Orestimba Creek Feasibility Study - Stanislaus County

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Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 Table 7-2: Net Benefits and Benefit-to-Cost Ratio Ranges – Final Array of Alternatives October 2011 Prices ($1,000’s), 4% Interest Rate Alternative IDC Annualized Cost + Total First Cost (1,000) 1 ($1,000) 2 O&M ($1,000) 3 Low (25%) Mid (50%) High (75%) Mid Low (25%) Mid (50%) High (75%) Annual Benefits ($1,000) 4 Annual Net Benefits ($1,000) 5 Low (75%) Mid (50%) High (25%) Benefit to Cost Ratio 5 Low Mean High Low Mean High SB-1: No Action 0 0 0 0 0 0 0 0 0 0 0 0 0 0.0 0.0 0.0 NED 33,736 34,843 36,017 2,205 1,669 1,723 1,781 1,282 2,679 4,363 22 1,054 2,133 1.0 1.6 2.2 LPP 41,285 42,927 44,260 2,719 2,042 2,123 2,189 1,282 2,679 4,363 -377 657 1,739 0.8 1.3 1.8 1 Cost Range: Min= 25% Mid=50% Max= 75% (confidence costs are less than given value) 2 IDC based on equal annual spending over a 2 year construction schedule. 3 First Costs plus IDC amortized over 50 years at 4% plus annual O&M. Annual O&M costs: NED = $164k, LPP = $180k 4 Benefit Range: Min=75% Mid=50% Max=25% (confidence benefits are greater than given value given all R&U) 5 Values are a result of Monte Carlo simulations using triangular distributions of annual benefit and annual cost confidence intervals as inputs. Mean = Mean result from Simulation. The 5% tails on the low and high end of the simulation result are not included. 48
Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012 Attachment A: Without Project Hydrologic and Hydraulic Relationships Used in the FDA Model Along with the economic stage-damage functions, hydrologic and hydraulic functions are part of the flood damage analysis model. The probability-discharge and stage-discharge relationships were provided and developed by the H&H members of the Orestimba study team. These relationships in Attachment A represent without project conditions. Probability Curves For both Rural and Urban Areas, Exceedence probability-discharge curves were developed for the HEC-FDA model. An analytical Log Pearson Type III curve was used for this study (Mean=3.0782, Std. Dev.=0.5636, Skew=-0.6000, N=45). The discharge values in these relationships represent total flows both in channel and out in the floodplain. Table A1 displays the probability function used for both damage areas in the study. Table A1 – Probability-Discharge Rural and Urban Impact Areas 49
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Orestimba Creek Feasibility Study - Stanislaus County

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