Modeling Knowledge Uncertainty in An Internal Erosion Risk Analysis
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Current practice in dam safety risk analysis is to use event trees to model potential failure modes and estimate the annual probability of failure.

Uncertainty is often modeled by defining a probability distribution for each node in the event tree and using Monte Carlo simulations to calculate a distribution on annual probability of failure. This approach blends different types of uncertainty that are involved in risk analysis. Aleatory uncertainty, sometimes called variability, is due to randomness of events, while epistemic uncertainty, sometimes called model or parameter uncertainty, is due to lack of knowledge about the dam system or site conditions. An advantage of this approach is the widespread availability of software tools that facilitate its implementation.

While not yet common in dam safety practice, these two types of uncertainty are accounted for separately when analyzing risk in other disciplines and applications. Instead of blending both types of uncertainty in the event tree, the uncertainties are separated by using an event tree for uncertainties due to randomness, and a logic tree for epistemic uncertainties. One of the benefits of using a logic tree coupled with an event tree is that it encourages and facilitates a deeper understanding of uncertainties related to the performance of the dam system under various load conditions. It also properly models correlations between nodal probabilities in the event tree. Ultimately, we believe combining a logic tree with an event tree results in a more complete representation of uncertainties in the risk estimates themselves and provides insight into aspects of the dam system performance that contribute most significantly to uncertainty in the risk estimates.

Publication Summary

  • Geosyntec Authors: Glenn Rix, Tiffany Adams, Christie Hale, Derek Morley
  • All Authors: Glenn Rix, Tiffany Adams, Christie Hale, Derek Morley
  • Title: United States Society on Dams (USSD) 2022 Annual Conference
  • Event or Publication: Event
  • Practice Areas: Dams; Dam Safety
  • Citation: United States Society on Dams (USSD) 2022 Annual Conference and Exhibition at the Town and Country Resort in San Diego, California on April 11 through 14, 2022.
  • Date: Tuesday, April 12 at 4:45 p.m. PDT
  • Location: San Diego, California
  • Publication Type: Platform Presentation