In response to large-scale damaging floods in California's Central Valley in 1997, the US Army Corps of Engineers (Corps), in cooperation with the Reclamation Board of California (Reclamation Board), initiated in 1998, the Sacramento and San Joaquin River Basins Comprehensive Study (Comprehensive Study). The study has two broad objectives: (1) to reduce flood damages; and (2) to integrate environmental restoration/protection into flood-damage reduction. Enhanced flood response and emergency preparedness (EFREP) in the Sacramento and San Joaquin River basins was proposed as one project to meet these objectives. (We assisted the Corps by developing the project plan.) But as with any Corps flood damage reduction project, a benefit and cost analysis was required. This created a dilemma, as procedures for such analysis for flood warning systems are not well known.
The Corps contracted with us to find an acceptable procedure for the benefit analysis, to apply the procedure, and to document the results.
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We conducted a detailed survey of methods proposed in the literature for evaluating damage reduction due to flood warning.
Finding little of practical value beyond the so-called Day curves that were proposed in the 1960s, we set out to develop new predictive functions. These were to relate damage reduction possible to depth of flooding and the mitigation time available to emergency responders and floodplain occupants. To develop the functions, we assembled a group of experts in flood damage analysis and flood emergency response. We elicited their opinions on damage reduction possible, given various mitigation times. We then analyzed the responses to develop the required damage-reduction functions.
We worked with staff of the California Department of Water Resources Flood Operation Center to estimate the flood warning and mitigation times available throughout the Sacramento and San Joaquin River basins. These estimates subsequently will be used for expected annual damage computations, with and without the proposed EFREP project.
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