There is a growing recognition of the value of using risk assessment as a supplement to traditional engineering approaches to dam safety decision making. This is referred to as a risk-informed approach in which decision making utilizes information obtained from a risk assessment along with other factors, including good engineering practice. Thus a risk assessment is not the sole basis for a decision, but rather it provides a systematic way of identifying what is important and where uncertainties exist. Risk assessment can also be valuable for justifying the extent and type of risk reduction and the phasing of risk-reduction measures. This webinar provides an explanation of the steps involved in performing a risk assessment for an individual dam and how the resulting insights and risk estimates can improve decision making. Examples are provided for evaluating an existing dam and for selecting between risk-reduction alternatives. This webinar serves as a pre-requisite for the follow-up webinar topic: Risk Management for a Portfolio of Dams.
David S. Bowles, Ph.D., P.E., P.H., D.WRE, F.ASCE
Since 1978 David and his colleagues have pioneered the development and practical application of risk-informed approaches to dam safety management. They have completed risk assessments for more than 750 dams in many countries, ranging from screening to detailed assessments with uncertainty analysis. David has assisted with the development of tailored frameworks for dam and levee safety risk management, including tolerable risk guidelines, for owners, regulators and national bodies. Clients have included Reclamation, USACE, TVA, World Bank, WMO, IAEA, EU, FERC, ANCOLD and NSW DSC. He has served as an expert witness for dam and canal failures, reservoir operation and hydropower generation, toxic tort, and urban flooding.
David has provided training programs on six continents. He is a coauthor of ICOLD Bulletin 130 on dam safety risk assessment and numerous other guidance documents. He has led software development for dam risk analysis (DAMRAE) and life-loss estimation (LIFESim) for USACE, portfolio risk assessment for a large UK dam owner (ResRisk), and real-time reservoir flood operation for Reclamation, USACE and SAFCA.
David is Managing Principal of RAC Engineers and Economists and Emeritus Professor of Civil and Environmental Engineering at Utah State University (USU). Previous positions include Director of Institute for Dam Safety Risk Management at USU, Director of Utah Center for Water Resources Research, Engineering Department Manager and Branch Manager for Law Engineering’s Denver office, and a construction and design engineer for a large international contractor based in the UK.
Factors that have lead to the use of risk assessment
Contrasting the traditional and risk-informed approaches
2. Some probability basics
3. Risk Assessment Process
Step 1 - Define the purpose
Step 2 - Perform Engineering Assessment and identify and screen potential failure modes
Step 3 - Develop risk model
Step 4 - Estimate flood and earthquake loading probabilities
Step 5 - Estimate system response probabilities
Step 6 - Estimate consequences
Step 7 - Calculate the risk
Step 8 - Evaluate the risk - what risk is tolerable?
Generalized and project-specific considerations
Tolerable risk limits
Broadly acceptable risk
Other evaluation considerations
Step 9 - Recommend and make the case for a decision
4. Example Risk Assessment for an Individual Dam
Baseline risk – existing dam
Risk-reduction alternatives – structural and non-structural
Recommend and make case for a decision including a comparison of the traditional and risk perspectives