Towards Risk-based Prioritisation of Primary Navigation Locks

Abstract

The operation and maintenance of most of the Dutch primary navigation locks are the responsibility of Rijkswaterstaat. The portfolio of Rijkswaterstaat consists of 52 primary navigation locks that are part of the primary flood defence. All these navigation locks are assigned a safety norm together with the adjacent water-retaining bodies. For both main functions, norms and acts are defined that prescribe a certain level of performance. Rijkswaterstaat is responsible that all its primary navigation locks do meet the safety or nautical requirements.Most of the primary navigation locks are built in the first two decades of the 20th century. In principle, Rijkswaterstaat considers a functional lifetime of their navigation locks, equal to 100 years. A number of these navigation locks are technically modified to extend the functional lifetime. In the coming decades, many of these navigation locks have to be renovated in order to meet new norms or requirements. It might that not all the renovation work can be executed in the same period of time. Therefore, the works have to be scheduled and given a priority when they will be renovated. In the existing method, the ”Vervanging&Renovatie” (V&R) prioritisation, one indicator is considered that entails the remaining lifetime as a function of the design lifetime.A risk analysis is conducted regarding the flood safety and nautical requirements of navigation locks. Given the requirements for the flood safety and nautical function, three drivers are defined that affect these functions: climate change, intensity growth, and ageing of material. For these drivers, a number of aspects are distinguished that affect either the flood safety or nautical function. The combination of aspects is framed in a method that can be used to assess the urgency of renovation, relative to the norms en requirements that are linked to the aspects. For each aspect, it is assessed at what moment in time the norm is exceeded. This result is compared to the existing V&R prioritisation of renovation works. Given both methods, it can be concluded whether or not the proposed moment of renovation is according to the required moment of renovation, to safeguard the nautical and flood safety functions.Validation of the proposed method of prioritisation is established via two case studies. The main conclusion of the case studies is that the existing method of prioritising the renovation work of primary navigation locks is not optimal. A number of aspects, as these are assessed in the case study, indicate that the required moment of renovation is before the moment according to the V&R prioritisation. This conclusion is based on the expected performance in the (near) future relative to the required performance that follows from legislation. Some aspects show deviations of up to 40 years relative to the V&R prioritisation Apart from the assessment of the aspects based on the norms, a criticality assessment is conducted. For all aspects as defined in the prioritisation method, the effect of a ”postponed” moment of renovation is balanced with a proposed mitigation measure. This is done with the use of a modified FMECA. It is assumed that the mitigation measure reduces the likelihood of occurrence of the aspect to zero. The costs that are the result of a mitigation measure are compared with the costs of ”doing nothing”. This implies that the consequences of a postponed renovation are expressed in financial terms, in order to balance this with the mitigation measure. In this way, the results of the case studies are financially weighted, independent of whether or not they serve the nautical function or the flood safety function.