WATERSHEDS: A watershed refers to land that is drained by an
interconnected system of rivulets, streams, rivers, lakes, and
groundwater. Water from a watershed eventually drains into a common
destination. Both rain and snow contribute to the watershed.
Watersheds can range in size from just a few square miles to many
hundreds, even millions of square miles.
Watersheds are important as habitats for many creatures, and as
a source of drinking and recreational water for many communities.
Because one watershed can often be connected to another watershed
that lies "downstream," the environmental quality of one watershed
can affect other watersheds. As more communities rely on watersheds
for their drinking water, the preservation of watersheds is
becoming more urgent.
To function properly, a watershed needs to be maintained in a
fairly undisturbed state, especially near watercourses. This
undisturbed habitat helps to keep unwanted pollutants and excess
soil and runoff from reaching the water course. The preservation of
watershed habitats is recognized as a priority by local, regional,
and national governments.
Watershed
FLOODS: Flooding, although it usually carries a negative
connotation, is a natural process and is simply the response of a
natural system (a river system) to the presence of too much water
during an interval of time. When this happens, water must move out
of the channel (the bed or deeper part) and out onto the
surrounding area, known as the floodplain.
Floods are caused by a variety of factors, both natural and
man-made. Some obvious causes of floods are heavy rains, melting
snow and ice, and frequent storms within a short time duration.
When humans build homes and towns near rivers, the result has been
the disastrous consequences of floods. Floods have historically
killed more people than any other natural disaster. Because of
this, humans have attempted to manage floods using a variety of
methods.
ALLUVIUM: One positive result of flooding, or streams leaving
their banks, is the deposition of silt, clay, gravel and organic
matter in floodplains. This material is called alluvium. Alluvium
results in very fertile soils. The Licking River floodplain that is
now underwater above the dam was fertile farmland resulting from
the deposit of alluvium. Many farmers and residents were displaced
when the dam was constructed. Now the dam prevents flooding of land
below the dam which also includes fertile alluvial farmland
residing in the floodplain of the river.
FLOOD INTERVENTION HAZARD ASSESSMENT: Because of the potential
of a flood to destroy life and property, men and women have, for
centuries, developed ways to prepare for and fight this natural
disaster. One common way to manage floodwaters is to construct dams
to stop excess water from inundating dry areas. Another way is to
divert floodwaters away from populated areas to planned areas of
flood storage. To this end, flood control reservoirs are kept
partially empty so that they can catch floodwaters when the need
arises. These reservoirs then release the water at a slower rate
than would occur under flood conditions; hence, reservoirs give the
soil time to absorb the excess water. About one-third of reservoirs
in the United States are used for this purpose.
Flood Intervention
HISTORY OF FLOOD CONTROL DAMS: Around 2950-2750 B.C, the ancient
Egyptians built the first known dam to exist. The dam was made of
rubble masonry walls on the outsides and filled with 100,000 tons
of gravel and stone. The dam was not watertight and water flowed
through the structure quickly eroding it away.
The second type of dam known to have been built was an earth dam
called Nimrod's Dam in Mesopotamia around 2000 BC. Around 100 AD
the Romans were the first civilization to use concrete and mortar
in their gravity dams. Both of these types of dams were watertight
methods of construction.
The evolution of flood control dams is too extensive to cover
here, but you get the idea. Mankind has been using dams for flood
control a very long time.
CAVE RUN LAKE: So, this Earthcache brings you to Cave Run Lake.
A river runs through it. That river is the Licking River. The head
(beginning) of the river is in Magoffin County. The mouth of the
river empties into the Ohio River across from Cincinnati. Early
explorers called the river "Great Salt Creek" because of the many
salt licks found along its banks. Indians called it "Nepernine"
(salt seeping waters).
Construction of a flood control dam on the river by the
Louisville District of the Corps of Engineers began in 1965 and was
completed in 1973. The dam was constructed with the primary purpose
of flood control, but the resulting lake provides an alluring
source of recreation as well.
The dam controls runoff from an 826 square mile drainage area or
watershed. Water is held back by the dam and released gradually so
that flooding does not occur downstream. There is a good diagram at
the posted coordinates showing how this works along with lots of
other interesting information. When I was a kid living at Zilpo
(upriver from the dam), there were times when we could not go to
school because floodwaters came across the road.
I hope you will take time to walk around a bit here to
experience and learn more about flood control dams. An "emergency
spillway" 650 ft. wide and 23 ft. lower than the top of the dam is
located at N 38 06.729 W 83 31.959. This is a safety measure that
would prevent water from overtopping the dam.
I also hope that you will consider what the land above the dam
was like before it was flooded. Imagine the Licking River flowing
through that area and fertile fields in the floodplains where
farmers most often grew corn. Imagine all of the streams and
rivulets draining rainwater from the land and into the river. In a
way, all of that is still there. A lot of it is just underwater
now.
Please email answers to the following questions to me to get
credit for this Earthcache:
- The watershed directly around Cave Run Lake primarily consists
of what type of land?
- What natural occurrence would have caused flooding in this
area?
- What type of land did the dam flood in order to provide flood
control downstream?
- How many river miles is it to the Ohio River from the dam?
- Without proper controls, a manmade dam could negatively impact
the river downstream. What two mechanisms does the dam incorporate
to lessen its effect on temperature and turbulence downstream?