Orestimba Creek Feasibility Study - Stanislaus County

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Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 Long-term risk provides the probability of having one or more damaging floods over a period of time. Assurance is the probability that a target stage will not be exceeded during the occurrence of a specified flood. Project performance statistics for each impact area is displayed by impact area for both without and with project conditions in the tables below. Table E- 8: Project Performance – With Project Conditions – Rural EIA Alternative Annual Exceedance Probability Median Expected 10 Year Period Long-Term Risk 30 Year Period 50 Year Period Assurance by Events 10% 2% 1% 0.20% 1. No Action 24.31% 24.22% 94% 99% 99% 6% 2% 1% 1% 2. Chevron Levee at 112.75ft 3. Chevron Levee at 114.8ft 24.31% 24.22% 94% 99% 99% 6% 2% 1% 1% 24.31% 24.22% 94% 99% 99% 6% 2% 1% 1% Table E- 9: Project Performance – With Project Conditions – Urban EIA Alternative Annual Exceedance Probability Median Expected 10 Year Period Long-Term Risk 30 Year Period 50 Year Period Assurance by Events 10% 2% 1% 0.20% 1. No Action 14.43% 15.13% 81% 98% 99% 13% 0% 0% 0% 2. Chevron Levee at 112.75ft 3. Chevron Levee at 114.8ft 0.01% 0.04% 0% 1% 2% 99% 99% 99% 98% 0.00% 0.00% 0% 0% 0% 99% 99% 99% 99% ES.7 Net Benefit Analysis With benefits calculations complete, annual costs need to be derived to complete the benefit cost analysis. Economic feasibility and project efficiency are determined through benefit cost analysis. For a project or increment to be feasible, benefits must exceed costs and the most efficient alternative is the one that maximizes net benefits (annual benefits minus annual costs). ES-xiv
Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 The NED Plan With the Channel Modifications increment dropping from the Federal Interest, the optimized Chevron Levee becomes the NED Plan. The Tentatively Recommended Plan The only difference between the Tentatively Recommended Plan and the NED Plan is the height of the chevron levee. The height of the chevron levee for the local plan must meet State of California requirements of being at least 3 feet above the with-project 200 year mean WSEL. This means a levee that is about 7.5 to 10 feet tall or approximately 2 feet taller than the federal interest levee. Benefits and Costs A more rigorous and detailed MCACES cost estimate was performed for the NED Chevron Levee and the LPP (Alternatives 2 and 3 respectively). Benefits and costs for these alternatives are provided in Table E- 10 below. ES-xv
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