Orestimba Creek Feasibility Study - Stanislaus County

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Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 Table E- 5: Optimization of the Chevron Levee Height at Stuhr Rd and CCID Canal Crossing Return Period Levee Elevation (ft.) *Annual Benefits ($1,000's) *Annual Costs ($1,000's) *Net Benefits ($1,000's) 1/50 111.21 6,079 749 5,330 111.25 6,188 753 5,435 111.5 6,412 777 5,636 111.75 6,612 800 5,812 1/500 112 6,785 823 5,962 112.25 6,910 847 6,063 112.5 6,990 870 6,120 112.75 7,035 893 6,142 113 7,056 917 6,139 113.25 7,064 940 6,124 113.5 7,066 964 6,103 113.75 7,067 987 6,080 114 7,067 1,010 6,057 114.25 7,067 1,034 6,034 1/200+3ft 114.8 7,067 1,085 5,982 * The Benefits and Costs shown here are different than those presented in Chapter 3 of the main report, because these show the actual values used for the sensitivity, while the main report has adjusted those values to reflect total project benefits and costs. Annual Benefits, Annual Costs and Net Benefits shown here do not reflect actual benefits and total costs used for final net benefit and BCR calculations. The index point used for this height optimization exercise is different from the one used for economic justification. Benefits and costs used for economic justification can be found in Table E- 10. More information about different index points and the effect on damages in this study area is available upon request. Sensitivity analysis was performed on other index locations along the levee alignment and the results were within 0.2ft, which is well within the error bands of the ground elevations. The optimized height is approximately 1.5ft above the existing 2% (1/50) WSEL, which is reasonable for an alluvial fan floodplain given uncertainty in ground elevations and stages. ES-x
Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 The Final Array of Alternatives The final array of alternatives is listed below. See the main report for a detailed description of all other alternatives that were evaluated and screened out during the plan formulation process. 1. No Action Plan 2. Chevron Levee: Chevron levee at optimized height. (TOL elevation of 112.75 feet) 3. Local Plan: Chevron Levee set at a height equal to the mean 0.5% (1/200) WSEL + 3 Feet. (TOL elevation of 114.8 feet) 1 . A map showing the locations for the chevron levee is shown in Figure E- 4 below. For a more detailed description of these alternatives, please see the main report. Annual Benefits The mean annual benefits for the final 3 alternatives can be found in Table E- 6 below. Note that there is no incremental benefit for the Local Plan because the incrementally higher levee height does not provide an additional measurable benefit to the city of Newman and is mainly just to comply with State of California requirements. Residual Damage in the Urban EIA with the Chevron Levee in place consist of existing storm drainage damages caused by rain events above a 10% annual chance frequency. 1 Senate Bill 5 (SB-5) in the State of California requires that levee’s be built to the mean 0.5% (1/200) annual chance exceedance event WSEL in order to qualify for state participation. ES-xi
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Orestimba Creek Feasibility Study - Stanislaus County

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