USE OF THERMONICS
IN FOUNDATION STUDIES IN KARST TERRANE AT WOLF CREEK DAM, KENTUCKY, U.S.A.
William M. Turner, Ph.D.
In 1971, AGW scientists carried out a Thermonic survey of Wolf Creek Dam in Kentucky
for the U.S. Army Corps of Engineers. The survey sought to determine whether there
were distinct zones of subflow in the dam foundation. This case history is based on
Turner (1977). The location of the dam is shown in Figure 1.
Wolf Creek Dam sits astride the Cumberland River near Jamestown, Kentucky. It was
completed in 1955. In 1965 a mud boil appeared in the tailrace area of the dam. This
led to speculation that subflow was occurring beneath the eastern edge of the embankment.
Limited tracer studies using fluorescein dye indicated that ground water moved at
20 feet per minute in some areas.
Rapidly moving ground water in the foundation of an earthen dam presents a significant
safety problem. In such cases, the high velocity ground water causes a low potential
head in the foundation and water within the foundation moves downward and into it carrying
with it the earthen material of the dam embankment. A condition known as piping
occurs. If unchecked, piping can cause the failure of the dam itself. This was the
cause of the Teton dam failure.
Extensive drilling, following the recognition of leakage, revealed a well-developed
system of solutionally enlarged joints in the limestone foundation. This was not a
complete surprise. Construction photographs of the key trench showed solution
caverns in the limestone bedrock with workers standing in them.
The Cumberland River, at the dam site, is a broad, meandering river that has entrenched
itself into a relatively flat lying sequence of shale, sandstone, and limestone. At
the dam site, a thin deposit of Quaternary alluvium and regolith debris overlies the
Leipers Limestone of Upper Ordovician age. The Leipers Limestone is a bluish-gray to
light-gray, arenaceous and argillaceous, medium- to coarse-grained, very fossiliferous
limestone that weathers to a brown rubble and forms gentle slopes. It is 80 feet
thick at the dam site.
The Leipers Limestone is overlain by the Cumberland Formation, a siliceous dolomite
also of Upper Ordovician age.
Overlying the Cumberland Formation unconformably is the Chattanooga Shale of Devonian
The most extensive rock unit exposed in the vicinity of the dam and reservoir is the
Fort Payne Formation of Lower Mississippian age. The Fort Payne Formation is
comprised of siltstone, shale, and limestone. It is about 270 feet thick in the area
of the dam.
The regional trend of major joints in the area is about N 54o W. and about
N. 27o E.. Other joints appear to trend N. 36o E. and N. 42o
E.. The axis of the dam embankment trends about N. 67o E..
During excavation of the key trench during construction of the dam, at least one large
alluvium-filled solution cavity was encountered in the foundation near the left bank.
Extensive drilling following recognition of leakage has revealed a well-developed system
of joints in the limestone foundation of the dam.
Traditionally, piezometric information has been of greatest importance for analyzing
the hydraulic characteristics of dam foundations. The piezometric information at
Wolf Creek indicated:
1. A decrease in hydraulic head downstream from the dam.
2. The river downstream of the dam is a gaining stream.
3. The source of the waters flowing beneath the earthen dam embankment is the reservoir
behind the dam.
4. A zone of high permeability exists in the dam foundation near the center of the
5. No specific indications of narrow zones of high flow are evident.
Conventional geophysical methods of ground-water exploration measure only the
properties of the rock medium in which ground water occurs rather than measuring
properties of the water itself. That is, the contrast in elasticity, density,
electrical conductivity, and magnetic susceptibility in fractured rock is generally
insufficient to enable resolution of features pertinent to ground-water occurrence and
movement. Thermonics, however, measures a property of the ground water itself,
namely its ability to redistribute rising geothermal heat. Thermonics is a powerful
new tool for quantitative and qualitative analysis of ground-water-flow systems.
This paper deals only with the application of Thermonics to tracing leakage beneath
earthen dam embankments in karst terrane.
Thermonics is based on three universally true physical principles:
1. There is a continuous flow of geothermal heat to the land surface from the hot
interior of the earth.
2. Water has a high heat capacity.
3. Ground water is usually in motion. It moves more rapidly through zones of high
permeability than through zones of low permeability under similar hydraulic head
The basis for Thermonics is the Stallman Equation.
In the saturated zone, geothermal heat is redistributed by moving ground-water such
that the heat flux above the base of the saturated zone is not evenly distributed in
At the time of the Thermonic survey, a total of 150 piezometers had been installed in
the dam embankment to define better the subflow system. We carried out the Thermonic
survey by measuring temperature profiles of each piezometer. The piezometers
terminated at the upper surface of the limestone bedrock, and no information was obtained
in the zones of leakage themselves. Because of the embankment slope, terraces, and
variable piezometer depths, temperature we corrected the data to make it comparable.
Because of the procedures required to correct the data for terrain differences and
variable piezometer depth, isogeotherms could not be plotted. The locations of the
zones of significant subflow beneath the dam were located using Thermonic data and the
paths taken by subflow downstream of the main dam embankment were traced. Two of the
significant subflow paths pass beneath sinkholes. Furthermore, the general trend of
the major subflow paths corresponds well with the regional trend of joints in the
limestone bedrock of the area. The accuracy of the locations of the major
ground-water-flow paths depends greatly on the density of the data network.
The Corps of Engineers classified the original work by AGW scientists for six years
pending the outcome of more work. Since the Thermonic study, an additional 150
piezometers were constructed. Data collected for almost 10 years from all of these
piezometers and computer studies performed by the Nashville office of the Corps of
Engineers, generally confirms the paths of subflow determined by the Thermonic survey
(written communication, Euclid C. Moore, Chief, Engineering Division, January 21,
The Corps of Engineers embarked on a major grouting program to stabilize the dam
foundation and prevent piping. The grouting program cost nearly as much as the
1. The flow directions in the zones of maximum subflow are consistent with the slope of
the piezometric surface and are towards the river. Ground-water flow generally does
not cross the equipotential lines at right angles. However, deviation from
perpendicular intersection of flow streamlines and equipotential lines is expected because
the Leipers Limestone is extremely heterogeneous and anisotropic for ground-water
2. The zones of relatively high ground-water flow are probably solution channels and
interconnected voids. Several zones of high flow pass directly below sink hole
3. Examination of both piezometric and Thermonic information indicates that piezometric
information alone is not sufficient to define the path of high ground-water flow.
4. The most significant conclusion reached is that Thermonics can define the entire
foundation flow pattern of a dam foundation prior to construction provided the foundation
is saturated. If Thermonics had been available at the time the Wolf Creek Dam was
under study, perhaps a better and safer site could have been chosen. Or, with a
complete definition of the flow system, the foundation could have been adequately treated
before the dam was constructed, at a great saving in cost.
Turner, W.M., 1977, Use of Thermonics in Foundation Studies in Karstic Terrane, in:
Hydrologic Problems in Karst Regions, eds. Ronald R. Dilamarter
and Sandor C.
Csallany, Western Kentucky Press, pp. 459 - 462.