report complements the main project report (Arcadis, 2017a). 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Questions or comments about this report should be sent to the project leader, David Groves ([email protected]). iii Contents Preface ............................................................................................................................................ iii Figures............................................................................................................................................. v Tables ............................................................................................................................................ vii Summary ...................................................................................................................................... viii Acknowledgments .......................................................................................................................... xi Abbreviations ................................................................................................................................ xii 1. Introduction ................................................................................................................................. 1 Sacramento–San Joaquin Delta Levees ...................................................................................... 1 Delta Levees Investment Strategy .............................................................................................. 1 Decision Support Tool ................................................................................................................ 1 2. Summary of Risk Evaluation Methodology ............................................................................... 6 Probability of Flooding ............................................................................................................... 6 Flood Risk Metrics ...................................................................................................................... 6 Risk to Life ............................................................................................................................. 7 Risk to Property ...................................................................................................................... 8 Risk to Water Supply .............................................................................................................. 8 Risk to Habitat ........................................................................................................................ 9 Risk to DAP .......................................................................................................................... 10 Changing and Uncertain Risks over Time ................................................................................ 11 Ranking Islands/Tracts by Risk ................................................................................................ 15 Evaluating Levee Investments .................................................................................................. 15 3. Overview and Use of DST ........................................................................................................ 17 Section 1. Instructions and Guide ............................................................................................. 17 Section 2. Islands and Vulnerable Assets ................................................................................. 18 Section 3. Assessing Risk (Risk Maps) .................................................................................... 25 Section 4. Identify High Risk Islands ....................................................................................... 31 Section 5. Ranking Islands by Risk .......................................................................................... 33 Section 6. Levee Investments and Change in Risk ................................................................... 36 Section 7. Draft Delta Levees Investment Priorities ................................................................. 41 Section 8. Developing a Portfolio of Levee Investments ......................................................... 41 4. Conclusion ................................................................................................................................ 45 References ..................................................................................................................................... 47 iv Figures Figure S.1. Overview of DST ........................................................................................................ ix Figure S.2. Delta Levees Investment Priorities .............................................................................. x Figure 1.1. Sacramento–San Joaquin Delta Islands and Tracts ...................................................... 2 Figure 1.2. Overview of DST ......................................................................................................... 4 Figure 1.3. Starting Screen for the Delta Levees Investment Strategy DST .................................. 5 Figure 2.1. Impacts of Uncertainty on EAD ................................................................................. 14 Figure 3.1. DST Overview (Panel 1.1) ......................................................................................... 17 Figure 3.2. Islands and Tracts (Panel 2.1) .................................................................................... 18 Figure 3.3. Population Vulnerable in the Delta (Panel 2.4) .......................................................... 19 Figure 3.4. Value of Property Vulnerable in the Delta (Panel 2.5) .............................................. 20 Figure 3.5. Important Islands for Protecting Water Supply (Panels 2.6a,b) ................................. 21 Figure 3.6. Estimate of Existing and Potential High-Value Non-Tidal Habitat (Panel 2.7) ......... 22 Figure 3.7. Potential High-Value Unleveed Habitat (Panel 2.8) .................................................. 23 Figure 3.8. Legacy Towns (DAP) (Panel 2.9a) ...........................................................................