Value of information in retrofitting of flood defenses Schweckendiek, T. (Timo); Vrouwenvelder, A. C. W. M. (Ton)
Dikes and levees play a crucial role in flood protection. The main causes of levee failures are of geotechnical nature; geotechnical failure modes are also the main contributors to the probability of failure of flood defences due to the typically large uncertainties in ground conditions. Hence, information on ground conditions and soil properties is crucial in safety assessments and retrofitting designs of levees. The present paper demonstrates how we can reduce these uncertainties and how we can provide input for rational decision making on investments in monitoring and site investigation. If working in a framework with an explicit target reliability, the value of such information can be expressed in terms of the savings that can be achieved in retrofitting costs. The key ingredients of the approach are Bayesian posterior analysis for reliability updating by incorporating the information from various sources and Bayesian (pre-posterior) decision analysis for estimating the uncertainty and expected values of the consequences and costs of the considered decision options. The optimal strategy is the one with the least expected cost to meet the pre-set reliability target (e.g. by a safety standard). Several examples and case studies addressing different sources of information, such as field observations and piezometer monitoring during floods or site investigation by Cone Penetration Tests (CPT), illustrate the impact of reliability updating and suggest that investments in inspection and monitoring are often worthwhile, especially when the prior uncertainties are large.
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