• Sealing concrete cracks around trunnion pins

• Replace bolts on gate arms

• Update hydraulic studies and flood inundation mapping

• Update emergency action plan

• Increased monitoring

• Perform Emergency Exercise

 

In all cases, interim risk reduction measures are taken to reduce the risk to public safety.

USACE developed a risk-informed screening tool to compare the condition of each dam with the risk associated with a new dam. Cadres of Corps professional personnel were trained in the use of the tool and evaluated each dam screened using information provided by the operating District. A group of senior engineers from across the Corps reviewed the screening information and established the DSAC for each dam.

The issues that have driven the DSAC II ratings are not new issues. What is new is how we assess our dams and are incorporating risk concepts into dam safety management, routine activities and programming decisions. 

DSAC I – URGENT AND COMPELLING (Unsafe)

DSAC II – URGENT (Unsafe or Potentially Unsafe)

DSAC III – HIGH PRIORITY (Conditionally Unsafe)

DSAC IV – PRIORITY (Marginally Safe)

DSAC V – NORMAL (Safe)

For purposes of the IRRM Plan, Potential Failure Mode Analyses
(PFMA) are limited to the loading conditions identified by the SPRA team as probably inadequate or inadequate.

 

PFMA is a new requirement for USACE. Training and implementation is being planned for the near future.

Funding for repairs at four of the five DSAC II dams has been received under the American Recovery and Reinvestment Act of 2009 (De Pere, Little Chute, Rapide Croche, and Cedars). The Detroit District is currently working on the design of the repairs at the fifth DSAC II project (Upper Appleton), and will request funding for repairs once the design is complete.

 

DSAC ratings are being used to set national priorities. Projects classified as DSAC III and IV will not receive funding until the higher risk DSAC I and II projects are addressed. Districts may elect to make partial repairs for DSAC III and IV projects with O&M funds.

 

Budgets for fiscal 2010 and beyond have not yet been determined. USACE will continue to request funding for DSAC I and II projects, and transition to fund future studies and repairs for DSAC IV projects as the repairs on the DSAC II dams are completed.

Requests for inspection reports will be evaluated on a case-by-case basis because of information that may expose a vulnerability that could be an operational security concern.

Interim risk reduction measures are a short-term approach to reduce dam safety risks while long-term solutions are pursued. They are an important step in returning the project to a stable and safe condition. In establishing IRRM, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses.

The criteria used in the screening are the current state-of-the art criteria for the design and construction of large dams.

In the context dam safety, failure is generally confined to issues of structural integrity, and in some contexts to the special case of uncontrolled release of a reservoir through collapse of the dam or some part of it.

In 2001, USACE conducted a comprehensive peer review of the USACE Dam Safety Program through the Association of State Dam Safety Officials (ASDSO). ASDSO recommended that USACE develop risk reduction, risk assessment, and risk management procedures for implementing a nationwide evaluation process that prioritizes the funding and allocation of dam safety resources Corps-wide. This ASDSO recommendation was the catalyst for initiating risk based screening of our USACE dams, and the subsequent Expert Panel review of our six highest risk dams.

 

Approximately one year before Hurricane Katrina, the Corps began an approach to provide consistent and systematic guidelines for appropriate actions to address the dam safety issues and deficiencies of USACE dams.

 

Following the first three years of risk-informed screening in 2005, 2006 and 2007, USACE categorized dams into Dam Safety Action Classes (DSAC) based on their individual dam safety risk considered as probability of failure and potential failure consequences.

 

Lessons learned from Hurricane Katrina have heightened the Corps' commitment to address risks attributed to our aging infrastructure, and take all actions necessary to prevent failure of a Corps dams.

Risk is the measure of the likelihood, chance, or degree of belief that a particular outcome or consequence will occur along with the outcome of the failure including immediate, short and long-term direct and indirect losses and effects. Losses may include human casualties; as well as impacts on water supply and hydropower benefits. Effects may include downstream damages and/or adverse environmental impacts.

There are two classification systems for dams:

 

The USACE Dam Safety Action Classification (DSAC) is a classification of dams accomplished by a team of Corps of Engineers' dam safety professionals as a means to group dams that exhibited certain characteristics for potential safety concerns. From 2005-2007, USACE conducted an initial risk-informed screening of approximately 202 dams and the remaining dams operated by USACE will be screened in the next two years.

DSAC classifications are based upon confirmed and unconfirmed dam safety issues and the probability of failure and life or economic consequences. USACE will only designate a dam normal or safe when there are no unconfirmed dam safety issues.