Periodic Assessments: are routine dam safety activities that the Corps performs every 10 years on all Corps-owned dams. We schedule Periodic Assessments conjunction with five-year Periodic Inspections. Multi-disciplinary teams and trained facilitators from outside of Portland District conduct the assessments. The Periodic Assessment includes a review of background information, a site-visit, a potential failure modes analysis, and a semi-quantitative risk assessment. The assessment also provides an opportunity to review the dam's risk classification and make recommendations for future study and operations and maintenance actions.
Issue Evaluation Studies: (more details below) are advanced dam safety risk assessments that the Corps prioritizes and funds on a national basis. We use the IES to evaluate the condition and risks associated with our dams. These studies provide data that will give us additional information to understand conditions within the dams and in their foundations, helping to evaluate risks and determine the degree of urgency for action within the context of the Corps’ national dam portfolio. The Corps completes an IES in phases, which include:
- Data gathering phase: field investigation, regional hydrologic analysis, regional potential seismic hazard analysis, advanced structural analysis, etc.
- Evaluation phase: assessing the probability and consequence of ways the dam could fail
- Documentation/report writing phase
- Decision-making phase: do we need to more evaluations, do we need to implement interim risk reduction measures, and/or do we need to fix something?
Dam Safety Modification Studies: are planning studies that evaluate long-term risk reduction actions and alternatives. The goal of the study is to formulate alternatives or combinations of alternatives that lower a dam's total risk to be within tolerable risk guidelines. The Corps evaluates the alternatives for their cost effectiveness of reducing the risk to, and below the minimum safety criteria. The resultant Dam Safety Modification Decision Document will present a comparison of alternatives and the recommended risk management plan – to include actions, implementation plans, detailed cost estimates and environmental analyses.
Interim Risk Reduction Measures: are short-term actions that the Corps can take to reduce risk, based on information gathered during risk assessments or inspections. We implement these to reduce risk while we study potential dam safety issues further, perform maintenance actions, or pursue long-term modifications. Examples of interim risk reduction measures include structural measures, increased inspection and monitoring, dam safety training, stockpiling of emergency materials, operational changes or restrictions, updating and exercising Emergency Action Plans, and increased risk communication and coordination.