|
What is a Watershed
By Jody Newton-McAllister
December 2007
|
A watershed describes an
area of land that contains a common set of streams and
rivers that all drain into a single larger body of
water, such as a larger river, a lake or an ocean. For
example, the Mississippi River watershed is an enormous
watershed. All the tributaries to the Mississippi that
collect rainwater eventually drain into the Mississippi,
which eventually drains into the Gulf of Mexico.
Rainwater that falls on more than half of the United
States subsequently drains into the Mississippi. |
The Mississippi River drains the largest area of any
U.S. river, covering more than 41% of the Continental
United States. |
A watershed
can cover a small or large land area. In the Portsmouth, Ohio
vicinity, for instance, the Scioto River is a small river
draining a relatively small amount of land. Small watersheds are
usually part of larger watersheds. The Scioto River watershed,
which is supplied by even smaller watersheds from dozens of
streams including Scioto Brush Creek, drains into the Ohio
River. All the streams flowing into small rivers, larger rivers,
and eventually into the ocean, form an interconnecting network
of waterways.
This aerial photograph shows the
confluence of Scioto Brush Creek and the Scioto River at
Rushtown.
Not only
does water run into the streams and rivers from the surface of a
watershed, but water also filters through the soil, and some of
this water eventually drains into the same streams and rivers.
Soil runoff that drained
into the Scioto River empties into the Ohio River at
Portsmouth. |
These two processes,
surface runoff and infiltration are important for a
number of reasons. For one, they affect water quality.
Think about it... The water that runs off the surface of
the Earth picks up water pollution and deposits the
pollution in streams and rivers as it drains the
watershed. Along with many different types of pollution
that are carried by surface runoff, soil also becomes a
water pollutant as it is eroded from farm lands. Water
that filters through the soil can also become
contaminated with pollution that is left over from
agricultural, industrial, commercial, and other types of
human activity.
The network of streams
and rivers that drain our watershed and carry water
pollution ultimately empty into larger bodies of water,
such as lakes and oceans. As the larger rivers carrying
water |
|
pollution from the land
flow into lakes and oceans, all of the pollution that
was in the rivers now is concentrated into these other
bodies of water. The oceans of the world become the
final resting place for tons of pollution. Through our
watersheds, pollution is distributed far away from its
original source. And obviously, polluted water affects
water quality. |
|
