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Key
Points
Key Points will give you the main information you should know to teach
the activity.
Detailed
Information
Detailed Information gives more in-depth background to increase your own
knowledge, in case you want to expand upon the activity or you are asked detailed
questions by students.
The force that moves the water in streams and rivers is not atomic energy, solar power or hamsters running in exercise wheels. It is gravity. The attraction of gravity pulls water from areas of high elevation to areas of low elevation. For this reason topography, the shape and form of the land, plays a major role in defining the size and shape of watersheds.
Watersheds, the area of land where all the water drains to one stream, river or lake, are surrounded by drainage divides. Drainage divides are areas of relatively high topography that separate two watersheds. Water that falls on one side of a divide will drain to a different basin than the water that falls on the other side. Drainage divides can be as high as the Rocky Mountains or as low as a small rise in the Lowcountry of South Carolina.
Continental land tends to rise in elevation as one moves inland from the coastline. For this reason almost all river and streams in watersheds across the world flow towards the coast and eventually will discharge into the ocean. There are exceptions, though, such as the Great Basin in the Southwestern United States. This is an area in Utah and Nevada of approximately 210,000 square miles. It contains the Great Salt Lake, a lake with no outlets that is three to five times saltier than the ocean. Its high salt content is caused by the salt and mineral deposits of the rivers flowing into the lake. With no outlets, the Great Salt Lake has been accumulating salt for centuries.
In
South Carolina, all of the watersheds flow into the Atlantic Ocean. This is
because of the elevation changes in the different regions of the state from
the northwest to the southeast. Each region of the state is characterized by
its topography. In the northwest corner of the state is the Mountains region.
This is part of the Blue Ridge Mountain Range and contains the highest elevations
in the state, up to 3500 ft. The next region in the state is the Piedmont, which
is characterized by rolling hills and valleys and presents a drop in elevation.
The next region is the Sandhills, which, as you may have guessed, are sandy
hills, the remains of ancient sand dunes and barrier islands. The next region
is the Coastal Plain, very flat land that gradually drops in elevation to sea
level. The final land region is the Coast, the lowest elevation in the state
at sea level.
The watersheds flow from northwest to southeast, from the mountains to the sea. The three major watersheds, the Santee, Pee Dee and Savannah River watersheds, all start in the Blue Ridge Mountains of South and North Carolina and flow downwards toward the Atlantic Ocean. The smaller coastal watersheds, such as the Ashley, Edisto and Ashepoo Rivers, all begin in the Coastal Plain and flow to the ocean.
(Click
on map to enlarge) The topography of South Carolina was formed by three
major forces: the continental collision that created the Appalachian Mountains,
the periodic rising and falling of sea level through the ages and the erosion
and deposition of streams and rivers. During the Paleozoic Era, the collision
of the North American and African continental plates pushed the rocks upward
that formed the Appalachian Mountains. This mountain growth occurred only at
a few inches a century, but on the geologic time scale, this is rapid. At their
tallest these mountains were as high as the Himalayas are today. This may be
hard to believe by looking at the mild mountains we are familiar with in our
time, but hundreds of millions of years of erosion have smoothed them down.
Sea level changes occur because the Earth's climate undergoes periodic changes in which the average temperature of the atmosphere will rise and fall. When it rises, the water frozen in the ice caps of the Arctic and Antarctic begins to melt and sea level will rise. As sea level rises, water begins to cover the land. In South Carolina, millions of years ago, the sea covered the Coastal Plain to the Sandhills in the mid-state near Columbia. The Sandhills are remnants of ancient sand dunes. When temperatures lowered, water was again captured in the icecaps and the coastline receded again. The ocean waters flattened most of the Coastal Plain, though ancient sand dunes and barrier islands have formed a few small hills.
(Click
on map to enlarge) In recent times, the topography of South Carolina has
been shaped by the erosion and deposits of streams and rivers. The soils of
the Piedmont are composed of sediment eroded from the Blue Ridge Mountains that
have been deposited in the area by streams and rivers. The rivers and streams
also have eroded the Piedmont region to form the low hills and valleys characteristic
of the Piedmont region, and brought the sediment that composes the beaches and
barrier islands. The erosion of streams and rivers do more to shape the topography
of the land than any other geologic force.
All of these features combine to give the watersheds in South Carolina their size and shape. Mountains, hills and even a small rise in elevation in the Coastal Plain can form the drainage divides that are the boundaries of the watersheds. The drop in elevation from the mountains to the sea causes all of the watersheds in South Carolina to eventually empty into the sea. Knowing about the topography of South Carolina leads to a better understanding of the watersheds of South Carolina.