Gathright Safety
Frequently Asked Questions
Why is the Corps inspecting the Gathright Dam?
The Norfolk District regularly inspects and continually evaluates Gathright Dam in accordance with the Federal Guidelines for Dam Safety issued in 1979 and contained in FEMA Publication 93. During normal operations, the dam is inspected daily by facility staff and semi-annually by district engineers. The dam is also inspected every five years by a multi-discipline team of district engineers.
Does the Corps/Norfolk District inspect the dam regularly?
Yes, during normal operations, facility staff inspects the dam twice daily and a district engineer inspects the dam semi-annually.
When did Norfolk District last inspect the dam?
The last inspection of the dam prior to its recent DSAC II rating occurred in May 2009.
Who conducted the Screening Portfolio Risk Analysis (SPRA)?
The Corps 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 trained in the use of the tool evaluated and screened Gathright Dam using information provided by the operating district. A group of senior engineers from across the Corps reviewed the screening information and established the DSAC rating for the dam.
What happens during an SPRA?
The team conducted a literature review to evaluate current dam behavior, how well the dam meets current design criteria, as well as potential consequences of dam failure. Those findings are reviewed by the Senior Oversight Group and a Dam Safety Action Classification is assigned based upon confirmed or unconfirmed dam safety issues, the combination of life or economic consequences should failure occur, and the probability of failure. This enables the Corps to prioritize dam safety actions to correct deficiencies, which includes Interim Risk Reduction Measures (IRRMs) to be undertaken while further investigations are conducted and/or remedial actions are implemented.
Are the SPRA findings peer reviewed?
The DSAC II rating is not currently peer reviewed. USACE Headquarters is sponsoring external peer reviews by nationally known dam safety experts for USACE flood damage reduction dams with DSAC I classification.
Is the DSAC rating system new? How does it work?
The Corps' Dam Safety Action Classification (DSAC) began in 2005 in response to a comprehensive peer review of the Corps' Dam Safety Program through the Association of State Dam Safety Officials. The ASDSO recommended the Corps of Engineers 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 Corps dams, and the subsequent Expert Panel review of the Corps' highest risk dams.
The Corps categorized dams into Dam Safety Action Classes (DSAC) based on their individual dam safety risk considered as probability of failure and potential failure consequences.
What are the DSAC ratings and definitions?
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)
What does the DSAC II rating mean?
Gathright Dam's DSAC II resulted from an evaluation that considers risk and engineering factors. Simply put, the risk – evaluated as probability of failure and potential failure consequences – combined with the unconfirmed (potentially unsafe) issues identified by the SPRA team led to the DSAC II rating. This rating requires interim risk reduction measures, investigation and remediation, if necessary, and prioritizes funding for those efforts.
What did the SPRA find that drove the DSAC II rating?
The SPRA identified concerns about possible increased seepage at the toe of the dam, an undetermined flow rate at the river spring a quarter mile downstream, and potential flow channels through karst limestone below the spillway during pool events above 1600 feet. Additionally, the team considered the probability of failure and potential failure consequences.
Did the Norfolk District know about these "concerns?"
Yes. For the 30 years since Gathright Dam became operational, district scientists and engineers have continuously monitored and evaluated seepage at the toe of the dam, the undetermined flow rate at the river spring a quarter mile downstream, and potential flow channels through limestone below the spillway during pool events above 1600 feet. In fact, experts identified many concerns related to building a dam at that location and mitigation actions were taken during the construction of Gathright Dam.
Is seepage at an earthen dam "normal?"
Yes, seepage is normal and expected on ALL earthen type dams. Gathright Dam was designed and engineered for controlled seepage.
What is causing the undetermined flow rate at the downstream river spring?
The river spring was identified prior to the completion of the Gathright Dam and the impoundment of water in the pool. For 30 years, members of the Norfolk District have been unable to find evidence connecting pool levels and the flow rate at the river spring. This issue will be investigated in 2010.
What are potential flow paths through the limestone under the spillway? What does that mean?
This particular item refers to the capability of water to move – or find pathways – through rock. In this case, the limestone present under the spillway. The concern is that during pool events above 1600 feet -- a pool level never before reached in Gathright's 30-year history -- water could potentially find and exploit pathways through the limestone under the spillway.
Why didn't Norfolk District examine these concerns before? What happens now?
During Gathright's 30-year operational history, the facility staff and district engineers have closely and continuously monitored these concerns, and evaluated the dam in accordance with the Federal Guidelines for Dam Safety issued in 1979. Our focus now is to implement immediate risk reduction measures that minimize to public safety in the short term while we investigate the safety concerns and pursue long-term permanent fixes, if required.
Has Gathright Dam been classified according to the Potential Hazard Classification in accordance with FEMA Publication 333, Hazard Potential Classification System for Dams? If so, what was that classification?
The Potential Hazard Classification developed in accordance with FEMA Publication 333, ranks a dam as Low, Significant, or High Hazard Potential based on the damages that would occur if the dam failed or operated improperly. The Gathright Dam is rated under this system as "High Hazard Potential." It's important to note that this hazard potential classification does not address the condition of the dam or its risk of failure.
A USCE matrix on the Internet states in the case of DSAC II "... the likelihood of failure from one of these occurrences, prior to remediation, is too high to assure public safety." Is Gathright Dam going to fail?
The screening and classification of this project does not mean failure is taking place and there is currently no evidence to suggest an emergency exists or is about to occur. While we recognize that we cannot completely eliminate risk with regard to Gathright Dam, we can reduce risk and have implemented measures to do just that. It's Corps policy that we will only designate a dam as normal or safe when there are no unconfirmed dam safety issues.
What does "failure" mean?
In the context of 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.
Can the Corps/Norfolk District guarantee us the dam will not fail?
Norfolk District has never been able to guarantee the dam will not fail, but we do believe the dam is safe and that we've taken measures to minimize risks to public safety, and to identify any potential threat to the dam. Throughout the dam's 30-year history, district engineers have not identified any signs of distress.
If the dam fails, what areas will be flooded? To what extent?
The type and extent of the failure will determine the areas and the extent of flooding. The inundation mapping currently contained in the district's dam safety plan identifies expected flooding for a dam failure during the spillway design flood – a worst-case scenario. The district will update these maps as part of the 2010 initiatives to examine additional failure inundation scenarios.
It's important to note that maps are provided to local and state emergency management agencies but, in accordance with U.S. Army, U.S. Army Corps of Engineers, and Department of Homeland Security policies, inundation maps are not provided to members of the public in digital or other formats. A member of the public may request, in writing, flood information for a specific property.
Is there an emergency action plan in place if the dam fails? How will I be notified to evacuate?
The district has an emergency action plan for a variety of scenarios at Gathright Dam and we are currently working with state and local agencies to evaluate and update the plan as part of our risk reduction measures. In the unlikely event of an evacuation, state and local emergency agencies will handle any necessary notifications and evacuations.
What are you doing to keep us safe?
Our immediate risk reduction measures include staffing the dam on a 24/7 schedule, a pool decline of 1 foot per week, and increasing daily inspections to three times per day, and updating our safety plan. Within the next 90 days, we'll also increase remote electronic monitoring and our compilation and analysis of monitoring data. Throughout 2010, we'll initiate a series of studies and investigations focused on the safety concerns identified by the Corps' Screening Portfolio Risk Analysis.
If we're safe, why are you lowering the reservoir levels?
We are lowering the reservoir to increase the safety of the dam while simultaneously implementing immediate and short-term risk reduction measures. The lower pool also increases available storage for rare flood events.
How low will you lower the reservoir? Will this have a negative impact on recreation activities?
We'll continue to lower the reservoir until a thorough review of the dam's performance has been conducted. We do anticipate a short term, negative impact on Lake Moomaw recreation activities, but our first priority is public safety.
Will a lower reservoir/increased flow rate damage wildlife or habitat in the reservoir or downstream?
The current drawdown rate should have minimal impact on wildlife and habitat in the reservoir and downstream during the next few months.
Will an increased flow rate cause flooding downstream or impact recreation, navigation and business interests? What if there's significant rainfall?
The increased flow required to maintain the 1-foot-per-week decline should have no significant impact downstream. It will not cause flooding. In the event of significant rainfall, we'll operate the dam to minimize any increase in reservoir levels while still performing the congressionally mandated mission of providing flood reduction.
Will an increased flow rate cause bank erosion or have other negative environmental impacts downstream?
The increased flow rate is a controlled release and should not cause bank erosion or other negative environmental impacts downstream.
How will this impact water supply and quality?
The short-term measure of lowering the reservoir should not adversely affect the quantity or quality of water released from Gathright Dam.
What are the long-term consequences of a lower reservoir? What if there is a drought next spring/summer?
The lowering of the reservoir is not expected to be a long-term risk reduction measure. If normal operations are resumed this winter, with normal or slightly below normal flows, the reservoir is expected to recover by next spring. After normal operations are resumed, the dam will be managed to maximize lake levels and provide sufficient releases for downstream water quality as it has in the past. If drought conditions exist, we'll coordinate with others to develop an appropriate release schedule, as we've done during five drought periods in the last 10 years.
What is the purpose of all the studies being conducted in 2010?
The studies and investigations proposed for 2010 will focus on further defining the potential safety risks identified during the Screening Portfolio Risk Analysis and determining what kind of remediation might be required to address those risks.
How much is all of this going to cost?
We're preparing an Interim Risk Reduction Measures Plan (IRRM), which will identify the 2010 studies and investigations contain estimated costs. This plan should be completed by December 2009.
How are these studies being funded? Is Recovery Act money involved?
We will use existing operations and maintenance funding for the immediate and short-term measures. The 2010 studies and investigations will be federally funded. We do not anticipate any funding through the American Recovery and Reinvestment Act of 2009.
What happens if the 2010 studies validate the DSAC II rating? Will the downstream communities be notified?
We consider communication with local communities a key component of our public safety/risk reduction focus. Throughout this process, district leadership will maintain regular contact with city and county leaders, and will communicate our progress to the public through a variety of traditional and social media tools. We've established a Web page specifically for this topic at www.nao.usace.army.mil/gathrightsafety.asp, and encourage the public to share questions and concerns by e-mailing them to gathrightsafety@usace.army.mil or posting them publicly at the district commander's blog, www.armyengineersnorfolk.blogspot.com/.
If the dam requires repairs, how much will it cost? Will repairs be federally funded?
The studies and investigations scheduled for 2010 will determine if any repairs are required. It's inappropriate to speculate on the need for repairs or their potential costs. If any repairs are required, they will be federally funded.
How long will it take the Corps to fund and make the repairs?
It's inappropriate to speculate on the need for repairs or a schedule for completion. However, we will actively communicate developments at Gathright Dam as we collect and analyze information.
Will people have to be evacuated in long-term repairs are required?
It's inappropriate to speculate on the need for repairs or the potential impacts on the local communities. However, we will actively communicate developments at Gathright Dam as we collect and analyze information.
Will repairs affect the local economy (tourists/water recreation, etc.)? If yes, to what extent?
It's inappropriate to speculate on the need for repairs or the potential impacts on the local communities. However, we will actively communicate developments at Gathright Dam as we collect and analyze information.
How much would it cost to repair the dam to full operational capacity DSAC V? Will Gathright ever be that safe?
It's inappropriate to speculate on the need for repairs or their costs. Currently, none of the Corps' 610 dams are rated DSAC V.
How many dams does the Corps operated nationwide?
The Corps operates and maintains 610 dams nationwide.
How many dams does the Norfolk District operate?
Gathright Dam is the only dam operated and maintained by the Norfolk District.
How many dams nationwide received a DSAC II rating?
More than 60 Corps' dams nationwide received a DSAC II rating.
Will there be public meetings held by the agencies involved?
We don't currently have any public meetings planned for the communities downstream from Gathright Dam, but will conduct meetings if there is enough public interest. We encourage the public to remain actively engaged in the conversation about Gathright Dam by sharing questions and concerns by e-mail to gathrightsafety@usace.army.mil or posting them publicly at the district commander's blog, www.armyengineersnorfolk.blogspot.com/.
What is the life expectancy of Gathright Dam? Can you provide background on when it was built?
Gathright Dam was not designed and constructed with a specific or implied "life expectancy." Congress authorized construction of the dam and reservoir in the Flood Control Act of 1946, to provide protection of industrial, commercial and residential properties along the Jackson and James Rivers, with immediate impact on Covington, Va., located about 19 miles downstream. Construction of the dam began in 1974 and was completed in 1979. Impoundment of water began in December 1979 and was completed in April 1982.
How much assumed risk is there with a dam?
There is risk associated with even the most mundane daily tasks so, as you might expect, the operation and maintenance of a dam is certainly no exception. Since it's impossible to eliminate risk from any activity, the key is to identify and minimize risk when and where possible. That approach is not only reflected in the Federal Guidelines for Dam Safety, but also in the Corps' robust Dam Safety Program, which includes risk reduction, risk assessment and risk management procedures in its nationwide evaluation process.
How much did it cost to build this dam and how was it funded?
Gathright Dam was federally funded and cost $80,670,527.
What is the purpose of building Gathright Dam? Would it be safer to decommission it?
Congress authorized construction of the dam and reservoir in the Flood Control Act of 1946, to provide protection of industrial, commercial and residential properties along the Jackson and James Rivers, with immediate impact on Covington, Va., located about 19 miles downstream. Decommissioning the dam is not being considered because it still performs a valuable flood control purpose. To date, it's estimated the Gathright Dam has prevented more than $280 million in flood-related damages.
Updated: 11-Feb-2010