Without dams, modern life as we know it would not be the same.
Since the first large scale dam was built in Egypt 5,000 years ago,
engineers have devised various types of dams to withstand the
forces of raging rivers.
Embankment dams are the most commonly built dams in the United
States. They are massive dams made of earth and rock. These dams
rely on their heavy weight to resist the force of the water. They
usually have some sort of water proof insides (called the core),
which is covered with earth or rock fill. The core is made from an
impermeable material to stop water passing through the dam.
The main force on an embankment dam is the force of the water.
The weight of the dam is also a force, but each material has a
different weight, so it is not shown here as one force the way it
is on the concrete dams. The uplift force is also acting on the
embankment dam, but some of the water seeps into the dam so the
force is not the same as on a concrete dam.
When constructing an embankment dam, earth or rocks are
compacted to pack their particles closer together pushing out the
spaces taken up by air. The material is placed in thin layers and
compacted using rollers. This makes the embankment stronger. It
also reduces the amount that the embankment material would settle
naturally under its own weight. If the materials were not
compacted, the dam would settle and its height would be reduced
noticeably after a short time.
Embankment dams are usually chosen for sites with wide valleys.
They can be built on hard rock or softer soils, as they do not
exert too much pressure on their foundations.
Embankments are made from natural materials like earth, gravel
and rock. Earthfill materials for a dam include clays, sands,
gravels and silts, and soils made up from a mixture of these. These
types of dam structures are used for carrying roads and railways
and are used to hold back water in reservoirs in valleys, and to
raise river banks to stop flooding.
A reservoir can be used to control the amount of water flowing
in a river after heavy rain. The water level in the reservoir is
kept low during the rainier periods of the year. When heavy rain
occurs, it is stopped by the dam and held back in the reservoir.
When the reservoir gets too full, the floodwater can be passed
ownstream over a spillway.
Side channel spillways are used mainly with embankment dams. The
water flows over the spillway, into a side channel. Then it flows
down a chute and joins the river downstream of the dam. Sometimes,
a tunnel is used which may divert the water elsewhere. A chute is
the means by which water is transferred over the crest to the river
bed below the dam. Its function is to prevent damage to the valley
walls that could endanger the dam. It may or may not serve to
dissipate some of the energy in the water. At most sites a concrete
lined chute is required. The chute width is determined by the
length and arrangement of the spillway crest, the total energy in
the water and the economical relation between the width (including
excavation costs) and the height of the side walls of the chute.
The height of the chute wall is also important because the water
could erode the side slopes.
Outlet towers are found in reservoirs, usually near to the dam.
The tower sits above an outlet pipe or tunnel used to transport
water out of the reservoir. It is built to house controls for
opening and closing valves or gates that control the flow of water
through the outlet. The controls are normally located inside in a
room at the top of the tower.
In a reservoir for water supply, a tower will often have a
vertical pipe inside with a number of horizontal pipes leading into
it from the reservoir. The horizontal pipes are used to draw-off
water from different levels in the reservoir. Water is let into
them by opening valves at their entrances. The vertical pipe then
connects to a horizontal pipe that takes the water away from the
tower through a tunnel to the water treatment works.
Engineering geologists investigate the geology of the dam site
and the area to be occupied by the reservoir. They provide an
overall picture of the types of soils and rocks below the earth's
surface, their thickness and the directions in which they slope.
They assess the quality of the ground to determine whether leakage
of water from the reservoir could occur. For embankment dams,
geologists investigate nearby areas where natural materials can be
excavated for their construction.
Engineering geologists also consider whether the site of the
proposed dam is in a region where earthquakes can occur. They look
for the presence of any faults in the rocks and consider whether an
earthquake could cause the fault to rupture.
Embankment dams are constructed upwards in a series of thin
layers. The thickness of the layer depends on the material being
used. Earthfill layers are about 300 mm thick and rockfill layers
can be up to 1 meter thick. When the dam has a core, that is also
constructed in layers to keep it at the same height as the rest of
the dam. Once the dam has been raised to its full height, a
protective layer is formed on its upstream face. This layer
protects the dam against damage by waves, and sometimes provides
waterproofing too.
Come visit an earthen embankment dam in Johnson County,
Kentucky. Construction of the Paintsville Dam, Spillway, and Outlet
Works began in 1975 and was completed by 1979 by the US Army Corps
of Engineers. The Dam is over 300 feet high and 200 feet long. The
earth-filled Dam was constructed of rock with a central clay core
which prevents water from passing through the Dam. A 1,140 acre
lake is formed behind the Dam from the waters of Paint Creek. The
lake saw the establishment of Kentucky’s newest State
Park-Paintsville Lake State Park.
The emergency Spillway is south of the Dam. The Spillway
contains gates which are used to control high water and prevent the
lake from flowing over its limits. The Outlet Works consists of an
intake structure and an outlet tunnel. The intake structure is
located north of the Dam. The Outlet Works contains the 8-foot by
4-foot gates which control the amount of water released.
Built primarily for flood control, the lake surface is kept at
an elevation of over 700 feet above sea level for recreational use
during the summer. During the fall, the lake is lowered to hold
additional water from winter and spring runoff. When flooding does
occurs, the gates in the intake structure are closed to the lowest
level. The water runs off from the Licking River drainage basin
behind the Dam. The water is then stored in the reservoir to
protect life and property downstream. When the danger of downstream
flooding has passed, the intake structure gates are opened to
lowerthe reservoir. Opening the gates is coordinated with other
dams on the Big Sandy and Ohio Rivers as a part of a larger flood
control system.
You will need to visit the downstream spillway of the dam
structure to make a few calculations. It is located just off of
Kentucky Route #40 just past the entrance to the state park. Follow
the sidewalk to the mouth of the spillway through the earthen
dam.
1. Estimate the height of the spillway opening.
a/ 30’ b/ 50’ c/ 70’
2. Estimate the width of the spillway opening between the two
rock facings.
a/ 25’ b. 50’ c/ 80’
3. What is the depth of the spillway concrete chute from the top
of the rail to the bottom of the stream bed?
a/ 10’ b/ 20’ c/ 30’
4. What is the elevation reading at the mouth of the ownstream
outlet?
Travel back across the foot bridge to the middle of the grassy
area at the base of the earthen dam (37 50.336 82 52. 239) and make
the following calculations.
5. What is the height of the earthen dam from it’s base here to
the guardrail along the roadway crossing the structure?
a/ 300’ b/ 350’ c/ 400’
6. What is the width of the earthen dam along it’s base here
from one side of the valley to the other?
a/ 200’ b/250’ c/ 300’
7. Take a picture of the earthen structure or the downstream
spillway and stream with yourself or your GPS in the forefront.
Post it with your log after you email the calculations above.
One incident did occur during construction of the dam here that
is note worthy. The Paintsville Herald called it "Exodus '78 -- one
of the largest and most orderly evacuations in the history of
Kentucky. What caused the necessity for the decision was nearly
eight inches of rain in a 36 hour period, much of which backed up
behind a temporary coffer dam here at the site of the new
Paintsville Dam. At 8:58 A. M. Saturday morning, December 9, the
water at the coffer dam reached almost precisely the predetermined
level - 675 feet above sea level - which the officials had agreed
upon as the critical level for an evacuation. Cars and trucks began
leaving Paintsville within minutes. Fortunately, the rain that
prompted the crisis stopped just in time and the temporary dam
held. Engineers and town folk were ecstatic that all was well and
the dam construction moved forward.
Besides providing years of recreational enjoyment for locals, it
has proven to be life saving and has prevented upwards of a billion
dollars in flood damage since it’s completion.
