Orestimba Creek Feasibility Study - Stanislaus County
Orestimba Creek Feasibility Study - Stanislaus County
Orestimba Creek Feasibility Study - Stanislaus County
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Economics Appendix – Draft Report - <strong>Orestimba</strong> <strong>Creek</strong> <strong>Feasibility</strong> <strong>Study</strong>, <strong>Stanislaus</strong> <strong>County</strong>, California – September 2012<br />
Table 6-2: Optimization of the Chevron Levee height at Stuhr Rd and CCID Canal<br />
Crossing<br />
Return<br />
Period<br />
Levee<br />
Elevation (ft.)<br />
*Annual Benefits<br />
($1,000's)<br />
*Annual Costs<br />
($1,000's)<br />
*Net Benefits<br />
($1,000's)<br />
1/50 111.21 6,079 749 5,330<br />
111.25 6,188 753 5,435<br />
111.5 6,412 777 5,636<br />
111.75 6,612 800 5,812<br />
1/500 112 6,785 823 5,962<br />
112.25 6,910 847 6,063<br />
112.5 6,990 870 6,120<br />
112.75 7,035 893 6,142<br />
113 7,056 917 6,139<br />
113.25 7,064 940 6,124<br />
113.5 7,066 964 6,103<br />
113.75 7,067 987 6,080<br />
114 7,067 1,010 6,057<br />
114.25 7,067 1,034 6,034<br />
1/200+3ft 114.8 7,067 1,085 5,982<br />
*The Benefits and Costs shown here are different than those presented in Chapter 3 of the main report,<br />
because these show the actual values used for the sensitivity, while the main report has adjusted those<br />
values to reflect total project benefits and costs. Annual Benefits, Annual Costs and Net Benefits shown<br />
here do not reflect actual benefits and total costs used for final net benefit and BCR calculations. The<br />
index point used for this height optimization exercise is different from the one used for economic<br />
justification. Benefits and costs used for economic justification can be found in Table 7-1. More<br />
information about different index points and the effect on damages in this study area is shown in Section<br />
5.5.<br />
6.1.4.1 Sensitivity of Optimization Height to Index Location<br />
The optimization of the levee height must use an index point at a location where the levee would<br />
be located to come up with a proper levee elevation. The particular index point location for the<br />
optimization was chosen because it was the first point that flooding overtopped the existing<br />
CCID canal (near Stuhr Rd), which is adjacent to the chevron levee’s location. This was the<br />
original location for the economic evaluation as well, but the index was changed later based on<br />
rating curve sensitivity for high probability events (see section 5.5) and likely overestimation of<br />
EAD. Because the CCID Canal location and the eventual urban economic analysis index<br />
location (intersection of Lundy Rd. and the Railroad) have rating curves with nearly identical<br />
slopes for lower probability events (2% (1/50) annual chance event and above), the difference in<br />
an optimization height was assumed negligible. To confirm this assumption, a sensitivity<br />
analysis was performed using the Lundy Rd. index location and the optimal heights were found<br />
to be within 0.2 ft of each other and well within error bands in stage/ground elevations. The<br />
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