FLOOD08495

• County: Statewide
• Community: Statewide
• Basin: Statewide
• Title: Methodology for Evaluation of Feasibility: Multijurisdictional Urban Drainage and Flood Control Projects
• Date: 2/1/1977
• Prepared By: UDFCD
• Floodplain - Doc Type: Educational/Technical/Reference Information

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A.

Procedure of Analysis

a. Development of a Cost versus Return Period Curve

Each of the alternatives considered for a Decision Unit
has associated with it a cost function, showing the
variation of project cost with design frequency. The
analyst should have available at least an approximation
of this relationship so that he can compare the costs.
The analyst should be able to identify the lowest cost
combination of measures to contain each of the design
flows considered. The plot of these lowest costs against
design frequency becomes the supply curve for providing
flood protection. For the development of the underlying
theory behind this approach, see James (4).

b. Development of the Benefit versus Return Period Curve

The demand curve for flood protection is more complicated
to develop. For each design frequency, there will be
certain "residual" average annual damages, For example,
if a channel is designed to convey the ten-year flood,
there will be damaging floods occurring for return periods
exceeding ten years, These damages, averaged over time,
become the damages "residual" to the ten-year facilities.
For any Decision Unit, the flood control benefit of
a project will be the reduction in average annual damages
due to the project. The details for calculation of this
reduction are given in Appendix A.