US Army Corps of Engineers
Portland District Website Website

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Phone: 503-808-4510

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Dam Safety - Managing Risk

Risk is a function of three components: The potential hazards or future loading, the dams performance given that loading and the consequences of a dam breach if the dam does not perform as intended. Potential hazards include large regional floods, earthquakes, landslides, rapid pool fluctuations, and other events. The expected performance of the dam is evaluated based on criteria used at the time of its design, construction documentation, historical performance, site investigations and advanced analysis. Consequences are estimated based on computer simulations of flood inundation extents, flood wave arrival times, warning times, the time of day at breach, and other factors.

Risk assessments

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.

Current & scheduled risk assessments in the Willamette Valley​ ​​

Issue Evaluation Studies

Construction crews built a road on Hills Creek Dam so Portland District could conduct field investigations, 2016.

The Corps uses Issue Evaluation Studies to evaluate the condition and risks associated with its dams. These assessments provide data that will give the Corps additional information to better 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.

 An IES is completed in phases, which include:

  1. Data gathering phase: field investigation, regional hydrologic analysis, regional potential seismic hazard analysis, advanced structural analysis, etc.
  2. Evaluation phase: assessing the probability and consequence of ways the dam could fail
  3. Documentation/report writing phase
  4. 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?

The Portland District is performing field investigations at some of its dams as part of the Issue Evaluation Studies. During these field investigations the Corps will collect data that will be used to:

  • Better understand how dam materials perform under various conditions, including  normal operating conditions, large storm events, or seismic activity
  • Measure water levels and movements within the dam
  • Update information related to seismic activity

Additional risk mitigation efforts

Portland District’s highest priority is ensuring the Corps’ dams are fully able to reduce flood damage to downstream communities on the Willamette and Rogue rivers, and that the Columbia River dams continue to safely function as designed. The primary objective of the Corps' Dam Safety Program is to maintain public safety by making sure the dams it owns and operates are as safe as possible, and that risks to the public are minimized. Work performed as part of the Dam Safety Program includes:

  • Periodic inspections and assessments
  • Emergency Action Plan exercises
  • Seismic and hydrologic studies
  • Foundation drain inspections
  • Survey monitoring
  • Instrumentation monitoring
  • Bridge inspections
  • Hydraulic steel structures inspections and evaluations

People living below dams need to understand their level of risk and take preparedness actions. It is always a good time to prepare for an emergency. Contact your county offices for local emergency preparedness information. All Corps dams have emergency action plans which are maintained in coordination with local emergency management officials.

Background

The U.S. Army Corps of Engineers owns and operates a large portfolio of dams that provide a variety of critical benefits to society, including flood risk management, navigation, hydropower and recreation. However, there are risks to life and property if a dam were to fail. The Corps monitors the condition and performance of these dams, using assessments and evaluations to provide information about the structures. The Portland District, as part of its Dam Safety program, monitors the condition and performance of the structures owned and operated by the District. These structures are within the Columbia, Willamette and Rogue river basins, and are well-designed, well-constructed and are functioning as intended. There is no evidence to suggest an emergency situation exists, or is about to occur. For more dam safety information, click here.

  • 19 dams
  • Mount St. Helens sediment retention structure
  • Five navigation locks
  • 13 hydropower plants

It is important that residents who live downstream from a dam are aware of the potential consequences should the dam breach, not perform as intended, or experience major spillway or outlet works flows.