APPLICATION OF A VULNERABILITY-BASED RISK ASSESSMENT TOOL FOR DAM SAFETY
Hamid Goharnejad (Meco)

Dam Safety is regulated provincially throughout Atlantic Canada and is governed by the Dam Safety Guidelines published by the Canadian Dam Association CDA. The Guidelines represent industry-best practices for analysis and design and use a mixture of standards-based criteria to establish safety. The safety criteria are event based and additive where the state of knowledge permits computational analysis, and subjective and opinion based where there is inadequate knowledge. The Guidelines cannot quantitatively answer ‘“how safe’” a dam is or if one dam is’” more safe’” than another dam. In these instances, the guidelines allow for risk-informed decision making RIDM without providing guidance on tolerable risk guidelines.

A vulnerability-based risk assessment tool can be used to rank a portfolio of dams or individual failure modes of a single dam so achieve maximum risk reduction for capital investment dollar. The Vulnerability method is an adaptation of the ‘“Risk Index Method’” presented at the 2008 CDA conference workshop entitled’“Risk and Uncertainty in Dam Safety’”. A vulnerability-based risk index, vbRisk, is computed for each structure as a function of consequence and vulnerability indices. The consequence index ranges from 0 to 5 based on dam classification. The vulnerability index values are derived from standards-based criteria evaluated for each dam or dam component and considering 23 vulnerability categories grouped into either a design loading condition sunny day, flood, or earthquake, physical condition, or measure of operational reliability. Annual tracking of key performance indicators provided by the risk assessment tool are considered an innovative method to measure the health of dams, assess the performance of the dam safety program, facilitate risk-informed decisions, and direct operating and/or capital expenditures.

This paper provides background on the risk assessment tool and methodology and demonstrates its practical application to dam safety.