2023 – RCEM at 10: Why Reclamation is Still Using an Empirical Approach to Consequence Estimation

Dom Galic

Risk informed decision making (RIDM) is widely used in the dam safety decision context, where both the risk of failure and the risk of life loss are considered. The latter was not necessarily a driving factor prior to the introduction of RIDM, as traditional approaches tended to be either upstream-looking (ability to pass a design flood) or limited to the structures themselves (ability to meet required safety factors). With RIDM, the failure-focused deterministic approaches did not become obsolete, but their role changed from that of decision criteria to sources of information for a risk analysis. Whereas a RIDM strategy focused exclusively on dam failure risk could just as easily have been developed, awareness of how the term “risk” was being used in other industries led to the adoption of life loss-based criteria, and to the need to estimate failure consequences. Over time, two major approaches developed: empirically based techniques and simulation based techniques. While both have been used successfully to support dam safety decisions, simulation based estimation has come to be viewed as more rigorous. However, the presumed advantages come at a price, and in the relentless pursuit of accuracy it can be easy to lose sight of the big picture. This paper highlights some key differences between empirical and simulation based approaches, and attempts to draw the line between consequence estimation as a risk analysis versus an emergency management tool. It explains why the Bureau of Reclamation is still using RCEM a decade after it was first developed, despite the availability of well publicized (and well supported) simulation based alternatives.