Acceptance of hazard in design of flood-prone structures.

Symposium Dates 26-29 May 1976

The community at large generally assumes that flood-prone structures are designed to eliminate, as far as possible, any hazard associated with the occurrence of floods. This applies to structures required to pass flood flows and to works and projects designed to mitigate the effects of floods. However, this expectation is not the actual objective in the practical design of flood prone structures. Overall optimum use of the community's resources dictates that design is carried out on the basis of a finite, and often quite high probability of failure. Occasional to frequent failures and consequent damage and hazard are thus to be expected. This approach to design on the basis of accepted risk is not well understood by either the public or by most of their public administrators. Indeed there is a lack of appreciation even amongst many designers. There is a need for greater understanding of this basis of design and its expected results. A primary objective of this paper is to draw attention to these facts. There is also a great need for clarification of the issues involved, and for collection of data on flood damages and the performance of existing structures. Several areas of research are suggested. These would generally improve design for flood prone structures where the design is primarily based on an expected frequency of flooding. The investment in this research would be repaid many times over in economic, social and environmental benefits