Development of an expert judgement debiasing method for assessing levee failure probabilities

Abstract

Expert judgment plays an essential role in assessing the safety of levees, since these very long structures are generally old, few data are available for them, and they are subject to complex failure mechanisms. Expert judgement is required to assess the failure probabilities of levees when carrying out risk analysis studies. However, expert judgement is subject to biases that are highly likely to impair the quality of the probabilistic assessments obtained. This article presents a method for reducing biases in expert opinion, illustrated by its application to the case of an existing levee. Initially, the method comprises the calibration of the opinions of a panel of six experts based on the results of a quantitative analysis applied to 30 levee cross-sections for which numerical calculations were performed. It then proposes a procedure to debias expert assessments using bias correction coefficients. Regarding its application, the assessments made by the experts were debiased for 30 calibration variables. The correction coefficients obtained were then applied for the assessment of 10 variables of interest. The results show a significant reduction of biases, associated with a readjustment of the uncertainty intervals given by the experts.