Walla Walla District

Dworshak Dam and Reservoir - Dam Safety Update

Project DescriptionDworshak Dam is a flood control dam located on the North Fork of the Clearwater River near Orofino, Idaho. Construction began in 1966, flood damage reduction operations began in June 1972, and power generation came online in 1973. The project includes the dam, reservoir, powerhouse, recreation facilities, wildlife mitigation and Dworshak National Fish Hatchery. The reservoir is 54 miles long and has a surface area of about 20,000 acres.

Public Safety is the Corps’ Highest Priority
The U.S. Army Corps of Engineers’ highest priority is public safety. While we cannot completely eliminate risk, we can reduce risk.
The objective of the Corps’ Dam Safety Program is to maintain public safety, make Corps dams safer and minimize risks. Since 2007, the Corps has used a risk-informed process to prioritize addressing dam safety deficiencies on a nationwide basis. What’s new is how we assess our dams and are incorporating risk management concepts into dam safety management, routine activities and programming decisions.

Walla Walla District dams and appurtenant (dam-related) levees were screened and assessed for dam safety issues and deficiencies and their potential risk to the public. After dams and dam-related levees were assessed, the Corps categorized them into five Dam Safety Action Classes (DSAC) based on individual dam safety risk.

As a result, our understanding of conditions at our dams has improved. In some cases, we gained new observations of symptoms of potentially serious problems. In other cases, we learned original design and construction methods do not meet current safety standards. The dam safety classifications assist the U.S. Congress and the Corps in prioritizing funding for dam safety infrastructure improvements.

The safety classifications are assigned by a Corps headquarters “Senior Oversight Group,” which also periodically reviews updated information about dam safety improvements. The five action classes, now included in the overall Corps of Engineers Dam Safety Program, are:

•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”)

Risk = Probability of Failure x Potential Failure Consequences
Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components. Potential consequences of failure are impacts to life, property, resources (such as hydropower generation), economies and environment downstream.

Dworshak Dam Status
Dworshak Dam was initially classified as DSAC-II “Urgent (Unsafe or Potentially Unsafe)” in October 2007 because of engineering unknowns related to structural stability and foundation seepage of concrete gravity sections.

In May 2012, Dworshak Dam received a more favorable or safer DSAC-III or “High Priority (Conditionally Unsafe)” rating from the Senior Oversight Group based on a completed “Phase I Issue Evaluation Study,” which improved Corps’ understanding of conditions at the dam. The primary reasons for the new ”High Priority” classification decision were 1) a confirmation of the robustness of dam design and historical performance of the structure; and 2) that potentially significant failure modes are a result of rare seismic events.

During the past several years, the Corps has taken “interim risk reduction measures” (IRRMs) to reduce public risk.

Interim Risk Reduction Measures
Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Completed Interim Risk Reduction Measures (as of June 2012)
• External stability study: Complete. The dam meets current criteria for external stability.
• Repair and upgrade instrumentation: The ARRA-funded instrumentation upgrade and automated system contract was awarded in June 2010 and completed by December 2011. The automated system is currently online and collecting data. Data evaluation is ongoing.
• Complete trunnion friction analysis: Contract for strain gauge instrumentation of trunnion gate bearings (the gate hinges for vertical raising) is completed and a report provided. Numeric evaluation of report data to determine trunnion friction is complete.

Ongoing/Remaining Interim Risk Reduction Measures (as of June 2012)
• Revise the dam safety emergency action plan
• Conduct emergency exercises: A tabletop exercise is planned for 2013-2014.
• Update emergency action plan inundation maps: The Corps’ Modeling, Mapping and Consequence Production Center (MMC) completed draft dam failure inundation maps. Reviewed by the District and comments were provided. Final draft pending from the MMC.
• Complete finite element analysis: This study will analyze internal stresses to more adequately model existing cracks in the dam. Completion is planned to occur during Phase 2 Issue Evaluation Study.
• Repair failed waterstops: Two 8-inch diameter urethane waterstop cylinders were installed in the Dam September-October 2010. The District’s contractor sent a final report in February 2011 stating that the urethane waterstop material is functioning as designed, although engineers observed that even with new waterstops in place, nuisance water flow through the dam hasn’t decreased. The next step is to identify the primary source of water still making its way through the dam, and determine repair alternatives.

Our Path Forward
A Phase II Issue Evaluation Study is in progress and is tentatively scheduled for completion in fiscal year 2013, contingent upon resources. The purpose of the Phase II Issue Evaluation Study is to further reduce remaining uncertainties identified in the Phase I Issue Evaluation Study. The Corps will diligently continue to pursue public risk reduction and keep the public informed.


Updated June 14, 2012

Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components.  Potential consequences of failure are impacts to life, resources (such as hydropower generation), property, economies and environment downstream.

Ice Harbor Lock and Dam Status

Ice Harbor Dam was screened and classified as DSAC-III “High Priority (Conditionally Unsafe)” in September 2009 primarily due to potential overtopping/erosion of embankment/abutment and potential upstream radial lock gate failure during high pool.

Although the probability of dam failure is low, the consequences of failure are potentially high. Currently there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Interim Risk Reduction Measures (ongoing/remaining as of February 2012)

·         Perform spillway tainter gate fit-for-service evaluation: Evaluation in progress.

·         Update probable maximum flood and generate water surface profile.

·         Complete a spillway hydraulic study.

·         Relocate spillway power generator and provide seismic bracing.

·         Conduct upstream gate reliability analysis.

·         Develop a navigation lock operation plan.

·         Conduct navigation lock monolith 6 analysis.

·         Develop right abutment closure plan.

·         Conduct a spillway (service) bridge study.

·         Stockpile emergency material such as sand and gravel.

·         Perform potential failure mode analysis.

·         Develop a dam surveillance plan for high water events.

·         Update emergency action plan inundation maps.

·         Conduct emergency exercises.

·         Update the dam safety emergency action plan.

Our Path Forward

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress.

Updated Feb. 13, 2012-1150

Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components.  Potential consequences of failure are impacts to life, resources (such as hydropower generation), property, economies and environment downstream.

Little Goose Lock and Dam Status

Little Goose Lock and Dam was screened and classified as DSAC-III “High Priority (Conditionally Unsafe)” in January 2009, primarily due to potential overtopping of the embankment and right abutment (at the railroad cut) under maximum flood conditions.

Although the probability of dam failure is low, the consequences of failure are potentially high. Currently there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Interim Risk Reduction Measures (ongoing/remaining as of February 2012)

• Perform a tainter gate fit-for-service evaluation: Evaluation in progress.
• Update the dam safety emergency action plan.
• Develop a navigation gate and floating bulkhead placement and operation plan.
• Update emergency action plan inundation maps.
• Stockpile emergency material such as sand and gravel.
• Complete spillway hydraulic study.
• Develop a navigation lock equipment flood damage mitigation plan.
• Recoat the tainter gate trunnion anchor caps with epoxy coating.
• Develop dam surveillance plan to address high water and emergency-related events.
• Conduct emergency exercises.
• Perform potential failure mode analysis.

Our Path Forward

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress.

 

Updated Feb. 13, 2012-1050

Lower Granite Lock and Dam - Dam Safety Update

Project Description

Lower Granite Lock and Dam is located on the Snake River at the upper end of Lake Bryan, upstream of Little Goose Lock and Dam. It is 107.5 miles above its confluence with the Columbia River and 24 miles northwest of Clarkston, Wash. Lower Granite Lake, with a drainage area of 103,200 square miles, extends behind Lower Granite Dam 39.3 miles to Lewiston, Idaho. It provides navigation, hydroelectric power, irrigation and recreation. Flood control is incidental to other purposes.

Lower Granite includes a powerhouse, navigation lock, and fish passage facilities. The dam is about 3,200 feet long with a normal operating hydraulic height of 100 feet. Construction began in July 1965 and completed in 1984. Dam-related backwater levees were constructed around Lewiston, Idaho. The project generates 810 megawatts of power. The Corps manages approximately 4,802 acres for public recreation purposes, wildlife habitat, wildlife mitigation, and water-connected industrial development. Approximately 515 acres are licensed either to State or local park agencies. Port districts own lands adjacent to the project for industrial development.

Public Safety is the Corps’ Highest Priority

The U.S. Army Corps of Engineers’ highest priority is public safety. While we cannot completely eliminate risk, we can reduce risk. The objective of the Corps’ Dam Safety Program is to maintain public safety, make Corps dams safe and minimize risks. Since 2007, the Corps has used a risk-informed process to prioritize addressing dam safety deficiencies on a nationwide basis. What’s new is how we assess our dams and are incorporating risk management concepts into dam safety management, routine activities and programming decisions.

Walla Walla District dams and appurtenant (dam-related) levees were screened and assessed for dam safety issues and deficiencies and their potential risk to the public. After dams and dam-related levees were assessed, the Corps categorized dams into five Dam Safety Action Classes (DSAC) based on individual dam safety risk.

As a result, our understanding of conditions at our dams has improved. In some cases, we gained new observations of symptoms of potentially serious problems. In other cases, we learned original design and construction methods do not meet current safety standards. The dam safety classifications assist the U.S. Congress and the Corps in prioritizing funding for dam safety infrastructure improvements.

The safety classifications are assigned by a Corps headquarters “Senior Oversight Group,” which also periodically reviews updated information about dam safety improvements. The five action classes, now included in the overall Corps of Engineers Dam Safety Program, are:

·         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”)

Risk = Probability of Failure x Potential Failure Consequences

Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components.  Potential consequences of failure are impacts to life, resources (such as hydropower generation), property, economies and environment downstream.

Lower Granite Lock and Dam Status

Lower Granite Lock and Dam was screened and classified as DSAC-III “High Priority (Conditionally Unsafe)” in January 2009, primarily due to potential dam embankment failure due to navigation lock wall overtopping; right side overtopping at the railroad cut; and dam overtopping due to spillway gate failure during maximum flood conditions.

Although the probability of dam failure is low, the consequences of failure are potentially high. Currently there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Completed Interim Risk Reduction Measures (as of February 2012)

• Develop a navigation gate and floating bulkhead placement and operations plan: Completed.

Ongoing/Remaining Interim Risk Reduction Measures (as of February 2012)

• Perform a spillway hydraulic study.
• Develop a navigation lock equipment flood damage mitigation plan.
• Stockpile emergency material such as sand and gravel.
• Perform tainter gate fit-for-service evaluation: Evaluation in progress.
• Perform potential failure mode analysis.
• Develop dam surveillance plan to address high water and emergency-related events.
• Update emergency action plan inundation maps.
• Update the dam safety emergency action plan.
• Conduct emergency exercises.

Our Path Forward

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress

Updated Feb. 12, 2012

Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components.  Potential consequences of failure are impacts to life, resources (such as hydropower generation), property, economies and environment downstream.

Lower Monumental Lock and Dam Status

Lower Monumental Dam was screened and classified as DSAC-III “High Priority (Conditionally Unsafe)” in September 2009, primarily due to potential embankment overtopping or erosion and navigation lock wall overtopping during maximum flood conditions.

Although the probability of dam failure is low, the consequences of failure are potentially high. Currently there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Interim Risk Reduction Measures (ongoing/remaining as of February 2012)

·         Perform spillway tainter gate fit-for-service evaluation: Evaluation in progress.

·         Update the probable maximum flood study and generate water surface profile.

·         Complete a spillway hydraulic study.

·         Develop a navigation lock operation plan for maximum flood event.

·         Develop navigation lock equipment flood damage mitigation plan.

·         Stockpile emergency material such as sand and gravel.

·         Conduct a spillway (service) bridge study.

·         Conduct an upstream lock gate reliability analysis.

·         Perform potential failure mode analysis.

·         Develop a dam surveillance plan for high water events.

·         Update emergency action plan inundation maps.

·         Conduct emergency exercises.

·         Update the dam safety emergency action plan.

 

Our Path Forward

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress.

Updated Feb. 13, 2012-1200

Risk = Probability of Failure x Potential Failure Consequences

 

Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components. Potential consequences of failure are impacts to life, property, resources (such as hydropower generation), economies and environment downstream.

Lucky Peak Dam Status

Lucky Peak Dam was screened and classified as DSAC-III “High Priority (Conditionally Unsafe)” in January 2009 because there is an unconfirmed potential for foundation seepage and piping and because of the potential for foundation instability during a large earthquake.

Although the probability of dam failure is low, the consequences of failure are potentially high. Currently there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Completed Interim Risk Reduction Measures (as of February 2012)

·         Conduct a potential failure mode analysis: Completed.

·         Dam safety instrumentation evaluation: Analysis of existing instrumentation was completed in FY2011 and recommended two additional piezometers. These instruments were installed in November 2011.

Ongoing/Remaining Interim Risk Reduction Measures (as of February 2012)

·         Updating the dam surveillance and monitoring plan to address updated potential failure modes and emergency-related event monitoring.

·         Update the dam safety emergency action plan: Scheduled to begin in FY2012.

·         Update emergency action plan inundation maps: In progress.

·         Conduct emergency exercises: A tabletop type emergency exercise with local officials and outside agencies was conducted in September 2011. This is planned to be a recurring measure.

Our Path Forward

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress.

Updated Feb 10, 201

McNary Levee System - Safety Update

Project Description

The McNary Levee System is a set of three levee systems built as part of the McNary Lock and Dam project that provide flood protection for portions of Kennewick, Pasco, and Richland, Wash. The System is located on the Columbia River and tributaries and is sometimes identified as the “Tri-Cities Levees.” The System includes about 15 miles of levees. Lake Wallula behind McNary Lock and Dam is about 63 miles long and includes 242 miles of shoreline and a water surface area of 38,800 acres. 

The three McNary Levee Systems are individually referred to as “Kennewick Levee System”; “Pasco Levee System”; and “Richland Levee System.” The entire System is operated by the Walla Walla District. Construction of the McNary Levee System began in 1950 and was completed in 1954. Ownership and operational responsibility for two levees and a pumping plant were transferred to the Port of Pasco in 1963. A 1992 report estimated that the McNary Levee System prevented nearly $59 million (1992 dollars) of flood damages annually.

Public Safety is the Corps’ Highest Priority

The U.S. Army Corps of Engineers’ highest priority is public safety. While we cannot completely eliminate risk, we can reduce risk.

The objective of the Corps’ Dam Safety Program is to maintain public safety, make Corps dams safe and minimize risks. Since 2007, the Corps has used a risk-informed process to prioritize addressing dam safety deficiencies on a nationwide basis. What’s new is how we assess our dams and are incorporating risk management concepts into dam safety management, routine activities and programming decisions.

Walla Walla District dams and appurtenant (dam-related) levees were screened and assessed for dam safety issues and deficiencies and their potential risk to the public. After dams and dam-related levees were assessed, the Corps categorized them into five Dam Safety Action Classes (DSAC) based on individual dam safety risk.

As a result, our understanding of conditions at our dams and dam-related levees has improved. In some cases, we gained new observations of symptoms of potentially serious problems. In other cases, we learned original design and construction methods do not meet current safety standards. The dam safety classifications assist the U.S. Congress and the Corps in prioritizing funding for dam safety infrastructure improvements.

The safety classifications are assigned by a Corps headquarters “Senior Oversight Group,” which also periodically reviews updated information about dam safety improvements. The five action classes, now included in the overall Corps of Engineers Dam Safety Program, are:

·         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”)

Risk = Probability of Failure x Potential Failure Consequences

Mathematically, the dam safety action classes are based on a calculation of each project’s  PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components. Potential consequences of failure are impacts to life, property, resources (such as hydropower generation), economies and environment downstream.

McNary Levee System Status

McNary Levees at Kennewick, Pasco and Richland were each screened and classified as DSAC-II “Urgent (Unsafe or Potentially Unsafe)” in September 2009. This is primarily because of potential seepage and piping due to failure at conduits through the levees under normal or extreme reservoir pool conditions. Also, during extreme water levels, potential overtopping and erosion of levees plus seepage and piping at embankments, foundations and abutments are concerns.

Although the probability of levee failure is low, the consequences of failure are potentially high. Currently there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Completed Interim Risk Reduction Measures (as of Feb. 2012)

·         Inspect and maintain levee system culverts. (Completed for the Pasco Levee System)

 Ongoing/Remaining Interim Risk Reduction Measures (as of Feb. 2012)

·         Update emergency action plan. Planned to start in FY2013.

·         Create inundation maps. In progress.

·         Develop surveillance plan for high water events.

·         Inspect and maintain levee system culverts for Kennewick and Richland Levee Systems

·         Complete vegetation maintenance (Richland Levee System only).

Our Path Forward

An Issue Evaluation Study (IES) is tentatively planned for FY2013, contingent on resources. The purpose of an Issue Evaluation Study is to focus on significant potential failure modes when evaluating risk, verify the current DSAC rating, guide the selection of and gauge the effectiveness of interim risk reduction measures, and justify the need to pursue or not pursue Dam Safety Modification studies.

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress.

Updated 2/10/2012

McNary Lock and Dam - Dam Safety Update

Project Description

McNary Lock and Dam is located in Oregon and Washington at river mile 292 on the Columbia River. McNary is a multipurpose project providing navigation, hydroelectric power generation, recreation, wildlife habitat and incidental irrigation. The project includes a power plant, navigation lock and two fishways. The McNary powerhouse has a total capacity of 980 megawatts. The Corps designed and supervised construction, which began in 1947. The project was dedicated in 1954. All power units were in operation by February 1957.

McNary Dam is 7,365 feet long and approximately 183 feet above the streambed. This includes a 1,620-foot-long earth embankment between the Washington shore and the navigation lock and a 2,465-foot-long earth embankment between the Oregon shore and the powerhouse. Lake Wallula behind the dam is 63 miles long with 242 miles of shoreline and a water surface area of 38,800 acres.

Public Safety is the Corps’ Highest Priority

The U.S. Army Corps of Engineers’ highest priority is public safety. While we cannot completely eliminate risk, we can reduce risk.

The objective of the Corps’ Dam Safety Program is to maintain public safety, make Corps dams safe and minimize risks. Since 2007, the Corps has used a risk-informed process to prioritize addressing dam safety deficiencies on a nationwide basis. What’s new is how we assess our dams and are incorporating risk management concepts into dam safety management, routine activities and programming decisions.

Walla Walla District dams and appurtenant (dam-related) levees were screened and assessed for dam safety issues and deficiencies and their potential risk to the public. After dams and dam-related levees were assessed, the Corps categorized them into five Dam Safety Action Classes (DSAC) based on individual dam safety risk.

As a result, our understanding of conditions at our dams has improved. In some cases, we gained new observations of symptoms of potentially serious problems. In other cases, we learned original design and construction methods do not meet current safety standards. The dam safety classifications assist the U.S. Congress and the Corps in prioritizing funding for dam safety infrastructure improvements.

The safety classifications are assigned by a Corps headquarters “Senior Oversight Group,” which also periodically reviews updated information about dam safety improvements. The five action classes, now included in the overall Corps of Engineers Dam Safety Program, are:

·         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”)

Risk = Probability of Failure x Potential Failure Consequences

Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components. Potential consequences of failure are impacts to life, property, resources (such as hydropower generation), economies and environment downstream.

McNary Lock and Dam Status

McNary Lock and Dam was screened and classified as DSAC-III “High Priority (Conditionally Unsafe)” in September 2009 because of potential failure of the navigation lock embankment area due to overtopping during maximum flood event conditions.

Although the probability of dam failure is low, the consequences of failure are potentially high. During routine operations there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

When safety classifications were initially assigned to each Corps dam, the Walla Walla District developed, prepared, and began implementing interim risk reduction measures at each of the District’s dams and appurtenant levees to reduce risk of damage to property and prevent loss of life.

Completed Interim Risk Reduction Measures (as of February 2012)

• Repair navigation lock derrick cranes: Completed, derrick cranes are back in service.
• Perform spillway end sill undermining inspection: End sill diving inspection completed.

Ongoing/Remaining Interim Risk Reduction Measures (as of February 2012)

• Complete navigation lock stoplog inspection and repairs: Downstream stoplogs have been inspected and repaired. Upstream stoplog inspection and repair is planned, pending receipt of funding.
• Develop and implement north side protection procedure: Engineering scope developed, awaiting funding to complete.
• Install additional powerhouse foundation instrumentation.
• Develop the Oregon and Washington fish ladders closure plan.
• Perform potential failure mode analysis.
• Stockpile emergency sand and gravel.
• Develop dam surveillance plan for high water events.
• Conduct emergency exercises.
• Update the dam safety emergency action plan: Update to be completed in FY2012.

Our Path Forward

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress.

Updated Feb 10, 2012

Mill Creek Diversion Dam - Dam Safety Update

Mill Creek Project’s Two Dams Divert and Store Flood Water

The Mill Creek Flood Control Project contains two dams—

1) a “Diversion Dam” to divert water from the Mill Creek mainstem to a storage reservoir, and 2) a 3,050-foot long, 120-foot high “Storage Dam” to safely hold water in the Bennington Lake storage reservoir. Diverting flood water helps reduce potential flood damage to the city of Walla Walla and adjacent downstream areas bordering Mill Creek, Yellowhawk Creek and Garrison Creek. The highest recorded flows coming out of the Mill Creek Project were approximately 3,500 cubic feet per second (cfs) in 1996.

Public Safety is the Corps’ Highest Priority

The U.S. Army Corps of Engineers’ highest priority is public safety. While we cannot completely eliminate risk, we can reduce risk.

The objective of the Corps’ Dam Safety Program is to maintain public safety, make Corps dams safe and minimize risks. Since 2007, the Corps has used a risk-informed process to prioritize addressing dam safety deficiencies on a nationwide basis. What’s new is how we assess our dams and are incorporating risk management concepts into dam safety management, routine activities and programming decisions.

Walla Walla District dams and appurtenant (dam-related) levees were screened and assessed for dam safety issues and deficiencies and their potential risk to the public. After dams and dam-related levees were assessed, the Corps categorized them into five Dam Safety Action Classes (DSAC) based on individual dam safety risk.

As a result, our understanding of conditions at our dams has improved. In some cases, we gained new observations of symptoms of potentially serious problems. In other cases, we learned original design and construction methods do not meet current safety standards. The dam safety classifications assist the U.S. Congress and the Corps in prioritizing funding for dam safety infrastructure improvements.

The safety classifications are assigned by a Corps headquarters “Senior Oversight Group,” which also periodically reviews updated information about dam safety improvements. The five action classes, now included in the overall Corps of Engineers Dam Safety Program, are:

·         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”)

 

Risk = Probability of Failure x Potential Failure Consequences

Mathematically, the dam safety action classes are based on a calculation of each project’s PROBABILITY of failure times the CONSEQUENCES of failure. Probability of dam failure is based on an analysis of potential deficiencies and potential failure modes of project components. Potential consequences of failure are impacts to life, property, resources (such as hydropower generation), economies and environment downstream.

Mill Creek Diversion Dam Status

The Mill Creek Diversion Dam was screened and classified as DSAC-II “Urgent (Unsafe or Potentially Unsafe)” in January 2009 because of potential seepage and piping of embankment, foundation and abutments during high flows, plus potential concrete spillway structural instability under static and seismic loading.

Although the probability of dam failure is low, the consequences of failure are potentially high. During routine operations there is no evidence to suggest an emergency situation exists or is about to occur. However, the Corps identified conditions that don’t meet industry safety standards, and the risk to public safety is unacceptable. Therefore, we have taken interim risk reduction measures (IRRMs) to reduce public risk.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

Completed Interim Risk Reduction Measures (as of February 2012)

• Increased gate capacity to Bennington Lake.
  
• Stockpiled emergency supplies and equipment.

• Revised/updated emergency action plan.

• Performed an overtopping and conveyance study.

Ongoing/Remaining Interim Risk Reduction Measures (as of February 2012)

·         Develop surveillance plan for high water events.

·         Update inundation maps: In progress.

·         Perform a potential failure modes analysis: Planned to be completed during Issue Evaluation Study.

·         Improve instrumentation: Additional instrumentation planned for Diversion Dam dike in FY2012.

·         Conduct a diversion dike embankment and foundation seepage stability analysis.

·         Conduct a concrete spillway stability and foundation seepage analysis: On hold pending start of Issue Evaluation Study.

Mill Creek System includes separately rated Mill Creek Storage Dam

The separately rated Mill Creek Storage Dam received a DSAC-III or “High Priority (Conditionally Unsafe)” rating in May 2011.

Our Path Forward

The Diversion Dam Issue Evaluation Study is tentatively planned to begin in fiscal year 2013. Following completion of the IES for the Diversion Dam, the Mill Creek System—including both the Storage Dam and the Diversion Dam—may be advanced into a Dam Safety Modification Study to address uncertain performance of the system at high pools.

Updated Feb 10, 2012

Mill Creek Storage Dam Status

The Mill Creek Storage Dam holding Bennington Lake was initially rated as DSAC-I or “Urgent and Compelling (Unsafe)” in August 2008 based on a brief one-day records-only review. The rating was primarily due to potential dam seepage and piping issues within the foundation of the dam when Bennington Lake is more than 17 percent full for an extended period of time.

Subsequently, in October 2009, the Storage Dam was upgraded to DSAC-II or “Urgent (Unsafe or Potentially Unsafe)” by the Corps headquarters Senior Oversight Group after additional data gathering and the preliminary Issue Evaluation Study (IES) showed risk for dam failure under normal operations was not as high as originally estimated. The purpose of an IES is to focus on significant potential failure modes when evaluating risk, verify current DSAC rating, guide selection of and gauge effectiveness of interim risk reduction measures, and justify the need to pursue or not pursue Dam Safety Modification studies.

In May 2011, Mill Creek Storage Dam received a more favorable or safer DSAC-III or “High Priority (Conditionally Unsafe)” rating from the Senior Oversight Group based on the completed IES. The IES identified both 1) low likelihood of dam failure and 2) low estimated loss of human life due to dam failure.

Interim Risk Reduction Measures

Interim risk reduction measures are short-term or ongoing efforts to reduce public 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 IRRMs, the prevention of loss of life is the first and foremost objective, followed by prevention of catastrophic economic or environmental losses. Risk reduction measures may be structural or non-structural.

Completed Interim Risk Reduction Measures (as of Feb. 2012)

·         Modified diversion operations to reduce frequency of reservoir levels above elevation 1214 feet (above top of concrete cutoff wall inside the dam).  

·         Modified outlet conduit operations to leave 54-inch sluice gate in open position for all operations.

·         Improved operations of intake canal headworks: installed electric motors on gates; increased gate height.

·         Increased monitoring and surveillance for pools above elevation 1214 feet.

·         Performed a potential failure modes analysis.

·         Completed a hydrologic re-evaluation of a site-specific Standard Project Flood (SPF).

·         Stockpiled emergency materials including coordinating with Walla Walla County on pre-positioning emergency supplies and contracts.

·         Revised/updated dam safety emergency action plan.

·         Conducted three emergency exercises on basis of DSAC-I rating.

·         Obtained portable floodlights and generator to assist with emergency operations at night.

·         Completed inundation maps revision.

·         Improved upstream gauge system.

·         Verifying dam and project elevations: The survey was completed in 2011 and a thorough evaluation of Projects operations found the design freeboard of 5 feet is still met. At its current elevation, there’s no increase in flood risk.

Ongoing/Remaining Interim Risk Reduction Measures (as of Feb. 2012)

·         Continue to update and test the dam safety emergency action plan as needed.

·         Working with Walla Walla County to develop a flood response plan including support for a county emergency alert system. A joint agency flood exercise was held in March 2011.

·         Conducting comprehensive dam seepage and stability analysis.

·         Evaluate increased channel capacity.

Our Path Forward

The separately rated Mill Creek Diversion Dam has carried a DSAC-II rating since its initial classification in January 2009 and is undergoing further review. The Diversion Dam Issue Evaluation Study is tentatively scheduled to begin in fiscal year 2013. Following completion of the IES for the Diversion Dam, the Mill Creek System—including both the Storage Dam and the Diversion Dam—may be advanced into a Dam Safety Modification Study to address uncertain performance of the system at high pools.

The Corps will continue to diligently pursue public risk reduction. We’ll continue to keep the public informed of dam safety issues, risk reduction measures and progress.

Updated Feb. 13, 2012