Orestimba Creek Feasibility Study - Stanislaus County

Economics Appendix – Draft Report - Orestimba Creek Feasibility Study, Stanislaus County, California – September 2012
There appears to be multiple evacuation routes of substantive capacity to handle the emergency
traffic load.
Highly unlikely abnormal flood events may occur overnight which could impact residents as
they may not be aware of the impending flood situation. Under this scenario it can be assumed
that a small percentage of the population would not be warned in time to escape the full force of
the flood event. Depths of the 1% flood event were compiled by the Corps of Engineers. These
depths are up to 3 feet in depth with an average of less than 1 foot.
Information received from McClelland and Bowles (2002) concerning risks to life identified the
following findings related to the computation of loss of life are:
For any structure: if event maximum depth < 2 feet or less than the first floor height of
structure, then there is no flood lethality zone and the people are considered as part of
the Cleared evacuation category;
For 1 story structures, if event maximum depth is 13 feet or higher then the population at
risk is assumed to be in a zone which are typically exposed to high life risk. It is
understood that even exposure to shallow, high velocity flooding, can sweep people off
their feet. However, high velocity flooding at shallow depths is normally not the case.
Depending on the nature of the flood, depths of under 13 feet are considered in the safe
zone. The safe zone fatalities were normally measured in the hundredths of one percent
of the population at risk.
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