Optimal maintenance decisions for dikes

To protect the Dutch polders against flooding, more than 2500 km of dikes h ave been constructed. Due to settlement, subsoil consolidation, and relativ e sea-level rise, these dikes slowly sink "away into the sea" and should th erefore be heightened regularly (at present, every 50 years). In this respe ct, one is interested in safe and cost-optimal dike heightenings for which the sum of the initial cost of investment and the future (discounted) cost of maintenance is minimal. For optimization purposes, a maintenance model has been developed for dikes subject to uncertain crest-level decline. On the basis of engineering know ledge, crest-level decline has been modeled as a monotone stochastic proces s with expected decline being either linear or nonlinear (i.e., linear afte r transformation) in time. For both models and for a particular unit time, the increments are distributed according to mixtures of exponentials. In a case study, the maintenance decision model has been applied to the pro blem of heightening the Dutch "Oostmoiendijk."