Cost Benefit Analysis of Urban Flood Protection

As engineers working in the local authority environment we are often asked to make decisions on the spending of public money to provide flood protection to existing at risk urban structures. Historically, and currently, in New Zealand there has been limited quantitative information available on which to base these investment decisions. This has lead to these decisions often being based on ad hoc assessments or political pressure rather than value for money.

This paper will describe a methodology adapted from international literature to provide a quantified cost benefit approach to flood protection investment decisions. It will describe the scenario, the approach adopted and the sources of flood damage cost information used. It will further describe the limitations of available information and the work needed to provide more robustness in this area.

These issues will be discussed in the context of a real life example of application of this methodology. The impacts (benefits) of implementing this methodology on an otherwise ad hoc decision making process will be described in terms of getting the best value out of the spending of the public purse.