US Army Corps of Engineers
Nashville District Website

Questions & Answers

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The Corps of Engineer's paramount concern is public safety and we will do everything necessary to ensure the safe operation of our dams. The consequence of failure at Wolf Creek Dam is enormous, including possible loss of life in excess of 100 and over $3 billion in flood damages, thus the magnitude of the resulting risk requires prudent management. Restrictions on pool elevation are necessary as part of a risk management program designed to ensure the safety of the dam.  Lowering the lake level is an emergency measure that directly reduces probability of failure.   Including operational restriction as part of the risk management plan is part of our effort to reduce risk. We will manage this risk with reduced pool levels while striving to maintain project purposes to the extent possible.
The risk is high given the consequences of failure.  We have a significant number of scientific instruments embedded in the dam that indicate seepage is occurring through the foundation.  Over time, if left unchecked, this seepage could threaten the embankment. The difficulty is in knowing the exact condition of the foundation several hundred feet below the dam. It cannot be observed directly, but using instrumentation, we can determine that imminent failure is unlikely. Again, left unchecked, seepage and erosion will continue and risk of failure will increase; however, we are actively reducing that risk by lowering the pool level and expediting the rehabilitation work, thereby slowing seepage in the foundation. 

Considering that the consequence of failure is large, it is logical that we take all prudent measures to lower the probability of failure as much as possible.  Proposed pool reductions will reduce the load on the foundation by approximately 10 to 25 percent.  These reductions, combined with previous pool restrictions and the ongoing rehabilitation efforts, significantly reduce the probability of any failure.

We are taking emergency measures by targeting an aggressive pool elevation that provides anticipated quantifiable reductions to the ongoing seepage problem.  These emergency measures are designed to prevent a condition where imminent failure would be a possibility.  We believe that conditions warrant this aggressive approach and consequently are taking these emergency changes to pool elevations as well as accelerating remedial repairs in an effort to lower the existing risk.
The project is currently on schedule for completion in December 2013.
Public safety is the Corps primary concern when we consider lowering the pool levels. These actions improve our confidence in the dam’s overall reliability.  Even though this decision has significant adverse impacts to nearby communities, the potential for failure causes grave concerns.  In addition to public safety concerns, we estimate over $3 billion in property damages would result from a sudden failure of Wolf Creek Dam. Lower pool elevations decrease the hydraulic load on the dam.  This translates into a reduction in risk we believe is necessary until significant repair work is completed.  We fully understand the significant cost to the region and the impacts this has on the people and businesses of the community.  In order to minimize the impact as much as possible, we will do everything within our ability to expedite construction in an effort to return to normal pool levels as soon as possible.  We do feel that this early notification allows business to plan for impacts and modify or change their operations if necessary.
The Corps will reevaluate lake levels as the contractor approaches closure of the initial grout line, and instrumentation gives significant evidence that the project is stable and improving.  We will continually monitor the seepage for indicators that the remedial measures are reducing risk. There is no guarantee, however, that pool levels will be allowed to increase until the work is totally completed if the element of risk remains at a high level.
The Great Lakes and Ohio River Division Commander, following a recommendation from the Nashville District Commander, made the decision. The decision was made with input and concurrence from our Division and Headquarters' staff, as well as input from outside, independent consultants that work with the Corps on Dam Safety issues.  This decision was not made lightly and was made considering the ramifications the drawdown would incur on the communities upstream and downstream of the dam, as well as other project functions such as hydropower production, recreation and water supply.
Public safety is the primary factor in determining desired pool elevations. Our goal is to reduce the lake levels to an elevation that reduces hydrostatic pressure on the dam and, to the extent possible, allows project purposes such as water quality, hydropower generation, water supply, navigation and recreation to continue. Our starting point was the elevation that provides the maximum reduction in hydrostatic load while maintaining project purposes to some extent. The final determination was based on the point to which we anticipate seeing quantifiable effects in reducing the ongoing erosion caused by seepage.  While the remedial repairs are underway we will continually assess the seepage to determine if additional measures are needed or if a higher pool could be allowed.
The origin of the problem is in the foundation below the earthen dam, thus, out of sight.  Seepage caused by the water from the reservoir puts enormous pressure on the foundation.  This pressure carries away soil through openings in the foundation rock and continually erodes away the earthen embankment.  While we can’t physically “see” this occurrence, we know it is happening through various scientific instruments embedded within the dam.  We do not know the exact rate or the full extent of the erosion. While there are no cracks visible in the dam, settlement has been observed at Wolf Creek Dam on a small scale. The instrumentation mentioned above provides additional signs of failure as do visible signs such as wet spots that are inspected daily.
There would be an increasing risk to public safety and probability of failure would eventually reach the point where imminent failure would be a possibility. If the pool is not lowered the dam will continue to experience higher pressures on the foundation which translates into a higher probability of dam failure in the future.  Also, with a higher pool, the consequences of a failure are greater due to the volume of water that would be released downstream.
Overall there will be a reduction in hydropower generation in the region.  A lower pool results in lower hydropower production and the need to keep the pool down will mean that generation will sometimes occur at periods other than high demand periods. Generation may have to be shifted to other projects in the Cumberland system. If that is not possible, some of the lost production will be picked up by other reservoir systems in the region, but there will probably be a need for higher fossil plant generation to offset the net loss of hydropower. 

 Additionally, the reduction in cold water available in Lake Cumberland may have an impact on downstream fossil fuel plants since they require large amounts of cooling water to maintain operation. We will strive to operate the Cumberland River basin in a manor that optimizes water availability for all project purposes.

 We will continually work with Southeastern Power Administration and TVA during this period so that they may best balance their power supply requirements through all sources available to them.

While the intent will be to operate Lake Cumberland at lower levels throughout the year, water supply will continue to be an important operating purpose.  It is likely some water intakes may be impacted in the future, but our goal is to give communities ample time to prepare and adjust for any impacts from lower pools.  We are recommending all intake users consider using this period to develop contingency plans that would include modifying their intakes, pumps and treatment options to operate at pool elevation 650.  We will work with them to facilitate the permitting process.
Water quality impacts will be dependent on the amount and timing of rainfall.  For generally dry conditions there will be only limited impacts to the immediate Lake Cumberland area.  Low Cumberland River flows resulting from the combination of a Lake Cumberland restricted operation and dry conditions will have more of a water quality impact to the Cumberland River from Cordell Hull Dam through Lake Barkley.  Wet conditions will threaten the coldwater regime and associated fisheries in both the lake and in the river downstream.  The Corps has increased water quality monitoring and will operate the system in a manner to protect these resources to the extent possible.
There will be minor impacts to navigation along the Cumberland River.  The Cumberland River navigation depends on flat pools which will be maintained despite the lower than normal flows during the summer and fall.  There may be some impact to navigation on the Lower Ohio River and Mississippi due to the lower flows available from the Cumberland system.
Unfortunately not; the United States reserves the right to manipulate the level of the pool without payment of damages. The Corps is actively seeking ways, within current authorities, to offset the impacts of the lower pool, including extending boat ramps and improving lakeside recreation areas.  Additional authority not currently available may be sought to increase the ways the Corps can lessen these impacts.

Wolf Creek Dam Safety Rehabilitation Project

Wolf Creek Dam Safety Rehabilitation Project Work PlatformThe U.S. Army Corps of Engineers Nashville District completed a Major Rehabilitation Report to evaluate alternatives to improve the long-term reliability of the Wolf Creek Dam. The recommended alternative will cost about $594 million. The main phase of construction began in March 2006 and was completed in March 2013 when the last concrete was placed for the 4,000-foot-long barrier wall through the dam’s earthen embankment.

In January 2007 a decision was made to lower the lake levels to the 680-foot elevation to reduce pressures on the dam.  This lake level was maintained until the spring of 2013 when the barrier wall was completed.  The lake was partially raised during 2013 as test on the barrier wall and in 2014 the lake levels returned to historic levels after the barrier wall performed as expected to the higher lake levels.  Construction efforts are continuing on the Wolf Creek Dam Safety project to restore the project to its pre-construction conditions and make improvements as appropriate.  For example, the haul road constructed as part of the barrier wall will be converted to the new access route to the Fish Hatchery and Kendall Campground in the spring/summer of 2015.  This new access road will eliminate the difficult intersection of the existing access road to Highway 127.

Seepage Problem

Wolf Creek DamWolf Creek Dam is on the Cumberland River in south central Kentucky.  It provides hydropower, flood control, water supply, and water quality benefits for the Cumberland River system and surrounding region. Lake Cumberland, along with Dale Hollow Dam, Center Hill Dam and J. Percy Priest Dam, provide an adequate supply of water to enhance navigation on the mainstem of the Cumberland River from Celina, Tenn., to the Ohio River. The lake is a source of recreation that has attracted more visitors (4.89 million) than Yellowstone National Park (2.87 million). Designed and constructed during the period 1938-1952, the 5,736 foot-long dam is a combination rolled earth fill and concrete gravity structure. It has a maximum height of 258 feet above founding level. A six- generator-unit power plant, with a capacity of 270,000 KW, is located immediately downstream. US Highway 127 crosses the top of the dam. Lake Cumberland, created by the dam, impounds 6,089,000 acre-feet at its maximum pool elevation of 760.  It is the largest reservoir east of the Mississippi and the ninth largest in the United States.

In 1968, muddy flows in the tailrace and two sinkholes near the downstream toe of the embankment signaled serious reservoir seepage problems. Investigations indicated the problems were due to the karst geology of the site characterized by an extensive interconnected network of solution channels in the limestone foundation. Piping of filling materials in these features and collapse of overburden and embankment into the voids caused the problems. The District immediately began an emergency investigation and grouting program between 1968 and 1970 that is generally credited with saving the dam. However, grouting was not a long-term fix and a more permanent solution was sought. After studying numerous alternatives, the District chose to construct a concrete diaphragm wall through the earth embankment into the rock foundation to block the seepage. This wall was constructed between 1975 and 1979.  

Since completion of the wall in 1979, District personnel have continued to closely monitor the project. Key instrumentation readings, persistent and increasing wet areas, and investigative borings that encountered soft, wet material at depth in the embankment confirm solution features still exist that have not been cut off. While the original wall interrupted the progression of erosion, seepage has since found new paths under and around the wall and perhaps through defects in the wall itself as erosion of solution features continues.  

To address the seepage problems, the District has prepared a Major Rehabilitation Report. It evaluates several alternatives to improve the long-term reliability of the dam. From this analysis, the recommended alternative, is a new concrete diaphragm wall constructed using newer technology that will reinforce the purpose of the original wall. This new wall will start immediately upstream of the right most concrete monoliths and run the length of the embankment into the right abutment which will take it 1,650 feet beyond the existing wall. It will be constructed to a depth which is deeper than the deepest sections of the original wall and as much as 75 feet deeper than the majority of the original wall. The cost is estimated at $309 million. The benefit to cost ratio is 7.1. Construction began in 2006 and is on track to be completed by December 2013.