Uncertainty in optimal decisions for dike maintenance

Decisions regarding the maintenance of structures subject to uncertain deterioration are usually made on the basis of expected costs. For example, the optimal frequency of preventive replacements is the one which entails the lowest expected costs. For this kind of investment strategy, the variance of costs can be large. However, the variance can only be easily calculated in a few simple cases. It is therefore not common to include the uncertainty about the outcome of the optimal strategy in the final decision. The variance of costs for maintenance strategies was one of the subjects professor Jan M. van Noortwijk worked on during his career. His research shows that the variance in the costs of an optimal strategy can be larger than in the case of less optimal strategies. This article reports on one particular application of this research, namely, the periodic heightening of the many dikes that protect the Netherlands against coastal and fluvial flooding. Two existing models for dike heightening are reviewed, and the variance of the costs is determined by assuming that floods occur in time according to a non-homogeneous Poisson process.