Orestimba Creek Feasibility Study - Stanislaus County

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Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 6.1.1 Project Conditions- Model Simulations Benefits were determined by incorporating residual with-project floodplains and rating curves into the FDA model that represent various with project improvements. Flood risk management benefits equal the difference between the without project damage conditions and the with project residual damages. The reduction in project flood plains in both extent and depth from the larger without project flood plains accounts for the decrease in damages of the given alternative. 6.1.2 Average Annual Equivalent Damages –With Project Conditions All benefit values in the remaining tables of this report included average annual equivalents, which because of our assumptions, equal Expected Annual Damages for the Orestimba Study. 6.1.3 Alternatives Evaluated – Preliminary Screening Net Benefit Analysis Incremental benefit evaluation to determine which plans to move forward for optimization into the final array was formulated based on reasonable separable project features and sizing. Features were identified and categorized based on potential flood reduction and magnitude of cost. Levee Design Height (height based on depth of water for the given flood event at levee location) was used to select reasonable increments for benefit evaluation. 2%, 1%, 0.5% and 0.2% annual chance design heights were considered. As mentioned earlier, details of the project components and selection can be found in the main report. With project residual damages and benefits were modeled for all of the increments/alternatives listed in Table 6-1. In total, seventeen different project increment combinations were modeled and analyzed economically during this screening process. Annual benefits in the table, represent the difference between the without and with project equivalent annual damages for each alternative. Costs are based upon preliminary reconnaissance costs, but are all at the same level of detail for this screening purpose. Because this analysis was done in 2009 and only serves as a screening to in order to choose plans to further optimize, price levels were not updated from October 2008. 32
Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 Table 6-1: Preliminary Screening Annual Benefits and Costs by Alternative Oct 2008 Prices ($1,000’s), 4.625% Interest Rate Project Condition Economic Impact Area Equivalent Annual Damages Total Damages Annual Benefits Annual Costs Net Benefits B/C Ratio WITHOUT Rural $1,166 Urban $2,260 $3,426 1/100 Short Levee Rural $1,261 Urban $119 $1,380 $2,046 $502 $1,544 4.07 1/200 Short Levee Rural $1,255 Urban $119 $1,374 $2,052 $506 $1,546 4.06 1/500 Short Levee Rural $1,263 Urban $114 $1,377 $2,049 $524 $1,525 3.91 1/200 Long Levee Rural $1,258 Urban $1 $1,259 $2,167 $899 $1,268 2.41 4000 cfs Channel Rural $496 Improvements (4,000cfs) Urban $896 $1,392 $2,034 $472 $1,562 4.31 1/200 Short + Rural $1,154 Interceptor Channel (IC) Urban $0 $1,154 $2,273 $799 $1,474 2.85 HYBRID 1 - 1/200 Rural $379 (1/200 Stuhr+4000cfs+IC) Urban $0 $379 $3,047 $1,312 $1,735 2.32 HYBRID 2 - 1/200 Rural $399 (1/200 Stuhr+4000cfs) Urban $43 $442 $2,984 $827 $2,157 3.61 1/100 Farm Rd. Rural $1,215 Urban $84 $1,299 $2,127 $122 $2,006 17.48 1/200 Farm Rd. Rural $1,210 Urban $33 $1,243 $2,183 $132 $2,051 16.53 1/500 Farm Rd. Rural $1,203 Urban $0 $1,203 $2,223 $139 $2,084 16.03 HYBIRD 3 - 1/50 Rural $469 (1/100yr Farm+4000cfs) Urban $12 $481 $2,945 $542 $2,403 5.43 HYBIRD 3 - 1/100 Rural $468 (100yr Farm+4000cfs) Urban $0 $468 $2,959 $542 $2,417 5.46 HYBIRD 3 - 1/200 Rural $468 (200yr Farm+4000cfs) Urban $0 $468 $2,958 $545 $2,413 5.43 HYBIRD 3 - 1/500 Rural $444 (500yr Farm+4000cfs) Urban $22 $466 $2,960 $610 $2,350 4.85 HYBRID 4 Rural $457 (1/200 Farm+4000cfs + IC) Urban $0 $457 $2,970 $1,089 $1,881 2.73 1/200 Dry Dam Rural $307 Urban $0 $307 $3,119 $4,069 -$950 0.77 33
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