A resilience loss assessment framework for evaluating flood-control dam safety upgrades

Dams that were designed and built decades ago may not meet current design standards that reflect our improved knowledge of extreme rainfall events. When comparing dam safety upgrades, cost-efficient options that reduce the probability of overtopping are preferred. However, these criteria neglect flood damage costs resulting from controlled water flow inherent to the design of the safety upgrades. Therefore, to address this shortcoming, we apply the concept of resilience to evaluate dam safety upgrade options from a flood damage mitigation perspective through a resilience assessment framework. In this study, resilience is defined as the ability to provide flood-control service after an extreme rainfall event and to recover a desired level of functionality as soon as practicable. This framework features four main steps: estimating the probable maximum flood for the dam under investigation, calculating the dam discharge for each of the upgrade options, quantifying the loss in system resilience, and converting the losses into monetary units. This framework is applied to two dam safety upgrade options (constructing an emergency spillway and increasing dam crest height) for a large dam in Andong, South Korea. In practice, the former option is typically preferred as it is cost-efficient. However, we find that the latter option is superior when accounting for flood damage costs caused by water that is intentionally released from the dam during a probable maximum flood event. This study will help to ensure sound decision making when evaluating dam safety upgrade options by considering not only construction costs but also flood damage costs.