Analysis of historic records has been, and will continue to be, a reliable means of gaining an understanding of surface water system behavior. If the design condition under consideration falls within the envelope of historic records, then it is possible to have a high degree of confidence in the analysis results used for design.
However, it is often the case that the set of historic records at a specific site is either non-existent or does not envelope the range of events for which the design is required. In such cases a designer will still seek to have a high degree of confidence in the analyses, and alternative approaches are required.
Such alternative approaches include extrapolation (of observations), detailed analysis using established hydraulic principles with detailed input data (modelling) and sensitivity assessment using statistical and other means. All of these approaches are intended for the same end point, this being a high degree in confidence in results that are to be used in design.
In this paper these approaches are benchmarked against each other using a case study. The results show that in some cases there are alternative approaches to the detailed hydrological and hydraulic modelling approach that result in the same end point conclusions being able to be reached (confidence in results). These alternative approaches will be demonstrated, and in this paper the relative time inputs to them are discussed using the case study examples.