Multi-hazard water system vulnerability assessments objectives, benefits and case study

Earthquakes are one of multiple hazards that can disrupt water system operation. Other hazards include, for example, flood, wind, ice storms, and turbidity events. The objective of a multi-hazard assessment is to evaluate the risk from these various hazards, to allow the system owner/operator to mitigate those of greatest concern. A multi-hazard vulnerability assessment quantifies each hazard, incorporating three elements : ○ Hazard Quantification - probability of exceedance and associated intensity ○ Vulnerability of Systems and Components - expected damage ○ Consequences of Damage - impacts on system function : flow and water quality The benefits of a multi-hazard assessment, compared to a single hazard assessment, include : 1) optimization of the use of the hazard mitigation budget, and 2) identification of mitigation alternatives that address multiple hazards. Multi-hazard assessments can be used to develop estimates on the probability of not meeting system performance objectives based on user needs and expectations. Hazard mitigation alternatives can be integrated in capital improvement and maintenance projects that address non-hazard issues such as system growth and water quality. This approach can increase the likelihood of mitigating hazard vulnerability projects, which by themselves often go unfunded. The City of Portland, Oregon, Bureau of Waterworks is currently conducting such an assessment. This paper will discuss the methods used, and the lessons learned in Portland.