Photo by U.S. Army Corps of Engineers - Huntington District,
July 6, 2001
A dam is a barrier across flowing water that obstructs, directs or
slows down the flow, often creating a reservoir, lake or
impoundment. Most dams have a section called a spillway or weir
over which, or through which, water flows, either intermittently or
continuously, and many have hydroelectric power generation systems
installed.
Other structures such as levees and dikes are used to prevent water
flow into specific land regions.
TYPES OF DAMS
Dams can be formed by human agency, natural causes, or even by the
intervention of wildlife such as beavers. Man-made dams are
typically classified according to their size (height), intended
purpose, or structure.
By Size:
International standards define large dams as higher than 15
meters and major dams as over 150 meters in height.
By Purpose:
Intended purposes can include providing water for irrigation or
water supply, improving navigation, creating a reservoir of water
to supply industrial uses, generating hydroelectric power, creating
recreation areas or habitat for fish and wildlife, flood control
and containing effluent from industrial sites such as mines or
factories. Few dams serve all of these purposes but some
multi-purpose dams serve more than one.
An overflow dam is designed to be over topped. A weir
is a type of small overflow dam that can be used for flow
measurement.
A check dam is a small dam designed to reduce flow velocity
and control soil erosion. Conversely, a wing dam is a
structure that only partly restricts a waterway, creating a faster
channel that resists the accumulation of sediment.
A dry dam is a dam designed to control flooding. It normally
holds back no water and allows the channel to flow freely, except
during periods of intense flow that would otherwise cause flooding
downstream. A diversionary dam is a structure designed to
divert all or a portion of the flow of a river from its natural
course.
By Structure:
Based on structure and material used, dams are classified as timber
dams, arch-gravity dams, embankment dams or masonry dams, with
several subtypes.
Two types of masonry dams are the arch dam and the gravity
dam. In the arch dam, stability is obtained by a combination of
arch and gravity action. If the upstream face is vertical the
entire weight of the dam must be carried to the foundation by
gravity, while the distribution of the normal hydrostatic pressure
between vertical cantilever and arch action will depend upon the
stiffness of the dam in a vertical and horizontal direction. The
most desirable place for an arch dam is a narrow canyon with steep
side walls composed of sound rock.
In a gravity dam, stability is secured by making it of such
a size and shape that it will resist overturning, sliding and
crushing at the toe. The dam will not overturn provided that the
moment around the turning point, caused by the water pressure is
smaller than the moment caused by the weight of the dam. When built
on a carefully studied foundation with stresses calculated from
completely evaluated loads, the gravity dam probably represents the
best developed example of the art of dam building.
A gravity dam can be combined with an arch dam, an arch-gravity
dam, for areas with massive amounts of water flow but less material
available for a purely gravity dam. Hoover Dam is a well-known
example of an arch-gravity dam.
Embankment dams are made from compacted earth, and have two
main types, rock-fill and earth-fill dams. Embankment dams rely on
their weight to hold back the force of water, like the gravity dams
made from concrete.
Rock-fill dams are embankments of compacted free-draining granular
earth with an impervious zone. The earth utilized often contains a
large percentage of large particles hence the term rock-fill. The
impervious zone may be on the upstream face and made of masonry,
concrete, plastic membrane, steel sheet piles, timber or other
material.
Earth-fill dams, also called earthen, rolled-earth or simply earth
dams, are constructed as a simple embankment of well compacted
earth. Because earthen dams can be constructed from materials found
on-site or nearby, they can be very cost-effective in regions where
the cost of producing or bringing in concrete would be prohibitive.
This makes it better for the environment, too.
A third type of embankment dam is built with asphalt-concrete core.
The majority of such dams are built with rock and/or gravel as the
main fill material. Almost 100 dams of this design have now been
built world-wide since the first such dam was completed in 1962.
All asphalt-concrete core dams built so far have an excellent
performance record. The flexible properties of the asphalt make
such dams especially suited in earthquake regions.
A cofferdam is a (usually temporary) barrier constructed to
exclude water from an area that is normally submerged. Made
commonly of wood, concrete or steel sheet piling, cofferdams are
used to allow construction on the foundation of permanent dams,
bridges, and similar structures. When the project is completed, the
cofferdam may be demolished or removed.
Timber dams were widely used in the early part of the
industrial revolution and in frontier areas due to ease and speed
of construction. Rarely built in modern times by humans due to
relatively short lifespan and limited height to which they can be
built, timber dams must be kept constantly wet in order to maintain
their water retention properties and limit deterioration by rot,
similar to a barrel. Very few timber dams are still in use. Timber,
in the form of sticks, branches and withes, is the basic material
used by beavers, often with the addition of mud or stones (see
below).
A steel dam is a type of dam briefly experimented with
around the turn of the 19th-20th Century which uses steel plating
(at an angle) and load bearing beams as the structure. Intended as
permanent structures, steel dams were an (arguably failed)
experiment to determine if a construction technique could be
devised that was cheaper than masonry, concrete or earthworks, but
sturdier than timber crib dams.
In the case of beaver dams, beavers create dams primarily
out of mud and sticks to flood a particular habitable area. By
flooding a parcel of land, beavers can navigate below or near the
surface and remain relatively well hidden or protected from
predators. The flooded region also allows beavers access to food,
especially during the winter.
CONSTRUCTION ELEMENTS
Power Generation Plant:
Most hydroelectric power comes from the potential energy of
dammed water driving a water turbine and generator. To boost
the power generation capabilities of a dam, the water may be
run through a large pipe called a penstock before the turbine.
A variant on this simple model uses pumped storage
hydroelectricity to produce electricity to match periods of
high and low demand, by moving water between reservoirs at
different elevations. At times of low electrical demand,
excess generation capacity is used to pump water into the
higher reservoir. When there is higher demand, water is
released back into the lower reservoir through a turbine.
As of 2005, hydroelectric power, mostly from dams, supplied some
19% of the world's electricity, and over 63% of renewable energy.
Much of this was generated by large dams, although China uses small
scale hydro-generation on a wide scale and is responsible for about
50% of world's use of this type of power.
Spillway:
A spillway is a section of a dam designed to pass water from the
upstream side of a dam to the downstream side. Many spillways have
floodgates designed to control the flow through the spillway. Types
of spillway include: A service spillway or primary spillway passes
normal flow. An auxiliary spillway releases flow in excess of the
capacity of the service spillway. An emergency spillway is designed
for extreme conditions, such as a serious malfunction of the
service spillway. A fuse plug spillway is a low embankment designed
to be over topped and washed away in the event of a large flood.
Notice the rainbow in this photograph of the Fishtrap spillway.
DAM CREATION
Siting (Location):
One of the best places for building a dam is in a narrow part of a
deep river valley. The valley sides can then act as natural walls.
The primary function of the dam's structure is to fill the gap in
the natural reservoir line left by the stream channel. The sites
are usually those where the gap becomes a minimum for the required
storage capacity. The most economical arrangement is often a
composite structure such as a masonry dam flanked by earth
embankments. The current use of the land to be flooded should be
dispensable.
Significant other engineering and engineering geology
considerations when building a dam include: permeability of the
surrounding rock or soil, earthquake faults, landslides and slope
stability, peak flood flows, reservoir silting, environmental
impacts on river fisheries, forests and wildlife, impacts on human
habitations, compensation for land being flooded as well as
population resettlement, and removal of toxic materials and
buildings from the proposed reservoir area.
Impact Assessment:
Impact is assessed in several ways: the benefits to human society
arising from the dam (agriculture, water, damage prevention and
power), the harm or benefits to nature and wildlife (especially
fish and rare species), the impact on the geology of an area -
whether the change to water flow and levels will increase or
decrease stability, and the disruption to human lives (relocation,
loss of archeological or cultural matters underwater).
Environmental Impact Dams affect
many ecological aspects of a river. Rivers depend on the
constant disturbance of a certain tolerance. Dams slow the
river and this disturbance may damage or destroy this pattern
of ecology. Temperature is also another problem that dams
create. Rivers tend to have fairly homogeneous temperatures.
Reservoirs have layered temperatures, warm on the top and cold
on the bottom; in addition often it is water from the colder
(lower) layer which is released downstream, and this may have
a different dissolved oxygen content than before. Organisms
depending upon a regular cycle of temperatures may be unable
to adapt; the balance of other fauna (especially plant life
and microscopic fauna) may be affected by the change of oxygen
content.
Older dams often lack a fish ladder, which keeps many fish from
moving up stream to their natural breeding grounds, causing failure
of breeding cycles or blocking of migration paths.
A large dam can cause the loss of entire ecospheres, including
endangered and undiscovered species in the area, and the
replacement of the original environment by a new inland lake.
In the case of Fishtrap Dam, the U.S. Fish and Wildlife Service's
Fisheries Mitigation Programs issued a report in May 2002
describing the effects of the dam on the indigenous fish species.
According to the report, the impoundment of the Big Sandy River and
the associated hypolimnetic discharges from Fishtrap Dam severely
depressed or eliminated the natural reproduction of indigenous
riverine fish species (i.e., smallmouth bass, walleye, paddlefish,
etc.). If not for the stocking of trout, many miles of river would
fail to provide even a marginal sport fishery. Wolf Creek National
Fish Hatchery supplies rainbow trout for stocking the Fishtrap
tailwater in order to mitigate for the warm/cool water fishery lost
due to the construction of Fishtrap Dam.
Depending upon the circumstances, a dam can either reduce or
increase the net production of greenhouse gases. An increase can
occur if the reservoir created by the dam itself acts as a source
of substantial amounts of potent greenhouse gases (methane and
carbon dioxide) due to plant material in flooded areas decaying in
an anaerobic environment. According to the World Commission on Dams
report, when the reservoir is relatively large and no prior
clearing of forest in the flooded area was undertaken, greenhouse
gas emissions from the reservoir could be higher than those of a
conventional oil-fired thermal generation plant. A decrease can
occur if the dam is used in place of traditional power generation,
since electricity produced from hydroelectric generation does not
give rise to any flue gas emissions from fossil fuel combustion
(including sulfur dioxide, nitric oxide, carbon monoxide, dust, and
mercury from coal).
Human Social Impact The impact on human society is also
significant. For example, the Three Gorges Dam on the Yangtze River
in China is more than five times the size of the Hoover Dam and
will create a reservoir 600 km long, to be used for hydro-power
generation. Its construction required the loss of over a million
people's homes and their mass relocation, the loss of many valuable
archaeological and cultural sites, as well as significant
ecological change.
This photograph shows a home being moved in preparation for the
construction of Fishtrap Dam (notice the man on roof).
Economic Impact Construction of a hydroelectric plant
requires a long lead-time for site studies, hydrological studies,
and environmental impact assessment, and are large scale projects
by comparison to traditional power generation based upon fossil
fuels. The number of sites that can be economically developed for
hydroelectric production is limited; new sites tend to be far from
population centers and usually require extensive power transmission
lines. Hydroelectric generation can be vulnerable to major changes
in the climate, including variation of rainfall, ground and surface
water levels, and glacial melt, causing additional expenditure for
the extra capacity to ensure sufficient power is available in low
water years.
Once completed, if it is well designed and maintained, a
hydroelectric power source is usually comparatively cheap and
reliable. It has no fuel and low escape risk, and as a renewable
energy source it is cheaper than both nuclear and wind power. It is
more easily regulated to store water as needed and generate high
power levels on demand, compared to wind power.
DAM FAILURE
With the potential for immense damage and loss of life, dam
failures are generally catastrophic if the structure is breached or
significantly damaged. Fortunately, dam failures are comparatively
rare. Routine deformation monitoring of seepage from drains in, and
around, larger dams is necessary to anticipate any problems and
permit remedial action to be taken before structural failure
occurs. Most dams incorporate mechanisms to permit the reservoir to
be lowered or even drained in the event of such problems. Another
solution can be rock grouting - pressure pumping portland cement
slurry into weak fractured rock.
The main causes of dam failure include spillway design error,
geological instability caused by changes to water levels during
filling or poor surveying, poor maintenance, especially of outlet
pipes, extreme rainfall, and human, computer or design error.
During an armed conflict, a dam is to be
considered as an "installation containing dangerous forces"
due to the massive impact of a possible destruction on the
civilian population and the environment. As such, it is
protected by the rules of International Humanitarian Law (IHL)
and shall not be made the object of attack if that may cause
severe losses among the civilian population. To facilitate the
identification, a protective sign consisting of three bright
orange circles placed on the same axis is defined by the rules
of IHL.
A notable case of deliberate dam failure (prior to the above
ruling) was the British Royal Air Force Dambusters raid on Germany
in World War II (codenamed "Operation Chastise"), in which three
German dams were selected to be breached in order to impact on
German infrastructure and manufacturing and power capabilities
deriving from the Ruhr and Eder rivers. This raid later became the
basis for several films.
THE STORY OF FISHTRAP DAM
Since the earliest Levisa Fork Basin settlements, the residents
faced the problem of frequent and severe flooding. The Levisa Fork
Basin has been a source of many damaging floods in the Pike County
& Floyd County area dating back to cases since 1861. Major
floods occurred in 1862, 1901, 1957, and 1963, prior to
construction of Fishtrap Dam.
The construction of Fishtrap Dam was authorized by the Flood
Control Act of 1965 and the Rivers and Harbors Act of 1946. The
Corps of Engineers developed the project, after extensive field
studies and cost estimates, for the primary purpose of flood
control along the Levisa Fork, with the secondary purposes of
recreation and water quality control.
The dam is built of native rock with a clay waterproof core. It is
195 feet high and 1,000 feet long. The job required moving five
million cubic yards of rock and earth. An outstanding job of rock
treatment called a 'stairstep' excavation at the left end of the
dam exposes the 330-million year old Pennsylvania Period strata.
Construction was started in 1962 and continued for the next six
years...
Inlet Structure
Diversion Tunnel Foundation
Diversion Tunnel Inlet
Diversion Tunnel Outlet
Spillway, Near Completion
President Lyndon B. Johnson, along with then-Lt. Governor Wendell
Ford, highly-regarded Congressman Carl D. Perkins, and other
dignitaries were on hand to dedicate the completion of the dam on
October 26, 1968, at 4:35 p.m. Speaking of the dam, President
Johnson said:
"This dam will protect your families, it will bring you
industries, it will protect your town. It will be a playground for
your children. During the next 10 years, it will save more than $50
million in flood losses alone. It will provide families for miles
around with a place to fish, a place to camp, a place to swim, or
just a place to go to enjoy themselves and have a good time.
This dam is another example of what is happening in a growing,
prospering, progressive Kentucky. It is an example of what can be
done by good men and good women who are unafraid to strike out and
pioneer in new directions."
(He then went on to stump for election of Hubert Humphrey in the
presidential election that was being held 10 days hence.)
FISHTRAP HISTORY & ARCHAEOLOGY
Fishtrap Dam is located in the community of Fishtrap, approximately
7 miles southeast of Pikeville. The community was established on
February 19, 1873, and is thought to have been named for the local
method of catching fish by setting traps in the river in the
vicinity of what is now the dam.
Archaeological investigations in the area resulted in the recording
of 33 prehistoric native American sites including 1 rock shelter, 8
late prehistoric village sites, and 24 open camp sites. Excavations
at what is called the Sloane site at Woodside recovered 65,000
artifacts, now stored at the University of Kentucky.
FISHTRAP LAKE
The dam's impoundment of the Levisa Fork forms Fishtrap Lake, which
is located entirely in Pike County. At its maximum (flood storage)
level, the lake would contain more than 54 billion gallons of
water. During the summer recreation season, the lake is 16.5 miles
long, has a surface area of 1,131 acres and contains about 12
billion gallons of water. It is 84 feet deep at the intake
structure during summer pool. Part of this water is released all
year for municipal water supply at Pikeville, 15 miles downstream
from the dam.
WATER FLOW
Release of water from the lake is controlled by gates in the
tower-like 'intake structure' located at the left end of the dam.
From that structure, the water flows through a 15-½ foot diameter
tunnel and discharges back into the Levisa Fork below the dam. If
the lake should rise above its maximum permissible level during
storage of potential floodwaters, then the four 'tainter' gates
located in the spillways would be used to control additional
releases. The tainter gates can be seen from the coordinates given
for the top of the dam.
Tainter Gates
Downstream from Spillway
RECREATIONAL ACTIVITIES
Fishtrap offers a wide variety of
recreational opportunities. Not surprisingly, fishing is among
the most popular, both near the spillway and on the lake.
There are also several picnicking areas, shelters, and
playgrounds. A developed hiking and horseback riding trail can
be accessed at the Lick Creek Recreation area where the trail
begins. Several local equestrians and hikers also use existing
oil/gas well roads. Other activities include bicycling and
boating. The area is also well-known as a haven for deer,
raccoons, and even the occasional grouse. There is a wildlife
display at the Visitor Center.
Camping is available at the Grapevine
Campground (28 campsites) and at the more recently developed
Friends of Fishtrap Campground, where there are eight
overnight campsites for recreational vehicles. This campground
is operated by the Millard East-Shelbiana Volunteer Fire
Department under contract from the Pike County Fiscal
Court.
For the self-motivated person, Fishtrap Lake offers many volunteer
activities including, campground host, lake clean ups, tree and
flower planting, wildlife enhancement programs such as, bird house
building and placement, food plot planting, and fish attractor
programs, just to name a few. For more information please contact
the Volunteer Program Coordinator at the project office. Restrooms
are located at various locations throughout the park area.
All recreational areas are open from 7:30 a.m. until 10:00 p.m.,
except for persons engaged in boating, fishing and camping.
HYDROELECTRIC POTENTIAL
In Pike County, Kentucky, like many other
Appalachian counties, coal is king. For many decades, the coal
of Pike County has fueled technological progress and helped to
supply electricity to the country. However, as finite fossil
fuel sources decline, many people are looking to renewable
energy sources to help meet the energy demands.
Fishtrap Partners, LLC has received a preliminary permit from the
Federal Energy Regulatory Commission to conduct a feasibility study
for the development of a hydroelectric plant at Fishtrap Dam. The
proposed project would have a total capacity of 5,000 kilowatts and
is estimated to be capable of generating 19 gigawatt hours of
energy annually.
The hydro project, however, will not interfere with the dam's flood
control function, nor will it disrupt normal water flow or affect
anything downstream. Flood control would continue to be the primary
function of the dam.
If the preliminary study finds the project to be feasible, the
facility could be built within 2-3 years.
ADDITIONAL FLOOD CONTROL
Even after the dam's completion, many Pike County communities
within the floodplain of the Levisa and Russell Fork and
tributaries were devastated by the April 1977 flood, which was the
flood of record for much of the region. A significant flood again
inundated the Levisa Fork communities in May of 1984. As a result
of this continued flooding, The Energy and Water Development
Appropriations Act of 1981 provided authorization for development
of flood protection measures for the Levisa and Tug Forks of the
Big Sandy River.
The study area, primarily residential in nature, includes the
incorporated areas of Pikeville, Coal Run, Elkhorn City, and
unincorporated areas in the county subject to flood damage from the
potential of a reoccurrence of the April 1977 flood. The project
requires providing flood protection measures to approximately 2,000
structures, 75 percent of which are residential. Alternatives being
initially considered include floodwall/levee systems protecting
Pikeville and Coal Run, non-structural flood-proofing and several
ring walls protecting individual structures.
The level of flood protection along the Levisa Fork will be the
1977 inundation limit or the 100-year flood event, whichever is
greater for nonstructural. Floodwall alternatives will be evaluated
at the Standard Project Flood (SPF) level. In February 2007, the
feasibility study was forwarded to Corps Headquarters in Washington
for review and approval.
LOGGING REQUIREMENTS
In order to log a find for this earthcache, you will need to
include with your log a photo of yourself with your GPS receiver
AND submit answers to the following questions:
1) In what direction is the water traveling as it emerges from the
spillway?
2) Using your GPS receiver, what is the elevation at the spillway
(at the given coordinates)?
3) Using your GPS receiver, what is the elevation at the top of the
dam (at the given coordinates)?
4) What is the total number of motors in place to operate the
tainter gates? (If you're not sure about this question, you might
need to read the listing again.)
5) About how many gallons of water does the lake contain during the
summer recreation season?
Thank you for visiting!
Permission for this earthcache has been granted by Rodney
Holbrook, Park Manager.
For more information, call (606) 437-7496.
Special thanks to Rzinkain for suggesting this earthcache and
for the old photographs.