By Sue Biondi - December 2020

This article is to inform members and the public about the Lake Anna Dam.  At times of flooding and at times of drought, many wonder why Dominion Power is not adjusting the water level according to the event.  Well, it’s not how the dam functions.  There are many factors that go into how the dam functions and this article will hopefully help answer your questions.

• The Lake Anna Dam is 5,200 feet long 
  
• The structure is 95 feet high
  
• It is powered by one electric diesel generator
  
• There are 3 radial gates and 2 skimmer gates 
  
• The Crest is 265 feet at mean sea level (msl)
  
• Normal lake level is 250 feet
  
• There is a daily operations inspection by Civil Engineers
  
• Monitoring is done with instruments
  
• There is periodic testing
  
• There are annual dam surveys
  
• There is a separate Emergency Action Plan (EAP)
  

Causes of Dam Failures

• Lake Level over topping the dam
  
• Probable maximum flooding (PMF)
  
• Gates failing to open resulting in no discharge
  
• Spillway failure due to PMF
  
• Failure of downstream slope due to earthquake
  
• Failure of spillway due to earthquake
  
• Failure of embankment due to internal erosion (piping)
  

• Potential for human casualties
• Property damage
• Civil penalties
• Financial cost of dam repairs
• Loss of power generation facilities supported by the lake

Impact of a Lake Anna Dam Failure

• Shutdown of both nuclear units for approximately three plus (3+) years. (Time to repair the dam plus the original estimate of 2+ years to fill the lake with normal precipitation)
• Operation of more expensive power facilities to meet demand or power purchase
• Regional business impact:  business revenue; jobs; tax revenue
• Reduced property values
• Loss of a major recreation area for the Commonwealth
• Potential loss of life downstream
• Flooding and resulting damage to downstream roads and properties
• Cost of downstream property damage
• Jeopardize river water withdraw capabilities for downstream businesses and counties

When are these emergency levels entered?

• Imminent and Potential - If the lake level reaches 262 feet, then Potential Failure is declared.  If the water level reaches 265 feet or water is flowing over the dam, then Imminent Failure is declared
• High Flow - When two radial gates get to 4 feet open, the EAP will be entered, notifications will be made and the Lake Anna Advisory Team will be notified.  At 8 feet on two radial gates, the Lake Anna Advisory Team will be activated.
• Non-Failure - Non-Failure is appropriate for an event at the dam that will not, by itself, lead to a failure, but requires investigation and notification of internal and/or external personnel.  This will be identified and taken care of by performing a “Main Dam Daily Inspection,” but EAP notifications are not performed.  

North Anna Dam Safety Program

• The Project is an integral part of the North Anna Power Station
• This Program defines for Federal Energy Regulatory Commission (FERC), Dominion’s commitment to ensure that the Project is operated in a manner that protects public safety, is operated in a manner that does not compromise dam safety or integrity, and inspection programs are in place and properly managed
• Aspects of the Project’s operation, maintenance, inspection, safety and emergency actions are governed in the same manner as programs required by the Nuclear Regulatory Commission (NRC) for the nuclear power station

Chief Dam Safety Engineer

• Responsible for oversight of the North Anna Dam Safety Program to ensure it is fully implemented
• Notifications to Site VP and Engineering Directors
• Routinely assess the organization's compliance with written dam safety program and report the findings to senior management
• Review audit report by Independent Consultant and prepare a summary for senior management

Summary

• The Lake Anna Dam is vitally important to NAPS, Dominion and local communities
• NAPS complies with the FERC rules and regulations
• The NRC believes downstream dam failures warrant an evaluation by the Generic Issues Program
• The economic impact of a Lake Anna Dam failure would be staggering
• The North Anna Dam Safety Program ensures we operate and maintain the dam to protect the health and safety of the public, the company and its customers.

Lake Anna DamAs you can see, when we are all out on a sunny afternoon in the summer enjoying all the recreational activities the lake has to offer, there is so much going on behind the scenes to ensure the safety and integrity of the dam.  If you drive by the power plant and see all the buildings and the two round reactors, take a minute to reflect on the purpose of the dam, the lake that you are enjoying, and saying a special thank you to all the people who make it what it is, that is your Lake Anna!