Dam Safety in the 21st Century

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The Reality of Risk
Dam Safety in the 21st Century

• PFMA as a Dam Safety Tool Joe Ehasz
• FERC Regulator Perspective Doug Johnson
• USACE Perspective Doug Boyer
• Owner Perspective - Bill Christman

Portland, OR February 19, 2013
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The Reality of Risk
Dam Safety in the 21st Century
The PFMA Process as a Dam Safety Tool
Joe Ehasz URS Energy
Construction, Inc
Portland, OR February 19, 2013
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The Reality of Risk
Potential Failure Mode Analysis (PFMA)

• The process utilized to determine the Potential
  Failure Modes
• pertinent to the dam under investigation
• Essentially asks the Question
• How could this dam fail
• What happens if it does
• Are the identified potential failure modes
  recognized
• What actions can be taken to reduce the dam
  failure likelihood

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The Reality of Risk

• Presentation of Three Actual Dam Failures that
• Were scheduled to have PFMA performed
• Failed prior to PFMA
• Failure could have been avoided if PFMA process
  had been done

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The Reality of Risk

• Three Actual Dam Failures
• Swift 2 Forebay Dam Washington - Failed
  April 21,2002
• Silver Lake Michigan - Failed May 14, 2003
• Taum Sauk Upper Reservoir Dam Missouri -
  Failed Dec. 14, 2005

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The Reality of Risk
Swift No. 2 Hydroelectric Project
Forebay Dam Failure
April 21, 2002
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The Reality of Risk
Swift No.2 Hydro Project

• Constructed - 1957 1958
• Length of water supply canal 3 miles
• Impoundment - 2400 ac-ft
• Embankment height in forebay 93 ft
• Max water depth 53 ft

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The Reality of Risk
Operating History

• Considerable leakage upon first filling
• Cracks and sinkholes in canal bottom
• Mud boils below canal levels
• Portions of dike removed and filter placed in
  canal bottom
• No further distress until 2002 when failure
  occurred

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The Reality of Risk

• Sinkholes developed in forebay at 300 AM
• Blowout followed at toe of embankment
• Orifice expanded upstream
• Embankment breached at about 630 AM
• Flooding destroyed powerhouse
• Discharge contained in the lower reservoir

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The Reality of Risk
April 21, 2002 Failure
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The Reality of Risk

• Sinkholes developed in forebay at 300 AM
• Blowout followed at toe of embankment
• Orifice expanded upstream
• Embankment breached at about 630 AM
• Flooding destroyed powerhouse
• Discharge contained in lower reservoir

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The Reality of Risk
Potential Things That Could Have Been Done to
Recognize the Problem?

• Periodic (annual) draining and inspection of the
  forebay and canal
• Install piezometers beneath the basalt to
  measure pressures
• Develop a complete water balance to establish
  the total loss of canal water
• More study and critical review of construction
  conditions and photos
• Perform a PFMA to develop the possible failure
  modes with consideration of the construction and
  series of repairs that were required upon first
  filling and later

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The Reality of Risk
Silver Lake Failure May 14, 2003

• High Rainfall Period
• Fuse Plug Failure
• Fuse Plug Foundation Eroded
• Entire Lake Empted
• Flooding Downstream Facilities

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The Reality of Risk
Silver Lake Reservoir
May 13, 2003
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The Reality of Risk
May 14, 2003
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The Reality of Risk
May 14, 2003
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The Reality of Risk
May 14, 2003
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The Reality of Risk
Taum Sauk Pumped Storage Project

• 450 MW Pumped Storage Project
• Located in Reynolds County, Missouri
• One of the First PSP, Started in 1963
• Licensed by FPC in August 1965
• Owned and Operated by Ameren UE
• Upper Dam is a Continuous Dike 6,562 Ft. Long
• Upper Reservoir Water Level Overtopped the Dam
• Upper Reservoir Dam Failed on December 14, 2005

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The Reality of Risk
Taum Sauk Upper Reservoir
Power Tunnel
Powerhouse
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The Reality of Risk

• Dumped and Sluced Rockfill
• Upstream Reinforced Concrete Lining
• Parapet Wall Placed atop the Rockfill Dam
• Underdrainage Concerns Upon First Filling
• Continued High Levels of Leakage Through Dam
• Large Settlements and Movements of Dam and Wall
• Relining in 2004 to Reduce Seepage
• Revised Water Level Instrumentation in 2004

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The Reality of Risk
Do you Really Operate This Full?
Taum Sauk Upper Reservoir Full
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The Reality of Risk
December 14, 2005
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The Reality of Risk
Potential Failure Mode Analysis (PFMA)

• Is a Good process because it does ask the tough
  questions
• How could this dam fail
• What happens if it does
• Are the identified potential failure modes
  recognized
• What actions can be taken to reduce the dam
  failure likelihood

Because of that, I believe that it actually can
minimize or even eliminate failures
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The Reality of Risk
Discussion Later!