Orestimba Creek Feasibility Study - Stanislaus County

Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012
Table 5-6: Index Point Sensitivity Runs
Event
Flow (cfs)
Urban IP (unmodified)
CCID IP
(Sensitivity 1)
Stage
Newman IP
(Sensitivity 2)
Rural IP
(Sensitivity 3)
Std.
Dev. (ft.)
99.9% 0 96.12 108.61 90.13 107.72 0.6
20.0% 3,634 96.12 108.61 90.13 119.74 0.6
10.0% 5,679 99.39 109.01 90.53 120.44 0.6
5.0% 7,946 99.48 110.54 90.7 120.75 0.6
2.0% 11,208 99.5 111.12 90.74 120.98 0.6
1.0% 13,831 99.6 111.33 90.86 121.08 0.6
0.5% 16,553 99.7 111.37 90.89 121.18 0.6
0.2% 20,255 99.79 111.47 90.93 121.27 0.6
Urban WO Project
EAD ($1,000's)
$3,434* $6,836 $10,138 $3,162 --
* For the final EAD used in this documentation, the Urban IP 99.9% ACE stage was modified in HEC-FDA to mimic the Rural
IP, roughly 12 feet below the 20% ACE stage. The resulting WO project EAD was used in this document and can be found in
Table 5-5.
5.6 EAD Future Conditions and Equivalent Annual Damages
The without-project equivalent annual damage reflects the damage value associated with the
without-project condition over the period of analysis and under changing hydrology, hydraulic,
and economic conditions in the study area. Essentially, equivalent annual damages are expected
annual damages that have been converted to a single present worth value and then amortized
over the analysis period using the federally mandated discount rate of 4%. The majority of
development within Newman is planned outside of the current 0.2% (1/500) annual chance
floodplains (and the current FEMA 1% (1/100) annual chance floodplain). With the current state
of the real estate market and development plans being halted all across California, it’s not safe to
assume that Newman will continue to grow at the same rate (approximately 7%) it had from
1987-2007. All new development that does happen to occur within existing floodplains will
likely build with the first floor foundation moderately out of the areas 1% floodplain, so any
damages would only occur for very infrequent events (0.5% and 0.2% annual chance).
Sensitivity runs have been made within FDA regarding future growth and even if Newman did
continue to grow at its past rate, very little would be added to the total damages/benefits (less
than 1% of the total) and would not impact the plan formulation process. Because of all these
circumstances, the PDT is assuming there will be no significant development within the
floodplain in the foreseeable future. Therefore, future conditions are assumed to be the same as
present conditions effectively making expected annual damages the same as equivalent annual
damages and will be referred to as such from this point forward.
5.7 Project Performance- Without Project Conditions
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