Lucas de Melo, PhD, PE, (Maryland) has published a paper on “Modeling Knowledge Uncertainty and Dam Safety: The Benefit of Using Logic and Event Trees” at the International Commission on Large Dams (ICOLD) Annual Meeting at the Swedish Exhibition and Congress Centre (Svenska Mässan) in Gothenburg (Göteborg), Sweden, on June 13 and 14, 2023.

Lucas’s co-authors are Paul Slangen of Landsvirkjun and Glenn Rix, PhD, PE. (Georgia).

Lucas is a Senior Principal Engineer with more than 25 years of experience supporting dams and mining projects, geotechnical design and field studies, risk quantification, and hazardous-materials remediation. He also designs coal-ash-disposal sites, solid waste management facilities, and capping systems for site closures. Lucas assesses stability, liquefaction potential, and stress-strain behavior of concrete and earth dams and designs retrofits for dams and embankments.

Glenn is a Senior Principal Geotechnical Engineer with more than 30 years of experience focused on geotechnical earthquake engineering and engineering seismology, including conducting seismic risk assessments of civil infrastructure. Glenn is a leading authority on in situ seismic methods and is a coauthor of Surface Wave Methods for Near-Surface Site Characterization and the forthcoming American Association of State Highway and Transportation Officials (AASHTO) Manual on Subsurface Investigations.

This year’s ICOLD will be hosted by the National Committee of Sweden, SwedCOLD. In a changing world still struggling with multiple crises from 2022 (dramatic droughts across the Northern Hemisphere, devastating floods in South Africa and Pakistan, and a global energy crisis compounded by the war in Ukraine), ICOLD works to offer solutions that address climate change adaptation and energy transition. ICOLD’s annual meetings and congresses are crucial to achieving these goals. The organization leads the profession in setting standards and guidelines that support safe, efficient, and economical dams that are environmentally sustainable and socially equitable.

Dam owners increasingly use risk-informed decision-making to manage the safety of their portfolio of dams. These processes involve dealing with uncertainties, namely aleatory and epistemic uncertainties. While aleatory uncertainty is associated with the random variation of events, epistemic uncertainty is associated with uncertainty about the condition or behavior of a dam system or component (i.e., it can be attributed to a lack of knowledge about the system rather than randomness of events). This paper presents the benefits of distinguishing between these types of uncertainties and illustrates how they can be modeled in a risk analysis for dam safety. To that end, an example of risk analysis using a logic tree to model epistemic uncertainties and an event tree is used to model aleatory uncertainties is discussed. The numerical outcome of using combined logic and event trees is a probability distribution instead of a single numerical value obtained by using only an event tree. This more comprehensive outcome can be obtained with similar level of effort to using only an event tree while characterizing sources of uncertainty and providing guidance to the allocation of limited resources to address risk-drivers in dam systems.

More information

About the event ICOLD-CIGB 2023
About ICOLD International Commission on Large Dams (icold-cigb.org)
For consultation regarding dam safety, contact Joe Goldstein at This email address is being protected from spambots. You need JavaScript enabled to view it.
Learn more about Lucas deMelo: Lucas de Melo (geosyntec.com)
Learn more about Glenn Rix: Glenn Rix (geosyntec.com)